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IftnitietrsitiQ  of  CllaUfornia ) 


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in  2007  with  funding  from 

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ELEMENTS 


OP 


CHEMISTRY 


isx  %  Mu  0f  Mlqt$,  ^mhmm,  m)s  3t\aal$. 


By  M.  V.  EEGNAULT. 

ILLUSTRATED    BY  NEARLY  SEVEN    HUNDRED  WOOD-CUTS. 


TRANSLATED  FROM  THE  FRENCH 

By  T.  FORREST    BETTON,  M.D.,M.A.N.S. 

FELLOW  OF  THE  COLLEGE  Or  PHYSICIANS  OF  PHILADELPHIA,  ETC. 


AND  EDITED  WITH  NOTES, 

By   JAMES    C.    BOOTH, 

MELTER  AND  REPINER  V.  S.  MINT,   AND 

WILLIAM    L.    FABER, 

METALLURGIST  AND  MINING  ENGINEEE. 


THIRD  EDITION,  GREATLY  IMPROVED. 

TO  WHICH  IS  APPENDED  A  COMPARATIYE  TABLE  OP  PEENCH  AND  ENGLISH 
WEIGHTS  AND  MEASUEES. 


IN  TWO  VOLUMES.-VOL.  H. 


PHILADELPHIA: 
J,     B.     LIPPIN^COTT     &     CO., 
NO.  20  NORTH  FOURTH  STREET. 
JOS.  A.   SPEEL,  211    CHESTNUT    STREET. 

18  56. 

"  V 

CaSIfornla  College  of  Pharmacy 


/Entered  according  to  Act  of  Congress,  in  the  year  1852»  by 
AMBROSE  W.  THOMPSON, 
in  the  Clerk's  Office  of  the  District  Court  for  the  Eastern  District  of 
Pennsylvania. 

Entered  according  to  Act  of  Congress",  in  the  year  1856,  by 
JOS.     A.     SPEEL, 

In  the  Clerk's  Office  of  the  District  Court  of  the  United  States,  in  and  for  the 
Eastern  District  of  Pennsylvania. 


PHILADELPHIA : 

FEINTED  HY  KING  k  BAIRD, 

NO.  9   SANSOM  STREJiT. 


TABLE  OP  CONTENTS  OF  VOL.11. 


PAGE 

Preparation  of  Ores 9 

Washing 10 

Crushing  by  cylinders 11 

Swing-sieve 15 

Jigging-machine 16 

Stamping  ore 17 

Deposite-trough 18 

Sleeping-table,  or  nicking-buddle 19 

Percussion-table,  or  brake-table 20 

Manganese 23 

«  oxides  of 23 

"  acids  of 25 

"  salts  of 2S 

"  sulphide  and  chloride  of.....  29 

"  analytic  determination  of....  31 

Iron,  metallic 36 

*'     oxides  of. 40 

<'     salts  of 44 

*'     sulphide  of. 47 

»'     chloride  of 49 

*'     cyanides  of 50 

"     carburet  of,  cast-iron....'. 53 

"     analytic  determination  of 54 

*'     ores  of 59 

"     reduction  of  its  ores,  by  the  Cata- 

lonian  forge 61 

Reduction  in  the  blast-furnace 66 

''     the  blast. 67 

"     mixing  ores 70 

"     blowing  the  furnace 71 

"     hot-blast 77 

"    waste-heat  of  blast-furnace 78 

*•'     re  melting  pig-metal 80 

"     conversion  of  cast  into  bar-iron....    82 

*'     refining  on  the  forge-hearth 83 

"  "     by  puddling 87 

"     blooming  and  rolling 92 

"     Making  sheet  and  tin  plate 99 

"     wire-drawing 101 

"     making  steel 102 

«  "      forge  steel 103 

"  "      blistered  and  cast-steel...  104 

"     tempering  steel 107 

"     dry  assay  of  iron-ores 108 

"    analysis  of  cast,  and  steel Ill 


PAQB 

Iron,  composition  of  bar  and  cast-iron, 

and  steel 116 

Chromium,  oxides  of 118 

"         chromic  acid 122 

"  salts  of 123 

"  chromates 125 

"  analytic  determination  of...  128 

Cobalt,  metal  and  oxides 130 

"       salts  of 131 

"       arsenical  ores 132 

"       analytic  determination  of 133 

"        smalt  and  zaff re 134 

"       Thenard's  blue 135 

Nickel,  metal  and  oxides  of 136 

"       salts  of.. 137 

"       German  silver 138 

"       analytic  determination  of 139 

Zinc,  distillation  of 141 

"    oxide  of 142 

"     salts  of 143 

"     suljihide  and  chloride  of 144 

"     analytic  determination  of 144 

"     metallurgy  of. 146 

"  "  in  Belgium 147 

"  "  in  Silesia 150 

"  "  in  England 151 

Cadmium,  compounds  of 153 

"        analytic  determination  of 154 

Tin 156 

"    oxides  of 158 

"    salts  of 160 

"    sulphides  of 161 

"    chlorides  of 162 

"    behaviour  of  salts  of 164 

"    metallurgy  of 166 

Titanium 169 

"       oxides  of 170 

«       chlorides  of. 171 

Columbium,   Niobium,   Pelopium,  II- 

menium t^ 174 

Lead 174 

*'     oxides  of,  litharge 175 

"     red,  or  minium 178 

«     salts  of 179 

"    acetates  of,  sugar  of  lead 183 


41985 


TABLE   OF   CONTENTS. 


PAGE 

Lead,  carbonate  of,  white-lead 184 

"     behaviour  of  salts  of 186 

"    sulphide  of 186 

"     chloride  of 188 

"     analytic  determination  of 188 

"    alloys,  type-metal,  and  soft  solder  189 

"     metallurgy  of. 190 

"                 "          reduction  by  iron....  192 
'*                 "          reverberatory     pro- 
cess   196 

"  "         Scotch  hearth 198 

"  "  oupellation 198 

"  "  Pattinson's  process..  202 

"    making  sheet,  and  pipe 202 

"     casting  shot 203 

Bismuth 204 

"       oxides  of 205 

"       salts  of,  pearl-white 206 

"       alloys  of,  fusible  metal 208 

"       analytic  determination  of 208 

"        metallurgy  of 209 

Antimony 211 

"         oxides  and  acids  of 212 

"         salts  of 214 

"         sulphides  of,  Kermes  mineral  215 

"         chlorides  of 217 

"        behaviour  of  salts  of 218 

"        analytic  determination  of.....  219 

"         detection  of,  in  poisoning 221 

"        alloys  of 221 

"         metallurgy  of 222 

Uranium,  and  its  oxides 224 

«         salts  of. 225 

"         analytic  determination  of 228 

Tungsten,  and  its  oxides 230 

"  analytic  determination  of....  232 

Molybdenum,  its  oxides  and  salts 233 

Vanadium 235 

Copper 236 

"      oxides  of 237 

"      salts  of 239 

«  "       blue  vitriol 240 

"  "       mineral    and     Scheele's 

green 242 

«  "       verdigris 243 

«      sulphides  of 243 

"      chlorides  of 244 

"      analytic  determination  of. 245 

"      metallurgy  of 247 

"  "  Mansfeld  process..  249 

"  "  eliquation  of  silver  251 

"  "  English  process....  256 

"      alloys  of,  and  zinc 263 

**  «  "  brass 264 

«  "  tin,  bronze 265 

"  "  "  cannon-casting  266 

"  "  tinning  copper  and 

brass 269 

"      analysis  of  brass  and  bronze 270 

Mercury 271 

"        purification  of...'. 272 

"         oxides  of 273 

«        salts  of 275 

"        fulminating 279 

"         amide-base  of 279 

"        sulphides  of,  cinnabar 281 


PAGB 

Mercury,  chlorides  of,  calomel 282 

"                "            corrosive   subli- 
mate   284 

"  "  white  precipitate  285 

"        iodides  of 286 

"        cyanide  of. 287 

"         analytic  determination  of 288 

"         amalgams  of,  mirrors 289 

"         metallurgy  of,  in  Idria 290 

"  "  at  Almaden...  291 

Silver 293 

"      oxides  of 294 

"      fulminating 295 

"      salts  of 296 

"  "       lunar  caustic 297 

«      sulphides  of. 300 

"      chlorides  of 301 

"      analytic  determination  of 303 

"       metallurgy  of. , 304 

"  "  Freiberg  process...  305 

«  "  Mansfeld       «  309 

"  "  American     "  310 

«      alloys  of. 311 

"  "      coin  and  plate 312 

"      assay  of  alloys  of,  by  cupella- 

tion 313 

"      assay  of  alloys  of,  in  the  wet 

way 318 

"      assay  of  ores  of 321 

Gold  and  its  compounds 322 

"      purple  of  Cassius 325 

"      analytic  determination  of 326 

"      metallurgy  of 326 

"  "  Tyrolese  bowls 328 

"     alloys  of 329 

"      separation  of,  and  silver,  by  sul- 
phuric acid 329 

"      separation  of,  and  silver,  by  ni- 
tric acid 331 

"     gilding  and  silvering 331 

"            "                 "          by  immer- 
sion   332 

"     galvanic  gilding 333 

"  "       silvering 334 

"     galvanoplastics 335 

"     assay  of  alloys  of,  by  quartation.  336 
"                        «            by  the  touch- 
needle 338 

Platinum 339 

"        black 340 

"        flameless  lamp 341 

"        oxides  of 342 

«        salts  of 343 

«         chlorides  of 345 

"         ammonia-bases  of 346 

"         analytic  determination  of.....  347 

«        extraction  of 349 

Osmium 350 

"      compounds  of 351 

"      extraction  of 352 

Iridium 353 

"      compounds  of. 354 

Palladium,  and  its  compounds 356 

Rhodium,  and  its  compounds 358 

Ruthenium 360 


TABLE  OF  CONTENTS. 


FOURTH  PART. 


ORGANIC  CHEMISTRY. 


PAGE 

Intkodttction 361-445 

Organized  and  organic  bodies 362 

Proximate  analysis  of  organic  sub- 
stances    363 

Ultimate  analysis  of  organic  sub- 
stances   366 

Ultimate  analysis,  determination  of 

carbon  and  hydrogen 367 

tritimate  analysis,  desiccation 369 

"  "      combustion 371 

"  "  of  non-volatile  li- 
quids   374 

"  "  of  volatile  sub- 
stances   375 

"  *'      of  gaseous  organic 

bodies 375 

**  "       determination     of 

carbonic  acid  by 

volume 377 

**  "  determination  of 
nitrogen  by  vo- 
lume   380 

Ultimate  analysis,  determination   of 

nitrogen  as  ammonia 382 

Ultimate  analysis,  determination  of 

sulphur 385 

Ultimate  analysis,  determination  of 

phosphorus 385 

Ultimate  analysis,  determination  of 
chlorine,  bromine,  iodine,  and  oxy- 
gen   386 

Constrtiction  of  a  formtda  for  an  organic 

substance 387 

«                     "       when  it  is  acid  387 
"                      "      from  its  mine- 
ral base 393 

"  "      when  it  is  basic  397 

"  "       when   neither 

acid  nor  basic  399 

Determination  of  density  of  vapours 406 

Simultaneous  temperatures  in  thermo- 
meters differently  constructed 413 

Air-thermometer  (note) 414 

Analysis  of  gases,  apparatus  for. 422 

"  "     absorbing  reagents...  430 

"  "      examples  of 433 

"  "     oxygen  and  nitrogen  433 

Analysis   of  gases,   oxygen,   nitrogen, 

and  hydrogen 435 

Analysis  of  gases,  oxygen,  nitrogen,  and 

carbonic  oxide 436 

Analysis  of  gases,  oxygen,  carburetted 

hydrogen,  etc 437 

Analysis  of  gases,  complex  mixtures....  443 
a2 


Vksn 

Essential  Proximate  Principles  of 

Plants 446 

Cellulose 446 

Lignin 449 

Albuminous  Vegetable  Substances 451 

Albumen 453 

Circular  polarization  (note) 454 

Gluten,  vegetable  fibrin,  and  casein...  460 

Amylaceous  Substances 461 

Inulin  and  lichenin 467 

Gums,  arabin,  cerasin,  bassorin 468 

Sugar 469 

Cane-sugar 470 

Caramel,  saccharic  acid 471 

Fruit-sugar 474 

Grape-sugar 475 

Glucic  acid 476 

Determination  of  sugar  by  oxide  of  cop- 
per   477 

Determination  of  sugar  by  polarization  478 

Gelatinous  Principles,  pectose 478 

Pectin  and  pectic  acid 479 

Table  of  pectic  acids 483 

Mannite 484 

Action  of  Acids  on  Lignin,  Starch,  and 

Sugar 485 

Dextrin 485 

British  gum 486 

Diastase 487 

Glucose,  manufacture  of 487 

Ulmin  and  humin 489 

Action   of  nitric  acid,  oxysaccharic 

acid 491 

Gun-cotton 491 

Collodion 492 

Mucic  acid 493 

Spontaneous  Decomposition  of  Plants...  494 

Mineral  fuel 494 

Varieties  of  coal 496 

Analysis  "    497 

Tables  of  composition  of  coal....  500,  503 

Alcoholic  Fermentation 505 

Yeast  or  ferment 507 

Alcohol 511 

Alcoholometry 513 

Sulphovinic  acid 515 

Ether 616 

Olefiant  gas 520 

Ethionic  acid 522 

Dutch  liquid 523 

Chlorinated  olefiant  gas 524 

Oil  of  wine 528 

Ethers  and  vinic  acids 529 

Phosphovinic  acid 530 


TABLE   OF   CONTENTS. 


PAGE 

Nitric  ether 530 

Nitrous  and  sulphurous  ethers 531 

Boracic  and  silicic  ethers 532 

Carbonic  ethers,  urethan 533 

Oxalic  ethers,  oxamic  ether 534 

Mucic  ether 535 

Sulphocarbovinic  or  xanthic  acid 536 

Chlorohydric  ether 536 

Bromo,  iodo,  and  cyanohydric  ethers  537 

Sulfhydric  ethers 538 

Mercaptan 539 

Oxidation  of  alcohol  and  ether 541 

Aldehyde 541 

Acetic  acid 542 

Manufacture  of  vinegar 543 

Pyroligneous  acid 545 

Acetates 546 

Acetic  ether 548 

Acetone 549 

Mesitylen 550 

Cacodyl,  alcarsin 551 

Chlorinated  chlorohydric  ether 554 

Chlorinated  ether 558 

Chloral 561 

Chloracetic  acid 563 

Chlorinated  compound  ethers 564 

Table  of  alcoholic  compounds  by  sub- 
stitution   566 

Ethyl  theory  (note) 568 

Lactic  and  butyric  fermentations 669 

Lactic  acid 573 

Butyric  acid,  butyramide..... 574 

Methylic  alcohol,  wood-spirit 575 

Methylic  ether 576 

Methylsulphuric  ether 577 

Compound  methylic  ethers 578 

Marsh-gas 582 

Formic  acid 583 

Methylal 585 

Chlorinated  methylchlorohydric  ether  585 

Chloroform 586 

Bromo,  iodo,  sulphoform 588 

Chlorinated  methylic  ether 588 

Table  of  methylic  compounds  by  sub- 
stitution   591 

Methyl! 593 

Acids  Existing  ix  Plants 594 

Oxalic  acid 594 

Malic  acid 595 

Equisetic  and  fumaric  acids 596 

Citric  acid 596 

Aconitic  acid 597 

Tartaric  acid 598 

Tartar  emetic 600 

Action  of  heat  on  tartaric  acid 601 

Racemic  acid 603 

Tannic  acid 605 

Gallic  acid 607 

EUagic  or  bezoaric  acid 609 

Meconic  acid 609 

Chelidonic  acid 611 

Quinic  acid,  quinone 611 

Organic  Alkaloids 612 

Quinin 613 

Cinchonin 614 

Morphin 615 

Narcotin 616 


Codein 617 

Strychnin  and  brucin 617 

Caffe'in  or  thein 618 

Nicotin 618 

Conicin 620 

Quinolein  or  leucole 620 

Anilin  or  kyanole 621 

Ethylammonia 622 

Methylammonia 623 

Amylammonia 624 

Neutral  Substances  in  Plants 625 

Piperin,  picro toxin,  cantharidin 626 

Asparagin,  aspartic  acid 627 

Phloridzin,  glycyrrhizin 628 

NiTRiLS 629 

Cyanogen,  products  of 630 

"  oxacids  of 631 

"  fulminic  acid 632 

"  sulphocyanides 633 

Essential  Oils 634 

Oil  of  terpentine  or  terebenthen 635 

Camphilen,  terebilen,  tereben 637 

Oils  of  lemon,  orange,  etc 638 

Camphor,  Japan 639 

"         Borneo 640 

Menthen,  cedren,  etc 641 

Benzoic  Series 641 

Oil  of  bitter  almonds 642 

Benzamide. 648 

Benzoic  acid 644 

"       ethers 645 

Sulpho-nitrobenzoic  acids 646 

Benzoin,  benzil,  benzin 648 

Benzene,  amygdalin 650 

Emulsin,  synaptase 651 

Salicin 652 

Saligenin 653 

Salicylous  acid,  oil  of  spiraea 654 

Salicylic  acid  and  ether 656 

Oil  of  wintergreen 650 

Oil  of  Cinnamon 658 

Cinnamic  acid,  cinnamon 659 

Balsams  of  Peru  and  Tolu 660 

Coumarin 661 

Oil  of  Aniseed,  anisic  acid 662 

Anisen,  toluidin 663 

Oil  of  Cumin,  cuminic  acid,  cymen 664 

Oil  of  Cloves,  eugenic  acid 665 

Amylic  Alcohol 665 

Amylin 666 

Amylic  ethers 667 

Valerianic  acid 669 

Enanthic  Acid 670 

Caoutchouc 671 

Gutta-percha 673 

Resins 673 

Pimaric  acid 674 

Oil  of  Garlic,  allyl 675 

Oil  of  mustard 678 

Thiosinnamin 676 

Myronic  acid 677 

Products  of  Dry  Distillation 678 

Naphthalin 678 

Paraffin 681 

Phenic  or  carbolic  acid 682 

Creasote 683 

Naphtha 683 


TABLE    OF   CONTENTS. 


PAGE 

Fats 684 

Glycerin 689 

Stearic  acid,  stearic  candles 690 

Margaric  acid 692 

Oleic  acid 693 

Action  of  sulphuric  on  the  fat  acids ..  694 

«  nitric  "      «    ..  695 

Succinic  and  adipic  acids 697 

Suberic  and  sebacic  acids 698 

Caproic,  caprylic,  and  capric  acids  ...  699 

Palm-oil,  castor-oil 700 

Spermaceti,  ethal 701 

Wax,  cerin,  myricin 703 

Organic  Colouring  Matters 704 

Madder 705 

Logwood 706 

Saffron,  Quercitron,  etc 707 

Euxanthic  acid 708 

Carotin 709 

Chlorophyll 709 

Cochineal 710 

Lichens 710 

Indigo 712 

White  indigo 714 

Isatin 715 

xA.CTiON  OF  Plants  on  the  Atmosphere  716 

Animal  Chemistry 719 

Bone 721 

Teeth,  cartilage,  horn 722 

Hair,  skin,  muscular  tissue 723 

Fibrin,  creatin 724 

Inosic  acid 725 

Gelatin,  glue 726 

Ichthyoeolla,  glycocoU 727 

Cerebral  substance 728 

Nutrition 729 

Digestion 730 

Blood,  circulation  of  the 732 

Respiration  and  animal  heat 734 

'Secretions 738 

Blood 738 

"    globules 739 


page 

Blood  hematosin 740 

"    coagulum 741 

"     analysis  of 742 

Lymph 743 

Saliva,  gastric  juice 744 

Bile 745 

"   cholic  acid 746 

Biliary  calculi  and  cholesterin 747 

Pancreatic  and  intestinal  juice 747 

Chyle  and  milk 748 

Lactometry 750 

Sugar  of  milk 751 

Casein , 752 

Making  butter 752 

Making  cheese 753 

Excretions , 754 

Urine 754 

Urea 755 

Uric  acid  and  derivatives 757 

Hippuric  acid 760 

Urine,  analysis  of 761 

Urinary  calculi 762 

Sweat 763 

Excrements 763 

Intestinal  gases 763 

Technical  Organic  Chemistry 763 

Manufacture  of  bread 764 

Brewing 766 

Cider  and  perry 768 

Wine-making 769 

Manufacture  of  beet-sugar 771 

"  cane-sugar 773 

Sugar-refining 775 

Manufacture  of  bone-black 777 

Soap-boiling 778 

Principles  of  dyeing 781 

Mordants 785 

Calico  printing 787 

Tanning 788 

Charring  wood  and  coal 790 

Manufacture  of  illuminating  gas 792 


ELEMENTS  OF  CHEMISTRY. 


THIRD  PART. 


§  732.  Although  the  metals  described  in  the  second  part  of 
this  work  are  never  technically  employed  in  the  metallic  state, 
they  still  find  very  extensive  application  in  the  state  of  various 
compounds,  all  of  which  are  manufactured  in  chemical  works  by 
processes  similar  to  those  employed  for  obtaining  them  in  the 
laboratory  on  a  smaller  scale. 

Among  the  metals  yet  remaining  for  our  examination,  however, 
a  considerable  number  are  employed  in  the  metallic  state,  and  are 
extracted  from  their  ores  by  processes  of  a  particular  kind,  called 
metallurgical  processes.  In  every  case  when  they  are  to  be  used 
in  the  metallic  state  they  must  fulfil  all  the  conditions  enumerated 
(§  276) ;  which,  however,  many  do  not,  as  some  are  of  rare  occur- 
rence, while  the  extracting  of  others  presents  too  great  practical 
difficulties,  and  still  others  have  as  yet  found  no  technical  applica- 
tion, being,  therefore,  of  purely  scientific  interest.  Nevertheless, 
on  account  of  the  great  analogy  existing  between  them  in  a  chemi- 
cal point  of  view,  the  study  of  those  which  find  a  technical  appli- 
cation cannot  be  separated  from  that  of  those  which  are  not  so 
applied.  The  latter  will,  therefore,  occupy  our  attention  as  well 
as  the  former,  but  to  a  much  more  limited  extent. 


MECHANICAL  PREPARATION  OF  ORES. 

§  733.  Under  the  general  name  of  ores  are  comprised  such  com- 
binations of  metals,  occurring  in  nature,  as  contain  a  sufficient 
proportion  of  metal  to  be  worked  with  profit.  The  proportion 
varies  with  the  marketable  value  of  the  metal,  and  according  to 
the  greater  or  less  facility  with  which  it  can  be  obtained  from  its 
combination  in  the  ore :  iron  ores,  for  instance,  the  commercial 
price  of  which  metal  is  very  low,  must  therefore  be  very  rich  if  they 
are  to  be  profitably  worked.    The  poorest  minerals  from  which  iron 

9 


10  PREPARATION    OF    ORES. 

could  be  extracted  must  contain  at  least  25  per  cent,  of  iron ;  and 
the  metal  must  moreover  exist  in  them  in  a  state  from  which  it  can 
be  easily  reduced,  in  order  to  be  iron  ores.  A  mineral  of  frequent 
occurrence  is  h'on  pyrites^  a  combination  of  iron  with  sulphur, 
which  contains  about  47  per  cent,  of  the  former,  but  still  cannot 
be  considered  as  an  ore,  as  the  treatment  to  which  it  must  be 
subjected  in  order  to  obtain  a  good  quality  of  iron  would  be  far 
too  costly.  Copper,  on  the  contrary,  the  commercial  value  of 
which  is  much  higher  than  that  of  iron,  can  be  extracted  with  ad- 
vantage from  ores  containing  only  a  few  per  cent,  of  the  metal, 
even  if  these  be  in  combination  with  sulphur ;  and  ores  which  con- 
tain only  some  thousandths  of  silver  or  of  gold  can  be  worked  to 
advantage. 

§  734.  An  ore,  of  whatever  kind  it  may  be,  is  seldom  sufficiently 
rich  to  be  at  once  subjected  to  metallurgical  processes,  but  is,  in 
general,  worked  with  greater  advantage  after  having  been  sorted, 
and  prepared  by  various  mechanical  operations,  which  tend  to 
separate  from  them  the  greater  part  of  the  earthy  substances, 
technically  termed  gangue^  with  which  they  were  mixed.  The 
larger  pieces  of  the  gangue  are  usually  separated  from  the  ore  in 
the  mine  itself,  and  used  to  fill  up  the  excavations  already  made 
in  the  rock;  so  that  only  such  fragments  are  taken  out  of  the  mine 
as  can  be  advantageously  prepared  for  smelting  by  mechanical 
operations. 

§  735,  The  ores  of  iron  employed  are  always  very  rich,  as  those 
which  are  not  so  have  not  sufficient  value  to  be  made  richer  by 
costly  mechanical  processes ;  in  general,  therefore,  the  argillaceous 
parts  are  merely  separated  by  washing  (debourbage).'^  Sometimes 
the  ore  is  left  exposed  to  the  atmosphere  for  several  months,  as 
the  clay  is  thus  rendered  more  friable  and  more  easily  detached. 
The  washing  of  iron  ores  is  performed  (in  France)  in  the  middle 
of  a  stream  of  water,  in  a  series  of  apparatus  called  patouillets.  It 
is  sometimes  considered  sufficient  to  turn  and  stir  the  ore  in  the 
stream  with  a  spade,  by  which  the  argillaceous  parts  are  detached 
and  carried  away ;  but  the  shaking  up  of  the  ore  is  more  frequently 
effected  by  means  of  a  small  water-wheel  R  (fig.  461),  set  in  motion 
by  the  stream.  The  ore,  thrown  with  a  spade  into  the  long  trough 
A,  where  the  water  running  over  it  frees  it  from  a  part  of  its  clay, 
is  thence  transferred  to  the  semi-cylindrical  box  B,  which  is  filled 
with  water,  where  it  is  stirred  by  iron  arms  attached  to  the  axle 
of  the  water-wheel.  The  muddy  water  runs  off  by  an  outlet  at  the 
top  of  the  box,  and  the  washed  ore,  which  is  taken  out  through 
the  orifice  o  in  the  lower  part  of  the  box,  falls  into  the  trough  I), 

*  Since  hard  ores  are  more  abundant  than  soft  in  the  United  States,  the  poorer 
clayey  ores,  instead  of  being  enriched  by  any  mechanical  process,  are  usually 
sought  after  to  mix  with  the  harder  ores  and  render  them  more  easy  of  fluxion 
in  the  furnace. — J.  C.  B, 


PREPARATION    OF   ORES. 


11 


whence  the  workman  removes  it  when  he  finds  it  to  be  sufficiently 
washed. 


Fig.  461. 

§  736.  The  ores  of  other  metals,  when  taken  from  the  mine, 
are  generally  sorted  by  the  hands  of  females  and  children,  who 
separate  them  into — 1st,  pieces  rich  enough  to  be  immediately 
sent  to  the  smelting-works ;  2dly,  fragments  composed  of  ore  and 
gangue,  which  must  be  subjected  to  mechanical  preparations ;  and 
3dly,  pieces  of  gangue,  which  are  thrown  aside  as  useless.  Let 
us  now  examine  the  mechanical  operations  to  which  the  second 
class  is  subjected.  When  the  metalliferous  mineral  is  so  intimately 
mixed  with  the  gangue  that  it  cannot  be  separated  by  the  hammer, 
the  pieces  are  reduced  to  a  small  size  between  cast-iron  cylinders 
or  under  stampers.  Fig.  462  represents  an  apparatus  of  crushing- 
cylinders,  and  figs.  463  and  464  show  the  arrangement  of  the 
cylinders.  Two  kinds  of  hard  cast-iron  cylinders  are  employed ; 
fiuted  (fig.  464),  and  smooth  ones  (fig.  463) ;  in  the  former  of 
which  the  large  fragments  are  broken,  while  the  smooth  cylinders 
reduce  the  pieces  furnished  by  them  to  a  still  smaller  size. 

Only  one  of  these  cylinders.  A,  receives  motion  from  the  water- 
wheel,  the  desired  velocity  being  given  to  it  by  a  system  of  cogs, 
while  the  second  cylinder  B  is  moved  by  the  former.  The  cylin- 
der A  is  borne  by  two  fixed  uprights  K,  while  the  supports  L  of  B 
are  movable  on  the  sliding-boards  ah^  cd.  The  cylinder  B  there- 
fore moves  away  from  A  whenever  a  piece  presents  itself  which 
would  oppose  too  much  resistance  to  crushing ;  but  at  other  times, 
it  is  kept  pressed  against  A  by  the  weight  P,  suspended  to  the  ex- 
tremity of  a  long  lever  ST. 

The  ore  is  brought  to  the  crushing  machine  by  cars,  moving  on 
a  railroad  FF'.  The  workman  throws  it  with  a  spade  into  a  wooden 
hopper  U  placed  above  the  cylinders ;  and  when  it  is  reduced  in 
size  by  passing  between  them,  it  falls  on  an  inclined  jolting-box  M, 
the  bottom  of  which  consists  of  a  wire  sieve,  with  very  small  open- 
ings at  the  top,  and  larger  ones  at  the  lower  part.     The  finest 


12 


PREPARATION   OF   ORES. 


Fig.  462. 

grains  pass  through  the  upper  sieves ;  while  those  fragments  which 
have  passed  the  under  ones  roll  to  the  bottom  of  the  box  M,  and 
fall  into  a  wheel  RR'E",  provided  with  boxes ;  which,  by  a  slow 
rotary  movement,  brings  the  pieces  of  ore  up  again  into  the  box  U, 

Fig.  463. 


Fig.  464. 


PREPARATION   OF   ORES.  13 

whence  they  again  pass  between  the  cylinders  with  the  ore  recently 
supplied  from  the  mine. 

The  ore,  when  broken  by  the  fluted  cylinders,  is  thus  sorted  by 
the  sieves  in  the  box  M  into  diiFerent  sized  grains,  from  the  heaps 
of  which  the  largest  pieces  are  often  removed  by  hand ;  then  such 
portions  are  separated  as  are  fit  for  immediate  smelting,  the  pieces 
of  gangue  are  thrown  aside,  and  the  mixture  of  ore  and  gangue 
which  requires  again  to  be  reduced  in  size  is  passed  through  the 
system  of  smooth  cylinders.  In  this  case  the  ore  is  not  thrown 
directly  into  the  box  U,  but  into  a  box  V  divided  into  different 
parts  (fig.  462),  the  bottom  of  which  consists  of  a  sieve,  which, 
keeping  back  the  too  large  fragments,  allows  only  those  of  the 
proper  dimensions  to  fall  on  the  cylinders.  The  .crushed  ore  is 
again  received  in  a  box  M,  the  sieves  of  which  are  much  finer  than 
those  which  receive  the  pieces  falling  from  the  fluted  cylinders. 
By  this  operation  pieces  of  4  or  5  millimetres  (about  J  inch)  are 
obtained,  which  is  a  convenient  size  for  the  subsequent  operations. 
The  forming  of  smaller  pieces  and  of  dust  cannot  entirely  be 
avoided,  although  it  is  sought  to  diminish  their  quantity  as  much  as 
possible.  ^ 

§  737.  The  ore,  reduced  to  more  or  less  fine  grains,  is  submitted 
to  further  operations  in  the  jigging  machine^  (crible  h  ddp6t,)  the 
theoretical  principles  of  which  are  the  following : 

If  bodies  differing  in  shape,  size,  and  specific  gravity  be  let  fall 
into  a  liquid  which  is  quiet  at  the  time,  these  bodies  will  experi- 
ence different  resistances  in  their  fall,  and  arrive  at  different  times 
at  the  bottom  of  the  liquid ;  so  that  a  kind  of  separation  is  effected, 
during  their  fall,  by  the  position  the  pieces  occupy  in  the  deposite 
formed  at  the  bottom  of  the  vessel. 

If  we  suppose  these  bodies  to  be  similar  as  to  shape  and  size,  but 
differing  in  their  specific  gravity,  then  they  will  all  experience 
equal  loss  in  the  totality  of  their  movement  in  the  liquid,  because 
the  resistance  a  body  meets  with  in  passing  through  a  liquid,  de- 
pends entirely  on  its  form  and  extent  of  surface,  but  not  on  its 
density.  But  the  loss  will  be  more  sensible  as  the  momentum  of 
the  bodies  is  greater,  that  is,  as  their  specific  gravity  is  higher ;  so 
that  the  least  dense  particles,  traversing  the  central  strata  of  the 
liquid  more  slowly  than  the  others,  will  arrive  last  at  the  lower  part 
of  the  vessel ;  and  the  deposite  formed  will  thus  consist  of  different 
layers,  in  which  the  particles  will  have  arranged  themselves  ac- 
cording to  their  specific  gravities,  the  most  dense  occupying  the 
lowest  place  and  the  lightest  ones  the  top. 

Supposing,  on  the  other  hand,  the  bodies  falling  into  the  liquid  to 
be  all  of  equal  density,  and,  moreover,  all  to  have  the  same  form, — 
for  example,  to  be  all  cubes  or  spheres, — but  differing  in  size,  then 
will  their  momentum  during  their  fall  be  in  proportion  to  their 
volume.     The  resistance  opposed  to  the  particles  by  the  liquid  will 


14  PREPARATION   OF   ORES. 

be  proportioned  to  their  surfaces,  as  we  have  supposed  both  their 
form  and  relative  position  while  passing  through  the  liquid  to  be 
the  same.  Therefore,  since  volumes  vary  as  the  cubes  of  homolo- 
gous dimensions,  'vvhile  surfaces  only  vary  as  the  squares  of  such 
dimensions,  the  momenta  of  the  bodies  will  stand  in  proportion  to 
the  cubes  di^  of  one  of  their  dimensions,  while  the  resistance  offered 
to  them  by  the  liquid  will  be  proportional  only  to  the  squares  cP' 
of  the  same  dimension.  If  M  and  m  represent  the  volumes  of  two 
bodies  of  the  same  density,  and  D  and  d  their  homologous  dimen- 
sions, then  will  their  momenta  be  proportional  to  M^  and  mg^  or  to 
D-^6^  and  d^bg ;  5  representing  the  specific  gravities  of  the  bodies, 
and  g  their  absolute  weight.  The  loss  of  momentum  they  experi- 
ence by  the  resistance  of  the  liquid  will  be  proportional  to  D^  and 
dj^ ;  and  is  a  fractional  part  of  the  whole  momentum,  larger  for  the 
smaller  bodies  than  for  those  of  a  larger  size,  this  fraction  being 
~^g  or  j^  for  the  largest,  and  J^  or  ^  for  the  smallest,  where  a 
represents  the  coefficient  of  resistance,  which  is  constant  in  both 
cases.  The  largest  particle  will  therefore  arrive  first  at  the  bottom 
of  the  liquid,  and  the  deposite  will  consist  of  strata  arranged  accord- 
ing to  the  size  of  the  pieces  constituting  them,  the  largest  occupy- 
ing the  lowest  situation. 

Lastly,  we  will  suppose  the  bodies  to  be  equal  as  regards  density 
and  volume,  but  differing  in  form, — some  for  instance,  being  cubes, 
and  others  laminated  rectangles ;  then  will  the  latter,  having  a 
greater  extent  of  surface  than  the  cubes,  meet  with  a  greater  re- 
sistance while  traversing  the  liquid ;  and  the  cubes,  arriving  first 
at  the  bottom  of  the  vessel,  will  leave  the  flattened  particles  in  a 
layer  on  the  upper  surface  of  the  deposite  formed. 

Let  us  now  examine  how  these  principles  may  be  applied  to  the 
preparation  of  ores.  We  have  seen  that  the  sieves  placed  under 
the  crushing-cylinders  divide  the  material  into  equal  classes,  each 
of  which  is  composed  of  pieces  of  a  nearly  uniform  size ;  but  we 
will  now,  to  make  the  reasoning  more  simple,  suppose  these  frag- 
ments, consisting  of  pure  ore,  or  pure  gangue,  or  a  mixture  of  the 
two,  to  be  exactly  equal  as  to  form  and  volume.  Metalliferous  ores 
being  in  general  much  heavier  than  the  gangue  by  which  they  are 
accompanied,  the  fragments  of  the  former  will  evidently  first  arrive 
at  the  bottom  of  the  vessel,  and  on  them  the  pieces  composed  of 
ore  and  gangue  will  deposit,  while  the  fragments  of  pure  gangue 
will  constitute  the  uppermost  layer.  The  deposite  can  then  be 
divided  into  three  parts :  pure  gangue,  which  lies  uppermost,  and 
is  rejected ;  pure  ore,  forming  the  lowest  stratum,  which  is  sent  to 
the  smelting-works ;  and  lastly,  an  intermediate  layer,  consisting 
of  ore  and  gangue  not  sufficiently  rich  for  immediate  smelting, 
which  must  again  be  crushed,  and  undergo  the  process  of  washing 
over  again. 

It  is  evidently  essential  for  the  process  of  separation  to  obtain 


PREPARATION    OF   ORES. 


15 


the  fragments  as  equal  as  possible,  regarding  both  form  and  size  ; 
but  this  condition  cannot  be  fulfilled  at  will.  By  means  of  sieves 
of  different  fineness  equality  of  size  can  be  attained  with  more  or 
less  accuracy;  but  by  no  known  process  can  the  pieces  be  obtained 
of  a  similar  form,  because  this  latter  character  depends  on  the 
molecular  constitution  of  the  minerals  to  be  separated,  on  their 
cleavage,  etc.  It  may  therefore  very  well  occur  that  a  species  of 
crushed  ore  may  contain  lamillar  fragments  of  pure  metalliferous 
ore,  and  cubic  or  spherical  pieces  of  gangue,  which  nevertheless 
passed  through  the  same  sieve ;  and  that  therefore  the  ore,  which 
by  virtue  of  its  greater  specific  gravity  tends  to  fall  faster  through 
the  water  than  the  gangue,  will  still  form  the  upper  layer  of  the 
deposite,  on  account  of  the  greater  resistance  the  liquid  offers  its 
lamillar  fragments  compared  with  that  opposed  to  the  cubic  pieces 
of  gangue.  As  all  these  circumstances  present  themselves  simul- 
taneously in  practice,  the  separation  of  ores  from  their  gangue  is 
prevented  from  being  as  perfect  as  it  would  be  if  the  simple  cases 
just  now  supposed  could  be  realized. 

§  738.  The  separation  of  ores  into  pieces  of  an  equal  size  is  of 
such  importance,  that  it  is  frequently  done  with  the  pieces  which 
have  already  been  sorted  by  hand,  or  with  the  larger  pieces  from 
the  crushing  cylinders.  Fig.  465  represents  the  swing-sieve  {crible 
a  secousses)  employed  for  this  purpose,  which  consists  of  two  boxes 


Fig.  465. 

A.BCD,  ef,  placed  one  above  the  other,  both  of  which  are  kept  m 
motion  by  the  rods  tr  and  uv,  connected  with  a  water-wheel.  Part 
of  the  water  led  into  the  first  box  by  means  of  the  canal  os  passes, 


16 


PREPARATION    OF   ORES. 


by  the  canal  g^  into  the  box  underneath ;  and  the  bottom  of  both 
boxes  consists  of  a  sieve,  the  meshes  of  which  are  larger  in  the  box 
ABCD  than  in  the  other.  A  part  of  the  ore  which  is  placed  in 
the  upper  sieve  falls  through  into  the  sieve  e/,  where  it  is  again 
sifted ;  and  the  ore  is  thus  divided  into  grains  of  three  different 
sizes.  That  which  is  too  coarse  to  pass  through  the  meshes  of 
the  sieve  in  ABCD  falls  on  the  platform  mn,  while  the  grains 
which  remained  on  the  sieve  in  e/are  collected  in  the  box  5R,  and 
lastly,  the  finest  quality,  which  has  escaped  through  the  under- 
most sieve,  is  received  by  a  box  placed  directly  underneath  the 
latter. 

§  739.  A  jigging  machine  (fig.  466)  consists  of  a  cylindrical  box 
C,  the  bottom  of  which  is  a  piece  of  wire-gauze  or  netting,  with 
meshes  of  sufiicient  fineness  to  retain  the  fragments  of  ore.     The 

sieve  is  suspended  by  an 
iron  bar  A,  attached  to  a 
horizontal  bar  qJi,  and 
counterbalanced  by  the 
weight  P ;  and  is  kept  in 
a  tub  B,  which  is  filled 
with  water.  The  work- 
man sets  the  machine  in 
motion  by  means  of  a  ver- 
tical wooden  pole  E,  which 
is  guided  by  moving  in 
the  slider  D.  Taking  the 
ore  to  be  washed  from  the 
table  A,  he  half-fills  the 
sieve  C,  and  then  keeps 
the  latter  in  a  lively  jolt- 
ing motion  in  the  water. 
The  sieve  receives  during 
its  descent  a  violent  con- 
cussion against  the  bottom 
of  the  tub,  when  the  water, 
penetrating  through  the 
sieve,  holds  in  suspension  the  ore,  which  by  the  shock  is  for  a  mo- 
ment not  influenced  by  its  own  weight ;  and  the  different  pieces 
which  fall  back  from  the  centre  of  the  liquid  have  a  tendency  to 
separate,  according  to  the  laws  developed  above.  When  the  height 
of  the  fall  is  small,  a  numerous  repetition  of  shocks  has  the  same 
effect  in  separating  the  pieces  as  when  they  fall  from  a  greater 
height.  The  workman  then,  after  some  time,  finds — 1st,  at  the  upper 
surface  of  his  sieve,  a  layer  of  pure  gangue,  which  can  be  thrown 
aside,  or,  at  least,  very  poor  ore,  which  must  be  stamped  to  powder 
in  order  to  separate  any  parts  that  might  be  worth  smelting ;  2dly, 
a  central  stratum,  consisting  of  fragments  of  ore  and  gangue  corn- 


Fig.  466. 


PREPARATION   OF   ORES. 


IT 


bined,  which  ought  to  be  reduced  in  size  before  being  again  jigged ; 
and  3dly,  at  the  bottom  of  his  sieve,  a  layer  of  ore  of  suflicieut 
purity  to  be  smelted.  The  central  layer  is  generally  set  aside, 
and,  when  a  sufficient  quantity  has  been  collected,  is  subjected  to 
another  jigging  without  being  first  reduced  in  size,  by  which  he 
obtains  again  a  quantity  of  ore  fit  for  smelting. 

In  well-arranged  works  the  jigging-machines  are  set  in  motion 
by  water-power,  in  which  case  apparatus  of  a  much  larger  size  may 
be  used,  and  may,  moreover,  be  superintended  by  children. 

By  this  process  very  small  fragments  of  ore,  of  the  diameter  of 
1  millimetre,  may  be  purified  ;  but  the  meshes  of  the  wire-gauze  in 
the  jigging-machine  must  then  be  much  finer  than  those  employed 
for  washing  larger  fragments. 

§  740.  Such  ores  as  cannot  be  sufficiently  enriched  by  the  use 
of  sieves  are  sent  to  the  stamping-mill  (fig.  467),  which  is  com- 
posed of  a  sys- 
^^mm  tem  of  stampers 

PP',  consisting 
of  pieces  of  tim- 
berP',shodatthe 
lower  end  by  cast- 
iron  pieces  P. 
All  the  stampers 
fall  into  a  single 
trough  u,  the  bot- 
tom of  which  con- 
sists of  a  strong 
sheet-iron  plate, 
sustained  by  a 
solid  foundation 
of  masonry,  while 
its  sides  are  made 
of  iron  sieves,  or 
plates  of  sheet- 
iron  pierced  with 
holes.  A  water- 
wheel  moves  the 
axle  xt/,  on  the  surface  of  which  cams  are  fixed,  which,  by  lifting 
the  catches  m,  set  the  stampers  in  motion.  (In  the  cut,  the  lateral 
walls  of  the  trough  are  supposed  to  have  been  removed  from  before 
three  of  the  stampers,  in  order  to  show  the  iron  ends  P  of  the  lat- 
ter.) The  cams  are  so  arranged  on  the  axle  rry,  that  by  always 
lifting  but  one  of  the  stampers  at  a  time,  the  strain  on  the  ma- 
chinery is  kept  as  constant  as  possible. 

A  current  of  water  constantly  flowing  through  the  trough  of  the 
stamping-mill,  into  which  ore  is  thrown  with  a  spade,  the  parts 
which  are  already  reduced  to  a  sufficient  fineness  flow  off  through 

Vol.  II.— 2 


Fig.  467. 


18  PREPARATION   OF   ORES. 

the  lateral  sieves,  being  held  in  suspension  by  the  water,  from 
which  they  tend  to  deposit  in  the  canals  CD,  E  extending  along 
the  whole  length  of  the  battery  of  stampers.  They  are  thence  led 
in  circuitous  windings,  called  a  labyrinth^  over  the  floor  of  the 
building.  The  coarser  particles  are  deposited  at  the  heads  of  the 
various  canals,  while  the  fine  grains  are  carried  farther  away ; 
and  as  the  waters,  which  traverse  the  channels  at  a  very  slow  rate, 
are  often  still  muddy  after  having  passed  through  the  whole  sys- 
tem, they  are  conducted  into  large  reservoirs,  where  they  deposit 
even  the  finest  particles  they  held  in  suspension.  The  deposite  in 
the  channels  is  called  sludge,  (schlich ;)  while  that  in  the  reservoirs, 
which  resembles  a  thin  mud,  is  termed  mud  or  fine  sludge,  (schlamm :) 
the  former  difi'ers  in  size  of  grain  as  well  as  in  metallic  richness, 
according  to  the  different  parts  of  the  canals  from  which  it  is 
taken,  and  is  thus  divided  into  several  classes,  each  of  which  is 
separately  subjected  to  further  operations. 

The  sludge  is  washed  in  three  different  kinds  of  apparatus  :  the 
deposit-trough,  (caisse  si  tombeau,)  the  sleeping-table  or  niching- 
huddle,  (table  dormante,)  and  the  percussion-table  or  brake-table^ 
(table  a  secousse.) 

§  741.  The  physical  principles  on  which  the  washing  of  sludge 
is  founded  are  rather  different  from  those  of  the  washing  in  sieves, 
as  the  latter  is  applicable  only  to  fragments  of  a  certain  size.  The 
ore  no  longer  acts  by  its  weight  in  a  quiet  liquid,  but  is  in  this  case 
submitted  to  the  action  of  running  water  on  an  inclined  plane.  The 
impulse  imparted  to  the  different  pieces  by  the  water  being  now 
proportional  to  their  surfaces,  but  independent  of  their  volumes 
and  densities,  they  would,  were  their  surfaces  equal,  be  carried 
more  or  less  far  by  the  impulse  of  the  liquid,  according  to  their 
weight ;  and,  if  their  form  were  similar  at  the  same  time,  those 
of  the  least  specific  gravity  would  be  carried  farthest.  But  if  their 
densities  and  volumes  were  equal,  those  presenting  the  greatest 
extent  of  surface  would  be  deposited  farthest  off;  and  lastly,  with 
equal  densities  and  forms,  the  smaller  particles  would  go  farther 
than  .the  larger  ones,  because  they  present  the  greater  relative 
extent  of  surface.  We  see,  therefore,  that  in  these  new  opera- 
tions, as  well  as  in  washing  with  sieves,  the  separation  of  the  ore 
depends  not  only  on  the  specific  gravities,  but  also  on  the  volumes 
and  forms  of  the  small  pieces  ;  for  which  reason,  the  ore  to  be 
washed  must  be  of  as  equal  a  grain  as  possible. 

§  742.  The  deposit-trough  consists  of  long  wooden  troughs  BO 
(fig.  468),  the  bottoms  of  which  are  slightly  inclined,  and  closed  at 
their  extremity  C  by  a  board  pierced  with  several  holes  at  different 
heights,  which  are  closed  with  stoppers  during  the  operation.  The 
sludge  to  be  washed  is  placed  on  the  benches  A  at  the  head  of  the 
machine,  where  it  is  met  by  a  current  of  water,  which,  taking  the 
ore  into  suspension,  falls  into  the  boxes  BO,  and  there  deposits  it 


PREPARATION   OF  ORES, 


19 


Fig.  468. 

again  at  diiFerent  distances  from  the  bench  A,  while  the  finest  par- 
ticles still  remain  in  the  water  and  render  it  muddy.  As  soon  as 
the  boxes  are  filled  with  water,  the  supplying  stream  is  turned  ofi*, 
and  the  openings  at  the  extremity  C  are  uncorked ;  the  muddy 
water,  then  running  through  the  canal  UU'  and  a  system  of  troughs 
into  reservoirs,  there  deposits  the  particles  it  carried  away.  The 
washing  of  a  fresh  quantity  of  ore  is  then  begun  immediately,  the 
sludge  and  mud  of  which  is  again  borne  by  the  water  to  the  reser- 
voirs and  there  deposited ;  and  so  on  until  the  deposit  has  attained 
the  thickness  of  a  foot  or  two ;  each  operation  difi'ering  from  the 
former  only  in  the  manner  in  which  the  water  is  let  ofi"  through  0, 
as  each  time  a  higher  opening  is  unplugged. 

The  deposite  of  ore  in  the  bottom  of  the  box  AB  is  divided  into 
three  parts,  which  are  treated  separately  in  the  subsequent  opera- 
tions. The  sludge  on  the  highest  part  of  the  inclined  is  often  rich 
enough  to  be  sent  to  the  furnaces  at  once ;  while  the  deposite  on 
the  centre  and  lowest  part,  the  latter  of  which  is  the  poorest,  are 
subjected  to  new  washings,  either  in  the  machine  just  described  or 
on  the  percussion  or  the  sleeping-tables. 

§  743.  The  sleeping -tables  (sometimes,  called  in  the  French,  tahles 
jumelles,  from  their  being  generally  arranged  in  pairs)  consist  of 
inclined  tables  AB  (fig.  469),  from  20  to  24  feet  long,  furnished  with 
borders  of  wood,  serving  to  keep  the  water  running  over  them  in 


Fig.  469. 


20 


PREPARATION   OF   ORES. 


its  place.     At  tlie  head  A  of  the  table,  two  laths  are  set  at  the 
angle  BAG  (fig.  470),  on  a  plane  which  is  more  inclined  than  the 

long  plane  ;  and  between  which  only 
a  small  aperture  A  is  left,  through 
which  the  water  with  suspended 
sludge  is  introduced.  Small  trian- 
gular prisms  of  wood,  set  up  on  this 
inclined  plane,  equally  divide  the 
arriving  stream,  and  cause  the  water 
to  flow  in  a  uniform  layer  over  the 
whole  surface  of  the  plane.  The 
ore  to  be  washed  is  thrown  into  a 
J1-     47Q_  trough  M   (fig.  469),  into  which  a 

thin  stream  of  water  is  constantly 
falling,  and  where  it  is  constantly  kept  in  motion  by  a  small  bucket- 
wheel,  which  again  is  moved  by  an  overshot  water-wheel,  fed  by 
the  canal  oo'.  The  ore  is  thus  put  in  suspension  in  the  water, 
which,  continually  flowing  into  a  canal  placed  lengthwise  at  the 
head  of  the  tables,  finds  its  way  on  to  the  sleeping-tables  through 
the  openings  A  (fig.  470) ;  and  the  plane  A  (fig.  469),  on  which  it 
first  arrives,  being  too  much  inclined  to  allow  any  ore  to  deposit, 
the  forming  of  a  deposite  first  commences  on  the  tables  intended  for 
the  purpose.  Here  the  richest  parts  will  form  the  sediment  at  the 
higher  end  of  the  table,  while  the  poorest  grains  will  only  be  de- 
posited at  the  bottom  of  the  inclined  plane,  or  even  carried  away 
into  the  canal  CC,  which  leads  them  into  other  canals  and  depo- 
siting reservoirs. 

As  soon  as  the  table  is  covered  with  a  suiEcient  quantity  of  ore, 
the  workman  cuts  off*  the  further  supply  of  sludge,  and,  after  having 
swept  all  the  ore  lying  between  A  and  uv  towards  A  with  a  broom, 
allows  a  current  of  clear  water  to  flow  over  the  tables,  by  which 
the  ore  is  again  spread  over  the  latter ;  and  while  the  poorer  parts 
collect  towards  the  bottom, of  the  inclined  plane,  that  lying  on  the 
higher  parts  can  in  general  be  at  once  sent  to  the  smelting-works. 
The  table  has  at  uv  a  transverse  opening,  which  remains  closed 
•during  the  washing  by  a  valve,  which  should  not  project  above  the 
table ;  but  at  the  close  of  the  operation,  the  valve  being  opened,  the 
workman  sweeps  the  sludge  through  the  opening  uv  into  boxes 
placed  beneath. 

The  sleeping-tables  are  more  or  less  inclined,  according  to  the 
nature  of  the  ore  to  be  washed;  the  finest  ores  requiring  the 
greatest  inclination. 

§  744.  The  percussion-table  serves  for  washing  the  same  kinds 
of  ore  as  the  sleeping-table,  the  one  or  the  other  being  preferred 
according  to  the  nature  of  the  ore  and  gangue  in  each  special  case. 
The  percussion-table  consists  of  an  inclined  board  BC  (fig.  471), 
resting  on  beams  of  wood  to  give  it  greater  weight  and  solidity. 


PREPARATION   OF    ORES. 


21 


The  whole  is  suspended  in  the  air  by  four  chains  or  bars  of  iron 
ah^  a'b\  tt\  tt\  of  which  the  former  two  are  attached  to  fi-xed  sup- 
ports, while  the  chains  tt'^  it'  are  fixed  to  a  long  movable  lever  LL', 
which  turns  by  the  axis  00',  and  serves  to  vary  the  degree  of  in- 
clination of  the  plank  BC,  being  held  in  the  height  desired  by 
means  of  iron  pins  entering  the  horizontal  beam  xy. 


Fig.  471. 

The  cams  cc  on  the  axle  XX',  which  is  turned  by  a  water-wheel, 
act  on  a  curved  wooden  lever  K,  which  pushes  forward  the  sus- 
pended plank  BC,  and  immediately  abandons  it  again,  so  that  the 
latter,  falling  forcibly  back  against  the  wooden  supporting  beams, 
receives  a  violent  shock  throughout  its  whole  mass.  Above  the 
head  B  of  the  suspended  plank  is  a  triangular  inclined  plane  A, 
fortified  with  small  prisms,  and  similar  to  that  in  fig.  470. 

The  ore  to  be  washed  is  heaped  in  the  box  V,  which  receives  a 
continual  stream  of  water  ;  from  there  it  spreads  over  the  slope  A 
and  the  suspended  plank  BC,  where  it  has  a  tendency  to  deposit. 
But  the  violent  shocks  the  plank  is  constantly  receiving,  causes  the 
particles  to  be  continually  detached  and  taken  into  suspension  by 
the  water ;  so  that  they  are  then  under  the  most  favourable  cir- 
cumstances to  be  carried  oif  precisely  according  to  the  order  of 
their  density  and  size.  The  inclination  of  the  plank,  the  violence 
and  frequency  of  the  shocks,  and  the  quantity  of  water  holding  the 
sludge  in  suspension,  are  varied  according  to  the  nature  of  the  ore 
to  be  washed. 

§  745.  By  these  different  methods  of  washing,  sludges  of  greater 
or  less  fineness  of  grain  and  richness  in  metal  are  obtained,  and 
are  sorted  accordingly.  Each  of  these  kinds  of  sludge  is  generally 
subjected  to  a  chemical  test,  to  ascertain  their  nature  and  richness 
in  metal.  They  are  then  mixed,  according  to  certain  proportions 
which  practice  has  shown  to  be  the  most  convenient,  foreign  sub- 
stances being  added  if  necessary.  These  mixtures,  called  charges^ 
are  then  ready  for  fusion  in  the  furnaces. 


22  PREPi\  RATION   OF   ORES. 

The  meclianical  preparation  of  ores  is  one  of  the  most  important 
operations  in  the  extraction  of  certain  metals.  Great  intelligence 
is  required  in  the  arrangement  of  such  works,  as  the  processes 
which  perfectly  succeed  in  one  locality  may  be  quite  inefficient  in 
another,  where  the  ore  occurs  in  a  different  gangue  or  presents  a 
different  state  of  aggregation. 

The  adjoined  plate  gives  a  connected  view  of  the  different  appa- 
ratus for  mechanical  preparation  and  washing  just  described,  as 
well  as  the  succession  of  canals  and  arrangement  of  the  depositing 
reservoirs,  which  are  generally  placed  under  the  flooring  of  the 
building.  The  canals  and  basins  form  a  large  labyrinth,  the  cor- 
responding parts  of  which,  coming  from  different  washing-machines, 
unite  at  points  where  the  muddy  water  contains  similar  substances 
in  suspension.  The  whole  apparatus  is  moved  by  the  same  water- 
wheel  E.R'. 


23 


MANGANESE. 

Equivalent  =  28  (350  -,  0  =  100.) 

§  746.  Manganese*  is  obtained  by  reducing  one  of  its  oxides  by 
cbarcoal  at  a  high  temperature.  A  pure  and  very  dense  protoxide, 
obtained  by  subjecting  carbonate  of  manganese  to  strong  calcina- 
tion in  a  closed  crucible,  is  mixed  with  J^^  its  weight  of  charcoal 
and  jV  of  fused  borax,  and  heated  to  the  highest  possible  tempera- 
ture in  a  forge-fire,  in  a  "brasqued"  or  charcoal  crucible.  The  borax 
added  facilitates  the  union  of  the  metallic  globules  into  a  button. 
The  carburetted  metal  thus  obtained  is  to  the  pure  metal  as  cast- 
iron  is  to  malleable  iron,  and  may  be  purified  by  a 
second  fusion  with  a  small  quantity  of  carbonate  of 
manganese,  in  a  small,  well-closed  porcelain  crucible, 
luted  into  an  earthen  crucible,  as  shown  in  fig.  472. 
The  manganese  thus  obtained  possesses  a  certain 
degree  of  ductility;  and,  although  it  may  be  filed, 
breaks  under  the  blow  of  a  hammer,  showing  a  gray 

fracture  much  resembling  that  of  certain  kinds  of 

Fig  472       cast-iron.      Its  specific  gravity  is  about  8.0 ;  and  it 

is  as  difficult  of  fusion  as  iron. 
Manganese  has  a  great  affinity  for  oxygen,  as  its  surface  becomes 
tarnished  by  exposure  to  a  moist  atmosphere,  and  covered  with 
dark-brown  rust.  It  decomposes  water  slowly  at  ordinary  temper- 
atures with  the  evolution  of  hydrogen,  but  effects  rapid  decom- 
position at  212°.  By  blowing  on  a  piece  of  manganese,  the  same 
disagreeable  odour  is  perceived  which  is  given  off  by  a  carburetted. 
metal  dissolving  in  a  weak  acid.  To  preserve  the  metal,  it  must 
be  kept  from  contact  with  the  air,  and  is  therefore  generally  kept 
in  naptha,  like  potassium ;  but  it  is  better  to  put  the  button  in  a 
hermetically  sealed  glass  tube. 

COMBINATIONS  OP  MANGANESE  WITH  OXYGEN. 

§  747.  Five  compounds  of  manganese  with  oxygen  are  known ; 
the  first  of  which  MnO  is  a  strong  base ;  the  second,  Mn^Og,  plays 
the  part  of  a  very  weak  base ;  the  third,  MnOgj-is  neither  base  nor 
acid;  while  the  two  last,  MnOg  and  Mn^Oy,  are  well  characterized 
acids. 

*  Peroxide  of  manganese  has  been  known  for  a  long  time,  but  it  was  not  until 
1774  that  Scheele  proved  it  to  be  a  peculiar  oxide,  from  which  Gahn  obtained  the 
metal  several  years  after. 


24 


MANaANESB. 


Protoxide  of  Manganese  MnO. 

§  748.  Protoxide  of  manganese  is  obtained  by  reducing  one  of 
the  higher  oxides  of  the  metal  with  hydrogen,  or  by  calcining  the 
carbonate  without  the  contact  of  air ;  which  is  effected  by  placing 

the  carbonate  in  a  glass 
bulb  A  (fig.  473),  blown 
on  a  tube  ah,  and  com- 
municating with  an  ap- 
paratus disengaging  dry 
hydrogen  gas.  As  soon 
as  the  air  is  completely 
driven  out  of  the  appa- 
ratus by  the  hydrogen, 
Fig.  473.  the    bulb   A    is   heated 

with  an  alcohol-lamp ; 
when  the  carbonate,  disengaging  its  carbonic  acid,  leaves  the  prot- 
oxide, the  hydrogen  preventing  the  latter  from  being  surrounded 
by  air.     The  parts  h  and  e  of  the  tube  (fig.  474)  are  then  drawn 

out  and  closed  by  means  of  a  lamp.   The 
protoxide  of  manganese  thus  prepared, 
is  a  clear,  delicate  green  powder,  which 
Fig  474  oxidizes  rapidly  in  the  air,  unless  it  has 

been  subjected  to  a  slightly  elevated 
temperature.  The  protoxide  is  better  aggregated  and  less  change- 
able when  the  decomposition  of  the  carbonate  has  been  efi*ected  in 
a  porcelain  tube  strongly  heated  in  a  reverberatory  furnace. 

By  heating  native  peroxide  of  manganese,  or  a  large  mass  of 
carbonate,  in  a  "  brasqued"  crucible  in  a  forge-fire,  a  well-aggre- 
gated, fine  green  mass  is  obtained,  which  the  air  does  not  afi'ect  at 
ordinary  temperatures.  The  surface  of  the  mass  often  consists  of 
a  thin  pellicle  of  reduced  metal ;  but  a  complete  reduction  is  not 
propagated  by  cementation,  the  immediate  contact  of  charcoal  being 
essential. 

Protoxide  of  manganese  is  a  powerful  base.  Caustic  potassa 
precipitates  it  from  its  solutions  as  white  hydrated  protoxide,  which 
rapidly  changes  into  brown  sesquioxide  by  absorbing  oxygen  from 
the  atmosphere. 

Sesquioxide  of  Manganese  MngOg. 

§  749.  Sesquioxide  of  manganese  MugOg  occurs  crystallized  in 
nature,  both  in  the  anhydrous  and  hydrated  state ;  the  latter  much 
resembling  in  its  external  appearance  the  peroxide,  with  which  it 
is  often  associated.  But  the  two  oxides  are  easily  distinguished  by 
the  colour  of  their  streak  or  powder,  that  of  the  peroxide  being 
dark  gray,  while  that  of  the  sesquioxide  is  brown. 


OXIDES    OP   MANGANESE.  25 

Peroxide  of  Manganese  MnOg. 

§  750.  This  oxide,  the  most  abundant  of  all  the  oxides  of  man- 
giinese,  is  also  the  most  valuable,  from  its  property  of  giving  with 
chlorohydric  acid  the  greatest  quantity  of  chlorine.  It  occurs  crys- 
tallized in  elongated  prisms  of  a  gray  colour  and  metallic  lustre. 
Hydrated  peroxide  of  manganese  is  obtained  as  a  dark-brown 
powder  by  decomposing  manganate  of  potassa  with  hot  water,  or 
by  passing  chlorine  through  water  containing  carbonate  of  manga- 
nese in  suspension. 

By  calcining  peroxide  of  manganese  in  an  earthenware  retort 
until  the  evolution  of  oxygen  ceases,  a  brown  powder  containing 
27.6  per  cent,  of  oxygen  is  obtained,  with  the  formula  MugO^.  It 
is  generally  called  red  oxide  of  manganese^  and,  as  it  behaves  as  a 
combination  of  protoxide  with  sesquioxide,  is  often  written  MnO, 
Mn^Os ;  for  when  it  is  treated  with  an  acid,  protoxide  is  dissolved 
and  sesquioxide  remains. 

Manganic  and  Permanganic  acids  MnOg  and  Mn^Oy. 

§751.  The  two  acid  combinations  of  manganese  with  oxygen 
are  obtained  by  treating  caustic  potassa  with  peroxide  of  manga- 
nese, either  with  access  of  air,  or  with  substances  possessing  high 
oxidizing  properties.  By  heating  equal  proportions  of  finely  pow- 
dered peroxide  and  caustic  potassa  without  access  of  air,  and  dis- 
solving the  substance  obtained  in  cold  water,  a  green  solution  is 
formed,  and  a  mixture  of  hydrated  sesquioxide  and  binoxide  re- 
mains as  a  reddish-brown  powder.  The  green  liquid  contains, 
besides  some  potassa  in  excess,  manganate  of  potassa  K0,Mn03,  a 
portion  of  the  binoxide  MnO^  having  been  reduced  to  sesquioxide 
MugOg,  by  giving  off  oxygen  to  another  portion  of  the  binoxide, 
which  was  thus  oxidized  to  manganic  acid  MnOg.  A  greater  pro- 
portion of  manganate  of  potassa  is  obtained  by  making  the  calcina- 
tion in  the  air ;  or  still  better,  in  an  atmosphere  of  oxygen.  Some 
peroxide  of  manganese,  reduced  to  an  impalpable  powder,  is  well 
mixed  with  some  caustic  potassa  dissolved  in  as  little  water  as  pos- 
sible ;  the  paste  is  dried  in  a  porcelain  capsule,  and  introduced  in 
fragments  into  a  glass  tube  difficult  of  fusion,  communicating  with 
a  retort  filled  with  chlorate  of  potassa.  The  tube  is  heated  to  a 
dull-red,  and  at  the  same  time  oxygen  is  disengaged  by  heat- 
ing the  chlorate ;  but,  in  order  to  obtain  a  considerable  quantity 
of  manganate,  the  operation  should  be  continued  for  some  time. 
The  substance  gives  with  cold  water  an  intense  emerald-green 
solution,  which,  after  being  filtered  through  a  small  plug  of  asbes-- 
tus  placed  in  the  bottom  of  a  glass  funnel,  is  evaporated  under  the 
receiver  of  an  air-pump,  over  a  capsule  filled  with  concentrated 
sulphuric  acid,  when  beautiful  green  crystals  of  manganate  of 


26  MANGANESE. 

potassa  are  obtained,  generally  mixed  with  white  crystals  of  hy 
drated  potassa,  which  may  be  easily  separated  by  hand.  The  green 
crystals  are  forced  from  the  mother  liquid  still  moistening  them, 
by  placing  them  for  a  time  on  a  piece  of  unburned  porous  clay. 

The  green  crystals  of  manganate  of  potassa  KOjMnOg  dissolve 
without  change  in  a  solution  of  caustic  potassa,  and  are  again  de- 
posited on  evaporating  the  liquid;  but  on  dissolving  them  in  pure 
water  immediate  decomposition  takes  place,  the  colour  of  the  solu- 
tion changing  to  a  beautiful  red,  and  a  brown  precipitate  of  brown 
hydrated  peroxide  being  formed.  The  red  solution  then  contains 
fermanganate  o//?o^assa  KO,Mn„Oy.  The  easy  decomposition  of 
manganic  acid,  even  when  in  combination  with  as  strong  a  base  as 
potassa,  renders  it  impossible  to  obtain  the  acid  isolated. 

By  heating  peroxide  of  manganese  with  soda  or  baryta  in  con- 
tact with  oxygen,  the  manganates  of  soda  and  baryta  are  obtained, 
the  latter  of  which  is  a  green  powder,  nearly  insoluble  in  water. 

When  the  green  mass  containing  the  mixture  of  manganate  of 
potassa,  caustic  potassa,  and  oxide  of  manganese  is  dissolved  in 
boiling  water,  and  boiled  for  several  minutes  longer,  an  intense 
red  solution  is  obtained,  which,  after  being  filtered  through  asbestus 
and  evaporated  under  the  receiver  of  an  air-pump,  gives  prismatic 
dark-red  crystals  of  permanganate  of  potassa.  But  the  most 
simple  process  for  obtaining  this  substance  in  any  quantity  is  the 
following  : — One  part  of  peroxide  of  manganese,  reduced  to  impal- 
pable powder,  is  mixed  with  one  part  of  chlorate  of  potassa, 
and  one  and  a  quarter  parts  of  caustic  potassa,  dissolved  in  the 
least  possible  quantity  of  water,  are  added  :  the  paste  thus  formed 
is  dried  in  a  porcelain  crucible,  during  which  process  a  considerable 
quantity  of  manganate  of  potassa  already  forms.  The  whole  is  af- 
terwards heated  slowly  to  a  dull-red  in  an  earthen  crucible,  then 
boiled  with  water  in  a  glass  flask,  filtered  through  asbestus,  and 
the  liquid  concentrated  in  a  porcelain  capsule  over  an  alcohol- 
lamp,  w^hen,  on  cooling,  crystals  of  permanganate  of  potassa  are 
deposited,  which  may  be  purified  by  recrystallization.  Perman- 
ganate of  potassa  is  not  very  soluble,  as  it  requires  16  parts  of 
water  to  dissolve  1  of  the  salt  at  59°,  while  warm  water  will  dis- 
solve much  more. 

On  adding  nitrate  of  silver  to  a  hot  solution  of  permanganate  of 
potassa,  fine  crystals  of  permanganate  of  silver  are  deposited  on 
cooling,  from  which  other  permanganates  may  be  prepared  by 
adding  to  it  an  equivalent  quantity  of  a  metallic  chloride,  for  the 
silver  combining  with  the  chlorine  leaves  its  permanganic  acid  to 
combine  with  the  metal  which  existed  as  chloride.  After  rubbing 
the  two  substances  with  water,  the  chloride  of  silver  may  be  sepa- 
rated by  decantation  or  by  filtration  through  asbestus. 

Free  permanganic  acid  can  be  obtained  in  aqueous  solution  by 
decomposing  permanganate  of  baryta  with  sulphuric  acid,  added 


MANGANATES  AND  PERMANGANATES.  27 

hj  drops ;  when  insoluble  sulphate  of  baryta  is  formed,  and  the 
decanted  liquid  contains  permanganic  acid.  The  solution  is  of  a 
fine  red  colour,  but  the  acid  decomposes  easily  even  in  the  cold. 

Organic  substances  rapidly  decompose  the  salts  of  both  manganic 
and  permanganic  acid  by  taking  up  a  part  of  their  oxygen,  for 
which  reason  their  solutions  must  not  be  filtered  through  paper-. 
If  a  red  solution  of  permanganate  of  potassa,  containing  caustic 
potassa,  is  filtered  through  paper,  the  filtrate  is  generally  green 
from  containing  manganate ;  but  if  the  solution  is  very  dilute,  or 
the  filtration  slow,  the  liquid  completely  loses  its  colour,  while  the 
paper  takes  a  deep-brown  tinge  from  the  hydrated  peroxide  which 
fills  its  pores. 

Caustic  potassa,  added  to  a  dilute  solution  of  permanganate  of 
potassa,  immediately  changes  the  colour  of  the  solution,  first  to 
violet  and  then  to  a  fine  emerald-green,  the  permangate  being 
reduced  to  manganate,  while  another  quantity  of  potassa  has  en- 
tered into  combination : 

K0,MnA+K0=2(K0,Mn03)+0. 

The  oxygen  remains  in  solution  in  the  water,  since  only  a  small 
quantity  was  disengaged,  and  the  permanganic  solution  is  very 
dilute.  The  decomposition  is  owing  to  the  strong  basic  properties 
of  the  potassa,  which  tends  to  saturate  as  much  acid  as  possible. 
The  changing  from  red  to  green  does  not  take  place  instantane- 
ously, and,  by  adding  the  potassa  in  small  quantities  at  a  time,  the 
liquid  passes  through  all  the  intermediate  shades  between  red  and 
green,  that  is,  through  all  the  shades  of  violet. 

It  was  stated  that  the  colour  of  a  green  solution  of  manganate 
of  potassa  changes  to  red  by  boiling,  hydrated  peroxide  of  manga- 
nese being  precipitated ;  but  this  takes  place  only  when  the  solu- 
tion is  not  too  concentrated.  Green  manganate  is  also  changed  to 
red  permanganate  in  the  cold,  without  any  visible  precipitation  of 
peroxide,  by  adding  more  and  more  cold  water,  the  oxygen  dis- 
solved in  which  effects  the  oxidation ;  the  liquid  again  passing 
through  all  the  shades  produced  by  a  combination  of  green  and 
red.  If  it  is  desirable  that  the  solution  should  not  be  very  dilute,  it 
is  sufficient  to  leave  it  in  contact  with  the  air,  or  to  pass  a  current 
of  oxygen  through  it.  The  name  of  chameleon  mineral  has  been 
given  to  this  substance,  on  account  of  the  phenomena  of  changing 
colour. 

Manganate  of  potassa  is  most  rapidly  converted  into  permanga- 
nate by  the  addition  of  any  acid,  even  of  carbonic ;  but  an  excess 
of  acid  completely  discolours  the  liquid,  by  forming  a  salt  with  the 
reduced  protoxide  of  manganese,  while  oxygen  is  given  off. 

Of  the  oxides  of  manganese,  only  the  protoxide  and  seaquioxide 
are  bases: 


28  MANGANESE. 


PROTOSALTS  OF  MANGANESE. 


§  752.  The  protosalts  of  manganese  are  of  an  amethyst,  or  light 
rose  colour,  which,  however,  very  soon  changes  by  agitating  the 
liquid  in  contact  with  the  air,  or  even  by  pouring  it  from  one  ves-^ 
sel  into  another.*  Caustic  potassa  or  soda  precipitates  white  hy- 
drated  protoxide,  which  soon  changes  to  brown  in  the  air ;  while 
ammonia  has  the  same  effect  in  a  smaller  degree,  a  similar  phe- 
nomena taking  place  to  that  mentioned  in  §  589  for  the  salts  of 
magnesia,  viz.  that  the  ammoniacal  salt  formed  combines  with  the 
salt  of  manganese,  and  gives  a  double  salt  which  an  excess  of  am- 
monia will  not  decompose.  A  perfect  precipitation  cannot  there- 
fore be  effected,  whatever  may  be  the  quantity  of  ammonia  added ; 
for,  if  the  salt  of  manganese  is  neutral,  the  first  drops  of  ammonia 
precipitate  some  protoxide,  but  at  the  same  time  a  corresponding 
quantity  of  ammoniacal  salt  is  formed,  which  is  soon  present  in  suf- 
ficient quantity  to  form  with  the  salt  of  manganese  yet  in  solution  a 
soluble  double  salt  which  is  not  decomposed  by  ammonia.  An  excess 
of  ammonia  redissolves  the  hydrated  protoxide  already  precipitated, 
by  entering  into  combination  with  it,  unless  the  precipitate  has  not 
already  changed  to  brown  sesquioxide,  which  is  insoluble  in  am- 
monia. By  exposing  the  ammoniacal  solution  of  protoxide  to  the 
air,  oxygen  is  absorbed,  and  the  manganese  is  at  last  completely 
precipitated  as  hydrated  sesquioxide. 

The  alkaline  carbonates  give  a  dirty  white,  and  ferrocyanide  of 
potassium  a  rose-coloured  precipitate.  The  alkaline  sulfhydrates 
precipitate  the  protosalts  of  manganese  with  an  orange  colour,  and 
Bulf  hydric  acid  will  not  throw  them  down  in  the  presence  of  a  slight 
excess  of  acid,  sulphide  of  manganese  being  easily  decomposed  by 
weak  acids. 

Sulphate  of  Manganese. 

§  753.  Sulphate  of  manganese  is  obtained  by  heating  native 
peroxide  with  concentrated  sulphuric  acid,  while  oxygen  is  given 
ofi";  but  the  residues  of  red  oxide,  which  remain  after  the  calcina- 
tion of  peroxide  for  obtaining  oxygen  gas,  are  also  profitably  em- 
ployed for  this  purpose.  The  sulphate  is  also  sometimes  prepared 
by  heating  the  protochloride  of  manganese  obtained  by  the  prepa- 
ration of  chlorine  with  sulphuric  acid.  The  sulphate  crystallizes 
with  different  quantities  of  water,  and  in  different  forms,  according 
to  the  temperature  at  which  the  crystallization  takes  place  :  thus, 
when  the  temperature  is  below  43°,  the  crystals  contain  7  equiva- 

*  The  pink  colour  of  protosalts  of  manganese  I  have  found  to  be  mostly,  if  not 
always,  due  to  the  presence  of  a  minute  percentage  of  cobalt,  which  is  rarely 
absent  from  the  ores  of  manganese.  I  have  these  ores  containing  from  0.01  up  to 
7.0  per  cent,  of  oxide  of  cobalt. — J.  C.  B. 


SESQUISALTS   OF   MANGANESE.  5J» 

lents  of  water,  and  are  isomorphous  with  sulphate  of  iron,  FeO, . 
SO3+7HO  ;  while  the  crystals  formed  at  a  temperature  between 
43°  and  68°  present  the  form  of  sulphate  of  copper  CuO,S03+ 
5H0,  the  sulphate  of  manganese  also  containing  5  equivalents  of 
water :  lastly,  between  68°  and  86°  the  salt  crystallizes  with  4 
equivalents  of  water,  and  is  isomorphous  with  the  sulphate  of  iron 
Fe0,S03+4H0,  which  has  also  been  obtained  crystallized.  These 
are  important  facts  for  the  theory  of  isomorphism. 

Carbonate  of  Manganese, 

§  754.  Carbonate  of  manganese  occurs  in  nature  in  rhombohe- 
drons,  which  present  the  same  form  as  those  of  carbonate  of  lime, 
and  are  generally  of  a  rose  or  violet  colour.  Carbonate  of  iron  and 
carbonate  of  lime  frequently  replace  part  of  the  carbonate  of  man- 
ganese in  the  same  crystal,  thus  oifering  a  new  proof  of  the  isomor- 
phism of  the  protoxides  of  iron  and  manganese.  Carbonate  of 
manganese  may  be  obtained  as  a  dirty  white  powder  by  adding 
carbonate  of  soda  to  a  solution  of  sulphate  or  chloride  of  manga- 
nese.    It  is  soluble  in  water  containing  carbonic  acid. 

Other  salts  of  manganese  are  easily  obtained  by  dissolving  the 
carbonate  in  the  corresponding  acids. 

SESQUISALTS  OF  MANGANESE. 

§  755.  Although  sesquioxide  of  manganese  combines  with  acids, 
the  salts  it  forms  are  not  durable.  By  slightly  heating  hydrated 
peroxide  of  manganese  with  sulphuric  acid,  the  former  dissolves 
with  a  beautiful  red  colour,  which  solution,  mixed  with  sulphate 
of  potassa  or  ammonia,  yields  by  evaporation  octohedral  crystals 
of  a  true  manganic  alum  K0,S03+Mn203,3S03+24H0,  the  exist- 
ence of  which  proves  sesquioxide  of  manganese  to  be  a  particular 
oxide,  and  not  a  combination  of  protoxide  with  peroxide.  Oxidizable 
substances  instantly  change  sesquisulphate  of  manganese  to  proto- 
sulphate,  the  liquid  losing  its  colour ;  a  property  of  the  sesquisul- 
phate which  is  often  made  use  of  in  the  laboratory  to  ascertain 
whether  an  oxide  is  present  in  its  highest  stage  of  oxidation, — for 
example,  to  ascertain  whether  sulphuric  acid  contains  any  sulphu- 
rous acid,  or  whether  nitric  be  free  from  nitrous  acid. 


COMBINATION  OF  MANGANESE  WITH  SULPHUR. 

§  756.  A  hydrated  protosulphide  of  manganese  is  obtained  by 
adding  a  solution  of  an  alkaline  monosulphide  to  that  of  a  proto- 
salt  of  manganese,  when  a  light-red  precipitate  is  formed,  which 
disengages  sulf hydric  acid  on  being  dissolved  in  acids.  Anhydrous 


30  MANGANESE. 

monosulphide  is  obtained  by  heating  peroxide  of  manganese  with 
sulphur,  when  sulphurous  acid  is  set  free  : 

MnO,+2S=MnS  +  SO,. 

The  excess  of  sulphur  is  driven  off  by  heating  to  redness,  but 
the  monosulphide  thus  prepared  is  almost  always  mixed  with  pro- 
toxide, and  may  be  obtained  in  a  state  of  greater  purity  by  decom- 
posing oxide  of  manganese  with  sulphide  of  carbon  at  a  red-heat. 


COMBINATIONS  OF  MANGANESE  WITH  CHLORINE. 

§  757.  Protochloride  of  manganese  is  prepared  by  heating  native 
peroxide  with  chlorohydric  acid,  while  chlorine  is  disengaged ;  but 
as  the  native  peroxide  always  contains  a  certain  quantity  of  iron, 
the  solution  usually  contains  some  perchloride  of  iron,  to  separate 
which  the  solution  must  be  completely  evaporated  to  dryness,  by 
which  the  excess  of  chlorohydric  acid  is  also  driven  off.  The 
residue  is  dissolved  in  water,  and  the  liquid  boiled  for  some  time 
with  a  little  carbonate  of  manganese,  which  effects  the  precipita- 
tion of  the  peroxide  of  iron,  while  carbonic  acid  is  disengaged,  as 
protoxide  of  manganese  is  a  much  stronger  base  than  peroxide  of 
iron.* 

Protochloride  of  manganese  crystallizes  with  4  equivalents  of 
water,  one-half  of  which  it  gives  off  at  212°  ;  but  when  heated  still 
higher,  it  becomes  completely  anhydrous  and  at  last  fuses.  When 
fused  in  contact  with  the  air,  the  oxygen  of  the  latter  expels  the 
chlorine,  and  the  protochloride  is  converted  into  protoxide.  Ex- 
periments have  been  made  to  turn  this  property  to  technical  use, 
by  regaining  part  of  the  chlorine  contained  in  the  protochloride  of 
manganese,  which  is  a  residue  in  the  manufacture  of  bleaching- 
powder ;  and  it  was  effected  by  roasting  the  protochloride  in  rever- 
beratories,  and  leading  the  gases,  which  were  highly  charged  with 
chlorine,  into  the  chambers  where  chloride  of  lime  is  prepared. 
The  roasting,  which  was  done  at  as  low  a  temperature  as  possible, 
converted  the  protochloride  into  sesquioxide,  which  was  treated 
with  chlorohydric  acid  to  obtain  a  new  quantity  of  chlorine.  But, 
as  the  oxide  thus  obtained  only  gives  one-half  the  quantity  of 
chlorine  that  an  equal  weight  of  peroxide  would,  and  as  the  opera- 
tions are  too  costly,  they  are  no  longer  continued. 

§  758.  Sesquichloride  of  manganese  MugClg,  is  obtained  by  treat- 
ing hydrated  sesquioxide  with  chlorohydric  acid,  without  applica- 
tion of  heat.  The  red  solution  obtained  develops  chlorine  by 
heating,  and  changes  into  protochloride. 

*  The  same  insolubility  of  the  perchloride  of  iron  is  effected  by  heating  the 
Baixture,  when  dry,  to  full  redness. — J,  C.  B. 


TESTING  THE   OXIDES   OF  MANGANESE.  31 


DETERMINATION   OF  MANGANESE,  AND  ITS  SEPARATION  FROM  THE 
METALS  PREVIOUSLY  DESCRIBED. 

§  759.  The  manganese  existing  in  a  solution  is  usually  deter- 
mined by  adding  carbonate  of  soda  to  the  boiling  liquid,  washing 
the  precipitated  carbonate  of  manganese  well  with  boiling  water, 
and  calcining  it  to  a  high  red-heat,  by  which  it  is  converted  into 
red  oxide  MugO^  containing  72.11  per  cent,  of  manganese.  The 
carbonate  is  dried  and  calcined  with  its  filter  in  a  platinum  crucible, 
which,  being  covered  with  its  lid,  is  placed  in  an  earthen  crucible 
and  heated  to  a  strong  red-heat.  When  the  liquid  from  which  the 
oxide  of  manganese  is  to  be  precipitated  contains  any  quantity  of 
ammoniacal  salt,  it  must  be  evaporated  with  an  excess  of  carbonate 
of  soda  and  the  residue  redissolved  in  water. 

§  760.  Manganese  is  separated  from  the  alkaline  metals  by  means 
of  carbonate  of  soda,  or  by  sulfhydrate  of  ammonia,  which  pre- 
cipitates it  as  sulphide,  which,  after  being  washed  with  water  con- 
taining some  sulfhydrate,  is  dissolved  in  an  acid,  and  reprecipitated 
by  carbonate  of  soda. 

It  is  easily  separated  from  baryta  and  strontia  by  adding  sul- 
phate of  soda  to  the  liquid,  which  precipitates  the  baryta  and 
strontia  as  sulphates.  It  is  separated  from  lime  and  magnesia  by. 
sulfhydrate  of  ammonia,  which  precipitates  only  the  manganese  as 
sulphide,  if  the  solution  is  sufiiciently  dilute. 

Its  separation  from  alumina  and  glucina  is  easily  effected  by 
boiling  the  liquid  for  some  time  with  an  excess  of  caustic  potassa 
in  contact  with  the  air,  when  the  manganese  is  precipitated  as 
hydrated  sesquioxide,  while  the  two  earths  dissolve  in  the  excess 
of  alkali. 

TESTING  THE  OXIDES  OF  MANGANESE. 

§  761.  In  works  where  bleaching-powder  is  made,  considerable 
quantities  of  peroxide  of  manganese  are  used,  the  commercial  vahie 
of  which  depends  on  the  quantity  of  chlorine  it  will  develop  when 
treated  with  chlorohydric  acid;  but,  as  the  native  peroxide  is 
always  mixed  with  more  or  less  gangue  and  sesquioxide  of  man- 
ganese, it  is  important  that  the  purchaser  should  be  able  to  deter- 
mine the  quantity  of  chlorine  which  a  given  weight  of  oxide  will 
develop  by  a  simple  process. 

One  litre  of  dry  chlorine  is  disengaged  by  3.98  gm.  of  perfectly 
pure  binoxide  of  manganese  at  32°  and  under  the  pressure  of 
760  mm. ;  and  if  it  be  absorbed  by  a  dilute  solution  of  caustic 
potassa,  and  water  added  until  the  volume  of  the  liquid  is  1  litre,  a 
solution  is  obtained  containing  precisely  its  volume  of  chlorine,  and 
therefore  marking  100  chlorometric  degrees.  But  3.98  gm.  of  a 
peroxide  of  commerce  will,  when  treated  in  the  same  manner,  give 


82  MANGANESE. 

a  solution  containing  a  less  volume  of  chlorine,  the  quantity  o^ 
which,  when  determined  by  the  common  chlorometric  processes 
(§  572),  expresses  the  value  of  the  peroxide  employed.  Supposing 
the  quantity  of  chlorine  found  to  be  60,  the  conclusion  follows  that 
the  oxide  in  question  only  gives  a  quantity  of  chlorine  represented 
by  60,  while  the  same  weight  of  pure  binoxide  yields  a  quantity 
represented  by  100 ;  and,  to  obtain  the  same  quantity  of  chlorine 
as  one  kilog.  of  pure  binoxide  would  give,  H^  =  1.67  kilog.  of  the 
other  oxide  must  be  employed. 

§  762.  An  average  sample  of  the  peroxide  to  be  examined  being 
first  made  by  picking  small  quantities  from  all  parts  of  the  mass,  it 
is  reduced  to  a  fine  powder,  of  which  exactly  3.98  gm.  are  intro- 
duced into  a  small  flask  A  (fig.  475),  about  5  centimetres  in  dia- 
meter.     By  means  of  a 
well-fitting  cork  the  flask 
is  furnished  with  a  tube, 
bent  as  in  the  figure,  to 
convey   the    gas   into    a 
long-necked  flask  B,  hold- 
ing about  J  litre.     The 
latter  is  placed  in  an  in- 
Fig.  475.  clined  position,  and  filled 

up  to  the  neck  with  a  weak 
solution  of  caustic  potassa.  The  peroxide  is  introduced  into  the 
flask  A  with  a  suitable  quantity  of  chlorohydric  acid,  which  is 
measured  in  a  tube  graduated  to  25  cubic  centimetres ;  and  after 
adjusting  the  cork,  the  temperature  is  gradually  raised.  The 
chlorine  first  expels  the  air  from  the  flask  A,  and  causes  it  to  fill 
the  upper  part  of  the  bulb  B^  while  the  water  it  displaces  rises 
in  the  neck.  Toward  the  end  of  the  operation,  the  liquid  in  A  is 
heated  to  the  boiling  point,  so  that  the  steam  generated  drives  all 
the  chlorine  into  the  alkaline  liquid.  The  fiask  B  is  then  taken 
away,  while  the  boiling  is  continued  in  A  to  prevent  any  absorp- 
tion, and  the  chlorine  is  determined  in  the  alkaline  liquid  by  one 
of  the  chlorometric  methods. 

§  763.  A  solution  of  sulphurous  acid,  perfectly  free  from  sul- 
phuric, may  be  substituted  for  the  alkaline  liquid  in  the  flask  B,  as 
the  chlorine,  when  led  into  the  former,  converts  a  corresponding 
quantity  of  sulphurous  acid  into  sulphuric,  the  quantity  of  which 
is  determined  by  adding  chloride ,  of  barium,  boiling  to  expel  the 
excess  of  sulphurous  acid,  collecting  the  precipitate  on  a  filter,  and 
weighing  it  after  calcination.  The  quality  of  the  peroxide  is  then 
proportional  to  the  weight  of  the  sulphate  of  baryta  obtained,  3.98 
gm.  of  pure  peroxide  giving  10.65  gm.  of  sulphate  of  baryta. 

As  the  sulphurous  acid  used  must  be  perfectly  free  from  sul- 
phuric, it  is  important  to  test  it  to  this  eff'ect  before  each  determi- 
nation, which  is  done  by  adding  a  few  drops  of  chloride  of  barium, 


TESTING   THE   OXIDES    OF   MANGANESE. 


33 


which  should  give  no  precipitate.  A  certain  qu3,ntity  of  chloride 
of  barium  may  at  once  be  added  to  the  liquid,  so  that  sulphate  of 
baryta  forms  as  the  sulphurous  acid  oxidizes  by  the  oxygen  of  the 
air ;  and  when  the  solution  is  to  be  used,  the  clear  liquid,  which 
of  course  is  free  from  sulphuric  acid,  can  be  decanted  off  from  the 
precipitate. 

The  best  method  of  conducting  the  experiment  is  that  repre- 
sented in  fig.  476.     Water,  freed  from  air  by  boiling,  and  some 


Fig.  476. 

chloride  of  barium,  are  introduced  into  the  flask  A,  into  which,  as 
soon  as  the  water  has  cooled,  a  current  of  hydrogen  is  led,  supplied 
by  the  generator  B.  As  soon  as  the  air  is  expelled  from  A  by  the 
hydrogen,  a  current  of  sulphurous  acid  gas  is  introduced,  obtained 
by  heating  concentrated  sulphuric  acid  with  copper  or  mercury  in 
the  flask  C,  and  purifying  it  by  washing  with  water  in  the  small 
flask  D.  Lastly,  the  3.98  gm.  of  peroxide  are  heated  in  the  flask 
E  with  chlorohydric  acid,  and  the  chlorine  disengaged  is  led  into 
the  flask  A,  where  it  oxidizes  a  corresponding  quantity  of  sulphur- 
ous acid  to  sulphuric,  which  precipitates  as  sulphate  of  baryta, 
while  there  is  no  fear  that  sulphuric  acid  might  form  by  the  contact 
of  sulphurous  with  the  air.  Toward  the  end  of  the  operation  the 
liquid  in  A  is  boiled  to  expel  the  excess  of  sulphurous  acid,  the 
oxidation  of  which  is  still  prevented  by  continuing  the  stream  of 
hydrogen ;  and  finally  the  sulphate  of  baryta  formed  is  collected 
on  a  filter. 

§  764.  The  finely  powdered  oxide  of  manganese  may  also  be 
heated  with  a  concentrated  solution  of  oxalic  acid,  which  forms 
protoxalate  of  manganese,  while  the  oxygen  given  off  by  the  re- 
duction of  the  higher  oxides  to  protoxide  converts  a  corresponding 
quantity  of  oxalic  into  carbonic  acid,  which  may  be  precipitated  as 
carbonate  of  baryta  by  being  led  into  a  solution  of  baryta,  or  better 
still,  may  be  conducted  into  a  weighed  bulb-apparatus  containing 
a  concentrated  solution  of  caustic  potassa,  the  increase  of  weight 
of  which  after  the  operation  corresponds  exactly  to  the  carbonic 

Vol.  II.— 3 


34  MANGANESE. 

acid.  In  either  case  the  gas  must  be  dried  by  being  passed  through 
a  tube  containing  concentrated  sulphuric  acid. 

§  765.  For  an  accurate  estimation  of  the  value  of  an  oxide  of 
manganese  it  is  not  sufficient  merely  to  determine  the  quantity  of 
chlorine  it  will  develop,  but  the  quantity  of  chlorohydric  acid 
required  to  disengage  the  chlorine  must  also  be  found.  If  the 
oxide  is  pure  binoxide,  the  chlorine  of  one-half  of  the  acid  is  neces- 
sarily disengaged,  while  pure  sesquioxide  will  only  give  one-third 
of  the  chlorine;  for  which  reason,  in  the  latter  case,  one  and  a  half 
times  the  quantity  of  acid  is  required  to  give  the  same  quantity 
of  chlorine  as  when  pure  binoxide  is  used ;  and  lastly,  if  the  oxide 
is  mixed  with  a  gangue  of  lime,  baryta,  or  oxide  of  iron,  these  bases 
will  neutralize  a  part  of  the  acid  without  disengaging  chlorine.  To 
find  the  quantity  of  chlorine  required,  the  acidimetric  percentage 
of  25  cubic  centimetres  of  the  acid  employed  is  first  determined, 
and  3.98  gm.  of  the  oxide  of  manganese  are  treated  with  other  25 
cubic  centimetres  of  the  same  acid,  the  flask  containing  the  mixture 
being  kept  heated.  The  chlorine  is  lost,  but  the  small  quantity  of 
chlorohydric  acid  which  might  distil  over  is  condensed  in  a  moist 
flask  through  which  the  gas  is  led.  When  all  the  chlorine  is  dis- 
engaged, the  small  quantity  of  liquid  in  the  moist  flask  is  added  to 
the  residue  in  the  flask  in  which  the  gas  was  developed,  the  liquid 
is  diluted  to  the  volume  of  half  a  litre,  and  the  remaining  acid  is 
determined  by  adding  a  standard  alkaline  solution  until  the  pre- 
cipitate of  hydrated  oxides,  which  forms  on  the  addition  of  every 
drop,  is  no  longer  redissolved  by  shaking  the  liquid.  This  experi- 
ment gives  the  quantity  of  acid  which  has  remained  free,  and  shows, 
when  compared  with  the  former  experiment,  the  quantity  of  acid 
required  by  the  oxide  of  manganese.* 

*  The  following  is  a  shorter  method  of  testing  peroxides  of  manganese.  The 
chlorine  disengaged  from  a  weighed  quantity  of  the  oxide  is  conducted  into  the 
solution  of  a  given  quantity  of  a  protosalt  of  iron,  an  equivalent  quantity  of  which 
it  oxidizes  to  peroxide ;  so  that,  if  the  remaining  quantity  of  protoxide  of  iron 
which  is  determined  with  permanganate  of  potassa  (as  will  be  described  in"  §  80i) 
be  subtracted  from  the  quantity  contained  in  the  protosalt  employed,  the  diifer- 
ence  will  be  in  proportion  to  the  chlorine  disengaged. 

The  protosalt  of  iron  best  adapted  to  the  purpose  is  the  protosulphate  of  iron 
and  ammonia,  which  is  easily  obtained  by  mixing  equal  volumes  of  saturated  solu- 
tions of  sulphate  of  iron  and  sulphate  of  ammonia,  when  the  liquid  on  evaporating 
yields  prismatic  crystals  of  the  salt,  the  formula  of  which  is  FeOjSOa+NH^O, 
SO3-I-6HO.  One  hundred  grammes  of  the  salt  are  dissolved  in  1837  cubic  centi- 
metres of  water,  so  that  the  solution  contains  5.44  per  cent,  of  the  salt;  or,  544 
parts  of  the  salt  corresponding  to  184  parts  of  pure  protoxide,  exactly  one  per 
cent,  of  protoxide  of  iron :  and  the  standard  solution  thus  obtained,  which  is  best 
prepared  in  larger  quantities  at  a  time,  is  used  for  all  chlorometric  determina- 
tions, as  well  as  for  that  of  chrome. 

Supposing  the  quantity  of  oxide  subjected  to  the  test  to  be  exactly  one  gramme, 
and  the  substance  to  be  pure  peroxide,  which  gives  one  equivalent  of  chlorine ; 
then  will  the  quantity  of  chlorine  developed  be  0.807  gm. ;  and  supposing  the 
quantity  of  the  standard  solution  of  iron  employed  to  be  200  cubic  centimetres, 
which  contain  2  gm.  of  protoxide,  only  1.63  of  which  are  oxidized  by  the  chlorine; 


TESTING   THE    OXIDES    OF    MANGANESE.  35 

then  will  the  0.37  gm.  of  protoxide,  determined  directly  by  permanganate  of  po- 
tassa,  and  subtracted  from  the  2  gm.  employed,  give  the  quantity  of  protoxide 
•which  was  oxidized,  viz.  1.63  gm.,  which  correspond  to  0.807  gm.  of  chlorine,  as  one 
equivalent  of  chlorine  oxidizes  two  equivalents  of  protoxide  of  iron. —  W.  L.  F. 

Another  method  of  determining  the  commercial  value  of  peroxide  of  manganese, 
better  than  that  described  in  the  text,  is  to  employ  dry  oxalate  of  soda,  which  is 
easily  prepared  and  preserved,  and  of  which  152|  grains  are  just  sufficient  for 
100  grs.  of  pure  binoxide,  in  order  that  its  oxalic  acid  may  be  wholly  converted 
into  100  grs.  of  carbonic  acid.  76  grs.  of  the  dry  oxalate  and  50  grs.  of  the  per- 
oxide are  introduced  with  about  J  oz.  of  water  into  a  small  flask  containing  two 
tubulures,  through  one  of  which  an  S-tube  passes,  and  through  the  other  a  small 
tube  connected  with  a  tube  of  sulphuric-pumice  or  chloride  of  calcium.  The 
whole  apparatus  being  weighed  at  once,  together  with  about  200  grs.  of  oil  of 
vitriol,  the  latter  is  gradually  poured  through  the  S-tube  into  the  little  flask. 
The  oil  of  vitriol  disengages  the  oxalic  acid,  which  is  oxidized  into  carbonic  acid 
by  the  excess  of  oxygen  over  that  in  the  protoxide,  and  since  it  cannot  pass  through 
either  escape-tubes  without  being  dried,  the  loss  of  weight  of  the  whole  apparatus 
indicates  the  loss  of  carbonic  acid  alone.  The  number  of  grains  of  loss  being 
doubled,  gives  the  percentage  of  peroxide  equivalent  to  pure  binoxide.  The  dif- 
ferent methais  of  arranging  the  apparatus  will  be  found  in  the  analytical  chemis- 
tries of  Rose  and  Fresenius,  and  others,  and  in  the  Encyclop.  of  Chem.  The  best 
commercial  varieties  contain  from  80  to  98  per  cent,  of  binoxide. — J.  G,  B. 


36 


IRON. 
Equivalent  =  28.0  (0=100;  350.0). 

§  766.  On  account  of  its  numerous  technical  applications,  iron 
is  the  most  important  of  all  the  metals.    It  is  used  in  three  states : 

1.  Bar  or  malleable  iron. 

2.  Steel. 

3.  Crude  or  cast-iron. 

Steel  and  cast-iron  are  combinations  of  iron  with  small  but  vari- 
able quantities  of  carbon  and  silicium. 

The  bar-iron  of  commerce  is  not  chemically  pure,  as  it  contains 
a  small  quantity  of  carbon,  and  often  traces  of  silicium,  sulphur,  or 
phosphorus,  which  latter  remarkably  affects  its  quality.  The  iron 
used  in  fine  locksmith's  work  approaches  a  state  of  purity  ;  but  the 
purest  iron  is  found  in  piano-forte  wires,  or  ordinary  wire,  because 
only  iron  of  great  purity  can  be  drawn  out  into  very  fine  threads. 

In  order  to  obtain  iron  chemically  pure,  some  wire  is  cut  into 
pieces  of  the  same  length,  and  tied  in  bundles  ;  when  their  surface 
is  oxidized,  by  heating  them  for  a  few  moments  exposed  to  the  air, 
or  better  still,  in  a  porcelain  tube  through  which  steam  is  passed. 
The  bundles  of  oxidized  iron  are  then  plac^  in  a  small  porcelain 
crucible  with  a  small  quantity  of  powdered  glass  ;  and  the  crucible 
being  set  in  a  second  earthen  crucible,  luted  externally  with  clay, 
is  heated  in  a  blast-furnace  at  the  highest  temperature  that  can  be 
produced.  The  small  quantities  of  foreign  matter  contained  in  the 
iron,  are  burned  by  the  oxygen  of  the  oxide,  while  the  excess  of  oxide 
of  iron,  combining  with  the  glass,  forms  a  slag.  If  the  temperature 
be  sufficiently  elevated  the  purified  iron  fuses  to  a  single  lump. 
Pure  iron  is  whiter  and  more  malleable  than  the  iron  of  commerce, 
but  less  tenacious. 

Pure  iron  may  likewise  be  obtained  by  the  reduction  of  one  of 
its  oxides  by  hydrogen,  which  takes  place  at  a  dull  red-heat,  and 
may  be  effected  in  the  small  apparatus  described  (fig.  473)  for 
the  preparation  of  the  protoxide  of  manganese.  The  metallic  iron 
remains  in  the  tube,  in  the  form  of  a  grayish-black  powder,  which 
may  be  preserved  by  closing  hermetically  both  ends  of  the  tube 
while  it  is  filled  with  hydrogen  gas  ;  for  very  finely  divided  iron 
has  so  great  an  affinity  to  oxygen  that  it  is  inflamed  by  contact 
with  the  air ;  a  property  which  has  given  to  it  the  name  of  pyro- 
phoric  iron.  If  the  reduction  be  made  in  a  porcelain  tube  at  a 
high  temperature,  the  metal  becomes  solid,  assuming  a  metallic 
lustre,  and  no  longer  oxidizing  in  dry  air. 


IRON.  87 

Perfectly  pure  Iron  may  also  be  procured,  by  heating  protochlo- 
ride  of  iron  in  a  glass  tube,  through  which  a  current  of  hydrogen 
gas  is  passed ;  when  the  iron  forms  on  the  sides  of  the  glass  a  glit- 
tering, brilliant  coating,  in  which  small  cubic  crystals  may  often 
be  seen. 

§  767.  The  texture  of  commercial  iron  varies  greatly,  according 
to  its  mode  of  manufacture.  Pure  iron  which  has  been  forged  and 
rolled  equally  in  all  directions,  exhibits  a  texture  of  very  small, 
brilliant  grains ;  but,  when  drawn  out  into  bars,  its  texture  is  often 
decidedly  fibrous,  the  fibres  always  running  in  the  direction  of  the 
bar,  which  may  be  readily  proved  by  breaking  the  latter.  The 
fibrous  texture  is  highly  esteemed,  because  the  iron  possessing  it 
is  much  more  tenacious  than  granular  iron,  and  bears  a  greater 
weight  without  breaking.  The  fibrous  texture  of  iron  is  generally 
regarded  as  an  index  of  its  go6d  quality ;  however,  skilful  work- 
men can  impart  this  quality  also  to  bars  of  an  inferior  sort.  Iron 
of  fibrous  texture  does  not  always  remain  in  that  state,  but  after 
some  time  changes  into  the  granular,  or  even  the  laminated  tex- 
ture ;  which  change  ensues  most  rapidly  when  the  bars  are  sub- 
jected to  vibration,  as,  for  instance,  when  they  support  the  floor 
of  a  suspension-bridge.  The  tenacity  of  the  metal  diminishes  at 
the  same  time  in  a  remarkable  manner,  and  it  frequently  breaks 
with  a  load  which  the  bar  would  easily  have  borne  when  its  tex- 
ture was  fibrous.  A  change  of  this  kind  is  frequently  observed  in 
the  axles  of  locomotives  and  railway-cars.* 

The  specific  gravity  of  wrought-iron  varies  from  7.7  to  7.9.  Iron 
is  the  most  tenacious  of  all  the  metals,  a  cylindrical  iron-wire  of 
2  millimetres  in  diameter  being  able  to  sustain  a  load  of  250  kilogs. 

§  768.  The  highest  temperature  that  can  be  produced  in  a  blast- 
furnace is  required  for  the  fusion  of  iron,  which,  however,  is  more 
easy  when  it  can  be  combined  with  carbon.  Iron  passes  from  the 
fluid  to  the  solid,  through  the  doughy  state,  and  therefore  belongs 
to  that  class  of  substances  which  crystallize  with  difficulty  by  fusion. 
However,  if  large  masses  of  iron,  heated  to  a  very  high  temperature, 
be  allowed  to  cool  very  slowly,  indications  of  crystallization  of  the 
cubic  form  are  found  in  the  interior  of  these  masses. f  Heated  to  a 
white-heat,  iron  becomes  sufficiently  soft  to  assume  any  form  under 
the  hammer ;  and  two  bars,  when  heated  to  redness,  can  be  readily 
soldered  to  each  other  without  the  interposition  of  another  metal, 
when  the  surfaces  to  be  joined  are  completely  free  from  oxide. 

*  The  fibrous  texture  of  iron  is  also  changed  to  the  granular  by  heating  the 
metal  to  redness,  and  immersing  it  while  hot  into  cold  water. —  W.  L.  F. 

f  Some  species  of  cast-iron,  as,  for  example,  that  made  from  the  manganiferous 
sparry  iron-ore  of  Muesen  in  Westphalia,  and  that  made  at  Easton,  in  Pennsyl- 
vania, the  latter  of  which  is  remarkable  for  its  extreme  ductility  when  converted 
into  bar-iron,  show  a  laminated  texture,  which  is  owing  to  its  being  an  aggregated 
mass  of  laminated  prismatic  crystals,  the  angles  of  which  are  about  112°. —  W.  L.  F. 


38  IRON. 

Now,  as  it  is  known  that  iron  heated  in  the  air  soon  oxidizes,  the 
blacksmith  generally  throws  a  small  quantity  of  sand  upon  the 
bars  he  wishes  to  solder,  which,  by  combining  with  the  oxide  of 
iron,  produces  a  very  fusible  silicate,  which,  forming  a  kind  of 
varnish  on  the  surface  of  the  metal  and  preventing  its  further  oxi- 
dization, is  afterward,  from  its  extreme  fluidity,  entirely  driven  off 
by  the  blows  of  the  hammer. 

§  769.  Iron,  cobalt,  and  nickel  are  the  only  metals  which  are 
remarkably  magnetic  at  the  ordinary  temperature.  A  piece  of  pure 
iron  immediately  becomes  a  magnet,  either  by  contact  with  or  at 
a  short  distance  from  a  native  magnet,  its  magnetic  properties  dis- 
appearing again  as  soon  as  the  magnet  is  removed ;  but  if  the  iron 
is  combined  with  a  small  quantity  of  carbon,  if  it  is  steely,  the 
magnetism  is  slower  of  development,  but  continues  longer  after  the 
removal  of  the  magnet.  A  bar  of  steel,  rubbed  against  a  magnet, 
acquires  permanent  magnetic  properties,  and  becomes  a  true  mag- 
net. The  magnetic  properties  of  iron  diminish  rapidly  with  the 
temperature,  an  iron  ball  heated  to  a  whitish  red-heat  no  longer 
exerting  any  influence  over  the  needle,  but  recovering  its  magnetic 
virtue  on  cooling. 

§  770.  Iron  remains  unchanged  for  an  indefinite  time  in  dry  air, 
and  even  in  dry  oxygen,  at  the  ordinary  temperature ;  but  soon 
alters  in  moist  air,  by  becoming  covered  with  rust.  The  rust  of 
iron,  which  consists  of  an  oxidation  of  its  surface,  is  most  readily 
formed  in  the  presence  of  carbonic  acid,  of  which  the  air  always 
contains  a  small  quantity.  Under  the  influence  of  the  carbonic 
acid  and  the  oxygen,  the  surface  of  the  iron  is  converted  into  proto- 
carbonate,  which,  on  absorbing  a  new  portion  of  oxygen,  is  trans- 
formed into  hydrated  peroxide  of  iron,  while  the  carbonic  acid 
disengaged  favours  the  oxidation  of  an  additional  quantity  of  metal- 
lic iron.  It  has  been  observed,  that  when  iron  has  begun  to  rust 
at  any  particular  point,  it  changes  very  rapidly  around  this  point, 
which  is  produced  by  a  galvanic  phenomenon  accelerating  the  oxi- 
dation. The  iron  and  thin  layer  of  oxide  which  forms  on  its  surface 
constitute  the  two  elements  of  a  pile  in  which  the  iron  becomes  posi- 
tive, and  thus  acquires  an  affinity  for  oxygen  sufficiently  great  to 
decompose  water  at  the  ordinary  temperature,  with  the  evolution  of 
hydrogen  gas.  This  phenomenon  is  rendered  very  evident  by  allow- 
ing moist  iron-filings  to  rust  in  the  air,  when,  after  some  time,  the 
odour  exhaled  by  hydrogen  gas*  made  from  the  carburetted  metals 
is  easily  recognised.  Rust  almost  always  contains  a  small  quantity 
of  ammonia,  the  presence  of  which  may  be  recognised  by  heating  it 
with  potassa,  and  is  explained  as  follows  : — It  has  been  shown  (§122) 

*  This  peculiar  odour  is  not  exhaled  by  hydrogen  gas,  but  is  that  of  a  certain 
substance  called  ozone,  and  shown  by  Bunsen  to  be  a  combination  of  one  atom  of 
hydrogen  with  three  of  oxygen,  which  forms  under  almost  all  circumstances  where 
a  galvanic  current  is  active. —  W.  L.  F. 


IRON.  39 

that  when  hydrogen  and  nitrogen  meet  in  the  nascent  state  in  a 
liquid,  they  combine  and  form  ammonia :  now,  the  water  which 
moistens  the  rust,  being  in  contact  wuth  the  air,  contains  nitrogen 
in  solution,  and  on  the  other  hand,  hydrogen  is  disengaged  by  the 
decomposition  of  the  water.  The  circumstances  under  which  am- 
monia can  form  by  the  direct  combination  of  hydrogen  and  nitro- 
gen are  therefore  realized.  The  peroxide  of  iron,  which  acts  with 
very  powerful  bases  the  part  of  a  feeble  acid,  retains  the  ammonia 
and  prevents  it  from  being  disengaged. 

It  is  important  to  be  aware  of  the  presence  of  ammonia  in  rust, 
as  it  has  been  long  since  admitted,  that  when  spots  of  rust  which 
w^ere  found  on  sidearms  or  steel  weapons,  suspected  to  have  been 
used  in  the  commission  of  a  crime,  evolved  ammonia  by  contact  with 
potassa,  it  was  a  proof  that  the  rust  was  formed  by  contact  with 
animal  matter,  and  these  spots  of  blood  were  the  cause  of  its  pre- 
sence. This  presumption  was  erroneous ;  for  as  we  have  just  seen, 
steel-rust  formed  by  the  contact  of  air  alone  may  contain  an  appre- 
ciable quantity  of  ammonia. 

Rust  soon  changes  in  fresh  water,  but  very  slightly  in  water 
containing  a  few  thousandths  of  carbonate  of  soda  or  potassa. 
During  the  last  few  years,  iron  has  been  preserved  from  rust  by 
covering  its  surface  with  a  very  thin  layer  of  metallic  zinc,*  and 
iron  thus  coated  is  called  galvanized  iron.  This  phenomenon  was 
explained  in  §  305. 

Iron  soon  oxidizes  by  contact  with  the  air  when  heated  to  red- 
ness, becoming  covered  with  a  black  pellicle  of  oxide,  which  falls 
off  under  the  hammer.  To  this  easy  combustion  of  iron  in  the  air 
may  be  attributed  the  property  which  it  possesses  of  giving  out 
sparks  when  struck  by  a  flint,  in  which  case  small  particles  are 
detached,  which,  being  strongly  heated  by  friction  against  the  flint, 
become  incandescent  by  combining  with  the  oxygen  of  the  air,  and 
may  easily  inflame  combustible  substances,  such  as  tinder.  If 
the  steel  be  struck  for  some  time  over  a  sheet  of  white  paper,  the 
latter  will  be  covered  with  small  black  particles,  which  are  attracted 
by  the  magnet,  and  are,  in  fact,  small  spherical  globules  of  mag- 
netic iron. 

§  771.  Iron  is  readily  acted  on  by  chlorohydric  acid,  protochlo- 
ride  of  iron  being  formed,  and  hydrogen  disengaged.  Dilute  cold 
sulphuric  acid  dissolves  it  with  the  evolution  of  hydrogen,  while 
the  concentrated  acid  also  attacks  it,  but  disengages  sulphurous 
acid.     Concentrated  nitric  acid  attacks  it  sharply  with  a  copious 

*  A  patent  has  lately  been  taken  out  in  Europe  (Vienna  ?)  for  preserving  iron 
from  rust  by  a  coating  of  metallic  cadmium,  which  at  the  same  time  imparts  a 
silvery  lustre  to  the  surface.  Silicate  of  potassa,  the  German  wasserglas,  has  also 
been  employed. —  W.  L.  F. 


40  IRON. 

disengagement  with  nitrous  fumes,*  while  the  dilute  acid  dissolves 
it  without  any  apparent  evolution  of  gas,  forming  at  the  same  time 
protonitrate  of  iron  and  nitrate  of  ammonia  (122). 

COMPOUNDS  OF  IRON  WITH  OXYGEN. 

§  772.  Three  compounds  of  iron  with  oxygen  are  known : 

1.  A  protoxide  FeO,  which  is  a  powerful  base,  isomorphous  with 
the  bases  of  which  the  formula  is  RO. 

2.  A  sesquioxide  FcgOg,  being  a  very  feeble  base,  analogous  to 
alumina,  and  isomorphous  with  the  oxides  of  which  the  formula  is 

B.O3. 

3.  Lastly,  an  acid  FeOg,  analogous  to  manganic  acid. 

A  fourth  compound  of  iron  with  oxygen,  of  the  formula  FcgO^,  is 
also  known,  and  is  called  magnetic  oxide',  but  as  it  behaves  like  a 
compound  of  protoxide  and  sesquioxide  FeOjFeaOg,  it  is  regarded 
as  such. 

Protoxide  of  Iron  FeO. 

§  773.  Protoxide  of  iron  has  hitherto  not  been  obtained  in  a 
state  of  purity.  When  a  large  bar  of  iron  heated  to  redness  is 
allowed  to  cool  slowly  in  the  air,  its  surface  oxidizes,  and  a  black 
pellicle  of  a  metallic  lustre  is  formed,  which  falls  ofif  under  the 
hammer,  and  is  called  finery  cinder.  If  a  thin  piece  of  cinder  be 
examined  with  a  lens,  it  is  seen  to  be  composed  of  several  layers ; 
the  outer  stratum  showing  nearly  the  composition  of  magnetic 
oxide  FcgO^,  while  the  inside  layer,  or  that  immediately  in  contact 
with  the  metal,  resembles  the  protoxide  very  closely. 

If  a  solution  of  caustic  potassa  be  added  to  a  protosalt  of  iron, 
a  white  precipitate  of  hydrated  protoxide  is  obtained,  which  soon 
turns  green  on  exposure  to  the  air,  by  forming  hydrated  sesqui- 
oxide by  absorption  of  oxygen.  If  boiling  solutions  be  used,  and 
the  ebullition  prolonged  for  some  time,  the  white  precipitate  loses 
its  water  of  hydration  and  becomes  black ;  but  the  oxide  has  such 
an  affinity  for  oxygen  that  it  is  impossible  to  collect  it  unchanged. 
It  even  decomposes  water  at  the  boiling  point,  and  is  ultimately 
converted  into  magnetic  oxide. 

French  bottle-glass  owes  its  hue  to  the  presence  of  this  oxide 
(§  684),  which  imparts  a  deep  green  colour  to  fluxes. 

*  Very  concentrated  nitric  acid  "will  not  dissolve  pure  iron  at  all,  owing  to  an 
electrical  phenomenon  by  which  the  iron  is  brought  to  the  passive  state,  and  changes 
its  electropositive  power.  The  iron  will  continue  in  this  state,  and  not  be  attacked 
by  the  acid,  even  on  diluting  the  latter  to  almost  any  degree ;  but  on  touching  the 
piece  of  passive  iron,  lying  in  the  diluted  acid,  with  a  piece  of  common  iron,  such 
as  a  key,  the  galvanic  current  produced  by  the  contact  of  the  two  pieces,  whose 
electromotive  power  is  yet  different,  instantly  changes  the  passive  iron  back  to 
its  natural  state,  and  renders  it  soluble. —  W.  L.  F. 


OXIDES    OF   IRON.  41 

Sesquioxide  of  Iron  FcgOg. 

§  774.  The  sesquioxide  FegOg,  or  peroxide,  is  a  substance  abun- 
dantly met  with  in  nature,  occurring  either  in  the  anhydrous  or  the 
hydrated  state.  The  anhydrous  peroxide  forms  flattened  rhombo- 
hedral  crystals,  very  brilliant  and  nearly  black,  while  their  powder 
is  of  a  deep  red  colour.  Mineralogists  call  it  specular  iron:  it  is 
found  in  veins  in  the  old  rocks.  In  the  fissures  of  volcanic  lavas, 
thin  and  brilliant  laminge  of  peroxide  of  iron  are  often  found, 
having  the  form  of  regular  hexagons,  and  also  belonging  to  the 
class  of  specular  iron.  Anhydrous  peroxide  of  iron,  which  is  also 
found  in  compact  masses,  of  an  intense  red  colour,  is  called  by  mine- 
ralogists red  hematite,  and  is  known  in  the  arts  by  the  name  of 
bloodstone,  a  substance  extensively  employed  for  polishing  metals. 

Peroxide  of  iron  is  prepared  artificially  by  calcining  protosul- 
phate  of  iron,  when  sulphurous  and  sulphuric  acids  are  disengaged, 
and  the  peroxide  remains  in  the  form  of  a  red  powder : 

2(S03,FeO)=FeA+S03+SO,. 

Peroxide  of  iron  thus  prepared  is  known  by  the  name  of  coleo- 
tliar,  and  used  for  painting,  for  polishing  silver,  and  for  giving  the 
last  polish  to  mirrors.  The  intensity  of  colour  of  peroxide  of  iron 
is  in  proportion  to  its  compactness. 

Peroxide  of  iron  may  be  obtained  in  the  form  of  small  crystal- 
line lamellge,  of  great  lustre  and  nearly  black,  by  calcining  in  a 
crucible  1  part  of  sulphate  of  iron  with  3  parts  of  sea-salt.  The 
calcined  matter  is  treated  with  boiling  water,  which  leaves  the  per- 
oxide. 

§  775.  Hydrated  peroxide  of  iron  is  prepared  by  adding  potassa 
or  ammonia  to  the  solution  of  a  sesquisalt  of  iron,  when  a  copious 
brown  precipitate  is  formed.  When  the  reaction  has  been  efiected 
by  caustic  potassa,  the  precipitate  always  retains  a  small  quantity 
of  alkali,  which  is  removed  with  difficulty  only  by  prolonged  boil- 
ing with  pure  water.  The  precipitation  may  be  made  by  a  solution 
of  carbonate  of  potassa  or  soda,  in  which  case  the  precipitate  is 
also  hydrated  peroxide  of  iron,  the  carbonic  acid  being  disen- 
gaged, or  combining  with  the  excess  of  neutral  carbonate,  which  it 
transforms  into  bicarbonate.* 

Hydrated  peroxide  of  iron  parts  readily  with  its  water  by  the 
application  of  heat,  but  when  heated  still  further,  a  temperature  is 
soon  attained  at  which  the  oxide  suddenly  becomes  incandescent 
from  a  spontaneous  evolution  of  heat.  This  incandescence  is  only 
momentary,  and  the  temperature  of  the  oxide  again  falls  to  that 
of  the  vessel  in  which  it  is  heated ;  but  its  physical  and  chemical 
properties  have  been  remarkably  modified,  as  it  has  become  more 
compact,  and  dissolves  with  great  difficulty  even  in  highly  concen- 


42  IRON. 

trated  acids.  Sesquioxide  of  iron,  heated  to  a  high  white-heat, 
loses  a  portion  of  its  oxygen,  and  is  converted  into  magnetic  oxide 
Fe30,. 

Peroxide  of  iron  colours  fluxes  of  a  reddish  yellow,  but  a  consi- 
derable quantity  is  necessary  to  produce  this  effect  in  glass.  The 
small  quantity  of  protoxide  which  imparts  a  deep  green  hue  to  a 
vitreous  flux,  does  not  colour  it  appreciably  when  converted  into 
peroxide  (§  674). 

Magnetic  oxide  of  iron  FegO^. 

§  776.  A  native  oxide  of  iron,  intermediate  between  the  prot- 
oxide and  peroxide,  is  often  found  in  very  regular,  brilliant  octa- 
hedrons, of  a  fine  metallic  lustre.  At  other  times  it  is  found  in 
the  old  rocks  in  compact  masses,  often  very  large,  and  is  worked 
as  an  iron  ore.  Large  quantities  of  it  are  found  at  Dannemora, 
in  Sweden,  and  from  this  ore  the  best  quality  of  iron  is  obtained. 
This  compound  has  been  called  magnetic  oxide,  from  its  possessing 
very  highly  developed  magnetic  properties.  Native  loadstone  is 
formed  of  this  oxide  of  iron. 

Magnetic  oxide  of  iron  is  only  produced  when  iron  burns  at  a 
high  temperature  in  the  air,  or  in  oxygen ;  for  example,  by  the 
rapid  combustion  of  iron-wire  in  pure  oxygen  (§  64).  But  the  most 
certain  method  of  obtaining  it  in  the  laboratory  consists  in  heating 
iron-wire  in  a  porcelain  tube,  in  a  current  of  steam,  as  in  the  ex- 
periment described  in  §  68,  when  the  surface  of  the  wire  becomes 
covered  with  an  infinite  number  of  small,  very  brilliant  crystals, 
which  by  the  aid  of  a  lens  are  seen  to  be  regular  octahedrons,  resem- 
bling those  of  the  native  magnetic  oxide. 

'  This  oxide  may  also  be  obtained  in  the  hydrated  state,  by  dis- 
solving the  magnetic  oxide  in  chlorohydric  acid,  and  adding  a 
large  excess  of  ammonia,  when  a  deep  green  precipitate,  becoming 
black  by  desiccation,  is  formed.  This  hydrate  is  magnetic,  like  the 
anhydrous  oxide.  Hydrated  magnetic  oxide  may  likewise  be  pre- 
pared by  pouring  into  ammonia  a  mixture  of  equal  equivalents  of 
persulphate  and  protosulphate  of  iron.  In  order  to  make  this 
mixture,  two  equal  volumes  of  the  same  solution  of  protosulphate 
of  iron  are  used,  one  of  which  is  transformed  into  persulphate  by 
evaporating  it  to  dryness  with  nitric  and  sulphuric  acids,  and  then 
redissolved  in  the  other  volume  of  protosulphate. 

The  magnetic  oxide  does  not  behave  like  an  oxide  per  se,  but 
rather  like  a  compound  of  protoxide  and  peroxide.  Its  formula  is 
properly  Fe0,re303,  analogous  to  that  of  red  oxide  of  manganese 
MnOjMngOg.  The  solution  of  magnetic  oxide  in  an  acid  possesses 
the  properties  of  a  mixture  of  a  protosalt  with  a  sesquisalt ;  and 
if  an  alkali  is  dropped  into  the  liquid,  the  peroxide  is  precipitated 
before  the  protoxide.     In  order  to  precipitate  the  two  oxides  in 


OXIDES    OF   IRON.  43 

combination  the  proceeding  must  be  inverted,  and  the  solution  of 
the  salt  of  iron  be  poured  into  the  alkaline  liquid.  We  shall,  more- 
over, soon  see  several  compounds  presenting  a  similar  chemical 
formula,  and  affecting  identical  crystalline  forms,  but  in  which 
the  peroxide  of  iron  is  often  replaced  by  alumina  or  by  oxide  of 
chrome,  while  magnesia,  protoxide  of  manganese,  or  oxide  of  zinc 
often  take  the  place  of  the  protoxide. 


Ferric  acid  FeO 


§  777.  The  third  compound  of  iron  with  oxygen  possesses  the 
properties  of  an  acid  corresponding  with  manganic  acid,  and  is 
formed  under  the  same  circumstances.  A  mixture  of  iron  filings 
and  nitrate  of  potassa  is  heated  to  redness  in  an  iron  crucible,  when 
a  beautiful  red  solution  of  ferrate  of  potassa  is  obtained  by  treating 
the  mass  with  water,  resembling  permanganate  of  potassa  in  colour. 
It  is  also  procured  by  passing  chlorine  through  a  concentrated 
solution  of  caustic  potassa,  containing  hydrated  peroxide  of  iron  in 
suspension.  Pieces  of  caustic  potassa  are  added  from  time  to  time, 
in  order  constantly  to  maintain  a  large  excess  of  alkali  in  the  liquid. 
Ferrate  of  potassa,  being  nearly  insoluble  in  a  concentrated  solu- 
tion of  potassa,  is  deposited  in  the  form  of  a  black  powder,  which 
may  be  almost  entirely  separated  from  the  mother  liquid  by  drying 
it  on  unglazed  porcelain.  Ferrate  of  potassa  is  still  less  fixed  than 
the  manganate,  and  has  not  yet  been  obtained  in  a  crystalline  form. 
Its  solution  cannot  be  filtered  through  paper,  as  it  immediately 
decomposes  when  in  contact  with  organic  matter,  forming  hydra- 
ted sesquioxide  of  iron. 

§  778.  The  following  is  the  composition  of  the  four  oxides  of  iron : 

Protoxide  FeO Iron 77.78  28 

Oxygen 22.22  8 

100.00  36 

Sesquioxide  Fe^Og Iron 70.00  ^Q 

Oxygen 30.00  _24 

100.00  80 

Magnetic  oxide  FeO,Fe  A Ii'on 72.42  84 

Oxygen. 27.58  32 

100.00  116 

Ferric  acid  FeOg Iron 53.84  28 

Oxygen 46.16  24 

100.00  ~52 

The  equivalent  of  iron  is  28,  or  350  when  that  of  oxygen  is  as- 
sumed as  100. 


44  IRON. 

SALTS  OF  PROTOXIDE  OF  IRON. 

§  779.  The  hydrated  protosalts  of  iron  are  of  a  bright  green 
colour,  which  they  nearly  lose  by  parting  with  their  water ;  and 
their  solutions  are  also  of  a  bright  green.  Their  taste  is  astringent 
and  metallic. 

Potassa  and  soda,  poured  into  the  solution  of  a  protosalt  of  iron, 
yield  a  white  precipitate,  which  immediately  turns  green  by  contact 
■with  the  air,  and,  when  left  exposed  to  the  atmosphere  for  an  in- 
definite time,  becomes  ochrous,  and  is  converted  into  hydrated  ses- 
quioxide.  This  property  distinguishes  the  protosalts  of  iron  from 
those  of  manganese,  the  latter  yielding  with  the  alkalies  a  white 
precipitate,  which  turns  brown  in  the  air,  without  passing  through 
the  intermediate  green. 

Ammonia  produces  with  the  protosalts  of  iron  a  reaction  re- 
sembling that  with  the  salts  of  manganese  (§  752).  An  excess  of 
ammonia  redissolves  the  protoxide ;  but  by  absorbing  the  oxygen 
of  the  air,  the  liquid  soon  becomes  clouded,  and  hydrated  sesqui- 
oxide  is  precipitated. 

The  alkaline  carbonates,  poured  into  a  very  cold  solution  of  a 
protosalt  of  iron,  throw  down  a  white  precipitate  of  protocar- 
bonate,  which,  not  being  very  fixed,  soon  parts  with  its  carbonic 
acid. 

Sulf  hydric  acid  does  not  precipitate  the  protosalts  of  iron,  how- 
ever slightly  acid  they  may  be,  while  the  sulfhydrates  give  black 
precipitates. 

Yellow  ferro-cyanide  of  potassium  yields  a  white  precipitate, 
"which  soon  turns  blue  by  absorbing  the  oxygen  of  the  air. 

The  red  ferro-cyanide  gives  a  beautiful  deep-blue  precipitate. 

Succinate  and  benzoate  of  ammonia  do  not  precipitate  the  proto- 
salts of  iron. 

Phosphate  of  potassa  gives  a  white  precipitate,  which  turns  blue 
by  exposure  to  the  atmosphere. 

Arseniate  of  potassa  yields  a  white  precipitate,  which  turns 
green  in  the  air. 

Tannin  forms  no  precipitate  with  the  protosalts  of  iron,  but  the 
liquid  soon  blackens  in  the  air. 

ProtosulpJiate  of  Iron. 

§  780.  The  sulphate  is  the  most  important  of  the  protosalts  of 
iron,  being  used  in  dyeing,  under  the  name  of  green  vitriol,  or  cop- 
peras. It  is  prepared  in  the  laboratory  by  dissolving  metal- 
lic iron  in  dilute  sulphuric  acid,  when  hydrogen  is  disengaged. 
This  process  is  sometimes  adopted  in  the  arts ;  but  copperas  is 
generally  obtained  from  the  native  sulphides  of  iron  or  pyrites, 
which  are  abundantly  found  in  nature,  but  cannot  be  used  as  iron 


SALTS    OP   IRON.  45 

ores,  because  the  reduction  of  the  metal  would  be  too  expensive, 
and  iron  of  an  inferior  quality  would  be  obtained ;  but  as  the  py- 
rites frequently  contain  some  hundredths  of  sulphide  of  copper, 
this  metal  is  extracted  from  them.  For  this  purpose  they  are 
roasted,  by  a  process  hereafter  to  be  described,  when  the  metals 
are  oxidized,  and  a  great  portion  of  the  sulphur  is  disengaged  in 
the  state  of  sulphurous  acid,  while  another  portion  is  oxidized  still 
higher,  and,  by  combining  with  the  metallic  oxides  as  sulphuric 
acid,  yields  sulphates  which  are  removed  by  washing. 

In  some  localities'  sulphur  is  obtained  from  pyrites  by  calcining 
them  in  retorts,  when  a  portion  of  the  sulphur  is  disengaged,  and 
a  disaggregated  magnetic  sulphide  of  iron  remains  in  the  retort, 
absorbing  rapidly  the  oxygen  of  the  moist  air,  and  changing  into 
a  sulphate. 

In  other  localities,  schistous  rocks  filled  with  small  crystals  of 
pyrites  are  found,  which  sometimes  change  rapidly  in  the  air  and 
fall;  that  is  to  say,  soon  become  reduced  to  powder.  The  sul- 
phide of  iron  is  then  changed  into  a  sulphate,  while  the  schist 
itself  is  more  or  less  decomposed,  and  yields  sulphate  of  alumina, 
when  the  two  sulphates  are  dissolved  in  water. 

The  vitriolic  liquids  are  evaporated  in  leaden  boilers,  and  con- 
ducted, when  suitably  concentrated,  into  a  large  vat,  where  they 
are  allowed  to  settle  for  some  time,  and  then  are  run  off  into 
large  crystallizing-vats.  Strings,  on  which  the  crystals  of  sul- 
phate of  iron  form,  are  suspended  in  the  liquid.  When  the  mother 
liquid  yields  no  more  crystals  of  the  sulphate,  even  after  additional 
concentration,  it  is  used  for  the  preparation  of  alum.  The  water 
contains  sulphate  of  alumina,  which  crystallizes  with  difficulty ;  but 
an  addition  of  sulphate  of  potassa  soon  effects  the  deposition  of 
crystals  of  alum,  which  are  purified  by  recrystallization. 

The  sulphate  of  iron  of  commerce  is  often  covered  with  a  basic 
persulphate,  rendering  its  surface  ochreous,  which  is  removed  by 
dissolving  it  in  water  and  boiling  the  solution  with  iron  filings, 
which  reduce  the  sesquisulphate  of  iron  to  protosulphate.  Sul- 
phate of  iron  crystallizes  at  the  ordinary  temperature  with  7  equi- 
valents of  water,  while  the  crystals  deposited  at  176°  contain  only 
4  equivalents.  The  same  salt  readily  parts  with  a  portion  of  its 
water  when  heated,  but  a  temperature  of  nearly  572°  is  requisite 
to  drive  off  the  last  particles  of  it.  Dishydrated  sulphate  of  iron 
forms  a  white  powder,  which,  if  heated  still  further,  is  decomposed 
by  disengaging  sulphurous  and  sulphuric  acids,  while  peroxide  of 
iron  remains  (§  138).  100  parts  of  water  at  59°  dissolve  73  of 
crystallized  sulphate,  and  at  212°  more  than  300  parts. 

Protonitrate  of  Iron, 
§  781.  This  salt  is  obtained  by  dissolving  metallic  iron  in  cold 
dilute  nitric  acid,  when  a  certain  quantity  of  nitrate  of  ammonia 


46  IRON. 

is  also  formed,  which  combining  with  the  nitrate  of  iron,  produces 
a  double  salt,  which  is  deposited  in  crystals.  The  formation  of 
nitrate  of  ammonia  is  owing  to  the  fact,  that  while  the  iron  is 
being  oxidized  at  the  same  time  at  the  expense  of  the  oxygen  of 
the  water  and  of  that  of  the  nitric  acid,  hydrogen  and  nitrogen 
gas  are  simultaneously  disengaged,  and  combine  in  the  nascent 
state  to  form  ammonia.  The  best  method  of  obtaining  protoni- 
trate  of  iron  consists  in  decomposing  a  solution  of  protosulphate 
of  iron  by  nitrate  of  baryta. 

Carbonate  of  Iron, 

§  782.  Carbonate  of  iron  is  found  in  nature  as  sparry  iron^ 
crystallized  in  rhombohedrons,  resembling  those  of  carbonate  of 
lime,  and  is  highly  esteemed  as  an  ore.  It  is  found  in  veins  in 
the  old  rocks.  Carbonate  of  iron,  heated  in  an  earthen  retort, 
yields  magnetic  oxide  of  iron  as  a  residue,  and  disengages  a  mix- 
ture of  carbonic  oxide  and  acid. 

Carbonate  of  iron  has  not  yet  been  artificially  prepared. 

Sesquisalts  of  Iron, 

§  783.  These  salts  are  prepared  by  dissolving  the  hydrated 
peroxide  in  acids,  or  by  subjecting  the  protosalts  to  an  oxidizing 
agency  in  the  presence  of  an  excess  of  acid.  Thus,  protosulphate 
of  iron  is  converted  into  a  persulphate  by  heating  it  with  nitric 
acid,  while  reddish  vapours  are  given  off,  and  the  substance  be- 
comes brown.  This  colour  is  owing  to  the  fact  that  the  deutoxide 
of  nitrogen  which  is  formed  dissolves  in  the  undecomposed  proto- 
sulphate, and  produces  a  highly  coloured  liquid  (§  114).  But 
protosulphate  of  iron  FeO,S03  can  only  be  converted  into  neutral 
persulphate  FeaOgjSSOa  by  adding  a  certain  quantity  of  sulphuric 
acid.  The  salts  of  protoxide  of  iron  are  likewise  changed  into 
salts  of  peroxide  by  treating  their  solution  with  chlorine,  in  the 
presence  of  an  excess  of  acid. 

Reciprocally,  it  is  easy  to  transform  a  sesquisalt  of  iron  into  a 
protosalt,  by  subjecting  it  to  a  deoxidizing  action :  for  example, 
by  boiling  its  solution  with  iron  filings,  or  treating  it  with  sulf- 
hydric  acid,  in  which  latter  case  sulphur  is  deposited,  rendering 
the  liquid  milky : 

re,03,3S03+HS=2(FeO,S03)+S03,HO+S. 

§  784.  The  salts  of  peroxide  of  iron  afford  yellow  precipitates, 
the  colour  of  which  is  deeper  in  proportion  as  they  approach  neu- 
trality. 

The  fixed  alkalis  and  ammonia  yield  a  brown  precipitate  of 
hydrated  peroxide,  insoluble  in  an  excess  of  ammonia. 

The  alkaline  carbonates  give  the  same  brown  precipitate  of  hy- 
drated peroxide. 


SALTS    OF   IRON.  47 

Sulfliydric  acid  produces  a  white  precipitate  of  very  finely 
divided  sulphur  (§  783),  while  the  sulfhydrates  give  brown  preci- 
pitates. 

Yellow  prussiate  of  potash  gives  a  beautiful  blue  precipitate. 

Red  prussiate  does  not  precipitate  the  sesquisalts  of  iron.  These 
two  characters  signally  distinguish  the  salts  of  peroxide  of  iron 
from  those  of  protoxide. 

Benzoate  and  succinate  of  ammonia  give  brown  precipitates. 

The  sesquisalts  of  iron  rarely  exist  in  the  neutral  state,  as  their 
solutions  always  contain  an  excess  of  acid.  A  neutral  salt  is  de- 
composed by  treatment  with  water  into  a  very  basic  salt  which  is 
precipitated,  and  an  acid  salt  which  remains  in  solution. 

Persulphate  of  iron  forms  alum  with  the  sulphates  of  potassa 
and  ammonia,  the  formulae  of  which  correspond  to  those  of  ordinary 
alum,  namely,  Fe,03,3S03+KO,S03+24HO  and  Fe,03,S03-f- 
NH40,S03+24H0.  They  crystallize  in  regular  octahedrons  of 
a  violet  hue,  and  are  obtained  by  adding  sulphate  of  potassa  or 
of  ammonia  to  a  solution  of  persulphate  of  iron,  prepared  by  the 
process  indicated  (§  776,)  and  evaporating  the  liquid  at  a  low 
temperature.     These  alums  are  easily  destroyed  by  heat. 

COMPOUNDS  OF  IRON  WITH  SULPHUR. 

§  785.  Several  compounds  of  iron  with  sulphate  are  known. 

Protosulphide  of  Iron  FeS. 

§786.  Protosulphide  of  iron  is  obtained  by  direct  combination 
of  iron  with  sulphur.  When  an  iron  bar,  heated  to  whiteness,  is 
plunged  into  fused  sulphur,  the  combination  takes  place  with  great 
evolution  of  heat,  the  bar  becomes  corroded,  and  the  fused  sulphide 
of  iron  falls  to  the  bottom  of  the  crucible.  A  more  convenient 
method  of  preparing  it  consists  simply  in  heating  a  mixture  of  iron 
filings  and  sulphur  in  a  crucible.  Protosulphide  of  iron  combines 
readily  with  an  excess  of  iron,  producing  sub-sulphides,  which  are 
met  with  in  several  metallurgic  processes ;  and  it  also  combines 
very  easily  with  a  greater  proportion  of  sulphur.  In  order  to 
obtain  pure  protosulphide  of  iron,  the  product  formed  in  the  pre- 
sence of  an  excess  of  sulphur  must  be  fused  in  a  crucible  covered 
with  damp  charcoal,  in  a  forge-fire ;  when  the  excess  of  sulphur  is 
disengaged  in  the  state  of  sulphide  of  carbon,  and  protosulphide 
remains  in  the  form  of  a  lump  possessing  a  metallic  lustre. 

This  sulphide  is  obtained  hydrated  in  the  form  of  a  black  powder, 
when  a  protosalt  of  iron  is  precipitated  by  a  solution  of  an  alkaline 
sulfhydrate. 

Sulphur  and  iron  combine  together  in  the  presence  of  water, 
even  at  the  ordinary  temperature.  If  iron  filings  and  flowers  of 
sulphur  are  intimate  mixed  in  an  earthen  vessel  and  moistened 
with  water,  the  temperature  soon  rises,  while  the  colour  of  the 


48  IRON. 

paste  becomes  deeper,  and,  in  a  few  hours,  the  two  substances 
have  combined  together.  This  preparation  is  sometimes  made  in 
the  laboratory,  as  the  product  finds  extensive  use  in  the  prepara- 
tion of  sulfhydric  acid.  When  the  quantity  of  material  acted  on 
is  at  all  considerable,  the  reaction  is  sometimes  very  powerful  and 
the  mixture  is  thrown  from  the  vessel :  great  care  is  therefore  re- 
quisite. Formerly  chemists  supposed  even  volcanos  to  be  produced 
by  similar  reactions,  for  which  r.eason  the  name  oi  Lemery's  volcano 
was  given  to  this  preparation. 

Sesquisulphide  of  Iron  FogSg. 

§  787.  Sesquisulphide  of  iron,  corresponding  to  the  sesquioxide, 
is  obtained  by  decomposing  hydrated  peroxide  of  iron  by  sulfhy- 
dric  acid,  at  a  temperature  of  212°.  This  compound  easily  de- 
composes. 

Bisulphide  of  Iron  FeSg. 

§  788.  Bisulphide  of  iron  FeSg,  which  corresponds  to  no  known 
oxide  of  iron,  is  abundantly  found  in  nature,  occurring  in  the 
form  of  brilliant  cubic  crystals,  of  a  brass-yellow  colour,  and  called 
by  mineralogists  iron  pyrites,  or  simply  pyrites.  Pyrites  are  often 
sufficiently  hard  to  strike  fire  with  steel.  The  same  product  may 
be  obtained  in  the  laboratory,  in  the  form  of  a  yellow  powder,  by 
heating  very  finely  dissolved  protosulphide  of  iron  with  half  its 
weight  of  sulphur,  until  the  excess  of  the  latter  is  volatilized.  Its 
density  is  4.98.  Bisulphide  of  iron  is  not  attacked  by  dilute  acids, 
while  the  protosulphide,  under  the  same  circumstances,  gives  off  sulf- 
hydric  acid  in  abundance.  Iron  pyrites,  subjected  to  the  action  of 
heat,  parts  with  a  portion  of  its  sulphur,  which  distils  over,  while  a 
sulphide  composed  of  100  parts  of  iron  and  68  of  sulphur  remains, 
which  may  be  considered  as  a  special  sulphide. 

Magnetic  Pyrites, 

§  789.  Native  sulphides  of  iron,  of  a  bronze  colour,  are  found  in 
crystalline  masses,  the  form  of  which  is  a  regular  hexahedral  prism : 
they  contain  less  sulphur  than  the  bisulphide,  or  ordinary  pyrites, 
and  are  called  magnetic  pyrites,  because  they  affect  the  needle. 
Their  composition  corresponds  in  general  to  the  formula  Fe-S  = 
5FeS+FeA. 

COMPOUND  OF  IRON  WITH  NITROGEN. 

§  790.  When  dry  ammoniacal  gas  is  passed  over  fine  iron-wire, 
heated  to  a  dull  red-heat  'in  a  porcelain  tube,  the  metal  becomes 
very  brittle,  and  increases  remarkably  in  weight,  while  a  nitruret 
of  iron  is  formed,  containing  12  or  13  per  cent,  of  nitrogen.  This 
product  is  more  readily  obtained  by  heating  anhydrous  protochlo- 
ride  of  iron  in  a  glass  tube,  in  a  current  of  dry  ammoniacal  gas. 


COMPOUNDS    OF   IRON.  49 

when  nitruret  of  iron  remains  in  the  form  of  a  metallic  sponge,  of  a 
silvery  whiteness. 

COMPOUND  OF  IRON  WITH  PHOPHORUS. 

§791.  A  combination  of  iron  and  phosphorus  is  obtained  by 
heating  a  mixture  of  phosphate  of  lime  and  charcoal  in  a  forge- 
fire,  in  a  crucible  covered  with  charcoal,  when  a  very  hard  and 
brittle  gray  metallic  lump  remains,  capable  of  a  fine  polish.  The 
composition  of  this  substance  corresponds  to  the  formula  Fe^P. 

A  very  small  quantity  of  phosphorous  changes  the  qualities  of 
iron  in  a  remarkable  manner,  and  renders  it  brittle  when  cold. 
Phosphuretted  ores  may  do  for  cast-iron,  but  never  are  fit  to  be 
rolled  into  good  bar-iron. 

COMPOUNDS  OF  IRON  WITH  ARSENIC. 

§  792.  Arsenic  readily  combines  with  iron  in  a  great  number  of 
proportions,  forming  in  all  cases  very  brittle  compounds,  several 
of  which  are  found  crystallized  in  nature.  The  mineral  called 
mispickel  is  a  compound  of  iron  with  arsenic  and  sulphur,  of  the 
formula  FeSg+FeAs^,  while  its  crystalline  form  is  that  of  a  right 
prism  with  a  rhombic  base. 

COMPOUNDS  OF  IRON  WITH  CHLORINE. 
§  793.  Two  combinations  of  iron  with  chlorine,  corresponding  to 
the  protoxide  and  sesquioxide,  are  known. 

ProtocJiloride  of  Iron  FeCl. 

§  794.  This  compound  is  obtained  when  iron  filings  are  heated 
with  chlorine,  care  being  taken  that  the  latter  is  not  in  excess,  as 
otherwise  sesquichloride  would  be  formed.  It  is  obtained  with 
greater  certainty  in  a  state  of  purity  by  heating  iron  in  a  current 
of  chlorohydric  acid  gas. 

Protochloride  of  iron  forms  a  brown  fluid  mass,  which  crystal- 
lizes on  cooling :  it  is  prepared  in  solution  in  water,  by  heating 
iron  filings  with  chlorohydric  acid  and  evaporating  the  liquid, 
when  green  crystals  of  the  formula  FeCl+6H0  are  obtained. 

Sesquichloride  of  Iron  FegClg. 

§  795.  Sesquichloride  or  chloride  of  iron  is  prepared  by  heating 
iron  in  a  current  of  chlorine,  and  volatilizing  the  product  in  this 
gas,  when  beautiful  rainbow-like  spangles  of  a  brown  or  deep  green 
colour  are  obtained.  The  chloride  dissolves  in  water,  yielding  a 
yellow  solution,  which  can  be  immediately  obtained  by  treating  iron 
with  aqua  regia.  The  solutions  of  sesquichloride  of  iron  in  alcohol 
and  in  ether  lose  their  colour  and  precipitate  protochloride  of  iron 
when  exposed  to  the  solar  light. 

Sesquichloride  of  iron  is  decomposed  by  steam  at  a  red-heat, 

Vol.  n.— 4 


50  IRON. 

when  chlorohydric  acid  is  disengaged,  and  on  the  sides  of  the  tube 
in  which  the  experiment  is  made  small  glittering  spangles  of  ses- 
quioxide  of  iron  are  deposited,  resembling  the  specular  oxide  found 
in  the  fissures  of  volcanic  lavas.  This  mineral  has  been  supposed 
to  have  been  formed  in  a  similar  manner. 

COMPOUNDS  OF  IRON  WITH  CYANOGEN. 

§  796.  Iron  forms  several  compounds  with  cyanogen,  particu- 
larly remarkable  for  their  multiple  combinations. 

If  cyanide  of  potassium  be  added  to  a  solution  of  a  protosalt  of 
iron,  protocyanide  of  iron  is  obtained  as  a  white  precipitate,  which 
retains  with  great  energy  a  portion  of  the  reagent  which  served  to 
produce  it.  It  is  obtained  in  greater  purity  by  treating  Prussian 
blue  with  sulfhydric  acid,  when  a  white  precipitate,  which  soon 
changes  to  blue  in  the  air,  is  formed. 

Cyanide  of  iron  combines  with  a  great  number  of  other  metallic 
cyanides,  producing  double  cyanides,  which,  besides  being  of  great 
technical  importance,  are  much  used  in  the  laboratory  as  reagents. 
In  these  compounds  the  iron  has  lost  its  habitual  characteristic 
properties,  being  no  longer  precipitated  by  the  reagents  which' 
usually  throw  it  down  from  its  saline  solutions  or  from  the  chlo- 
rides. The  characteristic  properties  of  the  simple  cyanides  are 
also  modified  in  such  double  salts,  for  which  reason  these  com- 
pounds have  been  considered,  not  as  real  double  cyanides,  but  as 
combinations  of  the  metal  with  a  compound  electro-negative  body, 
called  ferro-cyanogen. 

Double  Cyanide  of  Iron  and  Potassium,  or  Ferrocyanide  of  Potas- 
sium FeCy+2KCy. 

§  797.  This  double  cyanide,  which  is  also  called  prussiate  of  pot- 
ash, is  the  most  important  of  these  compounds,  and  is  brought  into 
commerce  in  the  form  of  beautiful  yellow  crystals,  of  the  formula 

EeCy4-2KCy+3HO. 

It  contains  12.8  per  cent,  of  water,  which  it  readily  loses  on  a 
slight  elevation  of  temperature :  100  parts  of  water  dissolve  25 
parts  of  the  salt  at  ordinary  temperature,  and  50  parts  at  the 
boiling  point.  This  double  cyanide  is  very  fixed,  being  neither 
decomposable  by  the  alkalis  nor  even  the  alkaline  sulf hydrates  ; 
while  the  action  of  heat  destroys  the  salt  and  evolves  nitrogen, 
when  the  residue,  treated  with  water,  yields  a  solution  of  cyanide 
of  potassium  and  an  insoluble  black  substance,  which  is  a  true  car- 
buret of  iron,  of  the  formula  FeCg. 

This  salt  is  prepared  on  a  large  scale  by  fusing  carbonate  of 
potassa  with  animal  charcoal,  which  must  be  prepared  expressly 
from  animal  matter  containing  but  few  phosphates.  Calcined 
bone,  dried  flesh,  skins,  and  principally  old  shoes  are  used  for  its 


PRUSSIATE   OF   POTASH.  51 

preparation :  these  substances  leave  a  carbonaceous  residue,  highly 
charged  with  nitrogen,  which  is  afterward  heated  with  about  its 
own  weight  of  carbonate  of  potassa,  in  large  cast-iron  kettles  into 
which  the  smoky  flame  of  a  reverberatory  furnace  enters.  The 
carbonate  of  potassa  is  first  fused  alone,  and  then  the  animal 
charcoal  is  added,  when  a  reaction  takes  place  accompanied  with 
eifervescence,  and  the  mass  is  continually  stirred  with  iron  rods. 
Cyanide  of  potassium  and  cyanide  of  iron  are  formed,  the  iron 
being  furnished  by  the  sides  of  the  kettle  and  the  rods ;  and  when 
the  reaction  is  ended,  the  matter  is  removed  and  treated  with 
boiling  water.  The  hot  solution  is  filtered,  and  evaporated  to 
crystallization ;  while  the  mother  liquid,  on  being  again  concen- 
trated, still  yields  crystals,  which,  with  the  former  ones,  are  puri- 
fied by  dissolving  them  in  boiling  water  and  allowing  the  liquid 
to  cool  slowly. 

Within  a  few  years,  cyanide  of  potassium  has  been  prepared  by 
the  direct  combination  of  carbon  with  nitrogen,  in  the  presence 
of  carbonate  of  potassa;  and  this  process  is  now  applied  to  the 
manufacture  of  prussiate  of  potash  on  a  large  scale.  Wood  char- 
coal, impregnated  with  a  concentrated  solution  of  carbonate  of 
potassa,  is  heated  to  a  high  temperature  in  brick  vent-holes,  in  a 
current  of  hot  air  which  has  been  deprived  of  its  oxygen  by  pass- 
ing over  a  long  column  of  burning  coke.  From  time  to  time  the 
portion  of  potashed  charcoal  at  the  lower  part  of  the  holes  is  with- 
drawn, and  additional  charcoal  is  introduced  through  the  upper 
opening  to  keep  the  supply  constant.  The  alkaline  charcoal,  in, 
this  operation,  is  exposed  for  10  hours  to  the  action  of  nitrogen, 
and  then  is  heated  in  an  iron  boiler,  with  water  and  finely  pow- 
dered sparry  iron.  The  liquid  yields  when  evaporated  beautiful 
crystals  of  very  pure  prussiate  of  potash,  while  the  residue  of  the 
charcoal  is  again  soaked  in  a  concentrated  solution  of  carbonate 
of  potassa  and  the  operation  recommenced. 

The  solution  of  prussiate  of  potash,  added  to  the  solutions  of  a 
great  number  of  metallic  salts,  affords  precipitates  which  are  often 
remarkable  for  their  brilliant  colours,  and  serve  as  distinguish- 
ing characters  of  the  metals.  In  these  double  decompositions,  the 
cyanide  of  potassium  alone  is  decomposed,  by  being  changed  into  a 
cyanide  of  the  metal  which  exists  in  the  reacting  solution,  while 
this  new  cyanide  combines  with  the  cyanide  of  iron.  If  prussiate 
of  potash  FeCy +2KCy  be  added  to  a  solution  of  sulphate  of  copper 
CuOjSOg,  a  characteristic  reddish-brown  precipitate,  of  the  for- 
mula FeCy+2CuCy,  is  obtained.  The  prussiate,  poured  into  a 
solution  of  sulphate  of  zinc  ZnO,S03,  gives  a  white  precipitate 
reCy+2ZnCy.  A  series  of  compounds  of  similar  formulae,  all  of 
which  contain  protocyanide  of  iron,  is  thus  obtained. 

The  formula  of  the  precipitate  obtained  with  a  salt  of  lead  is 
FeCy+2PbCy,  which,  by  treatment  with  sulfhydric  acid,  forms  an 


52  IRON. 

insoluble  sulphide,  and  an  acid  liquid  which  yields  white  crystals 
when  evaporated  under  cover  near  a  saucer  filled  with  concentrated 
sulphuric  acid.  These  crystals  are  formed  by  a  real  hydracid 
FeCy+2HCy,  called  f err o-Iti/drocj/ ante  acid,  or  hydrocyano-ferric 
acid,  or  ferro-cyanhydric  acid,  the  solution  of  which  is  inodorous 
and  posseses  none  of  the  properties  of  hydrocyanic  acid.  The 
double  cyanides  may  therefore  be  regarded  a^s  f err ocyanides. 

Prussiate  of  potash  yields  a  white  precipitate  with  protosalts  of 
iron,  composed  for  the  greater  part  of  protocyanide  of  iron,  but 
always  retaining  a  certain  quantity  of  alkaline  cyanide.  This  pre- 
cipitate soon  changes  in  the  air. 

With  the  salts  of  peroxide  of  iron,  prussiate  of  potash  gives  a 
beautiful  blue  precipitate,  called  Prussian  blue,  which  is  used  in 
dyeing  and  in  oil-painting.  The  following  reaction  ensues  between 
perchloride  of  iron  and  prussiate  of  potash : 

2Fe,Cl3-f3(FeCy+2KCy)=6KCH-(3FeCy-f2Fe,Cy3). 

The  formula  of  Prussian  blue  is  3FeCy+2Fe,Cy3. 

§  798.  If  a  current  of  chlorine  be  passed  through  a  solution  of 
prussiate  of  potash  and  the  liquid  boiled,  a  green  precipitate  is 
formed,  which,  when  heated  with  chlorohydric  acid,  gives  off  a  cer- 
tain quantity  of  mixed  oxides  of  iron,  and  leaves  a  green  residue,  of 
the  formula  FeCy-f  Fe3Cy3H-4H0.  It  is  a  compound  resembling 
magnetic  oxide,  if  the  water  of  combination  be  overlooked. 

§  799.  If  the  current  of  chlorine  be  stopped  at  the  moment  when 
the  solution  no  longer  throws  down  a  blue  precipitate  of  sesquisalts 
of  iron,  a  liquid,  yielding  beautiful  red  crystals  on  evaporation,  is 
obtained.  It  is  important  not  to  prolong  the  action  of  the  chlorine 
too  much,  and  to  keep  the  liquid  constantly  agitated.  The  solu- 
tion is  frequently  tested  with  a  sesquisalt  of  iron,  and  the  current 
of  chlorine  is  arrested  as  soon  as  a  precipitate  is  no  longer  formed. 
It  is  also  well  to  neutralize  the  liquid  gradually  with  a  little  potassa. 
The  red  salt,  which  has  been  called  cyanoferride  or  ferricyanide 
of  potassium,  has  the  formula  SKC j-hFe^Gj^ ;  and  contains  no 
water  of  crystallization.  The  reaction  from  which  it  originates  is 
the  following : 

2(FeCy+2KCy)-fCl=(3KCy-fFe,Cy3)-fKCl. 

The  red  prussiate  is  much  less  soluble  than  the  yellow,  38  parts 
of  cold  water  being  required  to  dissolve  1  part  of  it.  Protosalts 
of  iron  yield  with  red  prussiate  of  potash  a  beautiful  blue  precipi- 
tate of  the  formula  SFeCy+FcaCyg,  the  reaction  being  as  follows: 

(3KCy+Fe,Cy3)-f3(FeO,S03)=3(KO,S03)+(3FeCy+Fe,Cy3). 

Red  prussiate  of  potash  yields  with  salts  of  lead  a  precipitate 
3PbCy-|-FeaCy3,  which  gives,  when  treated  with  sulphuric  acid, 
a  precipitate  of  sulphate  of  lead  and  a  compound  SIICy+FeaCya, 


CAST-IRON.  53 

called  Jiydro-ferrieyanic  acid,  which  dissolves  with  a  red  colour. 
The  solution,  when  evaporated,  deposits  the  salt  in  yellowish- 
brown  crystals. 

COMPOUNDS  OF  IRON  WITH  CARBON. 

§  800.  Iron  combines  with  carbon  when  in  presence  of  this  sub- 
stance, at  a  very  high  temperature.  It  has  been  shown  (§  795) 
that  a  carburet  of  iron  FeC^  is  obtained  by  decomposing  prussiate 
of  potash  by  heat :  by  the  direct  combination  of  iron  with  carbon, 
compounds  so  rich  in  carbon  are  never  obtained,  as  the  most  car- 
buretted  products  only  contain  about  5  per  cent,  of  carbon,  their 
composition  resembling  the  formula  Fe^C.  These  carburetted 
irons  are  called  cast-iron,  which  is  again  divided  into  white  cast- 
iron  and  gray  cast-iron. 

Iron,  heated  in  blast-furnaces  at  a  very  high  temperature  in 
contact  with  charcoal,  passes  into  the  state  of  cast-iron,  which, 
by  cooling  suddenly  on  leaving  the  furnace,  forms  hard  and  brittle 
metallic  masses,  whiter  than  the  soft  iron,  and  consisting  of  white 
cast-iron.  If,  on  the  contrary,  the  iron  be  cooled  slowly,  the 
carbon  which  was  in  combination  with  the  iron  separates  by  crys- 
tallization, forming  an  infinite  number  of  small  black  graphitose 
spangles,  which  impart  a  deep  gray  colour  to  the  mass.  The  small 
spangles  of  carbon  are  scattered  through  the  iron,  the  greater  part 
of  which  is  decarburetted,  and  such  iron,  which  is  called  gray  or 
soft  cast-iron,  is  much  more  malleable  than  the  white  sort,  and  can 
be  cut  with  a  file. 

All  kinds  of  cast-iron  do  not  lose  their  combined  carbon  with 
equal  readiness ;  when  the  iron-ore  contained  phosphorus  or  sulphur, 
the  metal  retains  the  character  of  white  cast-iron,  even  after  a  very 
slow  cooling.  Certain  kinds  of  cast-iron,  which  contain  manganese 
in  combination,  possess  also  the  property  of  retaining  their  com- 
bined carbon,  and  present,  after  cooling,  a  crystalline  fracture,  with 
very  large  brilliant  laminae,  which  intersect  each  other  at  angles 
of  120° ;  hence  the  crystalline  form  is  inferred  to  be  a  regular 
hexahedral  prism. 

This  iron  is  called  lamellar  cast-iron,  and  is  obtained  from  the 
manganiferous  sparry  ores  (§  782). 

When  white  cast-iron  is  treated  with  chlorohydric  acid  or  dilute 
sulphuric  acid,  the  metal  dissolves  with  evolution  of  hydrogen  'gas, 
but  at  the  same  time  a  volatile  oil  of  a  nauseous  smell  is  generated, 
resulting  from  the  combination  of  the  hydrogen  with  carbon  in  the 
nascent  state.  If,  on  the  contrary,  gray  cast-iron  is  dissolved,  a 
certain  quantity  of  this  oil  is  produced,  by  the  combination  of  hy- 
drogen with  the  portion  of  carbon  which  was  in  combination  with 
the  iron,  while  the  free  carbon  remains  in  the  form  of  small  crys- 
talline spangles. 

Cast-iron,  under  certain  circumstances,  assumes  an  intermediate 


64 


IRON. 


State  between  the  gray  and  white,  when,  the  separation  of  graphite 
not  taking  place  throughout  the  whole  mass,  but  only  in  some  por- 
tions, the  substance  presents  the  appearance  of  white  cast-iron, 
more  or  less  spotted  with  gray.  This  kind  is  called  sjjotted  or 
mottled  cast-iron,  (fonte  truitde.) 

COMPOUND  OF  IRON  WITH  SILICIUM. 

§  801.  A  compound  of  iron  with  silicium  is  obtained  by  heating 
in  a  crucible  covered  with  damp  charcoal  a  mixture  of  iron  filings, 
silicic  acid,  and  charcoal,  in  a  forge-fire,  when  a  fused  metallic  lump, 
possessing  a  certain  degree  of  malleability,  is  formed.  Iron  can 
combine,  in  this  case,  with  9  or  10  per  cent,  of  silicium.  Cast-iron, 
particularly  that  made  in  blast-furnaces  at  very  high  temperatures 
with  coke,  generally  contains  1  or  2  hundredths  of  silicium. 

DETERMINATION  OF  IRON,  AND  ITS  SEPARATION  FROM  THE  METALS 
PREVIOUSLY  DESCRIBED. 

§  802.  In  chemical  analyses  iron  is  nearly  always  determined  in 
the  state  of  sesquioxide,  and  when  it  exists  as  such  in  its  solutions 
is  precipitated  by  ammonia  or  carbonate  of  ammonia.  It  is  best  to 
make  the  precipitation  in  a  hot  liquid,  as  the  hydrated  sesquioxide 
is  then  less  gelatinous  and  more  easily  washed  on  the  filter.  When 
the  iron  exists  in  the  state  of  protoxide,  it  must  be  converted  into 
sesquioxide  by  evaporating  the  liquid  with  nitric  acid,  or  by  passing 
a  current  of  chlorine  through  it ;  in  which  latter  case  the  excess 
of  chlorine  must  be  driven  ofi"  by  boiling.  Sesquioxide  of  iron  is 
then  precipitated  by  ammonia.  The  superoxidation  of  the  iron 
may  also  be  afi'ected  by  adding  chlorohydric  acid,  and  then  a  small 
quantity  of  chlorate  of  potassa,  to  the  liquid,  when,  by  boiling,  the 
chlorohydric  acid  and  chlorate  of  potassa  mutually  decompose  each 
Other,  while  chlorine  is  set  free,  which  produces  the  superoxida- 
tion of  the  iron.  Frequently  it  is  preferable  to  precipitate  sesqui- 
oxide of  iron  by  succinate  of  ammonia,  which  throws  it  down  more 
completely  than  ammonia,  as  an  excess  of  this  last  reagent  may 
redissolve  a  small  quantity.  The  precipitate  of  sesquisuccinate  of 
iron  is  decomposed  by  heat,  leaving  pure  peroxide  of  iron. 

In  some  cases,  sesquioxide  of  iron  must  be  precipitated  with 
caustic  potassa  in  excess ;  but  the  precipitate  then  retains  a  small 
quantity  of  potassa  with  great  obstinacy,  and  is  freed  from  it  only 
by  boiling  several  times  with  distilled  water.  When  the  precipi- 
tate is  copious,  it  is  better,  after  having  collected  it  on  the  filter 
and  washed  it  with  a  small  quantity  of  hot  water,  to  redissolve  it 
in  weak  chlorohydric  acid,  saturate  the  liquid  by  ammonia,  and 
precipitate  again  with  succinate  of  ammonia. 

When  the  solution  contains  organic  substances,  such  as  sugar, 
tartaric  acid,  etc.,  ammonia  no  longer  precipitates  sesquioxide  of 
iron,  nor  does  even  carbonate  of  ammonia ;  and  the  iron  must  then 


DETERMINATION    OF   IRON.  65 

be  precipitated  as  sulphide  by  sulf  hydrate  of  ammonia.  The  pre- 
cipitate is  collected  on  a  filter,  and  washed  with  water,  to  which  a 
small  quantity  of  sulfhydrate  of  ammonia  is  added,  in  order  to 
prevent  the  sulphide  of  iron  from  being  converted  into  sulphate  by 
contact  with  the  air ;  after  which  the  precipitate  is  redissolved  in 
chlorohydric  acid,  the  iron  brought  to  the  state  of  peroxide,  either 
by  means  of  chlorine  or  by  evaporating  the  solution  with  a  small 
quantity  of  nitric  acid,  and  the  sesquioxide  formed  is  then  precipi- 
tated by  succinate  of  ammonia. 

§  803.  In  order  to  separate  the  alkaline  metals,  ammonia  or 
succinate  of  ammonia  is  used  after  the  iron  has  been  brought  to 
the  state  of  sesquioxide.  It  is  separated  from  the  alkalino-earthy 
metals  by  the  same  reagents,  care  being  taken  at  the  same  time 
that  the  ammonia  contains  no  carbonate,  or  cannot  absorb  carbonic 
acid  from  the  air,  as  the  carbonate  of  ammonia  formed  would  cause 
the  precipitation  of  the  earths.  When  iron  is  to  be  separated  from 
magnesia,  a  quantity  of  sal  ammoniac  sufficient  to  prevent  the 
magnesia  from  being  precipitated  by  an  excess  of  ammonia  must 
be  added  to  the  liquid  ;  but  the  latter,  most  frequently,  already 
contains  free  acid  enough  to  produce  the  quantity  of  ammoniacal 
salt  necessary  during  its  saturation  by  ammonia. 

In  order  to  separate  iron  from  alumina,  the  iron  is  first  brought 
to  the  state  of  sesquioxide,  if  it  does  not  already  exist  in  that  state, 
and  then  an  excess  of  caustic  potassa  is  added ;  when,  by  boiling 
the  liquid  for  some  time,  all  the  alumina  dissolves  in  the, potash, 
leaving  only  the  sesquioxide  of  iron  as  a  precipitate.  The  filtered 
alkaline  liquid  is  then  supersaturated  with  chlorohydric  acid,  and 
the  alumina  precipitated  by  an  excess  of  carbonate  of  ammonia. 

The  separation  of  iron  and  manganese  is  easily  eifected  when 
the  iron  exists  as  sesquioxide,  and  we  have  seen  that  it  can  always 
be  readily  brought  to  that  state.  The  manganese,  moreover,  is 
always  present  as  a  protosalt ;  for  the  other  salts  of  manganese, 
not  being  very  fixed,  are  soon  converted  by  ebullition  into  proto- 
salts.  The  same  process  as  described  for  the  separation  of  sesqui- 
oxide of  iron  from  magnesia  is  adopted ;  that  is,  a  quantity  of 
ammoniacal  salt  sufficient  to  prevent  the  precipitation  of  the  oxide 
of  manganese  is  added  to  the  liquid :  generally,  however,  the  am- 
monia necessary  to  saturate  the  acid  liquid  is  sufficient  to  produce 
the  ammoniacal  salt  required.  The  sesquioxide  of  iron  is  then 
precipitated  by  ammonia  or  succinate  of  ammonia,  and  the  man- 
ganese is.  obtained  from  the  filtered  liquid  by  sulfhydrate  of  am- 
monia as  sulphide. 

When  a  solution  of  a  sesquisalt  of  iron  is  precipitated  by  ammo- 
nia or  carbonate  of  soda,  changes  of  colour  are  observed,  which  may 
guide  the  operator  in  the  separation  of  the  iron,  and  allow  the  iron 
and  other  metals  which  exist  in  the  liquid  to  be  successively  pre- 
cipitated.    The  sesquisalts  of  iron,  dissolved  in  an  acid  liquid,  are 


56  IRON. 

of  a  very  pale  yellow  colour,  and  when  ammonia  or  carbonate  of 
soda  are  added  by  small  quantities  at  a  time,  the  liquid  becomes 
more  and  more  deeply  coloured  as  it  approaches  saturation,  and  at 
last  assumes  a  deep  brown  colour  before  any  deposit  is  formed. 
If  it  is  then  subjected  to  ebullition,  the  peroxide  of  iron  is  com- 
pletely precipitated :  the  liquid  is  bleached,  retaining  still  all  the 
oxides  of  the  formula  RO  in  solution,  which  are  much  more  power- 
ful bases  than  sesquioxide  of  iron,  and,  in  general,  than  the  oxides 
of  the  formula  RgOg.  In  order  to  make  the  separation  properly, 
the  liquid  is  first  heated  to  boiling,  and  the  ammonia  or  carbonate 
of  soda  then  added,  stirring  it  continually,  and  discontinuing  when 
the  liquid  has  turned  brown.  It  is  then  boiled  for  some  time,  when 
a  brown  precipitate  of  hydrated  sesquioxide  of  iron  is  generally 
formed.  If  the  liquid  is  not  discoloured,  a  few  drops  of  the  reagent 
are  added,  it  is  again  boiled,  and  this  is  continued  until  discolora- 
tion takes  place.  It  is  then  filtered  while  boiling,  and  a  consider- 
able quantity  of  carbonate  of  soda  is  added  to  efi'ect  the  precipita- 
tion of  the  other  metallic  oxides  which  exist  in  the  solution.  There 
is,  therefore,  a  considerable  interval  between  the  moment  of  the 
complete  precipitation  of  the  oxides  of  the  formula  RgO^  and  that 
of  the  commencement  of  the  precipitation  of  the  oxides  RO. 

In  this  way,  sesquioxide  of  iron  may  be  separated  with  a  con- 
siderable degree  of  accuracy  from  all  protoxide  with  which  it  is 
mixed  in  the  liquid ;  but  the  admission  of  air  must  be  avoided  as 
much  as  possible,  as  its  oxygen  would  convert  a  portion  of  the 
protoxide  into  sesquioxide.  It  is  often  necessary,  in  the  analysis 
of  mineral  substances,  to  determine  the  relative  proportions  of  the 
sesquioxide  and  protoxide  of  iron  they  contain,  which  can  be  done 
exactly  when  the  mineral  dissolves  readily  in  non-oxidizing  acids, 
such  as  chlorohydric.  The  material  is  finely  powdered,  and  treated 
in  a  small  flask  with  hot  concentrated  chlorohydric  acid,  the  liquid 
being  continually  boiled,  in  order  that  the  steam  disengaged  may 
prevent  the  admission  of  air  into  the  flask ;  and  the  boiling  is  con- 
tinued until  the  greater  part  of  the  acid  in  excess  is  evaporated. 
It  is  then  treated  with  boiling  water,  and  the  sesquioxide  preci- 
pitated by  carbonate  of  soda,  added  by  drops,  avoiding  as  much  as 
possible  the  contact  of  the  air.  When  the  liquid  is  deprived  of 
colour,  it  is  allowed  to  rest  for  some  time  in  the  flask,  which  is 
corked  :  the  clear  liquid  is  decanted,  collected  rapidly  on  a  filter, 
and  washed  with  boiling  water.  The  filtrate  contains  the  prot- 
oxide of  iron,  which  is  brought  to  the  state  of  sesquioxide  by 
means  of  chlorine,  and  precipitated  by  an  excess  of  carbonate  of 
soda. 

§  804.  It  is,  however,  difficult  to  prevent  a  portion  of  the  prot- 
oxide of  iron  from  changing  into  sesquioxide  by  absorption  of  the 
oxygen  of  the  air.  Greater  exactness  is  obtained  by  another 
process,  which  may  be  applied  to  various  other  cases.     If  a  solu- 


DETERMINATION    OF   IRON.  57 

tion  of  permanganate  of  potassa  be  added  to  a  solution  of  a  proto- 
salt  of  iron,  the  permanganate  immediately  loses  its  colour,  by 
being  decomposed  into  protoxide  of  manganese  and  potassa,  which 
base  combines  with  the  acid,  and  into  oxygen,  which  converts  the 
protoxide  of  iron  into  sesquioxide.*  The  discolouration  of  the 
permanganate  of  potassa  takes  place  as  long  as  any  protoxide  of 
iron  remains  in  the  liquid ;  but  as  soon  as  all  the  protoxide  is  changed 
into  sesquioxide,  the  smallest  drop  of  the  solution  of  permanganate 
of  potassa  gives  the  liquid  a  very  decided  red  tinge.  If  the  solu- 
tion of  permanganate  of  potassa  is  of  standard  quality,  it  suffices 
to  measure  exactly  the  quantity  necessary  to  produce  a  permanent 
red  colour,  and  the  quantity  of  iron  which  existed  in  the  state  of 
protoxide  can  thence  be  directly  inferred. 

The  permanganate  of  potassa  used  to  make  the  standard  solu- 
tion is  prepared  by  heating,  for  two  hours,  in  an  earthen  crucible, 
a  mixture  of  2  parts  of  binoxide  of  manganese,  3  parts  of  caustic 
potassa,  and  1  part  of  chlorate  of  potassa.f  The  mass  is  broken  to 
pieces  after  cooling,  treated  with  3  or  4  times  its  weight  of  water, 
and  the  liquid  filtered  through  asbestus  or  powdered  glass,  to  sepa- 
rate the  sesquioxide  of  manganese.  Weak  nitric  acid  is  then 
added  until  the  liquid  assumes  a  beautiful  violet-red  colour.  The 
solution  is  preserved  in  a  well-corked  bottle,  as  it  would  be  soon 
changed  by  the  particles  of  organic  dust  floating  in  the  air.J 

In  order  to  determine  the  standard  of  the  solution,  1  gramme 
of  highly-polished  piano-forte  wire,  exactly  weighed,  is  dissolved  in 
25  cubic  centimetres  of  chlorohydric  acid,  and  the  liquid .  diluted 
with  water  recently  boiled,  so  as  to  increase  its  volume  to  about 
1  litre. §     Again,  100  divisions  of  the  solution  of  permanganate  of 


*  The  solution  must  necessarily  contain  free  acid  enough  to  dissolve  the  oxide 
of  manganese  formed. —  W.  L.  F. 

\  Another  proportion,  given  by  Gregory,  is  as  follows : — 8  parts  of  peroxide  of 
manganese,  10  parts  of  caustic  potassa,  and  3  parts  of  chlorate  of  potash.  But 
tiie  .best  method,  as  the  only  one  by  which  permanganate  of  potassa  can  be  ob- 
tained in  crystals  and  free  from  chloric  acid,  according  to  Liebig,  is  by  igniting 
pure  peroxide  of  manganese  with  a  fixed  alkali,  with  access  of  air. —  W.  L.  F. 

%  The  use  of  permanganate  of  potassa  as  a  means  of  determining  iron  in  any 
case  has  been  objected  to  by  many  chemists,  on  the  ground  that  a  standard  solu- 
tion would  not  keep  uniform  for  any  length  of  time.  This  objection  is  unfounded; 
for  a  solution  made  by  dissolving  crystals  of  the  salt  remained  perfectly  unaltered 
for  a  period  of  six  months,  during  which  time  it  was  often  tested.  The  solution 
must,  however,  be  kept  in  a  bottle  with  a  tight-fitting  ground-glass  stopper,  and 
the  bottle  ought  always  to  be  kept  as  full  as  possible.  The  manganate  should  be 
converted  into  permanganate,  rather  by  adding  a  quantity  of  boiling  water  to  its 
concentrated  solution  than  by  introducing  nitric  acid. —  W.  L.  F. 

§  As  not  even  piano-forte  wires  consist  of  pure  iron,  it  is  better  to  employ  a 
protosalt  at  once  :  of  these  the  protosulphate  of  iron  and  ammonia  is  most  com- 
mendable, as  being  least  of  all  subject  to  decomposition,  3,nd  easy  to  prepare. 
Of  this  salt,  6.429  gm.,  which  correspond  exactly  to  1  gm.  of  metallic  iron,  are  dis- 
solved, and  the  solution  having  been  made  acid,  the  permanganate  may  be  imme- 
diately added.—  W.  L.  F. 


IKON. 

potassa  are  introduced  into  a  graduated  alkalimeter  (fig. 
477),  and  poured  from  it  into  the  vessel  B  (fig.  478),  which 
contains  the  protochloride  of  iron,  stirring  constantly  to 
facilitate  the  mixture.  The  solution  of  the  permanganate 
is  added,  bj  small  quantities  at  a  time,  until  the  liquid  as- 
sumes a  permanent  roseate  tinge.  The  number  of  divi- 
sions and  fractions  of  a  division  necessary  to  produce  this 
result  are  noted  down :  supposing  this  number  to  be  75.5  div., 
the  conclusion  will  follow  that  75.5  div.  of  the  solution  of 
permanganate  correspond  to  1  gramme  of  protoxide  of  iron, 
and  consequently  that  1  div.  of  permanganate  corresponds 
to  0.01325  gr.  of  metallic  iron.* 

This  being  done,  in  order  to  analyze  a  substance 
containing  protoxide  and  sesquioxide  of  iron  at  the 
Fig.  478.  same  time,  1  gramme  of  it  is  dissolved  in  chlorohydric 
acid,  the  liquid  is  diluted  with  boiled  water  until  it  oc- 
cupies the  volume  of  about  1  litre,  and  then  the  standard  solution 
of  permanganate  of  potassa  is  carefully  added  until  the  liquid 
assumes  a  roseate  tinge.  Let  us  suppose  that  to  produce  this 
effect,  22.0  div.  of  the  solution  of  the  permanganate  were  required  ; 
the  gramme  of  the  substance  subjected  to  analysis  will  then  con- 
tain 22.0x0.01324  gr.,  or  0.291  gr.  of  iron,  existing  in  the  state 
of  protoxide,  or,  lastly,  0.374  gr.  of  protoxide  of  iron. 

The  quantity  of  sesquioxide  can  readily  be  determined  by  the 
same  process  : — 1  gramme  of  the  substance  is  again  dissolved  in 
concentrated  chlorohydric  acid,  and  then  4  grammes  of  sulphite 
of  soda,  dissolved  in  a  small  quantity  of  water,  are  poured  into  the 
solution  gradually  and  by  small  quantities.  The  sulphurous  acid 
which  is  set  free  by  the  reaction  of  the  chlorohydric  acid  on  the 
alkaline  sulphite  converts  the  perchloride  of  iron  into  protochlo- 
ride, so  that  all  the  iron  in  the  substance  then  exists  in  the  solu- 
tion as  protochloride.  The  liquid  is  boiled  to  drive  off  the  excess 
of  sulphurous  acid,  diluted  with  water  to  about  the  volume  of  1 
litre,  and  the  standard  solution  of  permanganate  is  added.  Sup- 
posing that  it  was  necessary  to  add  36.0  div.  of  the  alkalimeter,  in 
order  to  obtain  a  permanent  rose-colour,  the  conclusion  follows 
that  the  substance  contains  36.0x0.01324  gr.,  or  0.477  of  metallic 
iron.  Now,  as  it  has  been  already  found  to  contain  0.291  of  iron 
in  the  state  of  protoxide,  there  are  0.186  gr.  present  in  a  more 
highly  oxidized  state,  corresponding  to  0.266  gr.  of  sesquioxide. 

*  The  result  will.be  the  more  exact  the  more  dilute  a  solution  of  permanga- 
nate of  potassa  is  employed,  and  the  accuracy  of  the  determination  may,  in  fact, 
be  carried  to  almost  any  degree. —  W.  L.  F, 


METALLURGY  OF  IRON.  69 


METALLURGY  OF  IRON. 

§  805.  The  only  ores  of  iron  employed  are  the  oxides  and  the 
carbonate;  while  the  sulphides,  although  very  abundant  in  nature, 
are  not  used  for  the  extraction  of  iron,  as  the  process  would  be  too 
expensive,  and,  besides,  a  metal  of  inferior  quality  would  be  ob- 
tained.    The  principal  ores  which  are  worked  are — 

1.  The  magnetic  oxide,  found  in  considerable  masses  in  the  old 
rocks,  principally  in  the  micaceous  schists,*  in  which  well-defined 
octahedral  crystals  are  often  found  scattered,  is  generally  a  very 
rich  ore,  affording  iron  of  excellent  quality :  the  greater  portion 
of  Swedish  iron  is  procured  from  it. 

2.  The  anhydrous  peroxide  of  iron,  which  is  found  in  some 
transition  rocks,  and  in  the  secondary  rocks,  in  large  masses,  re- 
sembling sometimes  real  strata.  The  oxide,  in  this  case,  is  amor- 
phous, and  is  called  7'ed  hematite.  It  also  constitutes  veins  in  the 
old  rocks,  as  at  Framont,  in  the  Vosges.  This  ore  is  used  in 
many  of  the  foundries  in  the  north  of  Germany. 

Specular  iron  is  generally  found  in  veins,  but  rarely  in  suffi- 
cient quantity  for  foundry  use.  It  also  forms  considerable  masses 
in  the  old  rocks,  a  most  remarkable  example  of  which  is  the  de- 
posit in  the  island  of  Elba.f 

3.  Hydrated  peroxide  of  iron,  which  is  found  in  the  transition 
rocks,  or  at  the  junction  of  the  transition  and  secondary  rocks, 
in  the  form  of  concrete  brown  masses,  when  it  is  called  brown  hema- 
tite.    In  France,  the  foundries  in  the  Pyrenees  use  this  ore. 

4.  Hydrated  peroxide  of  iron,  which  is  also  found  in  small  con- 
crete grains,  and  is  called  granular  iron  ore.    It  forms  deposits  A 

(fig.  479)  at  the  time  of  separa- 
?^^^E^7:^ss^^^^-=^  tion  of  certain  strata  of  the 
Jurassic  rocks,  but  more  fre- 
quently in  the  middle  tertiary 
rocks,  covering  the  layers  of 
Jurassic  limestone  and  chalk. 
The  size  of  the  grains  varies  from  that  of  a  pea  to  that  of  a  millet- 
seed.  The  majority  of  the  foundries  in  the  middle  of  France,  and 
in  Champagne  and  Berry,  smelt  this  ore. 

An  ore  is  also  found  in  certain  stages  of  the  Jurassic  rocks,  con- 
sisting of  small  grains  of  hydrated  peroxide   of  iron,  adhering 

*  A  mistake  has  here  crept  into  the  text ;  magnetic  oxide  being  seldom  or 
never  found  in  micaceous  schists,  but  occurring  -in  abundance  in  talcose  and 
chloritic  schists,  and  in  sei'pentine  ;  while  the  largest  masses  of  it  are  found  in 
various  igneous  rocks  of  a  more  recent  origin,  especially  in  basalt  and  dolerite. 
—  >r.  L.  F. 

■}-  At  the  Serra  da  Piedade  and  the  Pico  da  Itabira,  both  in  Brazil,  specular 
iron  occurs  in  such  quantity  as  to  form  a  peculiar  species  of  rock,  called  itabirite, 
of  a  dense  and  slaty  character. —  W.  L.  F, 


60  IRON. 

firmly  to  each  other,  and  forming  real  strata ;  and  this  ore,  from 
its  resemblance  to  the  eggs  of  fish,  is  called  oolithic  ore. 

5.  Sparry  iron,  or  crystallized  protocarbonate,  sometimes  mixed 
with  considerable  proportions  of  carbonate  of  manganese,  which 
is  found  in  veins  in  the  old  and  transition  rocks.  It  sometimes 
also  accompanies  the  brown  hematites  which  are  met  with  at  the 
line  of  separation  of  the  old  and  transition  rocks.  This  ore, 
smelted  with  charcoal,  yields  laminated  cast-iron,  which  is  used  for 
manufacturing  steel. 

6.  In  the  argillaceous  strata  of  the  coal-fields,  flattened  nodules 
of  carbonate  of  iron,  mixed  with  clay,  are  frequently  found, 
and  are  sometimes  very  rich  in  iron,  constituting  an  ore  the  more 
valuable  because  it  is  found  in  the  midst  of  fuel,  and  is  easily  ex- 
tracted.    This  ore  is  very  abundant  in  England. 

7.  Lastly,  an  iron-ore  is  found  in  some  low  places,  immediately 
beneath  the  soil,  consisting  of  hydrated  peroxide,  mixed  with 
phosphate.  This  ore  yields  .phosphorous  cast-iron,  the  use  of 
which  is  limited.     It  is  called  bog  ore. 

Iron  is  sometimes  found  in  the  native  state,  forming  often  very 
large  compact  masses,  which  are  never  in  place,  but  have  fallen 
from  space  as  aerolites.  This  iron,  which  is  never  pure,  being 
always  more  or  less  mixed  with  nickel,  is  often  scattered 
through  a  grayish  stone,  the  surface  of  which  appears  to  have 
undergone  an  incipient  fusion.  These  masses  are  called  meteoric 
stones,  aerolites,  or  meteorolites.  Probably,  a  great  number  of 
such  meteors  circulate  in  space,  influenced  by  the  same  forces 
which  maintain  the  planets  in  their  orbit,  and  fall  to  the  surface 
of  the  earth  when,  by  virtue  of  their  motion,  they  approach  near 
enough  to  this  planet  to  be  acted  on  by  the  attraction  of  the  lat- 
ter. Sometimes  meteoric  iron  possesses  all  the  qualities  of  mal- 
leable iron,  and  cutting-instruments  even  have,  for  sake  of  curiosity, 
been  made  of  it. 

§  806.  Iron  ores  are  never  subjected  to  any  complicated  prelimi- 
nary operations.  The  granular  ores  are  generally  held  together 
by  a  clay,  very  poor  in  oxide  of  iron,  and  easily  removed  by  wash- 
ing (§  785). 

Other  ores  often  require  a  preliminary  roasting,  which  renders 
their  smelting  more  easy,  by  driving  ofi"  the  water,  and  carbonic 
acid,  if  the  ore  is  carbonated,  and  acting  especially  by  disagregat- 
ing  the  ore,  and  rendering  it  porous  and  more  friable. 

§  807.  We  have  seen  (§  766)  that  the  oxides  of  iron  are  very 
easily  reduced  when  heated  in  a  current  of  hydrogen :  their  reduc- 
tion is  also  efi'ected  under  the  same  circumstances  by  carbonic 
oxide  gas.  It  may  hence  be  supposed  that  the  reduction  of  oxide 
of  iron  in  ores  is  not  very  difficult ;  but  then  the  metallic  iron 
formed  is  still  intimately  mixed  with  the  gangue,  which  prevents 
its  particles  from  uniting  together.     If  the  gangue  were  very 


METALLURGY   OF   IRON.  61 

fusible,  it  would  be  sufficient  to  heat  the  ore  to  a  degree  sufficient 
to  fuse  the  former,  and  by  then  hammering  this  metallic  sponge, 
the  particles  of  iron  would  unite  together,  while  the  gangue  would 
be  pressed  out  in  the  form  of  scoriae.  But,  if  the  gangue  fuses 
with  difficulty,  it  would  melt  only  at  the  temperature  at  which  the 
iron,  in  contact  with  charcoal,  is  converted  into  cast-iron,  and  we 
should  no  longer  obtain  malleable,  but  cast-iron.  Now,  the  ordi- 
nary gangue  of  iron-ore  being  quartz  or  clay,  which  are  two  nearly 
infusible  substances,  two  processes  are  adopted  to  fuse  them.  If 
soft  iron  is  to  be  obtained  immediately  from  very  rich  ores,  the 
latter  are  heated  with  charcoal,  when  the  gangue,  combining  with 
a  portion  of  the  unreduced  oxide  of  iron,  forms  a  very  fusible 
double  silicate  of  alumina  and  protoxide  of  iron.  A  very  high 
temperature,  therefore,  is  not  required ;  the  iron  does  not  pass 
into  the  state  of  cast-iron,  and  it  suffices  to  hammer  the  spongy 
metal  to  unite  it  together  and  press  out  the  scoriae.  But  a  quantity 
of  oxide  of  iron,  proportioned  to  the  quantity  of  gangue  in  the  ore, 
is  necessarily  lost,  for  which  reason  this  process  can  only  be  adopted 
in  the  case  of  very  rich  ores. 

If,  on  the  contrary,  the  iron  is  to  be  extracted  completely  from 
the  ore,  the  silicate  of  alumina  must  be  made  fusible  by  giving  it 
another  base  than  oxide  of  iron.  The  only  base  which  can  be 
economically  substituted  is  lime  ;  but  as  the  double  silicate  of  alu- 
mina and  lime  is  much  less  fusible  than  that  of  alumina  and  iron, 
a  high  temperature  is  required,  and  the  iron  passes  into  the  state 
of  cast-iron,  which  liquifies  at  the  same  time  with  a  double  silicate, 
or  slag. 

As  may  be  seen,  the  results  of  these  two  methods  are  very  dif- 
ferent. The  first  is  used  only  in  a  few  places,  as  it  requires  rich 
and  very  pure  ores,  and  consumes  an  immense  quantity  of  fuel.  It 
is  adopted  in  the  Pyrenees,  and  known  as  the.  Catalan  method. 

TREATMENT  OF  IRON-ORE  BY  THE  CATALAN  METHOD. 

§  808.  The  Catalan  forge  consists  of  a  crucible,  or  hearth^  made 
by  a  quadrangular  cavity  U  (figs.  480  and  481),  of  about  0.7  ra.  in 
depth,  and  supported  by  one  of  the  walls  of  the  forge.  The  crucible 
is  built  in  solid  mason-work  of  dry  stones,  fastened  together  with 
clay.  The  part  of  the  mason-work  occupied  by  the  crucible  does 
not  rest  immediately  on  the  ground,  but  on  several  small  arches, 
which  prevent  the  dampness  from  penetrating  the  crucible  and 
deranging  the  hearth.  Above  the  arches  is  a  layer  of  scoriae  and 
clay,  covered  by  a  granite  slab,  which  forms  the  bottom,  or  the 
floor  of  the  hearth. 

The  four  lateral  faces  of  the  crucible  rise  above  the  bottom 
stone. 


62 


IRON. 


The  front  face  h  is  called  the  cMo,  or  floss- 
hole. 

The  opposite  face  i  is  called  the  cave. 
The  left  one  R  is  called  the  jjorges. 
Lastly,  the  right  face  I  is  called  the  ore  or 
contr  event. 

The  face  of  the  chio,  which  presents  a  ver- 
tical surface  of  about  0.65  m.,  is  formed  by 
three  pieces  of  iron  placed  end  to  end,  the 
two  extreme  ones  of  which  are  called  latai- 
roles;  that  in  the  middle,  the  restanque,  serves 
as  a  2^omt  d'appui  for  the  levers,  or  fire-irons, 
with  which  the  workmen  raise  the  mass  of 
iron  formed  during  the  process. 

The  left  face,  the  porges,  is  vertical,  and 
composed  of  pieces  of  iron  t,  t,  t  (fig.  483) 
laid  endwise  upon  each  other. 

The  right  face,  the  ore  or  contrevent, 
is  composed  of  pieces  of  iron  s,  s,  s  (fig. 

483),whichare 
wedge-shaped, 
and  slightly  in- 
clined, being 
so  arranged 
that  their  sur- 
face forms  a 
curve. 

The  cave  i, 
which  consists 
wholly  of  ma- 
son-work, fast- 
ened with  clay, 
is  slightly  in- 
clined outward 
to  5°  or  8°. 

The  tw7/erZ, 
which  conveys 
the  blast  into 
the      furnace, 

rests  on  the  upper  piece  of  the  porges,  and  is  made  of  a  conical  piece 
of  copper,  the  edges  of  which  are  merely  brought  together  without 
soldering.  The  position  of  the  twyer  exerts  great  influence  over 
the  operation:  its  inclination  varies  from  35°  to  40°.  The  wind 
is  conveyed  from  the  bellows  into  the  twyer  through  a  copper 
nozzle  T,  fastened  to  the  wind-trunk  G  of  the  bellows  by  a  leather 
tube. 


Fig.  481. 


METALLUKGT   OP   IRON. 


63 


The  depth  of  the  Catalan  furnace  is  about 0.7m. 

Its  average  width,  from  the  chio  to  the  cave 0.6 

Its  average  width,  from  the  porges  to  the  lower  part  of  the 

contrevent 0.7 

Its  average  width,  from  the  porges  to  the  upper  part  of  the 

contrevent 1.0 

The  bellows  of  the  Catalan  forges  of  Aridge  is  called  a  trumpet, 
(trompe,)  and  is  composed  of — 

1st.  An  upper  basin  A  (fig.  481),  fed  by  spring- water. 

2d.  Two  pipes  B,  of  about  6  metres  in  height,  formed  by  trees 
hollowed  out,  and  crossing  the  bottom  of  the  basin  A. 

3d.  A  lower  box  C,  having  two  openings,  one  at  D  below,  the 
other  above  at  E,  to  which  is  fitted  a  tube  EF,  terminated  by  the 
wind-trunk  G. 

The  upper  opening  of  the  tubes  B  is  contracted  by  the  boards  a 
a  which  are  supported  by  bars.  The  aperture  formed  by  the  lower 
part  of  the  boards  is  called  the  etranguillon,  on  a  level  with  which 
the  sides  of  the  tubes  are  pierced  with  inclined  holes  c  c,  called 
hreathmg -holes,  (aspirateurs.)  Lastly,  the  tubes  enter  the  upper 
wall  of  the  box  C,  and  open  at  a  small  distance  above  a  bench  d. 

The  water  of  the  upper  basin  A,  passing  through  the  etranguil- 
lon  into  the  vertical  pipes  B,  carries  with  it  the  external  air,  which 
in  this  way  passes  through  the  openings  c  c.  The  water  breaking 
over  the  bench  escapes  through  the  lower  orifice  D,  while  the  air 
passes  out  by  the  nozzle  G.  The  position  of  the  boards  forming 
the  etranguillon  is  regulated  by  wooden  wedges  g,  which,  being 
fixed  to  the  end  of  a  jointed  lever,  which  a  man  works  by  a  chain 
at  the  bottom  of  the  forge,  is  elevated  or  depressed  in  order  to 
obtain  the  quantity  of  air  necessary  for  the  various  stages  of  the 
operation. 

The  beetle,  or  tilt-hammer,  used  in  forging  iron,  represented  in 
fig.  482,  consists  of  a  cast-iron  face  P,  weighing  about  600  kilogs., 
mounted  on  a  helve  of  beech-wood,  and  secured  by  iron  bands, 
while  the  gudgeons  on  which  the  hammer  turns  are  fastened  to  a 
cast-iron  piece  H  fixed  to  the  helve. 


Fig.  482. 


64 


IRON. 


The  hammer  is  raised  by  means  of  iron  cams  5,  5,  h  on  the  water- 
wheel  A. 

The  iron  anvil  S  is  fastened  by  a  tenon  <?  to  a  piece  of  cast-iron 
r.  which  is  itself  solidly  set  by  means  of  wooden  wedges  into  a  lar^re 
block  of  wood,  or  a  piece  of  granite,  B.  In  order  to  accelerate  tlie 
fall  of  the  hammer,  which  should  strike  from  100  to  125  blows 
per  minute,  a  stone  on  which  the  heel  strikes  is  placed  under  the 
latter. 

§  809.  These  general  arrangements  of  the  forge  being  understood, 
let  us  now  examine  it  in  operation. 

We  shall  suppose  that  the  mass  or  stack  of  the  preceding  opera- 
tion has  been  removed  from  the  furnace  to  be  forged  under  the 
hammer ;  and  that  the  workmen  are  therefore  occupied  in  getting 
up  the  fire  for  another  smelting.  For  this  purpose  they  withdraw 
from  the  hearth  the  hot  coals  which  are  still  there,  detach  from 
the  bottom  and  sides  the  adhering  slag,  and  return  the  hot  coals 
to  the  hearth,  which  is  thus  filled  as  high  as  the  twyer.  A  work- 
man divides  the  hearth  into  two  parts,  by  a  shovel  which  he  places 
vertically  and  parallel  to  the  porges,  so  that  the  division  between 
the  shovel  and  the  porges  shall  be  double  of  that  between  the  former 
and  the  contrevent.  Other  workmen  heap  charcoal  in  the  division 
between  the  shovel  and  the  porges,  and  ore,  broken  to  the  size  of  a 
walnut,  between  the  shovel  and  the  contrevent.  The  shovel  is 
gradually  raised,  as  the  space  below  is  filled,  and  a  wall  of  ore  is 

thus  formed  rising  to  about  0.2  m. 
above  the  contrevent.  The  ore 
is  spread  so  as  to  form  a  saddle- 
back dfg  (fig.  483),  of  which  the 
edge  /  rests  on  the  one  side 
against  the  cave,  and  on  the  other 
on  the  bench  of  the  cliio. 

The  surface  fg  is  covered  by 
a  layer  of  hrasqtie,  (damp  char- 


coal.) well  heaped  up,  while  the 
space  M,  comprised  between  the 
wall  of  ore  and  the  furnace,  is 
filled  with  charcoal. 

The  furnace  being  thus  charged, 
the  blast  is  admitted,  at  first 
slowly,  and  then  its  force  is  in- 
creased. The  ore  is  thus  gradu- 
ally reduced ;  while  the  workmen 
pi-    432  take  advantage  of  this  period  to 

forge  into  bars  the  stack  of  the 
preceding  operation,  which  they  have  divided  into  four  parts,  as 
we  shall  presently  see.  To  do  this,  they  heat  these  masses  of  iron 
in  the  furnace,  by  placing  them  in  the  middle  of  the  burning  char- 


METALLURGY  OF  IRON.  65 

coal  in  the  space  M  above  the  twyer.  When  they  are  sufficiently 
heated,  they  are  removed  and  forged. 

As  the  charcoal  diminishes,  fresh  fuel  is  added,  and  small  ore, 
called  greillade^  which  is  made  by  the  breaking  of  the  ore  as  it 
comes  from  the  mine,  is  thrown  in,  being  slightly  moistened  with 
water,  to  prevent  it  from  falling  too  easily  between  the  interstices 
of  the  charcoal. 

Influenced  by  the  wind  projected  through  the  twyer,  the  char- 
coal burns  to  carbonic  acid  in  the  space  near  the  twyer,  while 
farther  off  the  carbonic  acid  is  reduced,  by  the  charcoal  in  excess, 
into  carbonic  oxide  gas,  the  greater  part  of  which,  being  obliged 
to  pass  through  the  highly  heated  ore,  reduces  the  oxide  of  iron  to 
the  state  of  metallic  iron.  But  the  whole  of  the  oxide  is  not  re- 
duced, as  a  portion,  remaining  in  the  state  of  protoxide,  combines 
with  the  gangue  of  the  ore,  forming  a  very  fusible  compound  sili- 
cate, a  large  portion  of  which  runs  off  and  collects  in  the  bottom 
of  the  hearth,  whence  it  is  removed  by  a  small  opening  in  the  chio. 

In  two  hours,  the  greillade  which  falls  with  the  fuel  has  depo- 
sited a  certain  quantity  of  iron  at  the  bottom  of  the  hearth,  and 
the  workman  then  commences  the  formation  of  the  mass.  He 
increases  the  draught  of  air,  and,  by  carefully  introducing  a  bar 
between  the  ore  and  the  contrevent,  draws  that  ore  which  seems 
more  advanced  near  to  the  twyer,  and  adds  at  the  same  time  an- 
other charge  of  charcoal  and  greillade. 

Five  hours  after  the  commencement  of  the  operation  the  ore  has 
entirely  fallen  into  the  hearth,  and  the  workman  endeavours  to  unite 
the  various  fragments  of  spongy  iron. 

During  the  last  hour  of  the  process,  the  workmen  break  the  ore 
under  the  forge-hammer,  and  then  sift  it,  in  order  to  separate  the 
pulverulent  material  constituting  the  greillade,  of  which  we  have 
spoken. 

They  then  remove  the  mass  from  the  furnace  and  carry  it  to  the 
hammer,  where  the  liquid  scoriae  are  pressed  out,  and  the  spongy 
iron  is  rendered  more  compact.  The  mass  is  then,  by  means  of  a 
long  iron  wedge,  divided  into  two  equal  parts,  called  massoques, 
which  are  hammered  into  long  parallelopipedons,  and  again  cut  into 
two  equal  parts.  Four  pieces  of  iron,  called  massoquettes  are  thus 
obtained,  which  are  rolled  into  bars  in  the  first  stage  of  the  suc- 
ceeding operation. 

A  smelting  by  the  Catalan  method  generally  lasts  6  hours,  pro- 
ducing 140  to  150  kilogs.  of  merchantable  iron,  from  470  kilogs. 
of  ore  and  about  500  kilogs.  of  charcoal. 

The  direct  extraction  of  iron  in  the  state  of  ductile  metal  is  now 
performed  only  in  the  Pyrenees,  Corsica,  and  a  few  provinces  of 
Spain,  the  greater  portion  of  iron  being  obtained  by  means  of  blast- 
furnaces, in  which  the  metal  is  separated  from  its  ores,  as  perfectly 
as  possible,  by  using  a  very  high  temperature,  at  which  the  iron 

Vol.  IL— 6 


66  IRON. 

coDibines  with  a  certain  quantity  of  carbon,  forming  a  much  more 
fusible  compound  than  ductile  iron. 

TREATMENT  OP  IRON-ORES  IN  THE  BLAST-FURNACE. 

§  810.  The  blast-furnace  (fig.  484)  is  composed  of  two  truncated 
cones  C,  B,  united  at  their  bases.  The  upper  cone  C,  called  the 
bellf/,  (cuve,)  is  made  of  an  inner  lining  ^^'  of  refractory  bricks,  sur- 
rounded by  a  stratum  of  scoriae,  or  broken  slag,  which  separates  it 
from  a  second  brick  lining  W,  built  against  an  outer  wall  |?p',  qq^ 
of  cut  stone  or  common  brick,  constituting  the  main  part  of  the 
blast-furnace.     The  upper  opening  G  of  the  belly  is  called  the 


Eig.  484. 

tunnel-head,  (gueulard,)  and  is  surmounted  by  a  chimney  F,  having 
one  or  several  doors,  through  which  the  charges  are  introduced. 
The  lower  cone  B,  called  the  boshes,  (etalages,)  is  generally  made 
of  quartzose  stones  difficult  of  fusion,  and  which  must  be  very 


METALLURGY   OF   IRON. 


6T 


carefully  selected,  as  on  them  the  duration  of  the  furnace  greatly 
depends.  In  some  furnaces  the  boshes  are  made  of  refractory 
bricks.  They  are  sometimes  joined  to  the  belly  by  a  cylindrical 
union  or  curve  A,  in  order  to  avoid  a  re-entering  angle. 

Below  the  boshes  is  a  prismatic  space  E,  called  the  top  of  the 
hearth,  made  of  refractory  stones,  [fire-stone.)  Three  of  its  sides 
descend  to  the  bottom  of  the  furnace,  or  the  crucible  D,  while  the 
fourth  t  stops  at  a  few  decimetres  above  the  bottom:  this  side, 
which  is  called  the  tymp-plate,  is  supported  by  strong  pieces  of  iron 
let  into  the  side-walls  of  the  hearth. 

The  bottom  of  the  hearth  is  formed  of  a  quartzose  stone,  beneath 
which  are  openings  to  allow  the  air  to  circulate  freely  below  the 
furnace  ;  and,  in  order  to  prevent  the  accumulation  of  water,  which 
would  cool  the  hearth,  and  even  give  rise  to  serious  accidents,  the 
main  body  of  the  blast-furnace  is  built  on  arched  galleries  II. 
Three  of  the  walls  of  the  crucible  are  merely  prolongations  of  its 
sides,  while  the  fourth  is  formed  by  a  prismatic  stone  d,  called 
dam-stone,  and  which  is  slightly  in  front  of  the  tymp-plate;  so 
that  the  anterior  part  of  the  hearth  has  an  opening  between  the. 
dam-stone  and  the  tymp-plate.  We  shall  call  that  part  of  the  fur- 
nace on  which  the  dam-stone  and  tymp-plate  rest  the  anterior 
part;  the  opposite  will  therefore  be  the  posterior  part,  and  the 
other  two  the  sides,  • 

The  posterior  part  and  two  sides  have  lateral  openings  o,  called 
the  tuyeres,  or  twyers,  through  which  the  pipes  which  convey  air 
enter  the  furnace :  these  openings  are  on  the  same  horizontal 
plane,  a  little  above  the  lower  edge  of  the  tymp-plate. 

To  assist  the  workmen,  four  niches,  allowing  them  to  approach 

the  twyers  and  hearth,  are  made 
in  the  main  body  of  the  furnace, 
while  lateral  galleries  R  permit 
them  to  walk  more  freely  around 
the  furnace  and  to  examine  the' 
twyers.    The  arrangement  of  the- 
twyers  and  the  pipes  which  con- 
vey the  air  from  the  blast-machine 
is  seen  in  fig.  485,  which  repre- 
sents a  horizontal  section  of  the 
furnace    at    the    height   of   the  • 
twyers.     Each  wind-trunk  has  a 
register  or  valve,  to  regulate  the 
quantity  of  air  admitted. 

The  blast-furnace  is  generally 

built,  when  practicable,  against  a 

hill  (fig.  484),  and  strengthened 

by  mason-work.      A  terrace   is 

Fig.  485.  made,  at  the  height  of  the  mouth, 


68 


IRON. 


on  the  sides  or  top  of  the  hill,  a  bridge  aa'  communicating  between 
this  terrace  and  the  platform  'pjp'  of  the  mouth.  The  terrace  is 
reached  by  an  inclined  plane,  to  which  the  ore  and  fuel  are  con- 
veyed by  machinery.  The  material  is  then  transported  in  wagons 
on  a  railway  to  the  platform  f^'. 

The  twyers  of  blast-furnaces  are  double  conical  tubes  abed  of 
cast-iron,  or  copper  (fig.  486),  and  as  their  ends  might  melt,  in  con- 
sequence of  the  high  temperature  to  which  they  are  exposed,  a 
current   of  cold  water  is    continually  circulated   through    them, 

which,  being  introduced  through  the 
small  tube  ^,  runs  off  through  the 
tube  t\  The  openings  of  the  twy- 
ers advance  as  far  as  the  inner  wall 
of  the  hearth.  The  nozzle  of  the 
wind-tube    B    is   disposed   in   the 


Fig.  486. 


twyer,  and  communicates  with  the 


cast-iron  tubes  of  the  blowing-machine  by  a  flexible  leather  tube  A. 
The  three  twyers  are  on  the  same  horizontal  plane,  but  the  axes 
of  the  two  twyers  on  the  sides  of  the  hearth  are  not  prolongations 
of  each  other,  being  separated  by  some  centimetres,  so  that  the 
two  currents  of  ,air  may  not  interfere  with  each  other. 

§  811.  The  blowing-machine  of  a  blast-furnace  consists  of  a  large 
cast-iron  cylinder  A  (fig.  487),  in  which  works  a  cast-iron  piston 

P,  packed  with  tow  or  leather  to 
render  it  air-tight.  The  cylinder 
is  closed  above  and  below,  and  on 
the  upper  lid  is  a  stuffing-box  w, 
through  which  the  piston  passes. 
The  lid  has  also  two  side-openings 
c,  c\  one  of  which  c  communicates 
with  the  external  air  and  is  fur- 
nished with  a  valve  which  opens 
from  without  inward,  while  the 
other  g'  communicates  with  a  late- 
ral cast-iron  cylinder  B  and  has 
a  valve  opening  from  within  out- 
ward. The  bottom  of  the  cylinder 
has  also  two  openings ;  one  at  e, 
having  a  valve  which  opens  from 
p.     4gy  without    inward,    establishing    a 

communication  between  the  lower 
part  of  the  cylinder  and  the  external  air ;  and  one  at  e',  which 
communicates  with  the  lateral  cylinder  B,  opening  from  within 
outward. 

Let  us  suppose  that  the  piston  has  reached  its  maximum  ascent, 
and  begins  to  descend.  If  the  valves  <?,  c'  are  closed,  the  air  will  be 
expanded  in  the  upper  part  of  the  pump,  and  its  elastic  force  will 


METALLURGY   OF   IRON.  69 

be  more  and  more  feeble ;  when,  the  external  exceeding  the  inter- 
nal pressure,  the  valve  c^  will  be  forcibly  applied  against  the  open- 
ing c'  and  intercept  the  communication  between  the  upper  part 
of  the  pump  and  the  lateral  cylinder  B.  The  valve  <?,  on  the  con- 
trary, will  open,  and  the  external  air  will  enter  the  upper  part  of 
the  pump,  while  the  air  contained  in  the  lower  part  will,  on  the 
other  hand,  be  compressed  into  a  smaller  and  smaller  space  as  the 
piston  descends ;  its  elastic  force  will  be  superior  to  that  of  the 
external  air,  the  valve  e  will  be  pressed  against  the  opening  e,  the 
valve  e'  will  open,  and  the  internal  air  will  be  driven  into  the 
lateral  cylinder  B,  and  thence  through  the  opening  o,  into  the 
cast-iron  pipes  which  convey  it  into  the  twyers.  Thus,  during  the 
descent  of  the  piston,  the  external  air  is  inspired  by  the  upper  part 
of  the  pump,  while  that  of  the  lower  part  is  sent  to  the  twyers,  the 
inverse  taking  place  during  the  ascent  of  the  piston,  when  the  lower 
part  aspires  the  external  air,  and  the  upper  part  sends  its  air  to  the 
twyers.  The  blowing-machine  therefore  sends  a  continual  stream 
of  air  to  the  furnace  during  both  motions  of  the  piston,  the  blast 
being,  however,  sensibly  weakened  at  the  moment  the  piston  changes 
the  direction  of  its  movement,  that  is,  at  the  dead-points  of  the 
alternate  movement ;  and  as  it  is  important  that  the  blast  should 
be  as  regular  as  possible,  a  large  reservoir  is  interposed  between 
the  cylinder  B  and  the  twyers,  so  as  to  prevent  the  variations  from 
being  felt  in  the  latter. 

The  working  of  the  blowing-machine  exerts  great  influence  over 
the  blast-furnace ;  and  it  is  important  that  the  steam  engine  which 
moves  it  should  be  able  to  impart  greater  force  than  is  usually  re- 
quired during  the  regular  working  of  the  furnace,  in  order  that 
more  air  may  be  sent  to  the  twyers  when  the  furnace  begins  to 
slacken.  A  manometer  or  gauge  fitted  to  the  regulating  reservoir 
enables  the  workmen  to  judge  of  the  quantity  of  air  sent  to  the 
furnace. 

In  large  establishments  several  blast-furnaces  are  often  fed  by 
the  same  blowing-machine. 

§  812.  The  construction  of  the  blast-furnace  being  well  under- 
stood, let  us  now  study  the  process  of  smelting.  We  will  suppose 
that  the  furnace  has  been  just  built,  or  but  recently  repaired ;  so 
that  the  first  process  is  then  to  get  up  the  fire.  It  is  begun  by 
drying  the  whole  furnace  very  slowly,  as  the  sudden  application 
of  heat  would  crack  the  mason-work,  and  endanger  its  stability. 
The  anterior  part  of  the  hearth  is  open  and  the  dam-stone  d  not 
yet  fixed.  In  the  hearth  and  the  arched  space  preceding  it,  fagots 
are  placed  to  which  fire  is  applied ;  and  while  the  belly  of  the 
blast-furnace  acts  as  a  chimney,  the  inner  lining  first  dries,  and 
then  gradually  the  main  body.  The  fire  is  kept  up  for  several 
days,  until  all  danger  of  cracking  the  walls  by  the  application  of 
greater  heat  is  over ;  after  which  the  dam-stone  is  fixed,  and  fuel 


70  IRON. 

thrown  in  at  the  mouth  until  it  reaches  the  height  of  the  boshes. 
When  the  desiccation  is  still  more  advanced,  the  belly  is  filled  with 
fuel  intended  for  smelting  the  ore,  and  some  air  is  admitted,  the 
blast  being  gradually  increased ;  and  when  the  fuel  has  sunk  low 
enough  in  the  belly,  a  small  charge  of  ore,  uniformly  spread  over 
the  charcoal  or  coke,  is  introduced.  After  some  time,  more  fuel 
is  added,  and  above  it  another  layer  of  ore,  which  process  is  gradu- 
ally continued,  several  days  being  required  to  introduce  the  charge 
which  will  be  retained  during  the  smelting. 

The  fuel  being  the  great  point  of  expense  in  the  metallurgy  of 
iron,  economy  of  this  article,  that  is,  to  smelt  the  greatest  quantity 
of  ore  with  the  same  quantity  of  fuel,  has  long  been  the  subject 
of  experiment.  The  proportion  of  ore  is  increased  as  long  as  the 
furnace  works  well  and  the  iron  is  of  good  quality ;  but  the  charge 
of  ore  must  be  reduced  when  it  fuses  with  difficulty  and  furnishes 
inferior  cast-iron. 

§  813.  The  ore  can  rarely  be  smelted  without  the  addition  of  a 
foreign  substance.  Its  ordinary  gangue  is  quartz  or  clay ;  and 
now,  as  in  the  blast-furnace  the  gangu^  and  the  metal  must  be 
reduced  to- perfect  fluidity,  in  order  that  they  may  separate  in  the 
hearth  by  their  respective  gravity,  and  as,  moreover,  it  is  pur- 
posed completely  to  extract  the  iron  ;  if  the  gangue  of  the  mineral 
is  quartz,  this  substance,  being  infusible  at  the  temperature  of  the 
blast-furnace,  can  only  melt  if  one  or  several  bases  are  added  to 
it,  so  as  to  form  a  silicate  fusible  at  this  temperature.  If  a  fo- 
reign base  be  not  added,  the  quartz  combines  with  a  portion  of  the 
oxide  of  iron  of  the  ore,  which  it  thus  preserves  from  reduction, 
and  forms  a  fusible  slag ;  in  which  case  a  considerable  proportion 
of  the  iron  is  lost.  But  a  proper  quantity  of  carbonate  of  lime 
will,  when  added  to  the  ore,  pass  into  the  belly  of  the  furnace  in 
the  state  of  caustic  lime,  which  combining  with  the  silicate  of 
alumina,  will  form  a  fusible  double  silicate  of  alumina  and  lime, 
containing  base  sufficient  to  prevent  it  from  combining  with  the 
oxide  of  iron,  and  preventing  its  reduction.  When  the  ore  only 
contains  quartz,  both  clay  and  carbonate  of  lime  must  be  added ; 
but,  as  the  argillaceous  ores  are  much  more  common  than  those 
in  quartzose  gangues,  the  latter  are  always  mixed  with  the  argil- 
laceous ores,  so  that  carbonate  of  lime  alone  is  needed.  The  car- 
bonate of  lime  intended  for  this  purpose  is  in  France  called 
castine. 

In  some  foundries,  where  ores  of  which  the  gangue  is  calcareous 
are  smelted,  silicate  of  alumina  must  be  added  to  obtain  a  proper 
slag.  In  general,  argillaceous  ores  which  introduce  a  sufficient 
quantity  x)f  silicate  of  alumina  are  mixed  with  the  calcareous  ores. 
Forge  scoriae,  formed  of  a  silicate  of  the  protoxide  of  iron,  very 
rich  in  iron,  are  often  added. 

The  fusibility  of  the  double  silicates  of  alumina  and  lime  varies 


METALLURGY    OF   IRON.  71 

with  the  proportions  of  their  constituent  principles.  Experiment 
hns  shown  the  most  fusible  compound  of  the  kind  to  be  that  in 
which  the  oxygen  of  the  silicic  acid  is  double  the  oxygen  contained 
in  the  two  bases  united.  The  ratio  between  the  two  bases  is, 
moreover,  not  a  matter  of  indifference  ;  the  most  fusible  compound 
being  obtained  by  adding  to  native  clay,  the  composition  of  which 
varies  but  little,  f  of  its  weight  of  carbonate  of  lime. 

§  814.  The  fuel  used  in  blast-furnaces  is  charcoal  or  coke. 
Charcoal  produces  but  little  ashes,  which,  moreover,  are  easily 
fusible,  and  introduce  no  element  which  can  injuriously  affect  the 
qualities  of  the  cast-iron.  It  is  sought,  in  charcoal  furnaces,  to 
obtain  a  slag  as  fusible  as  possible,  and  as  free  as  may  be  from  any  con- 
siderable quantity  of  oxide  of  iron.  The  composition  of  this  slag  there- 
fore resembles  closely  thnt  of  a  most  fusible  double  silicate  of  alu- 
mina and  lime,  that  is,  of  one  in  which  the  oxygen  of  the  silex  is 
double  of  the  oxygen  of  the  bases.  Coke,  on  the  contrary,  gives 
a  considerable  proportion  of  ashes,  and  sometimes  contains  a  large 
quantity  of  pyrites  yielding  sulphide  of  iron,  which  dissolves  in 
the  cast-iron  and  injures  its  quality.  If  it  is  now  still  sought  to 
obtain  the  most  fusible  double  silicate  of  alumina  and  lime,  a  large 
quantity  of  sulphur  will  enter  into  the  cast-iron,  which  greatly 
deteriorates  its  quality.  Experiment  has  proved  that,  in  order  to 
avoid  this  inconvenience,  the  proportion  of  the  flux  must  be  greatly 
increased,  and  a  slag  must  be  obtained  in  which  the  oxygen  of  the 
silex  is  only  equal  to  that  of  the  united  bases.  The  lime  then  pre- 
vents the  greater  portion  of  the  sulphur  of  the  pyrites  from  passing 
into  the  cast-iron,  and  sulphide  of  calcium  is  formed,  which  re- 
mains in  the  slag.  But,  the  slag  of  coke  furnaces  being  much 
less  fusible  than  that  of  charcoal  furnaces,  it  is  evident  that,  in 
order  to  obtain  a  slag  sufficiently  fusible,  the  temperature  of  the 
coke  furnaces  must  be  much  higher. 

§  815.  The  dimensions  of  blast-furnaces  vary,  according  as 
charcoal  or  coke  is  the  fuel  used.  Charcoal  furnaces  are  generally 
30  feet  in  height,  from  the  bottom  of  the  hearth  to  the  tunnel- 
head,  and  commonly  have  only  two  twyers  on  the  sides.  Coke 
furnaces  are  from  45  to  54  feet  high,  the  capacity  of  their  belly 
is  much  Targer  than  that  of  the  charcoal  furnace,  and  they  are 
fed  with  air  by  three  twyers.*  The  blowing  machine  impels  the 
air  with  three  or  four  times  as  much  force  as  that  used  for  char- 
coal furnaces.     The  height  of  a  column  of  mercury  balancing  the 


*  In  England,  from  six  to  ten  twyers  are  usually  employed,  and  in  the  former 
case  are  sometimes  disposed  round  the  furnace  in  five  arched  openings,  the  sixth 
being  introduced  through  the  tymp-stone,  a  foot  or  two  higher  than  the  others, 
80  that  six  jets  of  air,  intersecting  each  other  at  angles  of  00°,  are  introduced: 
when  ten  twyers  are  used,  one  penetrates  the  front,  while  the  rest  are  disposed 
as  in  fig.  485,  each  arched  opening  containing  three  instead  of  one. —  W.  L.  F. 


72 


IRON. 


pressure  of  the  air  in  the  pipes  which  convey  it  to  the  twyers,  is, 
in  general,  as  follows  : 

In  a  furnace  fed 

By  very  light  pine-wood 0.8  to 

*'  good  quality  pine-wood. ..1. 2  " 

"  hard  charcoal 1.6  " 

"  easily-burning  coke 3.1  " 

"  hard  and  compact  coke... 5.0  " 

The  whole  quantity  of  air  projected  depends  on  this  pressure 
and  the  diameter  of  the  nozzle.  Large  charcoal  blast-furnaces 
receive  at  least  1080  cubic  feet  (40  cubic  metres)  of  air  per  minute. 
Coke  furnaces  never  receive  less  than  1620  cubic  feet,  (60  cubic 
metres,)  and  frequently  as  much  as  2160  or  2700. 

§  816.  Let  us  now  examine  a  blast-furnace  in  its  regular  work 
(fig.  488),  and  study  the  various  chemical  reactions  and  physical 


1.2  inches, 

or    2  to  3  centim. 

1.6      " 

u     3  "  4       " 

2.4      " 

"     4  "  6       " 

5.0      " 

u     8  "13       " 

9.0      " 

"13  "19       " 

phenomena  which  take  place  in  this  vast  apparatus.  We  have  said 
that  the  ore  and  fuel  are  charged,  layer  by  layer,  through  the 
mouth  G  of  the  furnace :  the  charges  descend  regularly  toward 


METALLURGY   OF   IRON.  73 

the  belly  A.  The  temperature  is  not  very  high  in  the  upper  part 
of  the  throat,  but  is  greater  in  the  boshes  B ;  and  lastly,  in  the 
hearth  at  E,  a  little  above  the  twyers,  it  has  reached  its  maximum. 
The  air,  impelled  through  the  twyers,  meets  with  the  incandescent 
fuel,  when  the  combustion  is  very  powerful  on  account  of  the  excess 
of  oxygen.  The  charcoal  burns  to  carbonic  acid,  and  evolves  all 
the  heat  it  is  capable  of  yielding  by  combustion  with  oxygen.  The 
combustion  by  oxygen  often  continues  even  in  the  lower  part  of 
the  boshes,  but  is  much  less  lively  there,  because  the  greater  part 
of  the  oxygen  of  the  air  is  already  converted  into  carbonic  acid. 
The  gas  reaching  the  middle  of  the  boshes,  which  is  composed  of 
nitrogen  and  carbonic  acid,  attains  a  very  high  temperature,  and 
imparts  a  portion  of  its  heat  to  the  fuel  and  the  ore  filling  the  fur- 
nace. Now,  we  have  seen  (§  256)  that  when  carbonic  acid  gas  is 
passed  over  burning  charcoal,  the  former  combines  with  a  quantity 
of  carbon  equal  to  that  which  it  already  contains,  and  is  changed 
into  oxide  of  carbon,  which  occupies  a  volume  double  of  that  of 
carbonic  acid.  But  this  inverse  combustion  of  the  carbon,  followed 
by  a  great  expansion  of  the  gaseous  product,  far  from  evolving 
heat,  absorbs  it  to  a  remarkable  degree :  the  temperature,  there- 
fore, instead  of  rising,  falls,  in  the  lower  part  of  the  belly,  much 
below  what  it  would  be  if  the  gaseous  current,  highly  heated  by 
the  combustion  taking  place  in  the  hearth,  merely  shared  its  heat 
with  the  materials  it  met  with.  The  temperature,  which  in  the 
boshes  is  of  a  reddish  white,  only  reaches  a  red-heat  in  the  lower 
part  of  the  belly.  The  gas  in  the  upper  part  of  the  boshes,  being 
composed  of  nitrogen  and  oxide  of  carbon,  there  meets  with  the 
fuel  and  the  ores  heated  to  a  dull  red-heat ;  and  as,  at  this  tem- 
perature, carbonic  oxide  gas  readily  decomposes  oxide  of  iron,  the 
latter  is  entirely  reduced,  and  there  results  a  mixture  of  gangue 
and  very  finely  divided  metallic  iron.  The  reduction  of  the  oxide 
of  iron  regenerates  a  portion  of  the  carbonic  acid,  and  the  flux 
itself  evolves  its  carbonic  acid,  by  changing  into  quicklime,  so 
that  the  gas  issuing  from  the  tunnel-head  consists  of  nitrogen  and 
a  mixture  of  carbonic  acid  and  oxide.  There  is,  moreover,  a  small 
quantity  of  hydrogen  and  carburetted  hydrogen,  evolved  by  the 
fuel,  which  is  always  imperfectly  carbonized,  and  of  which  the  car- 
bonization is  completed  in  the  belly  of  the  furnace.  A  certain 
quantity  of  hydrogen  and  oxide  of  carbon  is  also  formed  at  the 
expense  of  the  watery  vapour  existing  in  the  air  impelled  by  ihe 
twyers,  and  which  is  decomposed  in  the  boshes  by  the  burning 
charcoal.  The  gas  leaves  the  mouth  in  a  very  cold  state,  but  is 
highly  inflammable,  on  account  of  the  great  quantity  of  oxide  of 
carbon. which  it  contains. 

§  817.  Thus,  while  examining  only  the  ascending  column  of  gas 
which  traverses  the  blast-furnace,  we  see  that  the  gas  is  eminently 
oxidizing  in  the  hearth,  where  the  combustion  is  most  active,  and 


74  IRON. 

where  the  highest  temperature  prevails^  It  is  often  more  oxidizing 
in  the  lower  part  of  the  boshes,  but  much  less  than  in  the  hearth, 
because  the  greater  part  of  its  oxygen  is  already  converted  into 
carbonic  acid:  the  temperature  is  also  much  lower,  for  the  combus- 
tion is  less  active.  Toward  the  middle  of  the  boshes,,  the  gas  no 
longer  contains  oxygen,  the  carbonic  acid  being  converted  into  car- 
bonic oxide  by  contact  with  the  burning  charcoal;  and  as  this 
transformation  takes  place  with  absorption  of  heat,  the  tempera- 
ture falls  rapidly  in  this  part  of  the  furnace.  Above  the  boshes, 
the  gas  is  reducing,  because  it  is  composed  only  of  nitrogen  and 
oxide  of  carbon;  and,  as  the  temperature  is  still  that  of  a  red-heat, 
the  oxide  of  carbon  reacts  on  the  oxide  of  iron  in  the  ore  through- 
out the  whole  of  the  lower  part  of  the  belly,  reducing  it  to  metallic 
iron.  But  the  temperature  is  not  sufficiently  elevated  to  separate 
the  iron  from  the  gangue.  As  both  by  the  reduction  of  the  ore 
and  the  calcination  of  the  flux,  carbonic  acid  is  disengaged,  the  gas 
issuing  from  the  mouth  must  contain  a  considerable  quantity  of  this 
gas,  the  temperature  of  which,  however,  is  greatly  lowered,  from  its 
having  passed  through  the  upper  layers  of  recently  introduced  fuel 
and  ore,  and  there  cooled,  not  only  because  they  have  abstracted 
from  it  heat  necessary  to  elevate  their  own  temperature,  but  also 
because  a  great  portion  of  the  heat  has  become  latent,  in  conse- 
quence of  the  vaporization  of  the  water  which  moistened  the  fuel 
and  the  ore,  or  which  was  in  combination  with  the  oxide  of  iron. 

§  818.  Let  us  now  follow  the  downward  march  of  the  ore  and 
the  fuel.  These  substances  dry  in  the  upper  part  of  the  furnace, 
and,  when  they  have  fallen  some  metres,  reach  a  temperature  at 
which  the  hydrated  sesquioxide  of  iron  loses  its  water.  A  little 
lower,  the  reduction  of  oxide  of  iron  takes  place,  and  the  flux  begins, 
to  lose  its  carbonic  acid ;  while  the  reduction  of  the  oxide  and  the 
calcination  of  the  flux  are  completed  in  the  lower  part  of  the  belly 
and  the  boshes.  When  the  charges  reach  the  bottom  of  the  boshes, 
where  a  much  higher  temperature  exists,  the  lime  combines  with 
the  gangue  of  the  ore  and  with  the  ashes  of  the  expended  fuel, 
forming  multiple  silicates,  which  come  into  fusion  at  a  lower  point 
and  constitute  the  slag.  The  metallic  iron,  finding  itself  at  a  high 
temperature  in  contact  with  charcoal,  in  an  atmosphere  very  slightly 
oxidizing,  combines  with  a  certain  quantity  of  carbon,  and  passes 
into  the  state  of  cast-iron.  A  small  quantity  of  silicic  acid  is  also 
reduced  by  the  contact  of  the  charcoal  and  iron,  if  the  tempera- 
ture be  very  high,  as  it  is  in  coke  furnaces ;  and  its  silicium  com- 
bines with  the  metal.  The  substances,  thus  prepared,  enter  the 
boshes  of  the  furnace  with  the  balance  of  the  fuel.  Combustion 
there  is  very  active,  and  the  cast-iron  and  silicates,  becoming  very 
fluid,  fall  by  drops  into  the  hearth.  But  as  the  air  in  the  latter 
part  is  very  oxidizing,  they  must  fall  rapidly,  as  otherwise  a  con- 
siderable portion  of  the  iron  would  again  be  oxidized  and  combined 


METALLURGY   OF   IRON.  75 

with  the  dross.  It  is  therefore  very  important  that  the  belly  should 
be  contracted,  in  order  that  the  substances  may  soon  pass  through 
it.  The  cast-iron  and  slag,  falling  indiscriminately  into  the  hearth, 
separate  according  to  their  densities,  the  cast-iron  occupying  the 
lower  part/  of  the  hearth,  and  leaving  the  slag  above.  Very  soon, 
the  layer  of  slag  reaches  the  upper  level  d  of  the  dam-stone,  and 
flows  over  it,  when  the  current  of  slag  thus  occasioned  is  directed 
over  the  inclined  plane  hd^  and  removed,  as  fast  as  it  becomes  solid 
on  the  floor  of  the  foundry.  The  volume  of  slag  is  at  least  5  or  6 
times  greater  than  that  of  the  cast-iron,  and  the  hearth  is  not  en- 
tirely filled  with  the  latter  until  after  the  lapse  of  12  or  24  hours. 
It  is  essential  to  keep  a  layer  of  slag  over  the  cast-iron,  to  prevent 
the  latter  from  being  oxidized  by  the  air  from  the  twyers. 

The  next  step  is  to  tap  it.  The  workmen  have  made  a  series 
of  small  lateral  canals,  or  rills,  in  sand,  on  the  floor  of  the  foundry, 
connecting  with  a  longitudinal  canal,  which  communicates  with 
a  hole  in  the  damstone,  called  the  tap-hole.  The  tap-hole,  which 
is  made  in  the  hearth,  near  one  of  the  lateral  edges  of  the  dam- 
stone,  is  closed  during  the  smelting  with  a  stopper  of  clay.  In 
order  to  draw  off  the  melted  iron,  the  workman  removes  the  stopper 
with  a  bar,  when  the  liquid  cast-iron  runs  into  all  the  rills;  and 
when  it  begins  to  solidify,  he  throws  a  little  sand  upon  it  to  retard 
its  cooling.  During  the  tapping,  the  blast  through  the  twyers  is 
arrested,  and  the  blowing-machine  is  set  at  work  again  only  when 
the  tap-hole  is  closed  and  the  hearth  empty.  Tlie  cast-iron  is  thus 
run  into  semi-cylindrical  pieces,  called  pigs,  or  pig-metal. 

§  819.  Large  objects,  such  as  water-pipes,  pillars,  and  parts  of 
steam-engines,  etc.,  are  sometimes  cast  immediately  from  the  blast- 
furnace. The  cast-iron  is  then  run  into  moulds  of  sand,  con- 
structed in  ditches  in  the  floor  of  the  foundry,  at  a  short  distance 
from  the  furnace,  small  canals  connecting  the  moulds  with  the 
canal  which  leads  the  cast  metal  from  the  tap-hole.  When  the 
moulds  are  filled,  the  surplus  is  run  into  pigs. 

A  great  number  of  smaller  objects,  such  as  pots,  plates,  grates, 
etc.,  are  moulded  in  the  same  way.  It  is,  in  that  case,  not  neces- 
sary to  wait  until  the  hearth  is  filled,  but  the  process  can  be  carried 
on  without  interruption  during  the  smelting.  The  foundry  building 
must  be  large,  as  the  moulds  occupy  a  considerable  amount  of  space. 

The  fused  metal  is  received 
at  the  tap-hole  in  sheet-iron 
vessels  (fig.  489)  lined  with 
clay,  and  carried  by  two  men  ; 
Fig.  489.  and  the    tap-hole  is  closed; 

after  the  metal  has  run  out,  by  a  clay  stopper  fastened  to  the  end 
of  an  iron  rod,  so  that  it  can  be  removed  at  will. 

§  820.  The  fused  metal  of  charcoal  furnaces  can  be  almost  always 
used  immediately  for  casting,  when  the  ores  are  not  too  impure, 


76  IRON. 

which  is  not  the  case  when  coke  furnaces  are  used  ;  metal  for  cast- 
ing being  obtained  in  the  latter  only  by  directing  the  smelting  in 
a  peculiar  way,  and  using  a  coke  which  does  not  contain  too  much 
pyrites.  We  have  seen  (§  800)  that  there  are  three  species  of  cast- 
iron — white,  gray,  and  mottled  iron ;  but  of  these  the  gray  and 
mottled  iron  only  are  fit  for  casting ;  white  iron  being  too  brittle 
for  ordinary  purposes.  When  gray  iron  is  to  be  obtained,  the 
proportion  of  the  ore  must  be  less  than  the  maximum  power  of  the 
charcoal,  as  otherwise  the  least  derangement  in  the  working  of  the 
furnace  would  produce  white  cast-iron. 

The  working  of  the  blast-furnace  may  be  ascertained  by  the 
flame  at  the  tunnel-head,  by  that  at  the  tymp-plate,  the  appear- 
ance of  the  twyer,  that  of  the  cast-iron,  the  regularity  of  the 
descent  of  the  charges,  and  principally  by  the  nature  of  the  slag. 
The  workmen  thus  can  know  when  it  may  be  necessary  to  increase 
or  diminish  the  charge  of  ore. 

§  821.  The  relative  dimensions  of  the  various  parts  of  the  blast- 
furnace greatly  influence  its  working.  Now,  several  of  these  parts, 
principally  the  belly  and  boshes,  become,  after  a  time,  altered  by 
the  corroding  action  of  the  slag  and  the  high  temperature  to  which 
they  are  subjected ;  and  when  the  furnace  then  works  to  a  disad- 
vantage, it  is  often  necessary  to  modify  the  relative  proportions  of 
the  fuel  and  ore,  to  introduce  more  charcoal,  and  even  to  stop  and 
blow  out  the  furnaee^  when  the  cast-metal  can  no  longer  be  obtained 
of  suflBciently  good  quality. 

At  the  beginning  of  the  smelting,  the  belly  is  narrow,  and  the 
materials  descend  into  it  slowly.  If  the  fuel  falls  in  suflScient 
quantity,  the  materials  remain  long  enough  in  the  region  of  the 
highest  temperature  for  the  cast-iron  and  slag  to  acquire  the  flu- 
idity necessary  for  the  perfect  separation  of  these  substances  in 
the  crucible  part ;  but  if  the  charcoal  burns  easily,  as  it  does  when 
made  from  light  wood,  and  if,  moreover,  the  blast  be  strong,  then 
but  little  charcoal  will  reach  the  belly,  the  oxidizing  space  will  rise 
very  high  in  the  boshes,  the  reduced  iron  will  not  remain  long 
enough  in  contact  with  the  charcoal  to  combine  with  the  quantity 
of  carbon  necessary  to  convert  it  into  an  easily  fusible  cast-iron, 
and  a  portion  of  the  iron  will  be  oxidized  by  passing  through  the 
air  of  the  twyers,  and  pass  into  the  slag.  The  crucible  will  there- 
fore contain  only  a  half-refined  cast-iron,  not  suflSciently  fluid,  and 
the  yield  of  the  furnace  will  be  small,  because  a  considerable  quan- 
tity of  the  iron  will  be  lost  in  the  slag.  Frequently,  also,  masses 
of  non-carburetted  iron,  which,  consequently,  are  difficult  of  fusion, 
adhere  to  the  sides  of  the  boshes  immediately  above  the  twyers, 
where  they  are  cooled  by  the  blast,  and  obstruct  the  draught. 

If,  on  the  contrary,  the  belly  is  too  large,  and  not  sufficiently  high ; 
if,  moreover,  the  charcoal  burns  with  difficulty,  or  the  blast  is  too 
feeble,  then  the  combustion  will  be  very  active  in  the  belly  imme- 


METALLUGRY   OF   IRON.  77 

diately  above  the  twyers,  but  the  temperature  will  be  too  low  in 
the  boshes.  The  materials  will  not  be  sufficiently  prepared  on 
their  arrival  in  the  boshes,  not  having  had  time  to  attain  the  pro- 
per temperature ;  the  slag  will  be  doughy,  and  the  furnace  may 
become  choked. 

An  inconvenience  of  the  same  nature  occurs  when  ore  in  com- 
pact rocks,  impervious  to  gases,  or  forge-cinders  are  smelted.  The 
oxide  of  iron  is  reduced  with  great  difficulty  by  the  carbonic  oxide 
gas  in  the  upper  parts  of  the  furnace,  because  the  reducing  gas 
cannot  penetrate  the  small  masses  of  metal ;  the  reduction  is  there- 
fore effected  by  the  charcoal  alone  and  in  the  belly  itself,  when 
the  fused  materials  flow  on  the  fuel.  The  materials  do  not  remain 
long  enough  in  contact  with  the  charcoal  to  effect  the  perfect  re- 
duction and  separation  of  the  cast-iron.  The  ore  is  then  said  to 
be  difficult  to  melt,  to  be  refractory ;  but  it  would  be  incorrect  to 
say  that  it  is  difficult  to  reduce.  This  inconvenience  is  lessened, 
in  the  case  of  the  compact  ores,  by  subjecting  them  to  a  prelimi- 
nary roasting,  which  disaggregates  and  renders  them  porous. 

Generally  speaking,  the  working  of  a  blast-furnace  must  be 
stopped  when  its  belly  and  boshes  become  too  much  enlarged  by 
the  corroding  action  of  the  slag.  As  it  would  then  be  necessary 
greatly  to  increase  the  quantity  of  fuel,  it  is  more  profitable  to 
stop  and  repair  the  furnace.  A  well-constructed  furnace  should 
continue  in  blast  for  at  least  2  years ;  but,  under  favourable  cir- 
cumstances, some  furnaces  have  lasted  for  4,  5,  and  even  6  years. 
When  the  furnace  is  out  of  service,  it  is  emptied  completely, 
allowed  to  cool,  and  the  interior  torn  out,  while  the  main  body 
rarely  requires  any  repairs,  and  need  not  be  touched. 

§  822.  The  cold  air  impelled  into  the  blast-furnace  absorbs  a 
considerable  portion  of  the  heat  developed  by  the  combustion  in 
the  boshes,  in  order  to  attain  the  temperature  which  there  exists. 
This  absorption  of  heat  is  diminished,  arid,  consequently,  all  other 
things  being  equal,  the  temperature  rises  higher  in  the  boshes  if, 
instead  of  using  cold  air,  an  equal  weight  of  air  previously  heated 
to  400°  or  600°  is  impelled.  The  materials  which  are  difficult  of 
fusion,  and  do  not  become  sufficiently  fluid  in  a  cold-blast  furnace, 
melt  perfectly  when  it  is  fed  by  hot  air,  while  such  charcoal  as  is 
of  difficult  combustion  burns  more  easily,  because  the  combusti- 
bility of  charcoal  is  in  proportion  to  the  elevation  of  tempera- 
ture. The  most  refractory  materials  may,  therefore,  be  fused 
with  hot  air,  and  dense  fuel  may  be  used  which  would  burn  with 
difficulty  in  a  cold-blast  furnace. 

When  a  hot-blast  furnace  is  set  at  work  with  the  ore  and  fuel 
adequate  for  a  good  smelting  in  a  cold-blast  furnace,  the  propor- 
tion of  the  fuel  may  be  considerably  diminished,  and  a  good  blast 
yet  be  obtained ;  but  it  is  important  to  remark  that  the  substitu- 
tion of  heated  for  cold  air  remarkably  modifies  the  reactions  which 


78  IRON. 

take  place  in  the  various  parts  of  the  apparatus.  The  quantity 
of  charcoal  is  smaller,  and,  moreover,  it  burns  more  rapidly ;  and, 
therefore,  the  quantity  of  air  introduced  being  in  proportion  to  the 
charcoal  burned,  the  weight  of  gas  which  traverses  the  furnace 
during  the  rotation  of  the  hot  air  is  less  in  comparison  with  the 
weight  of  the  ores.  Now,  as  the  temperature  of  the  boshes  is 
supposed  to  be  the  same  in  both  cases,  there  will  be,  in  the  middle 
and  upper  part  of  the  furnace,  less  heat  with  the  hot  blast  than 
with  the  cold,  and  the  charcoal  being  more  combustible,  the  space 
of  the  maximum  of  temperature  will  be  more  confined.  These 
two  causes  determine  important  modifications  in  the  nature  of  the 
chemical  reactions  which  take  place  in  the  various  parts  of  the  fur- 
nace, particularly  in  front  of  the  twyers,  and  they  may  exert  a  con- 
siderable influence  on  the  quality  of  the  cast-iron  obtained. 

The  economy  of  fuel  eff'ected  in  the  blast-furnace  by  the  use  of 
hot  air,  would  lose  a  great  deal  of  its  importance  if  it  were  neces- 
sary to  burn  charcoal  to  heat  the  air ;  and  the  combustible  gases 
which  issue  from  the  tunnel-head  are  therefore  applied  to  this 
purpose.  To  eff'ect  this,  an  oven  is  built  above  the  mouth  or  im- 
mediately at  its  side,  surmounted  by  a  chimney,  in  which  cast-iron 
pipes,  traversed  by  the  air  of  the  blowing-machines,  are  inserted. 
The  flame  of  the  tunnel-head  enters  this  oven,  and  if  the  pipes  are 
properly  arranged,  the  air  may  be  heated  to  500°  or  600°. 

In  the  majority  of  foundries  in  which  hot  air  has  been  substi- 
tuted for  cold,  there  is  considerable  economy  of  fuel  eff'ected,  while 
unforeseen  difl[iculties  have  also  arisen,  causing  this  new  applica- 
tion to  be  abandoned,  so  ,that  only  few  hot-blast  furnaces  are  now 
in  use.  The  working  of  the  furnace  was  more  diflficult,  and  the 
quality  of  iron  yielded  very  irregular. 

§  823.  The  combustible  gases  which  escape  from  the  blast-fur- 
nace are  capable  of  producing  by  burning  a  quantity  of  heat  greater 
than  that  developed  in  the  blast-furnace  itself,  and  not  one-half  of 
the  heat  evolved  by  the  fuel  in  this  apparatus  has  yet  been  ad- 
vantageously applied. 

In  fact,  experiment  has  proved  that  1  litre  of  vapour  of  carbon 
produces,  by  its  complete  combustion,  2  litres  of  carbonic  acid,  and 
evolves  7858.  units  of  heat;  that  is,  a  quantity  of  heat  capable- of 
raising  the  temperature  of  7858  times  its  weight  of  water  by  one 
degree  [Celsius).  Two  litres  of  oxide  of  carbon,  containing  1  litre 
of  vapour  of  carbon,  consume  1  litre  of  oxygen,  and  yield,  by 
burning,  2  volumes  of  carbonic  acid  and  6260  units  of  heat.  The 
quantity  of  heat  evolved  by  the  transformation  of  1  litre  of  va- 
pour of  carbon  into  2  litres  of  oxide  of  carbon  is  therefore  only 
1598  units,  or  0.234  of  the  total  quantity  of  heat  which  the  same 
quantity  of  carbon  evolves  by  complete  combustion  and  conversion 
into  carbonic  acid.  It  may  be  easily  concluded  thence  that  car- 
bonic acid,  by  being  converted  into  oxide  of  carbon,  absorbs  a 


METALLURGY    OF   IRON.  79 

considerable  quantity  of  heat;  and  thus  is  explained  the  cooling 
■which  takes  place  in  the  blast-furnace  above  the  boshes.  In  fact, 
J  litre  of  vapour  of  carbon  yields,  by  complete  combustion,  1  litre 
of  carbonic  acid,  and  disengages  3929  units  of  heat,  while  1  litre 
of  carbonic  acid  combines  with  J  litre  of  vapour  of  carbon,  yield- 
ing 2  litres  of  oxide  of  carbon,  which,  by  complete  combustion  and 
transformation  into  2  litres  of  carbonic  acid,  evolve  6260  units  of 
heat.  Thus,  in  these  successive  combustions,  1  litre  of  vapour  of 
carbon  has  yielded  a  sum  total  of  heat  disengaged  equal  to  3929 -f 
6260=10189.  The  same  litre  of  vapour  of  carbon,  burning  com- 
pletely immediately  and  being  converted  into  carbonic  acid,  would 
disengage  7858  units  of  heat.  The  conversion  of  1  litre  of  car- 
bonic acid  into  2  litres  of  carbonic  oxide,  therefore  absorbs  a 
quantity  of  heat  represented  by  10189—7858=2331  units,  which 
are  again  evolved  when  the  oxide  of  carbon  burns  in  order  to  be 
transformed  into  carbonic  acid. 

The  heat  disengaged  by  a  J  litre  of  vapour  of  carbon  burning 
in  the  belly  of  the  furnace,  and  being  converted  into  carbonic  acid, 
is  represented  by  3929  units.  In  the  boshes,  the  carbonic  acid 
formed  combines  with  a  J  litre  of  vapour  of  carbon,  and  causes 
2331  units  to  pass  into  the  latent  state.  If  the  very  feeble  calo- 
rific effects  which  are  produced  during  the  reduction  of  the  ores 
by  the  combustible  gases  be  neglected,  there  is  no  other  evolution 
of  heat  in  the  blast-furnace,  and  combustible  gases  therefore 
burn  at  a  dead  loss,  or  escape  from  the  tunnel-head  of  the  fur- 
nace, by  disengaging  6260  units  of  heat,  which  is  a  quantity  of 
heat  nearly  double  of  that  used  in  the  blast-furnace  itself. 

In  latter  years,  attempts  have  been  made  profitably  to  use  this 
great  loss  of  heat.  We  have  said  that  it  had  been  used  to  heat 
the  air  projected  into  the  blast-furnace ;  but  it  has  been  also  em- 
ployed for  the  preliminary  roasting  of  the  ore,  and  is  now  applied 
to  heating  the  boilers  of  the  steam-engine  which  drive  the  blow- 
ing-machines, as  the  gases  from  the  mouth  of  the  furnace  evolve, 
while  burning,  a  quantity  of  heat  sufiicient  to  give  the  necessary 
motive-power.  Still  further  progress  has  been  made  in  some 
foundries :  the  gases  from  the  blast-furnace  have  been  drawn 
out  at  the  distance  of  several  metres  below  the  mouth,  and  carried 
by  pipes  into  reverberatory  furnaces,  where  they  were  burned 
with  a  proper  quantity  of  air,  by  which  means  a  temperature  was 
obtained  in  these  furnaces  sufficiently  elevated  to  perform  many 
metallurgic  operations,  especially  the  transformation  of  cast  into 
bar  iron.* 

*  This  is  a  mistake ;  for  although  experiments  have  been  made,  simultaneously, 
in  different  parts  of  Southern  Germany,  in  Hungary,  Bohemia,  and  in  France,  and, 
at  a  later  period,  also  in  the  United  States,  to  employ  the  lost  heat  of  blast-fur- 
naces for  puddling,  etc.,  they  were  all  a  signal  failure,  having  been  made  in  works 
where  charcoal  was  employed  as  fuel,  which,  developing  a  more  limited  quantity 


80  IRON. 

§  824.  The  cast-iron  used  for  moulding  immediately  as  it  leaves 
the  furnace  is  generally  the  fine-grained,  gray  cast-iron,  as  free 
as  possible  from  graphitous  particles,  which  would  make  the  iron 
porous.  Frequently  objects  of  cast-iron  are  made,  the  surface  of 
which  should  be  very  hard ;  as  for  example,  certain  cylinders  used 
in  rolling.  A  thick  cast-iron  mould  is  used,  into  which  the  fused 
metal  is  poured,  generally  through  the  lower  part  of  the  mould. 
The  metal,  suddenly  cooled  by  the  contact  of  the  thick  mould, 
wdiich  is  a  good  conductor  of  heat,  passes  into  the  state  of  white 
cast-iron  in  the  neighbourhood  of  the  mould,  and  its  surface  be- 
comes very  hard,  while  the  interior  of  the  cylinder  remains  in  the 
state  of  gray  cast-iron,  and  retains  malleability  sufficient  to  prevent 
the  piece  from  breaking. 

§  825.  A  large  portion  of  cast-iron  is  used  in  foundries  remote 
from  the  furnaces  in  which  it  is  made.  These  foundries  are 
generally  situated  in  large  cities  or  their  environs,  so  as  to  be  able 
to  cast  at  short  notice  the  objects  ordered.  Sometimes,  very  large 
pieces  are  required,  demanding  more  metal  than  can  be  contained 
in  the  hearth  of  a  single  furnace ;  and,  in  such  cases,  the  mould- 


of  combustible  gases  than  bituminous  coal,  could  not  afford  sufficient  heat  for  the 
purpose  ;  and  besides,  as  fast  as  the  cast-iron  was  purified  by  the  process  of  pud- 
dling, fresh  impurities  were  constantly  being  brought  in  with  the  gases.  Another 
great  difficulty  was  that  of  obtaining  a  constant  temperature.  The  remarks  in  the 
text  probably  refer  to  a  patent,  taken  by  Sire,  in  1888,  in  Fraijce,  which,  to  the 
best  of  my  knowledge,  never  was  worked,  and  consisted  in  drawing  off  the  blast- 
furnace gases  at  the  boshes,  and  burning  them  in  reverberatories  immediately 
adjacent;  a  process  by  which  the  working  of  the  blast-furnace  m*ist  necessarily 
be  greatly  impaired. 

The  method  now  almost  universally  employed  to  make  use  of  the  waste  heat,  is 
the  invention  of  M.  Faber  du  Faur,  of  Wurtemberg,  consisting  of  drawing  off  the 
gases  a  short  distance  below  the  tunnel-head  of  the  furnace,  and  burning  them, 
partly  in  chambers,  in  which  the  pipes  conveying  the  blast  are  arranged,  by 
which  the  air  is  heated  to  600°  or  800°,  and  partly  under  the  steam-boilers  of  the 
blast-machine,  with  jets  of  air. 

Experience  has  shown  that  combustible  gases  cannot,  without  affecting  the 
process  in  the  blast-furnace,  be^drawn  off  at  more  than  one-sixth  of  the  whole 
height  of  the  furnace  below  the  tunnel-head.  The  best  process  is,  however,  de- 
cidedly that  employed  in  several  furnaces  in  England  since  1851,  especially  at 
Ebbw-Vale ;  in  which  case,  a  truncated  inverted  cone  is  inserted  in  the  tunnel- 
head,  while  the  under  opening  is  entirely  closed  by  another  cone,  placed  upright, 
and  held  in  its  place  by  a  chain,  lever,  and  counterpoise.  The  charge  is  thrown 
into  the  funnel  thus  formed,  and  sinks  into  the  furnace  by  lowering  the  under 
cone :  the  advantage  of  spreading  the  charge  perfectly  equally  in  the  furnace  is 
thus  gained,  and  all  the  waste  gases  are  drawn  off  by  flues  set  above  the  level  of 
the  charges.  The  working  of  the  furnace  is  not  in  the  least  impaired  by  having 
the  mouth  closed. 

The  gases  escaping  from  furnaces  where  certain  kinds  of  bituminous  coal  are 
employed,  contain  a  percentage  of  ammonia,  which  may  be  obtained  by  leading 
the  gases  through  a  solution  of  dilute  chlorohydric  acid,  or  chloride  of  calcium, 
which  is  cheaper :  a  solution  of  sal-ammoniac  is  thus  obtained  after  some  time, 
from  which  the  salt  may  be  gained  by  evaporation  and  sublimation.  If  the  gases 
are  to  be  burned  after  the  washing,  they  will,  moreover,  have  lost  their  carbonic 
acid,  which  has  entered  into  combination  with  the  lime  of  the  chloride  of  calcium, 
and  will  thus  be  greatly  improved  in  quality. —  W.  L.  F. 


METALLURGY   OF   IRON. 


81 


ing  is  done  after  a  second  fusion.  For  small  objects,  as  those 
made  of  Berlin  iron,  the  cast-iron  is  again  melted  in  large  earthen 
crucibles,  heated  in  a  forge-fire  or  blast-furnace,  while,  for  larger 
objects,  reverberatories  or  cupola-furnaces  are  employed. 

The  cupola  consists  of  a  furnace  A  made  of  fire-bricks  (fig.  490), 
from  9  to  12  feet  high,  and  bound  together  by  cast-iron  plates. 
The  fire-bricks  do  not  extend  as  far  as  the  outer  casing  of  iron, 
but  are  separated  from  it  by  a  layer  of  sand  or  broken  forge-cin- 
ders. The  furnace  is  built  on  mason-work,  covered  by  a  large 
cast-iron  plate  ef,  which  serves  as  a  base  for  the  furnace  and  its 

iron  case;  while  the 


upper     end 
furnace    is 


Fig.  490. 


of  the 
covered 
by  a  plate  of  cast- 
iron  DC,  holding  the 
outer  case  together, 
and  provided  with  an 
aperture  correspond- 
ing to  the  mouth. 
Two  or  three  layers 
of  fire-bricks  are  laid 
^^^on  the  plate  ef  and 
upon  them  clay  is 
heaped,  so  as  to  form 
a  plane  lig^  slightly 
inclined  toward   the 


tap-hole  g.  so  that  it  acts  like  the  floor  of  a  hearth  for  the  fused 
metal. 

The  cupola-furnace  is  fed  by  a  blowing-machine,  which  impels 
the  air  through  two  twyers,  placed  sometimes  above  each  other,  as 
in  the  furnace  represented  in  fig.  490,  and  sometimes  near  each 
other  in  the  same  horizontal  plane. 

The  bottom  of  the  furnace  being  first  filled  with  charcoal  and 
lighted  wood,  coke  is  thrown  on,  the  air-blast  admitted,  and  when 
the  combustion  is  in  active  operation,  the  fuel  and  cast-iron  are 
added  in  successive  layers.  The  fused  metal  collects  at  the  bot- 
tom of  the  furnace,  and  the  smelting  must  be  effected  as  rapidly 
as  possible,  in  order  that  the  cast-iron  may  not  be  changed  in 
quality  in  passing  before  the  twyer.  When  the  cupola  contains  a 
sufficient  quantity  of  fluid  iron,  it  is  tapped ;  and  if  large  objects 
are  to  be  cast,  the  moulds  are  arranged  near  the  furnace,  the 
melted  metal  being  run  into  them  by  rills  communicating  with  the 
tap-hole.  Sometimes,  three  or  four  cupola-furnaces  are  required 
to  furnish  the  amount  of  fluid  metal  necessary.  When  small  ob- 
jects are  to  be  cast,  the  fused  iron  is  received  in  vessels  like  that 
represented  in  fig.  489,  and  carried  to  the  moulds  in  the  different 
parts  of  the  foundry. 

Vol.  II.— 6 


82  IRON. 

As  reverberatory  furnaces  permit  the  remelting  of  a  larger  quan- 
tity of  iron  than  cupola-furnaces,  and  consume  less  fuel,  they  are 
preferred  for  casting  large  pieces ;  but  in  the  former  the  cast-iron 
is  subject  to  more  alteration  than  in  the  cupola-furnaces,  because 
it  meets  with  a  more  oxidizing  air,  which  deprives  it  of  a  portion 
of  its  carbon.  It  is  essential  that  the  air  entering  these  furnaces 
should  pass  through  a  grate,  so  as  to  possess  as  feeble  an  oxidizing 
power  as  possible.  Lastly,  the  fusion  must  be  made  rapidly ;  for 
which  reason  the  cast-iron  is  placed  on  the  floor  of  the  hearth 
only  when  the  furnace  is  in  full  blast. 

All  kinds  of  cast-iron  cannot  be  moulded  after  a  second  fusion : 
they  must  be  rich  in  carbon,  so  as  to  be  able  to  lose  a  small  quan- 
tity of  it,  without  becoming  too  difficult  of  fusion. 

OF  THE  CONVERSION  OF  CAST-IRON  INTO  BAR-IRON. 

§  826.  In  order  to  convert  cast-iron  into  bar-iron,  the"  carbon 
and  silicium  combined  with  it  must  be  removed,  which  is  effected 
by  subjecting  it  to  an  oxidizing  action,  which  changes  the  carbon 
into  carbonic  acid  and  the  silicium  into  silicic  acid,  which  latter, 
combining  with  the  bases,  principally  with  the  oxide  of  iron,  forms 
fusible  silicates,  which  separate  in  the  form  of  slag.  When  the 
cast-iron  contains  small  quantities  of  sulphur  and  phosphorus, 
which  is  sometimes  the  case,  these  must  also  be  separated  during 
the  refinery,  as  they  injure  the  quality  of  bar-iron,  and  may  even 
render  it  unfit  for  use.  This  separation  is  very  difficult,  and  oc- 
casions considerable  waste ;  the  presence  of  these  two  metalloids 
in  cast-iron  is  therefore  avoided  as  much  as  possible.  If  sulphur 
exists  in  the  ores,  it  is  separated  almost  completely  by  previous 
roasting ;  but  if  it  is  furnished  by  the  fuel,  as  happens  when  coke 
made  from  pit-coal  is  used,  a,  large  quantity  of  flux  is  required  in 
the  blast-furnace,  in  order  that  the  slag  may  retain  the  sulphur  in 
the  state  of  sulphide  of  calcium.  Cast-iron  containing  any  con- 
siderable quantity  of  sulphur  or  phosphorus  always  yields  iron  of 
an  inferior  quality. 

When  a  blast-furnace  only  produces  iron  intended  for  refining, 
the  smelting  is  generally  so  conducted  that  a  white  cast-iron,  con- 
taining but  little  carbon,  is  obtained,  which  is  effected  by  intro- 
ducing a  great  deal  of  ore,  and  forcing  the  air  so  as  to  cause  a 
rapid  descent  of  the  materials ;  but  this  can  only  be  done  with 
very  pure  ores  and  fuel,  as  otherwise  an  impure  cast-iron,  yielding' 
iron  of  inferior  quality,  would  be  obtained. 

If  cast-iron  be  kept,  at  a  high  temperature,  in  contact  with  the 
air,  its  surface  becomes  covered  with  oxide  of  iron,  which  reacts  on 
the  inner  layer  of  the  iron  :  the  carbon  of  the  cast-iron  reduces  the 
oxide  of  iron,  and  is  disengaged  in  the  state  of  carbonic  oxide  gas, 
while  the  silicium  effects  a  similar  reduction  and  produces  silicic 


METALLURGY   OF   IRON.  83 

acid,  which,  combining  with  a  portion  of  the  undecomposed  oxide 
of  iron,  forms  a  fusible  silicate,  the  composition  of  which  varies  a^;- 
cording  to  the  proportion  of  oxide  of  iron  which  enters  into  it ;  but 
generally  it  assumes  the  formula  SFeOjSiOg.  If,  in  fact,  a  more^ 
basic  silicate,  such  as  6FeO,Si03,  be  heated  in  contact  with  cast- 
iron,  a  portion  of  the  oxide  of  iron  is  reduced  by  the  carbon  of  the 
cast-iron,  and  the  silicate  has  a  tendency  to  assume  the  composi- 
tion 3FeO,Si03.  Cast-iron  reacts  even  on  this  latter  silicate,  but 
less  readily  and  at  a  higher  temperature ;  so  that  the  silicates 
which  have  a  tendency  to  form  resemble  closely  the  formula 
3FeO,Si03.  The  conversion  of  cast  into  bar  iron  is  founded  on 
this  reaction.  The  silex  of  the  scoriae  is  furnished  not  only  by 
the  silicium  of  the  cast-iron,  or  the  grains  of  sand  adhering  to  its 
surface,  and  which  come  from  the  moulds  in  which  it  has  been 
cast,  but  a  great  portion  is  also  produced  by  the  ashes  of  the  fuel 
used  for  the  refinery. 

Two  different  processes  are  used  for  refining  cast-iron : 

1.  Refinery  with  charcoal,  called  refinery  in  the  small  fwnace, 

2.  Refinery  with  pit-coal,  called  refiner^  by  the  English  method^ 
or  refinery  by  puddling. 

Refinery  by  the  small  furnace, 

§  827.  The  refinery  is  effected  in  a  small  quadrangular  furnace 
U  (figs.  491  and  492),  made  of  iron  plates,  covered  with  clay,  the 
depth  of  which  is  9  inches,  its  width  varying  from  IJ  to  2  feet. 
The  air  is  conveyed  by  a  twyer  f,  which  enters  the  furnace  to  the 
distance  of  about  4  inches,  in  such  a  direction  that  its  prolonged 
axis  would  cut  the  opposite  face  of  the  hearth  at  its  lower  edge. 
The  copper,  or  baked-clay  twyer,  which  is  represented  in  fig. 
493,  generally  receives  the  nozzles  of  two  wooden  bellows  S,  S' 
(figs.  491  and  492),  moved  by  a  water-wheel.  The  bellows  are 
arranged  so  as  to  afford  a  continuous  blast ;  and  while  the  movable 
frame  of  the  one  descends  and  impels  the  air  into  the  furnace,  the 
other  ascends  and  inspires  the  external  air;  the  quantity  of  air 
being  regulated  by  the  flow  of  water  on  the  wheel.  The  blowing- 
machine  we  have  figured  is  very  imperfect ;  and  double  cylindrical 
machines,  resembling  that  in  fig.  487,  the  blast  of  which  is  regu- 
lated by  a  register  in  the  air-pipe,  are  substituted  for  it  in  modern 
forges. 

In  the  front  of  the  furnace  is  a  cast-iron  plate  aba'b',  placed  at 
the  height  of  the  upper  opening  of  the  furnace,  and  slightly  inclined. 
At  the  lower  part  of  the  hearth  is  a  tap-hole,  which  opens  at  the 
bottom  of  the  hearth,  and  serves  for  the  escape  of  the  scorias.  The 
furnace  is  covered  by  a  basket-funnel  C,  having  a  chimney  which 
carries  off  the  gases  arising  from  the  combustion,  and  sheet-iron 
plates  P  are  fastened  to  the  funnel,  to  protect  the  workmen  from 
the  heat. 


84 


Fig.  493. 


Fig.  492. 

The  furnace,  while  containing  the  charcoal  kin- 
dled in  a  preceding  operation,  is  filled  with  fresh 
charcoal  and  the  air  admitted.  The  cast-iron  to  be 
refined  is  either  in  the  form  of  pigs  or  plates,  and, 
when  melted,  drops  to  the  bottom  of  the  hearth, 
passing  the  air  of  the  twyer.  The  smelting  lasts  from  3  to  3J  hours. 
The  workmen  take  advantage  of  the  high  temperature  developed  by 
the  combustion  of  the  charcoal  which  is  placed  above  the  cast-iron, 
to  forge  bars  of  refined  iron  arising  from  the  preceding  operation, 
as  we  shall  presently  explain.  The  surface  of  the  drops  of  cast- 
iron,  passing  through  the  air  of  the  twyer,  becomes  oxidized,  and 
a  very  basic  silicate  of  iron  is  formed,  which  reacts  on  the  carbon 
of  the  cast-iron,  so  that  the  latter,  when  it  has  arrived  at  the  bot- 
tom of  the  hearth,  has  lost  a  great  portion  of  its  carbon,  and 
becomes  much  less  fusible.  From  tfine  to  time,  the  scoriae  are 
withdrawn  by  opening  the  tap-hole,  a  sufficient  quantity  to  con- 
tinue the  decarbonizing  action  always  being  left.  Frequently  the 
workman  allows  the  air  of  the  twyer  to  blow  directly  on  the  cast- 
ixon,  to  increase  its  oxidation. 


METALLURGY   OF   IRON. 


85 


When  the  mas^  of  iron,  partly  refined,  has  become  consistent, 
the  workman  raises  it  with  his  bar  above  the  fuel,  which  he  heaps 
at  the  bottom  of  the  furnace,  when  the  air  then  blowing  below  the 
rfkss  subjects  it  to  a  powerful  oxidizing  action.  Fresh  charcoal  is 
added  and  the  force  of  the  blast  increased,  so  as  to  fuse  the  metal 
a  second  time.  After  the  second  fusion,  the  refining  is  very  far 
advanced ;  and  the  iron  forms  spongy  masses,  which  the  workman 
collects  together  and  welds  into  one  single  piece;  while  he  some- 
times draws  those  pieces  which  do  not  appear  sufficiently  refined 
nearer  to  the  twyer.  When  the  operation  is  terminated,  the  scoriae 
are  completely  removed,  the  mass  of  iron  is  withdrawn,  its  sides 
are  beaten  with  iron  bars,  and  it  is  then  carried  to  the  hammer. 

The  hearth  is  then  cleansed.  A  portion  of  the  scoriae  is  left  in 
the  furnace,  and  the  remainder  withdrawn,  but  generally  preserved 
for  use  in  the  following  operation  during  the  smelting  of  the  iron, 
for  which  the  scraps  of  iron  detached  during  the  forging  of  the 
lump  are  also  made  use  of.  When  the  iron  plate  forming  the 
bottom  of  the  hearth  becomes  too  hot,  it  is  cooled  by  a  small 
quantity  of  water. 

§  828.  iThe  process  to  which  the  lump  is  subjected  when  it  leaves 
the  furnace,  consists  in  placing  it  on  an  anvil,  when  it  is  beaten  in 
all  directions  by  a  heavy  hammer  (fig.  494).     The  anvil  E  is  gene- 


Fig.  494. 

rally  of  cast-iron,  while  the  hammer  is  frequently  made  of  wrought- 
iron,  with  a  steel  face.  The  head  P  of  the  hammer  weighs  from 
600  to  1200  pounds,  and  is  mounted  on  a  wooden  helve  oa, 
strengthened  by  bands  of  iron.  The  helve  is  held  in  a  cast-iron 
ring,  provided  with  two  gudgeons  o,  on  which  it  revolves,  and 
which  rest  on  cast-iron  collars  fastened  to  uprights.  To  give 
additional  solidity  to  the  anvil,  it  is  placed  on  a  large  block  of 
wood,  resting  on  pile-work  driven  into  the  floor  of  the  foundry. 
The  hammer  is  raised  by  cams  c,  c,  averaged  on  an  anvil  AB, 
which  is  turned  by  a  water-wheel,  and,  when  it  is  elevated  to  b, 


86  IRON. 

strikes  against  a  piece  of  wood  SR,  called  a  robot,  or  check, 
which  prevents  it  from  rising  too  high ;  while  the  check  also,  hy 
virtue  of  its  elasticity,  imparts  to  it  a  rapid  descending  motion, 
which  prevents  it  from  meeting  the  following  cam  before  striking 
on  the  anvil.  The  flight  of  the  hammer,  or  its  greatest  separation 
from  the  anvil,  varies  from  IJ  to  2  feet.  The  hammer  first  de- 
scribed, is  called  &  forge-hammer  {msLrtean  si  soulevement). 

§  829.  In  order  to  carry  the  glowing  bloom  to  the  anvil,  the 
workmen  use  strong  iron  tongs,  during  which  operation  the  ham- 
mer is  held  in  the  air  by  means  of  a  chock.  As  soon  as  it  is  com- 
pleted, the  chock  is  removed  and  the  water-wheel  set  in  motion,  at 
first  slowly,  the  rapidity  being  gradually  increased,  when  the  very 
fluid  scoriae  scattered  through  the  spongy  metal  are  expressed  by 
the  compression  and  run  out,  while  the  metallic  particles  are  welded 
to  each  other.  The  workmen  turn  the  bloom  on  its  various  faces, 
in  order  to  strike  it  in  all  directions  ;  when  it  takes  the  form  of  an 
elongated  prism,  with  a  square  base,  which  is  cut  into  4  or  5  pieces, 
called  lopins,  with  an  iron  knife,  the  back  of  which  is  exposed  to 
the  hammer.  When  the  furnace  has  been  arranged  for  a  new 
smelting,  the  lopins  are  introduced  into  it,  covered  with  charcoal, 
and,  when  they  have  attained  a  sufficient  temperature,  are  forged 
into  bars. 

§830.  The  forge-hammer  is  sometimes  used  for  this  purpose, 
but  most  generally  a  smaller  hammer,  called  a  tilt-hammer,  is  em- 
ployed. This  hammer,  represented  in  fig.  495,  which  gives  a  greater 


Fig.  495. 

number  of  blows,  and  does  not  rise  so  high,  is  moved  by  its  heel, 
by  means  of  cams  on  the  shaft  R  of  the  water-wheel.  The  axis  of 
rotation  0  is  placed  at  J  of  the  length  of  the  helve,  starting  from 
the  heel  C ;  and  the  cams  bear  from  above  downward  on  the  heel 
of  the  helve,  and,  in  this  way,  elevate  it.  They  are  much  more 
numerous  around  the  circumference  of  the  shaft  than  those  of  the 
forge-hammer.  In  order  that  the  hammer  may  fall  quickly,  after 
the  cam  has  passed,  its  heel  is  made  to  strike  against  a  piece  of 
iron,  fixed  in  a  block  of  wood  D,  which  actively  repels  it,  and  allows 


METALLURGY   OF   IRON.  8T' 

the  hammer  to  fall  back  on  the  anvil  before  being  raised  by  the 
succeeding  cam. 

Refinery  in  the  small  furnace  yields  72  to  76  parts  of  bar-iron 
from  100  of  cast ;  the  iron  always  being  of  very  good  quality  when 
the  cast-iron  is  not  very  impure,  because  the  metal  has  been  forged 
and  beaten  in  every  way.  Good  quality  iron  may  also  be  obtained 
from  very  moderate  quality  cast-iron ;  but  the  loss  is,  in  that  case, 
much  greater. 

§  831.  Hot  air  is  also  used  for  the  refinery  of  cast-iron  in  the 
small  furnace  ;  the  air,  before  reaching  the  twyer,  being  conducted 
through  a  series  of  pipes  arranged  in  a  serpentine  form  above  the 
furnace,  and  in  the  chimney  surmounting  it.  It  has  been  ascertained 
that  it  is  only  necessary  to  use  hot  air  during  the  first  stage  of  the 
process,  that  is,  during  the  smelting  of  the  cast-iron,  because  it  then 
was  effected  more  rapidly ;  and  to  throw  in  cold  air  during  the 
second  stage,  when  the  oxidation  should  be  more  active.  But  the 
use  of  hot  air  during  the  operation  of  refining  has  been  abandoned 
in  the  majority  of  foundries  which  at  first  adopted  it,  because  the 
working  is  more  irregular  than  with  cold  air. 

It  has  been  endeavoured  to  substitute  coke  for  charcoal  in  refi- 
nery by  the  small  furnaces,  but  the  quality  of  the  iron  was  always 
indifferent. 

Refinery  hy  pit-coal,  or  the  English  method. 

§  832.  In  all  countries  where  wood  is  scarce,  and  mineral  fuel, 
on  the  contrary,  plentiful  and  cheap,  a  process  of  refinery  very 
different  from  that  just  described  is  adopted,  called  refinery  hy  the 
English  method,  because  it  originated  in  England.  This  operation 
is  divisible  into  two  consecutive  parts,  which  are  executed  in  differ- 
ent furnaces. 

In  the  first  operation,  the  cast-iron  is  fused  in  a  kind  of  refining 
crucible,  in  contact  with  charcoal  and  exposed  to  the  air  of  the 
twyer,  when  the  melted  metal  runs  into  a  large  rill,  where  it  as- 
sumes the  shape  of  a  plate.  By  this  fusion  under  the  twyer,  the 
cast-iron  has  lost  a  portion  of  its  carbon  and  nearly  all  its  silicium, 
and  forms  a  white,  short,  and  brittle  metal,more  or  less  blistered, 
and  called  fine-metal.  The  furnace  in  which  this  fusion  is  executed 
is  called  a  running-out  fire. 

The  refinery  of  fine-metal  is  completed  by  exposing  it  in  a  re- 
verberatory  furnace,  at  the  same  moment,  to  a  very  high  tempera- 
ture and  to  a  current  of  oxidizing  air,  when  the  carbon  of  the  cast- 
iron  burns  to  carbonic  acid,  while,  at  the  same  time,  the  iron  oxi- 
dizes on  its  surface,  and  yields  magnetic  iron,  which,  partly  com- 
bining with  the  silicic  acid  produced  by  the  silicium  yet  contained  in 
the  fine-metal,  forms  a  kind  of  slag,  which  covers  the  small  frag- 
ments of  metal  arising  from  the  disaggregation  effected  by  heat. 
The  oxide  of  iron  in  the  scoriae,  reacting  on  the  carbon  which  still 


88 


IRON. 


remains  in  combination,  disengages  carbonic  oxide,  which  burns 
Tvith  a  small  bluish  flame,  while  sometimes  scoriae  rich  in  oxide  of 
iron  are  added  to  hasten  the  combustion.  When  the  workman 
thinks  the  refinery  is  completed,  he  collects  the  fragments  of  metal- 
lic iron  scattered  over  the  floor  of  the  reverberatory  furnace  into 
the  shape  of  balls,  which  he  removes  in  succession,  carrying  them 
to  the  shingling  hammer  to  be  worked  into  bars.  This  second 
operation  finishes  the  refinery,  and  is  called  puddling :  the  iron  is 
called  puddled  iron. 

Refinery  by  the  English  method  corresponds  to  the  first  fusion 
of  the  cast-iron  under  the  air  of  the  twyer  in  refinery  by  the  small 
furnace.  The  fine-metal  presents  nearly  the  same  composition  as 
the  fused  metal  which  collects  at  the  bottom  of  the  small  furnace 
after  the  first  smelting. 

§  833.  The  running-out  fire  is  composed  of  a  rectangular  cru- 
cible A  (figs.  496  and  497),  made  of  cast-iron  boxes  U,  through 


Fig.  497. 


METALLURGY   OF   IRON.  S^ 

which  a  current  of  cold  water  circulates  continually  to  prevent 
them  from  melting.  The  bottom  of  the  crucible  is  made  of  sand; 
and  the  blast  is  furnished  by  6  twyers,  disposed  on  the  two  sides. 
The  twyers  are  of  cast-iron,  double,  and  resembling  those  (fig. 
486)  used  in  blast-furnaces.  Cold  water,  coming  from  the  boxes  v, 
and  regulated  by  stopcocks  r,  circulates  constantly  in  the  twyers 
to  prevent  their  fusing  at  the  high  temperature  of  the  furnace.  A 
cylindrical  blowing-machine,  worked  by  a  steam-engine,  furnishes 
the  air  necessary,  which,  impelled  by  the  machine,  first  enters  a 
cylindrical  reservoir  T,  whence  it  is  distributed  through  the  pipes 
t,  furnished  with  nozzles  fitting  the  twyers.  The  reservoir  T  has 
a  register  s,  by  means  of  which  the  quantity  of  air  projected  into 
the  furnace  can  be  regulated.  The  twyers  are  so  inclined  that 
their  prolonged  axes  would  cut  the  opposite  vertical  faces  of  the 
crucible,  at  a  little  distance  from  their  lower  edge.  The  furnace 
is  surmounted  by  a  chimney  C  to  carry  off"  the  gaseous  products  of 
the  combustion,  supported  by  a  cast-iron  frame  B  having  several 
apertures,  through  which  the  men  can  work  in  the  crucible.  The 
front  part  of  the  crucible  is  furnished  with  a  tap-hole  oo',  for  the 
escape  of  the  melted  metal,  which  flows,  with  the  scoriae,  into  an 
oblong  iron  trough  D,  for  sudden  congelation. 

§  834.  The  operation  of  the  running-out  fire  is  continuous.  After 
the  metal  has  run  out,  the  workmen  clean  the  crucible,  remove  the 
scoriae,  introduce  the  burning  charcoal,  cover  it  with  the  proper 
quantity  of  coke,  and  heap  upon  it  iron  pigs,  which  are  about  3  feet 
in  length,  and  weigh  from  90  to  120  pounds.  The  pigs  are  ar- 
ranged symmetrically  over  the  surface  of  the  furnace :  the  charge 
generally  consists  of  from  20  to  24  cwt.  Sometimes  the  cast-iron 
is  gradually  introduced.  When  the  furnace  is  charged,  the  blast 
is  let  on,  feebly  at  first,  when  the  iron  melts  and  drops  through 
the  air  of  the  twyers,  where  the  portion  of  it  which  is  oxidized 
forms  a  slag  with  the  ashes  of  the  fuel  and  the  silicic  acid  arising 
from  the  oxidation  of  the  silicium  of  the  cast-iron  ;  the  slag,  which 
is  very  rich  in  oxide  of  iron,  again  exerting  a  decarbonizing  influ- 
ence on  the  cast-iron  which  it  covers.  The  workman  judges  of  the 
progress  of  the  refining  by  the  appearance  and  consistence  of  the 
fluid  metal ;  when  the  latter  has  entirely  fallen  into  the  crucible, 
the  air  of  the  twyers  is  allowed  to  blow  for  some  time  over  the 
surface  of  the  liquid  bath,  and  then  the  man  proceeds  to  open  the 
tap-hole,  when  the  metal  flows  into  the  large  trough  D,  where  it 
spreads  in  a  sheet-like  form,  and  the  scoriae  flow  over  it.  When  the 
crucible  is  empty,  water  is  thrown  on  the  fine-metal  to  congeal  it 
rapidly  and  render  it  very  brittle.  If  the  metal  still  retains  some 
sulphur,  a  very  decided  smell  of  sulphuretted  hydrogen  is  evolved. 
[The  scoriae  are  removed  and  the  fine-metal  broken  with  a  hammer. 
The  colour  of  the  fracture  of  this  metal  is  of  a  grayish-white,  the 
upper  layers  being  filled  with  blisters,  while  the  lower  ones  are 


90  IRON. 

compact.     During  this  operation,  the  cast-iron  has  lost  all  its  sili- 
cium,  but  only  a  portion  of  its  carbon. 

An  idea  of  the  chemical  change  which  cast-iron  undergoes  by 
refining,  may  be  formed  from  the  following  analyses : — A  cast-iron 
composed  as  follows, 

Carbon 8.0 

Silicium 4.5 

Phosphorus 0.2 

Iron 92.3 

100.0 
yielded  a  fine  metal  composed  of 

Carbon 1.7 

Silicium 0.5 

Iron 97.8 

100.0 

Cast-iron  loses,  in  the  running-out  fire,  about  10  per  cent,  of  its 
weight,  the  consumption  of  coke  being  about  16  cubic  feet  for 
every  ton  of  fine-metal  obtained. 

§  835.  The  puddling-furnace  is  a  reverberatory  furnace  of  which 
fig.  499  represents  a  horizontal,  and  fig.  498  a  vertical  section, 
while  fig.  500  gives  a  perspective  vieW.  The  floor  of  the  furnace 
is  perfectly  horizontal ;  but  posteriorly,  at  B,  there  is  a  depression 

B 


leading  to  an  opening  o,  through  which  the  scoriae  are  withdrawn, 
and  which  remains  shut  during  the  operation.  The  floor  is  separated 
from  the  grate  F  by  a  fire-bridge  of  about  9  inches  in  height,  while 
the  draught  is  efi'ected  by  a  brick  stack  C,  from  30  to  45  feet  high, 


METALLURGY    OF    IRON. 


9* 


and  furnished  with  a  register  R,  which  the  workman  can  reguhite 
from  the  foundry  by  means  of  a  chain.     The  walls  of  the  reverbe- 

ratory  furnace  are  built 
of  refractory  bricks, 
and  covered  externally 
by  iron  plates,  held  in 
place  by  iron  tie-rods. 
The  furnace  has  seve- 
ral doors  ;  those  F  and 
G  communicating  with 
Fig.  499.         •  the  grates,  and  serving 

for  charging  the  fuel,  are  closed  by  registers.  The  doors  D  and 
E  communicate  with  the  floor  of  the  furnace ;  D  is  chiefly  used 
during  the  refinery,  and  can  be  closed  by  a  register ;  E  is  closed 


Fig.  500. 

during  the  operation,  and  is  used  only  for  cleaning  the  floor  and 
charging  the  metal  to  be  refined.  The  floor  is  often  made  of  a 
simple  iron  plate,  under  which  the  air  circulates  freely,  to  prevent 
it  from  becoming  hot  enough  to  fuse.  At  other  times  it  is  covered 
by  a  layer  of  sand ;  while,  lastly,  in  some  foundries,  the  floor  is 
made  of  fire-bricks  covered  by  a  bed  of  scoriae  heated  nearly  to  a 
fusion. 

The  grate  of  an  ordinary  puddling-furnace  is  square ;  and  about 
3  to  3J  feet  deep.  The  floor  is  5  to  6  feet  in  length,  3J  feet  in 
its  greatest  width  toward  the  grate,  and  IJ  feet  near  the  chimney. 

§  836.  The  following  is  a  description  of  the  operations  in  pud- 
dling. The  furnace  being  heated  to  a  white  red-heat,  from  4  to  5 
cwt.  of  metal  are  introduced  and  spread  over  the  floor,  while  about 
1  cwt.  of  rich  scoriae  or  scraps  of  iron  are  added ;  after  which  the 
doors  are  closed  hermetically,  and  the  register  in  the  chimney 
opened.    As  soon  as  the  metal  fuses,  the  register  R  in  the  chimney 


02 


IRON. 


is  gradually  lowered  to  diminish  the  draught.  The  half-melted 
metal  is  covered  with  liquid  scoriae,  and  the  workman  stirs  it  con- 
tinually with  a  bar,  which  he  passes  through  the  door  D — opening 
this  door  to  as  small  an  extent  as  possible,  so  as  not  to  allow  the 
introduction  of  too  much  fresh  air  in  the  furnace,  lest  the  iron 
should  become  too  completely  oxidized.  He  then  opens  the  regis- 
ter R,  when  the  carbon  of  the  cast-iron  reacting  on  the  oxide  of 
iron  of  the  scoriae,  causes  a  great  quantity  of  carbonic  oxide  gas  to 
be  evolved,  which,  escaping  through  the  scoriae,  causes  them  to  boil 
up  and  swells  the  whole  mass.  The  gas  burns  with  a  small  blue 
flame.  The  workman  continues  to  ^tir  the  mass  with  his  bar,  until 
he  recognises,  by  the  appearance  and  pulverulent  consistence  of  the 
metal,  that  the  refining  is  sufficiently  advanced ;  after  which  he 
allows  a  portion  of  the  scoriae  to  run  off",  and  collects  the  portions 
of  refined  iron  together  with  the  bar,  welding  them  to  each  other 
by  pressure.  When  he  has  thus  formed  a  metallic  ball,  he  rolls 
it  over  the  floor  of  the  furnace  covered  with  red-hot  fragments 
of  iron,  which  adhere  to  the  ball,  which,  when  it  has  attained  a 
sufficient  size,  he  pushes  toward  the  bridge,  and  immediately 
begins  to  make  a  second.  In  this  way  he  makes  4  or  6  balls, 
which  are  carried  successively  to  the  hammer,  beginning  with  the 
one  first  made. 

Fourteen  or  sixteen  charges  are  generally  made  in  24  hours ; 
the  loss  of  the  fine-metal  being  about  7  or  8  per  cent.,  while  about 
100  parts  of  pit-coal  are  consumed  for  100  parts  of  puddled  iron. 

The  previous  refining  of  the  cast-iron  is  indispensable  in  very 
^siliceous  metal  produced  in  coke  blast-furnaces  fed  with  impure 
ores  or  a  fuel  containing  a  large  quantity  of  pyrites.  When  the 
metal  to  be  refined  is  very  pure,  as  that  produced  in  charcoal 
furnaces,  or  the  very  pure  gray  cast-iron  yielded  by  certain  coke 
furnaces,  the  previous  run-out  fire  is  often  omitted,  and  the  iron  is 
puddled  immediately.  In  this  case,  the  operation  occupies  rather 
a  longer  time,  and  occasions  a  greater  loss. 

§  837.  The  hammer  with  which  the  blooms  from  the  puddling- 
furnace  are  wrought  is  represented  in  fig.  501,  and  consists  entirely 
of  cast-iron,  weighing  from  3  to  6  tons.     The  axis  o  of  the  helve 


Fig.  501. 


METALLURGY   OF  IRON. 


93 


turns  in  collars  let  into  the  cast-iron  support  S :  the  pane  or  head 
p  is  of  steely  iron,  and  composed  of  three  parts  fastened  bj  wedges 
into  the  cast-iron  helve.  The  wood-cut  represents  the  usual  shape 
of  the  pane  of  the  hanamer  and  the  anvil  q.  The  hammer  is  raised 
by  its  head,  by  means  of  cams  c,  c  mounted  on  a  ring  of  cast-iron, 
called  the  cam-ring  hag,  which  is  itself  fastened  to  a  horizontal 
shaft  R,  moved  by  a  water-wheel  or  steam-engine.  The  flight  of 
this  hammer  varies  from  IJ  to  2J  feet,  the  number  of  blows  being 
about  75  to  100  per  minute. 

§838.  The  rougUng-rolls  (fig.  502) 
are  composed  of  two  horizontal  cylin- 
ders, placed  upon  each  other,  having 
their  surfaces  grooved  in  various 
ways,  according  to  the  shape  to  be 
given  to  the  bars.  The  axes  of  the 
two  cylinders  must  be  exactly  in  the 
same  vertical  plane,  and  they  are 
driven  by  equal  forces,  but  in  oppo- 
site directions,  the  lower  roller  re- 
ceiving its  motion  directly  from  the 
machine  on  the  axis  of  which  it  is 
fixed,  while  the  upper  cylinder  is 
moved  by  the  first,  by  means  of  the 
gearing  c,  c',  and,  consequently,  re- 
volves in  an  opposite  direction.  The 
cylinders,being  set  in  cast-iron  frames, 
A,  A,  rest  on  brass  chains,  and  their 
separation  is  regulated  by  a  screw  a. 
The  cylinders  A  and  B  are  connected 
with  each  other  and  with  the  rotat- 
ing axis  of  the  machine,  by  cast-iron 
collars  m,  which  pass  over  both  axes 
and  are  fastened  with  keys  ;  the 
cylinders  are  thus  readily  taken 
apart  and  put  together  again.  The 
cylinders  A,  A'  are  furnished  with 
square  grooves,  which  decrease  regu- 
larly from  the  first  to  the  last,  and 
are  intended  for  the  manufacture  of 
square  bar-iron.  The  cylinders  B,  B', 
on  the  contrary,  are  arranged  for  the 
production  of  flat  bar-iron. 

In  order  to  prevent  the  cylinders 
from  becoming  too  much  heated 
during  the  process,  small  streams  of 
water,^  furnished  by  the  tubes  t,  t,  t, 


94  IRON. 

communicating  with  the  pipe  I  I',  are  allowed  to  fall  on 
them. 

In  orcjer  to  introduce  the  heated  bars,  the  workmen  hold  them 
with  pincers,  and  rest  them  on  a  plate  of  sheet  or  cast  iron,  called 
an  apron,  placed  on  a  level  with  the  line  of  separation  of  the  two 
cylinders  ;  while  a  second  plate,  the  edge  of  which  is  notched  so 
as  to  allow  the  grooves  of  the  lower  cylinder  to  pass,  is  arranged 
on  the  other  side  of  the  cylinders  at  the  same  height,  and  is  in- 
tended to  receive  the  bar  on  its  exit,  and  prevent  it  from  wrap- 
ping around  the  lower  cylinder.  When  the  bar  has  passed  out,  a 
workman  seizes  it  with  his  tongs,  passes  it  above  the  upper  cylin- 
der, where  the  roller  receives  and  present  it  to  a  second  groove, 
of  which  the  section  is  smaller.  The  operation  is  facilitated  by 
resting  the  bar  on  hooks  suspended  to  chains,  the  ends  of  which 
slide  along  horizontal  bars.  The  puddling-rolls  generally  make 
30  or  40  revolutions  per  minute. 

§  839.  After  this  short  description  of  the  machinery  for  rolling 
iron,  let  us  return  to  the  process  of  puddling.  The  puddled  bloom, 
withdrawn  from  the  fire,  is  dragged  along  the  floor  of  the  foundry 
to  the  anvil,  on  which  it  is  placed  by  means  of  strong  tongs,  called 
a  po7'ter.  The  hammer  is  raised  as  high  as  possible  by  a  wedge, 
and,  in  order  to  set  it  in  motion,  the  cam-ring  bag  is  made  to  re- 
volve, while  a  bar  of  iron  is  applied  to  one  of  the  cams,  exactly  as 
it  passes  near  the  face  of  the  hammer.  The  hammer  is  then 
raised,  the  wedge  removed,  and  the  former  goes  on  working.  The 
scorise  scattered  through  the  spongy  metal  flow  out  copiously, 
while  the  metallic  particles  are  welded  to  each  other,  and  the  bloom 
being  hammered  in  various  directions,  assumes  the  shape  of  an 
elongated  prism  with  a  square  base.  The  hammering  does  not 
last  more  than  a  minute,  so  that  the  bloom  is  still  very  hot,  and 
may  be  sent  immediately  to  the  rollers.  When  the  iron  has  suc- 
cessively passed  through  the  several  grooves  of  the  roughing-rolls 
and  the  rollers,  it  has  assumed  the  shape  of  flat  bars  of  about  half 
an  inch  in  thickness  and  2  or  2J  inches  in  breadth. 

§  840.  Recently,  a  hinge-press  (fig.  503)  has  been  substituted 
for  the  hammer  above  described  for  compressing  the  blooms  from 
the  puddling-furnace,  consisting  of  two  cast-iron  jaws  AB  and  D 


fig.  5U3. 


METALLURGY   OF   IRON. 


95 


joined  together  like  a  pair  of  scissors;  but,  instead  of  cutting 
edges,  they  have  plane  surfaces,  slightly  grooved,  between  which 
the  spongy  iron  is  forcibly  compressed.  The  lower  jaw  D  is  made 
of  a  cast-iron  box  through  which  water  can  circulate,  while  the 
upper  jaw  is  moved  by  an  iron  crank  ah,  mounted  on  a  shaft  b  set  in 
motion  by  a  machine.  The  press  occasions  less  loss  than  the 
hammer,  and  enables  the  bloom  to  pass  sooner  through  the  rollers. 
§  841.  Lastly,  a  new  apparatus  has  been  invented,*  which  pre- 
sents great  advantages  even  over  the  press,  for  the  forging  of  the 
bloom,  and  the  working,  in  general,  of  large  masses  of  iron :  the 
Htamping-hammer  ^ox  steam-hammer.      The   hammer  (fig.  504)  is 

composed  of  a  cast-iron 
stamper  C,  weighing  from 
3  to  5  tons,  and  terminat- 
ing below  in  a  steely-iron 
pane  A,  to  which  any  de- 
sired shape  is  given.  The 
stamper  moves  in  iron 
grooves  ah,  cd,  fixed  in  a 
solid  cast-iron  frame,  and 
is  supported  by  an  iron  rod 
tt,  attached  to  a  piston 
which  moves  in  a  pump  P, 
erected  on  the  upper  plat- 
form of  the  frame  :  the 
anvil  B  being  immovably 
fixed  at  the  bottom  of  the 
same  frame.  In  order  to 
raise  the  stamper,  high- 
pressure  steam  is  intro- 
duced into  the  trunk  of  the 
pump  P,  below  the  piston, 
which,  rising  in  the  pump, 
carries  the  stamper  with  it. 
Fig.  504.  jf  ^jjg   communication   be- 

tween the  pump  P  and  the  boiler  be  cut  ofi",  and,  on  the  contrary, 
a  communication  established  with  the  atmosphere,  the  steam 
escapes,  the  excess  of  pressure  which  caused  the  stamper  to  ascend 
is  removed,  and  it  falls  with  its  whole  weight  on  the  anvil.  This 
operation  is  easily  effected  by  slide-valves  such  as  are  used  in  a 
steam-engine.  A  workman,  standing  on  the  platform  R,  works  the 
valves  by  hand  and  regulates  at  will  the  play  of  the  hammer.  The 
rapidity  and  number  of  the  blows  may  be  thus  regulated,  and  the 
hammer  can  be  arrested  at  any  distance  from  the  anvil,  which  last 
condition  is  very  valuable,  because  an  exact  size  can  be  given  to 


*  Invented  by  Mr.  Nesmith,  of  Patricroft,  near  Manchester,  England. —  W.  L.  F. 


IRON. 


the  pieces  forged.  The  steam-hammer  is  of  immense  importance 
in  iron-works,  particularly  for  the  forging  of  large  pieces,  such  as 
the  shafts  of  the  wheels  of  large  steam-vessels. 

§  842.  Puddled  iron  is  always  of  inferior  quality,  being  badly 
?prelded  and  filled  with  cracks  or  flaws;  but  it  generally  possesses 
great  hardness,  and  is  well  adapted  to  certain  uses  in  which  a 
better  quality  of  iron  is  unnecessary.  The  rails  of  rail- 
roads are  always  made  of  puddled  iron ;  the  bars  intended 
for  their  manufacture  being  passed  through  rollers,  the 
grooves  of  which  are  so  arranged  as  to  give  them  the  shape 
«.    <rAr  generally  adopted  for  rails,  a  section  of  which  is  seen  in 

§  843.  The  quality  of  puddled  iron  is  greatly  improved  by  re- 
heating it  to  a  white  welding-heat  and  again  hammering  and 
rolling  it.  To  do  this,  the  bars  of  puddled  iron  are  cut  into 
lengths  of  about  8  inches,  by  means  of  shears  (fig.  506)  composed 


Fig.  606. 

of  two  jaws  terminating  in  steel  cutting-edges  A,  B.  The  lower 
jaw^  B  is  fixed,  while  the  upper  jaw  A  turns  around  a  horizontal 
shaft  fastened  to  the  lower  jaw,  and  ends  in  a  long  iron  heel  AC, 
moved  by  an  eccentric  wheel  DE,  of  which  the  axis  of  rotation  R 
is  turned  by  water  or  steam  power. 

The  divided  ends  of  the  puddled  iron  are  placed  upon  each  other, 
so  as  to  form  bundles,  each  of  which  contains  the  quantity  of  iron 
necessary  to  make  a  bar ;  and  the  bundles  are  introduced  into  a 
reverberatory,  called  a  reheating  furnace,  and  represented  in  figs. 
507  and  508.  This  furnace  difi"ers  from  the  puddling-furnace,  in 
having  a  larger  capacity  A  and  a  greater  surface  of  grate  F :  it 
has  only  two  doors,  one  for  charging  the  fuel,  while  the  other  o,  at 
the  back  part  of  the  furnace,  immediately  below  the  chimney, 
serves  for  the  introduction  of  the  bundles  of  iron  to  be  reheated, 
and  for  their  removal  when  completed.  This  door  is  closed  by  a 
register  r.  It  is  important  to  admit  only  air  entirely  deprived  of 
its  oxygen  into  the  furnace,  in  order  to  prevent  the  iron  from 
oxidizing  and  occasioning  considerable  loss  ;  for  which  reason  the 
doors  of  the  furnace  must  be  kept  as  closely  shut  as  possible,  so 
that  no  air  shall  enter  but  that  which  has  passed  over  the  grate. 
As  the  working-door  is  immediately  below  the  chimney,  the  exter- 


METALLURGY   OF   IRON. 
Fig.  607. 


m 


Fig.  508. 

rial  air  does  not  enter  the  furnace  when  it  is  opened  to  remove  a 
bundle,  but  goes  directly  up  the  chimney.  When  the  bundles 
have  attained  the  temperature  of  a  white  welding-heat,  they  are 
successively  removed,  and  passed  between  the  extension-rollers, 
which  are  much  more  carefully  made  than  those  for  the  puddled 
iron ;  being  exactly  turned,  so  as  to  give  clean  surfaces  and  sharp 
edges  to  the  bars.  They  also  revolve  more  rapidly,  especially  for 
objects  of  small  size,  as  it  is  important  in  this  case  that  the  bars 
should  pass  rapidly,  in  order  that  they  may  retain  sufficient  heat 
until  the  dimensions  required  are  attained. 

§  844.  In  order  to  accelerate  the  process  of  rolling  small  objects, 
three  grooved  cylinders,  placed  one  above  the  other,  are  generally 
used,  the  middle  one  of  which  is  moved  by  the  machinery,  and 
turns  the  others  in  opposite  directions  by  suitable  gearing.  The 
bar  is  first  passed  between  the  first  and  second  cylinders,  when 
the  workman  on  the  other  side  receives  it,  and  immediately  passes 

Vol.  IL— 7 


^8  IRON. 

it  between  the  second  and  third  cylinders,  the  rollers  making  from 
150  to  200  revolutions  per  minute. 

§  845.  In  latter  years  it  has  been  attempted  to  use  the  gases 
escaping  from  the  mouth  of  the  blast-furjiace  as  fuel  for  puddling 
cast-iron.  The  gases  were  drawn  off  by  pipes  placed  a  few  metres 
below  the  tunnel-head,  and  conveyed  into  the  puddling-furnace, 
the  chimney  of  which  was  sufficient,  when  the  furnace  was  in  blast, 
to  produce  the  proper  degree  of  draught.  The  combustible  gases, 
the  current  of  which  was  regulated  at  will,  were  burned  with  a 
proper  quantity  of  atmospheric  air,  and  yielded  a  long  flame  which 
extended  through  the  furnace.  The  temperature  thus  obtained 
was  sufficient  for  puddling,  but  the  process  was  difficult,  the  loss 
being  often  greater  than  in  puddling  with  pit-coal,  and  the  quality 
of  the  iron  being  irregular ;  for  which  reasons,  puddling  with  com- 
bustible gases  taken  from  the  blast-furnace  has  been  nearly  aban- 
doned, despite  its  great  economy  of  fuel.  These  gases  have  been 
more  profitably  used  in  heating  the  boilers  of  the  steam-engines 
which  furnish  the  motive-power ;  but  it  is  then  necessary  to  have 
at  least  one  auxiliary  boiler,  which  can  be  heated  directly  by  coal, 
in  case  the  working  of  the  furnace  should  be  deranged :  this  is  an 
indispensable  precaution  when  the  engine  is  intended  to  drive  the 
blowing-machines,  the  blast  of  which  must  be  increased,  if,  by  any 
accident  in  the  blast-furnace,  a  more  considerable  volume  of  air  is 
required.* 

Manufacture  of  Sheet-iron  and  Tin-plate. 

§  846.  Iron  rolled  out  into  thin  laminae  is  called  sheet-iron.  For 
its  manufacture,  iron  heated  to  redness  is  compressed  several  times 
successively,  either  by  hammers  or  rollers — one  single  operation 
not  being  sufficient  to  reduce  the  sheet  to  the  degree  of  thinness 
required. 

The  hammer  used  for  the  manufacture  of  sheet-iron  resembles 
the  forge-hammer  used  for  forging  bar-iron,  and  weighs  about 
4  cwt.,  the  dimensions  of  its  plane  being  about  13  inches  by  36. 
The  face  of  the  anvil  is  slightly  convex,  and  varies  in  breadth  from 
2  to  4  inches. 

Two  sets  of  cylinders  are  used  for  rolling  sheet-iron — a  roughing 
and  a  finishing  set,  differing  merely  in  the  fact  of  the  cylinders  of  the 
latter  being  turned  with  more  accuracy.  Fig.  509  represents  a  set 
of  rolling  cylinders.  The  cylinder  A  is  moved  by  machinery,  and, 
by  means  of  the  cog-wheels  F,  turns  the  cylinder  A'  in  an  opposite 
direction ;  the  separation  of  the  cylinders  being  regulated  by  the 
screws  a,  a'  which  bind  together  the  pedestals  of  the  upper  cylinder. 

We  shall  not  stop  to  describe  the  process  of  making  sheet-iron 
by  hammering,  as  it  is  fast  disappearing  before  the  improvements 

*  See  the  note  at  page  79.— TF.  L.  F. 


MANUFACTURE    OF    SHEET-IRON.  99 

made  in  rolling.    Hammering  produces  strong  sheet-iron  of  a  good 
quality,  but  rarely  of  uniform  thickness. 


m 


Fig.  509. 

The  iron  used  in  the  manufacture  of  sheet-iron  should  be  soft 
and  malleable ;  iron  made  with  charcoal  being  requisite  for  thin 
sheets  used  in  the  manufacture  of  tin-plate,  and  such  thicker 
plates  which  are  exposed  to  great  resistance,  as  boiler-iron.  The 
thick  plates  are  made  of  puddled  iron,  but  they  are  always  of 
inferior  quality,  unless  the  iron  has  been  subjected  to  several 
puddlings. 

The  iron,  when  wrought  into  flat  bars,  of  a  size  proportioned 
to  that  of  the  sheets  to  be  made,  is  cut  with  shears  into  pieces, 
called  Mdons,  equal  in  length  to  the  intended  width  of  the  sheet, 
while  the  bars,  still  hot,  are  withdrawn  from  the  extension-cylin- 
ders. After  a  quick  reheating  in  a  reverberatory  furnace,  the 
bidons  are  passed  between  the  rollers,  the  length  of  the  bar  being 
parallel  to  the  axis  of  the  rollers,  and  are  thus  passed  3  or  4  times 
between  the  cylinders,  which  are  approximated  to  each  other  every 
time  by  means  of  the  screws  a,  a'  (fig.  509) ;  after  which  the  sheets 
are  heated  in  a  second  furnace,  from  which  any  air  that  might  ox- 
idize their  surface  is  carefully  excluded.  The  reheated  sheets  are 
passed  through  the  finishing-rollers,  which  give  them  the  thickness 
and  dimensions  required,  and  the  plates  of  sheet-iron  obtained  are 
then  freed  from  the  adhering  oxide,  by  being  hammered  with  a 
wooden  mallet.  When  the  sheet-iron  is  required  for  the  manufac- 
ture of  tin-plate,  and  consequently  must  be  made  very  thin,  several 
sheets  are  laid  upon  each  other,  and  after  being  heated  to  a  dull 
red-heat  to  anneal  them,  are  compressed  between  two  plates  by  a 
hydraulic  press,  which  renders  their  surface  perfectly  plane. 

§  847.  Sheet-iron,  on  account  of  its  cheapness  and  great  tenacity, 
is  very  extensively  used,  but  the  readiness  with  which  it  oxidizes  in 
a  moist  atmosphere  would  limit  its  application,  were  not  this  incon- 
venience remedied  by  the  process  of  tinning,  which  is  described  in 
the  following  manner. 

The  sheet-iron  is  first  scraped  perfectly  clean,  by  being  dipped 


100  IRON. 

for  a  few  moments  into  dilute  sulphuric  acid,  and  then  heated  to 
redness  in  a  reverberatorj  furnace ;  and  it  is  then  passed  between 
highly  polished  rollers,  and  allowed  to  remain  for  24  hours  in  a 
fermented  acid  liquid.  Being  taken  out  of  this  liquid,  it  is  plunged 
for  a  few  moments,  first  into  a  dilute  solution  of  sulphuric  and 
chlorohjdric  acids,  then  into  fresh  water,  and  lastly,  it  is  dried  by 
rubbing  it  with  bran.     The  sheets  are  then  ready  for  tinning. 

Several  rectangular  boxes  are  arranged  alongside  of  each  other 
in  the  same  furnace :  a  first  box  A  (fig.  510)  contains  melted 
grease,  in  which  the  sheet-iron  is  left  for  IJ  hour.  The  workman 
then  dips  it  into  the  box  B,  containing  melted  tin,  where  it  remains 
also  IJ  hour.  The  sheets  are  then  put  to  drain  on  an  iron  grat- 
ing, after  which  the  workman  dips  them  into  a  third  box  C  con- 
taining impure  tin,  which  detaches  the  excess  of  tin  remaining  on 
the  sheets  after  their  first  immersion  in  the  melted  metal ;  after 
which  they  are  removed  and  cleaned  with  a  brush.     The  surface 

of  the  sheets  then  retains  only  the  tin 
which  is  incorporated  with  the  iron,  by 
having  formed  a  true  alloy.  Lastly,  the 
workman  plunges  them  into  a  fourth  box 
„.     _-^  D,  containing  very  pure  tin,  which  covers 

^^'       *  them  with  a  brilliant  coating ;  and  after- 

ward he  places  them  in  a  fifth  box  E,  containing  melted  tallow,  which 
causes  the  surplus  of  tin  to  run  ofi"  and  collect  in  a  small  ball  to- 
ward the  lower  edge  of  the  sheet.  It  suffices  to  immerse  this  edge, 
for  a  few  moments,  in  a  sixth  box  F,  containing  melted  tin  to  a  few 
centimetres  in  depth,  to  detach  the  little  ball. 

§  848.  The  surface  of  the  tin  covering  sheet-iron  is  frequently 
perfectly  smooth  and  brilliant,  while  its  internal  texture  is  crystal- 
line, which  can  be  shown  by  dissolving  the  superficial  layer  by  an 
acid ;  when  the  surface  of  the  sheets  becomes  watered,  and  often 
presents  a  beautiful  appearance  in  reflected  light.  The  acid  liquid 
used  for  producing  this  metallic  watering  is  a  kind  of  aqua  regia, 
made  of 

2  parts  of  chlorohydric  acid, 
1      "of  nitric  acid, 

3  "     of  water. 

The  patches  in  the  watering  vary  in  size  according  to  the  slowness 
of  cooling  of  the  tin,  the  appearance  of  which  can,  however,  be 
altered  at  will.  By  passing  a  hot  soldering-iron  over  the  reverse 
of  the  watered  surface,  the  tin  is  again  melted,  but  solidifies  as 
soon  as  the  hot  iron  is  removed,  thus  causing  a  new  crystallization ; 
but  as  it  takes  place  much  more  rapidly  than  the  first  crystalliza- 
tion, a  finer  watering  results,  which  forms  figures  in  the  original 
watering.  The  watered  tin-plates  should  be  immediately  coated 
with  a  transparent  varnish,  which  may  be  of  difi'erent  colours,  to 


MANUFACTURE   OF  IRON-WIRE. 


101 


prevent  their  tarnishing  in  the  air,  which  would  soon  take  place 
without  this  precaution.* 

Manufacture  of  Iron-wire,  or  Wire-drawing. 

§  849.  Very  tenacious  and  ductile  iron  alone  can  be  used  for  the 
manufacture  of  wire,  unless  steel  is  to  be  employed.  The  process 
of  wire-drawing  is  very  simple,  consisting  merely 'in  passing  iron 
rods  through  perforations  in  a  steel  plate,  called  a  wire-plate,  which 
are  perfectly  round,  their  diameters  decreasing  as  the  wire  is  ex- 
tended. 

Formerly,  thick  iron-wire  was  made  by  drawing  the  iron  rod, 
the  end  of  which  was  seized  with  a  pincers,  through  the  wire-plate, 
by  means  of  machinery ;  but  it  was  mashed  wherever  it  had  been 
grasped  by  the  pincers. 

In  the  more  modern  processes,  the  iron  is  first  wrought  into  rods 
of  from  J  to  J  inch  in  diameter,  generally  by  heating  square  bars 
of  iron,  rolled  in  ordinary  rollers  and  cut  into  lengths  of  from  1 J  to 
3  feet,  to  whiteness  in  a  reheating  furnace,  and  then  passing  them 
through  the  rollers  described  §  844,  which  revolve  about  250  times 
per  minute.  The  first  groove  of  the  cylinders  is  oval,  while  the 
remainder  are  circular.  The  iron  bar,  which  passes  in  less  than  a 
minute  through  10  of  these  grooves,  and  comes  out  in  the  shape 
of  a  round  rod  of  J  to  J  inch  in  diameter,  is,  after  cooling,  coiled 
into  a  circle,  and  then  heated  to  a  dull  red-heat  in  a  furnace,  to 
give  it  all  the  malleability  possible  by  suitable  annealing.  It  is 
then  rolled  on  the  bobbin  FG  (fig.  511)  of  the  drawing-bench,  the 


Fig.  511. 

free  end  of  the  wire  being  pointed,  ana  passed  through  the  first 
hole  of  the  wire-plate  AB.  A  second  cast-iron  bobbin  C,  slightly 
conical,  is  furnished  with  a  small  chain  and  pincers,  which  seizes  the 
iron-wire  as  it  leaves  the  wire-plate,  and  obliges  it  to  wind  around 

*  The  described  process  of  watering  tin-plate  is  called  yopawnm^. —  W.  L.  F. 


102 


IRON. 


the  bobbin  C,  which  is  turned  by  bevelled  wheels  pr,  pq^  of  which 
the  axis  ah  is  moved  by  machinery,  while  a  click  and  spring-work  i 
(fig.  512)  enables  it  to  be  adjusted  to,  or  de- 
tached from,  the  vertical  shaft  mn.  The  wire- 
plate  is  moved  vertically  in  the  gallows  D,  so 
that  the  wire  may  have  always  the  proper  di- 
rection. When  the  wire  has  passed  through 
the  first  hole,  it  is  again  wound  around  the 
bobbin  FG,  and  its  pointed  extremity  inserted 
^^  into  the  second  hole  of  the  wire-plate  having 
a  smaller  diameter,  and  so  on,  until  the  wire 
is  of  the  size  required.  But,  in  consequence 
of  the  repeated  drawing,  the  wire  becomes 
very  brittle,  and  would  infallibly  break,  were 
it  not  annealed  from  time  to  time  ;  for  which 
reason  it  is  now  and  then  detached  from  the 
bobbin  in  the  form  of  a  roll,  placed  in  a  cir- 
cular cast-iron  box,  hermetically  sealed,  heated 
to  a  dull  red-heat  in  a  furnace,  and  then 


Fig.  512. 


allowed  to  cool  slowly. 

Manufacture  of  SteeL 

§  850.  The  manufacture  of  steel  may  be  conducted  by  two  oppo- 
site processes :  either  by  partially  decarbonizing  very  pure  cast-iron, 
or  by  combining  wrought-iron  with  a  certain  quantity  of  carbon 
by  the  process  of  cementation,  that  is  by  heating  bars  of  iron,  for 
a  long  time,  in  contact  with  charcoal.  The  steel  obtained  by  the 
partial  refining  of  cast-iron  is  called  native,  or  forge-steel,  while 
that  prepared  by  cementation  bears  the  name  of  bar  or  blistered 
steel.  To  render  both  native  and  bar  steel  homogeneous,  the  bars 
are  generally  broken  into  pieces,  made  into  bundles,  and  heated  to  a 
white  welding-heat,  to  be  again  forged  into  bars,  either  by  the  ham- 
mer or  the  extension-cylinders.  These  operations  are,  frequently, 
repeated  several  times,  and  the  steel  resulting  is  called  refined  steel, 
or  shear-steel ;  while  steel  rendered  homogeneous  by  heating  it  to 
the  fusing  point  in  earthen  crucibles  bears  the  name  of  cast-steel, 
and  possesses  entirely  peculiar  properties. 

Steel  differs  from  wrought-iron  chiefly  in  the  peculiarities  it 
acquires  by  tempering,  that  is,  by  suddenly  plunging  it  when  hot 
into  cold  water,  which  operation  renders  it  very  hard  and  brittle, 
while  the  properties  of  malleable  iron  are  not  sensibly  altered  by  a 
similar  process.  The  iron  which  hardens  most  by  tempering  is  the 
steelg  kind,  and  is  most  esteemed  for  certain  purposes. 

§  851.  Steely  iron  is  often  endeavoured  to  be  manufactured  by 
the  metallurgic  treatment  of  ores  according  to  the  Catalan  method 
(§  808).  The  workman  then  lessens  the  quantity  of  greillade  which 
he  generally  adds  during  the  operation,  hastens  the  fusion  of  the 


STEEL.  108 

ore,  frequently  cleans  away  the  scoriae,  in  order  to  diminish  their 
decarbonizing  action  on  the  metal,  and  keeps  the  bloom  covered 
with  hot  coals,  to  protect  it  against  the  action  of  the  current  of  air. 
He  knows,  moreover,  by  the  physical  characters  of  the  bloom,  when 
to  stop  the  operation.  The  blooms  are  drawn  as  usual,  but  the 
bars,  still  hot,  are  plunged  into  cold  water,  by  which  the  steely 
parts  become  very  brittle,  and  are  easily  hammered  off.  Steely 
iron  is  chiefly  used  for  agricultural  implements,  such  as  plough- 
shares, scythes,  etc. 

§  852.  Native,  or  forge  steel,  which  can  be  made  only  from  very 
pure  cast-iron,  is  extensively  manufactured  in  Germany,  principally 
at  Siegen,*  in  Styria,  and  in  Silesia.  The  brilliant  laminated  cast- 
iron  yielded  by  the  manganiferous  sparry  ores  in  charcoal  furnaces 
is  generally  used,  and  is  refined  in  a  small  furnace  resembling 
that  for  the  refinery  of  cast-iron  made  with  charcoal.  The  hearth 
being  filled  with  burning  coals,  6  or  7  plates  of  laminated  cast-iron, 
arranged  vertically  in  the  furnace,  are  successively  melted  in  it, 
under  the  influence  of  a  strong  blast ;  a  certain  quantity  of  rich 
scoriae  and  scraps  of  iron  being  added  at  the  commencement  of  the 
operation.  When  the  first  plate  has  fallen  to  the  bottom  of  the 
hearth  the  material  is  at  first  perfectly  liquid,  but  the  oxidizing 
action  of  the  scoriae,  very  soon  depriving  it  of  sufiicient  carbon  to 
destroy  its  fluidity,  renders  it  doughy.  The  second  plate  is  then 
fused,  which,  falling  to  the  bottom  of  the  hearth,  liquefies  the  whole 
mass.  Under  the  oxidizing  action  of  the  air  and  the  scoriae,  the 
material  again  loses  its  fluidity  by  parting  with  a  portion  of  its 
carbon,  and  then  a  third  plate  is  added,  and  melted  in  the  same 
manner  as  the  first,  but  so  that  the  liquid  drops  shall  fall  into  the 
centre  of  the  doughy  mass  at  the  bottom  of  the  hearth.  This  time 
the  mass  does  not  liquefy  entirely,  the  central  parts  alone  becoming 
fluid.  The  process  is  continued  in  this  manner  until  6  or  7  plates 
are  melted,  making  a  weight  of  from  3  to  4  cwt. ;  the  scoriae  are  then 
removed,  and  the  bloom  is  withdrawn  and  divided  into  7  or  8  wedge- 
shaped  pieces,  the  composition  of  each  of  which  is  similar,  while  they 
still  are  far  from  being  homogeneous  in  all  their  parts,  as  there  exists 
a  great  difi'erence  between  the  centre  and  the  circumference  of  the 
mass.  They  are  hammered  out  and  converted  into  bars  of  about  2 
inches  square,  during  the  fusion  of  the  cast-iron  in  a  second  opera- 
tion, and  are  plunged,  while  still  hot,  into  cold  water  to  temper  them, 
and  then  handed  to  the  refiners.  During  this  incomplete  refinery 
of  the  cast-iron,  the  consumption  of  charcoal  is  very  considerable, 
and  reaches  846  cubic  feet  of  charcoal  for  every  ton  of  crude  steel. 

§  853.  Bars  of  crude  steel  vary  very  much  in  difl'erent  parts  of 
their  length,  as  one  of  the  ends  is  always  more  carburetted  than 

*  The  steel  manufactured  at  Lohe,  near  Siegen,  is  thought  to  be  the  best  article 
of  the  kind:  the  ore  employed  is  the  manganiferous  sparry  iron  of  the  celebrated 
iron  mountain  (Stahlberg)  at  Muesen. —  W.  L.  F. 


104  IRON. 

the  other.  The  refiner,  holding  the  bar  by  its  less  carburetted  end, 
strikes  it  across  an  anvil,  thus  causing  the  harder  portion  instantly 
to  break  oiF;  by  striking  still  harder,  he  eiFects  the  separation  of 
a  second  portion,  less  steely  than  the  first,  and  a  bar  of  steely  iron 
remains  in  his  hand,  which  he  cannot  break  by  a  blow,  and  which 
he  sets  aside  to  be  used  for  sharp  agricultural  implements.  The  por- 
tions detached  by  the  blow,  destined  for  the  manufacture  of  steel  of 
superior  quality,  are  sorted  according  to  the  appearance  of  their 
grain,  and  are  rendered  more  homogeneous  by  several  successive  pro- 
cesses of  refining.  The  workman  lays  a  bar  of  hard  steel  on  one  of 
softer  steel,  melts  the  whole  at  a  white  welding-heat,  and  transforms 
it  under  the  hammer  into  a  flat  bar,  which  he  immediately  tempers. 
These  flat  bars  are  again  broken  into  pieces  and  tied  in  bundles, 
taking  care  always  to  place  a  hard  and  soft  bar  together,  by  which 
successive  operations  the  material  becomes  more  and  more  homo- 
geneous, but  the  waste  and  consumption  of  fuel  is  rapidly  increased. 
The  material  also  loses  more  and  more  of  its  carbon  during  the 
reheatings,  and  would  be  converted  into  pure  iron  if  the  bundles 
were  not  covered  with  a  coating  of  pure  clay,  which,  melting  by 
the  assistance  of  a  small  quantity  of  oxide  of  iron,  preserves  the 
material  from  the  direct  contact  of  the  air. 

§  854.  Bar  or  blistered  steel  is  prepared  by  heating  thin  bars  of 
iron  for  a  length  of  time  in  contact  with  charcoal  at  a  high  tem- 
perature, always,  however,  below  the  point  of  fusion  ;  when  the 
carbon,  first  combining  with  the  iron  of  the  surface,  soon  penetrates 
it  and  unites  successively  with  the  various  layers.  It  is  evident 
that  a  homogeneous  cementation  cannot  take  place  throughout  the 
whole  thickness  of  the  bars,  as  the  external  parts  have  already 
become  steel  while  the  inside  is  still  in  the  state  of  wrought-iron, 
and  are  converted  into  hard  steel  when  the  inside  has  just  com- 
menced to  become  soft  steel ;  and  lastly,  the  former  approach  the 
composition  of  cast-iron  when  the  central  portions  are  hard  steel. 
The  cementation  of  iron  is  efi'ected  in  large  rectangular  boxes  C 
(fig.  513),  made  of  refractory  bricks,  in  an  arched  oven  M,  the 


Fig.  513. 


STEEL.  105 

hearth  of  which  is  at  F.  The  flame  and  smoke  escape  through 
small  vent-holes  o,  o  into  the  chimney  V.  The  boxes,  resting  on 
small  bridges  of  brick,  and  surrounded  by  vacant  spaces  through 
■which  the  flame  circulates,  are  from  7J  to  15  feet  in  length,  from 
2J  to  3  feet  in  width,  and  as  much  in  height.  Wood  or  pit-coal  is 
burned  on  the  grate. 

The  cement  is  made  of  powdered  charcoal,  to  which  J^  of  its 
weight  of  ashes  and  a  little  sea-salt  are  frequently  added.  The  part 
played  by  these  two  substances  in  the  process  of  cementation  has 
not  been  yet  explained.  In  order  to  charge  a  cementation-box,  a 
layer  of  cement  to  the  depth  of  about  2  inches  is  first  spread  in  it, 
and  on  this  a  layer  of  iron  bars  is  arranged  edgewise,  so  as  to  leave 
between  them  a  space  of  somewhat  less  than  a  J  inch.  The  bars 
are  not  quite  so  long  as  the  box,  so  as  to  allow  room  for  free  ex- 
pansion :  a  section  of  them  is  a  rectangle  of  about  1\  to  2  inches 
by  J  to  J  inch.  Between  and  above  the  bars  a  layer  of  cement 
about  J  inch  in  thickness  is  placed,  then  a  second  layer  of  bars, 
and  so  on,  until  the  box  is  filled  to  within  about  6  inches  of  the 
top.  It  is  then  closed  hermetically  with  refractory  bricks,  or  better 
still,  with  a  layer  of  quartzose  sand.  The  two  boxes  of  a  furnace 
contain  from  10  to  20  tons  of  iron,  according  to  their  size. 

Each  box  has  several  openings  corresponding  to  working-holes 
in  the  wall  of  the  furnace,  through  which  some  of  the  bars  can  occa- 
sionally be  withdrawn  to  estimate  the  progress  of  the  operation  by 
iheir  appearance.  The  proper  temperature,  which  is  nearly  that 
of  the  fusing  point  of  copper,  is  attained  in  24  hours,  and  kept  up 
for  7  or  8  days.  Cementation  advances  more  rapidly  at  a  higher 
temperature,  but  in  that  case  the  products  are  still  less  homogene- 
ous. When  the  cementation  is  supposed  to  be  completed,  the  fur- 
nace is  allowed  to  cool  for  several  days  before  being  emptied,  when 
the  surface  of  the  bars  is  covered  with  small  bubbles,  or  blisters, 
from  which  circumstance  the  steel  has  received  the  name  of  blistered 
steel.  This  steel  can  be  used  only  after  having  been  made  more 
homogeneous  by  fagoting  or  by  fusion.  About  50  lbs.  of  pit-coal 
are  used  for  2  cwt.  of  crude  steel. 

Bar-steel  is  refined  nearly  in  the  same  way  as  bar-iron.  Bundles, 
made  of  several  bars,  sorted  by  placing  the  hard  on  the  softer  bars, 
are  heated  in  small  blast-furnaces  fed  with  pit- coal,  and  then  new 
bars  are  made  of  them,  either  by  hammering  or  rolling,  which  are 
tempered  and  then  broken  into  several  pieces.  Other  bundles  are 
made  of  the  fragments,  and  they  are  again  forged.  The  fagoting 
is  repeated  once,  or  several  times,  according  to  the  quality  of  steel 
to  be  manufactured,  as  the  steel  becomes  softer  at  each  fagoting 
by  losing  a  portion  of  its  carbon. 

§  855.  Iron  or  steel  articles,  when  finished,  are  sometimes  sub- 
jected to  cementation,  by  an  operation  called  case-hardening,  in 
order  to  harden  their  surface.     The  articles,  arranged  in  layers 


106 


IRON. 


with  cement,  in  sheet-iron  boxes,  are  heated  to  a  high  temperature 
in  boxes  surrounded  by  hot  walls,  which  are  renewed  until  the  pro- 
cess is  judged  to  be  completed,  which  is  known  by  pieces  of  iron- 
wire,  penetrating  the  boxes  and  removable  at  pleasure.  The  ce- 
mented articles  are  tempered  by  immersion  in  cold  water.  Steel 
objects,  of  which  the  surface  has  been  softened  so  that  they  might 
be  more  easily  wrought,  are  often  case-hardened.  In  order  to 
soften  the  surface  of  a  steel  object,  it  is  heated  in  a  heap  of  iron 
filings,  and  then  allowed  to  cool  slowly. 

§856.  Steel  acquires  a  perfectly  homogeneous  character  only  by 

fusion,  and  then  takes  the  name  of  cast- 
steel.  The  fusion  is  effected  in  fire-clay 
crucibles,  in  a  common  furnace,  consist- 
ing of  a  small  rectangular  chamber  A 
(fig.  514),  of  3  feet  in  depth,  and  of 
which  a  horizontal  section  is  1 J  by  1 J 
feet.  The  chamber  is  lined  with  an 
infusible  quartzose  grit,  and  communi- 
cates with  the  chimney  C  by  a  hori- 
zontal throat  B,  the  draught  being  re- 
gulated by  a  register  r  in  the  chimney. 
The  upper  part  of  the  furnace  is  open, 
to  allow  the  introduction  of  the  cru- 
cible and  the  fuel,  but  the  opening  is 
covered  by  a  lid  made  of  refractory 
grit,  or  fire-bricks  held  together  in  an 
iron  frame.  Several  of  these  melting- 
furnaces  are  generally  arranged  along- 


Fig.  514. 

side  of  each  other,  while  their  chimneys  are  united  in  the  same 

stack. 

The  crucibles,  a  vertical  section  of  one  of  which  is  seen  in  fig. 

515,  are  made  of  very  refractory  clay.  One  of  the  crucibles  is 
placed  in  the  furnace,  covered  with  burning  pit-coal,  and 
the  furnace  is  then  filled  with  coke,  merely  to  heat  the  sides 
of  the  furnace,  the  chimney,  and  the  crucible.  Thirty 
pounds  of  cemented  steel,  broken  into  pieces,  are  then  in- 
troduced into  the  crucible,  which  is  covered  with  its  lid  A, 
and  the  temperature  is  rapidly  elevated.  The  fusion  of  the 
steel  generally  requires  4  hours,  after  which  the  crucible  is 
removed,  the  lid  taken  off,  and  the  fused  steel  poured  into 
cast-iron  ingot-moulds.     The  crucible   is  immediately  re- 

Fig.  615.  placed  in  the  furnace,  and  a  new  charge  introduced  for  a 

second  fusion,  which,  however,  requires  only  3  hours.     The  same 

crucible  may  serve  for  a  third  melting,  but  is  afterward  rejected  as 

useless. 

A  cast-steel  of  very  superior  quality,  and  known  by  the  name 
Wootz,  has  long  been  manufactured  in  India.     It  is  made  in  small 


STEEL.  107 

pieces,  weighing  at  most  from  2  to  4  lbs.,  bj  heating  iron  at  a  very 
high  temperature  in  contact  with  certain  vegetables  which  are  car- 
bonized hy  heat. 

Steel  remarkable  for  its  great  hardness  is  obtained  by  fusing 
ordinary  steel  with  very  small  proportions  of  certain  metals,  such 
as  silver  and  platinum. 

§857.  Steel,  heated  to  a  very  high  temperature,  and  then  al- 
lowed to  cool  slowly,  becomes  as  soft  as  cast-iron,  and  can  be  cut 
with  a  file,  or  turned  in  a  lathe,  but  on  being  heated  to  redness  and 
then  suddenly  cooled  by  dipping  it  into  cold  water,  is  rendered  very 
hard  and  brittle.  The  steel,  which  is  less  dense  than  annealed 
steel,  is  then  said  to  be  tempered.  By  heating  it  again  to  redness 
and  allowing  it  to  cool  slowly,  it  regains  its  original  malleability. 

Steel  objects  are  first  made  of  annealed  steel,  with  the  hammer, 
file,  or  lathe,  and  the  proper  degree  of  hardness  is  then  given  by 
tempering ;  but  as  they  generally  become  too  hard  and  brittle  by 
this  process,  they  must  be  again  heated  to  bring  them  to  a  proper 
degree  of  softness.  The  great  skill  of  the  workman  consists  in 
knowing  the  exact  moment  of  the  completion  of  the  annealing,  in 
which  he  is  guided  by  the  often  very  brilliant  colours  displayed  on 
the  surface  of  the  metal  during  the  annealing,  and  which  corre- 
spond exactly  to  certain  temperatures.  The  colours  are  produced 
by  thin  pellicles  of  oxide  reflecting  various  colours  according  to 
their  thickness :  in  a  word,  the  cause  of  this  phenomenon  is  the 
same  as  that  which  produces  the  beautiful  iridescence  of  a  soap- 
bubble. 

Tempered  steel,  reheated  at  220°  produces  a  straw-yellow  colour. 

"  golden-yellow 


240° 

255° 

265° 

285° 

295° 

315° 

u 

brown  " 

purple 
bright  blue 
indigo-blue 
very  deep  blue 


The  reheating  is  carried  to  the  production  of  any  particular  colour, 
according  to  the  quality  of  the  steel  and  the  nature  of  the  object. 

Many  cutting  instruments  are  made  by  forging  together  bars  of 
steel  and  soft  iron,  by  which  proceeding  they  are  rendered  less 
brittle,  but  also  less  hard,  than  those  of  pure  steel.  Gun-barrels 
are  usually  made  in  this  manner. 

When  the  surface  of  an  object  made  of  non-homogeneous  steel 
is  attacked  by  a  feeble  acid,  the  heterogeneous  structure  of  the 
material  is  evinced,  and  difi"erent  agreeable  designs  result,  which 
vary  according  to  the  process  adopted.  The  steel  is  then  said  to 
be  damasked.  When  the  steel  is  combined  with  small  quantities 
of  foreign  metals,  which  are  irregularly  scattered  through  its  sub- 
stance, the  efi'ect  of  the  figuring  becomes  very  beautiful. 


108  IRON. 

TESTING  OF  IRON-ORES. 

§  858.  The  richness  of  an  iron-ore  may  be  ascertained,  either  by 
the  dry  or  the  humid  way.  Testing  by  the  dry  way  is  an  imita- 
tion in  miniature  of  the  blast-furnace,  and  yields  the  same  pro- 
ducts, viz.  cast-iron  and  slag,  and  has  the  advantage  of  allowing 
the  operator  to  judge,  by  the  small  lump  obtained  in  the  assay, 
of  the  quality  of  cast-iron  which  the  ore  would  produce  in  the 
blast-furnace. 

Nevertheless,  before  making  the  assay  in  the  dry  way,  some  pre- 
liminary experiments  in  the  humid  way  are  generally  performed, 
as  they  more  clearly  determine  the  nature  of  the  ore,  and  show  the 
quantity  of  flux  necessary  to  be  added  to  obtain  a  good  smelting. 

We  shall  divide  the  ores,  which  it  may  be  necessary  to  assay, 
into  four  classes :  1st.  Those  ores  which  contain  iron  in  the  state 
of  hydrated  sesquioxide  ;  2d.  Ores  formed  by  anhydrous  sesqui- 
oxide ;  3d.  Ores  of  magnetic  oxide  of  iron  ;  4th.  Sparry  ores,  that 
is,  those  formed  by  protocarbonate  of  iron. 

1.  The  ores  of  the  first  class,  which  are  much  the  most  abun- 
dant in  France,  are  tested  in  the  following  manner : 

Ten  grammes  of  the  ore  are  first  calcined  to  redness  in  a  plati- 
num crucible,  to  disengage  water  and  carbonic  acid.  Let  p  be  the 
weight  of  the  calcined  substance,  then  will  (10—^)  represent  the 
weight  of  the  water  and  carbonic  acid. 

Ten  other  grammes  of  finely  powdered  ore  are  then  treated  with 
very  weak  nitric  acid,  which  dissolves  only  the  carbonates  of  lime 
and  magnesia  which  may  be  in  the  gangue.  (If  none  existed,  there 
would  be  no  eff'ervescence,  and  the  use  of  the  weak  nitric  acid 
would  be  superfluous.)  When  the  efiervescence  has  ceased,  even 
after  the  addition  of  a  fresh  quantity  of  acid,  the  residue  is  col- 
lected on  a  small  filter,  washed  with  a  little  water,  and  calcined  in 
a  platinum  crucible.  If  p'  be  the  weight  of  this  residue,  (10— p') 
will  represent  the  weight  of  the  water,  carbonic  acid,  and  lime 
contained  in  the  ore ;  and  consequently,  {p—'p')  will  be  the  weight 
of  the  lime. 

Lastly,  10  gm.  of  powdered  ore  are  attacked  with  concentrated 
chlorohydric  acid,  and  the  solution  boiled  until  the  residue  has  en- 
tirely lost  its  colour.  The  quartz  and  clay,  which  alone  remain 
as  a  residue,  are  collected  on  a  filter  and  weighed  after  calcination. 
Their  weight  being  represented  by  p'',  we  shall  have  for  the  compo- 
sition of  the  ore,  by  collecting  the  results  of  all  these  operations  : 

Water  and  carbonic  acid {10— p) 

Lime iP'^P') 

Quartz  and  clay p^' 

Oxides  of  iron  and  manga- 
nese, (difi'erentially) 10— (10— p)--(^— y)— y«(y— y). 

If  the  ore  contains  only  a  small  quantity  of  manganese,  which  is 


TESTING   OF   IRON-ORES. 


109 


easily  recognised  by  the  ochreous  colour  of  its  powder,  the  weight 
{p'—p")  will  represent  pretty  exactly  the  weight  of  the  anhydrous 
sesquioxide  of  iron  in  the  ore,  and,  consequently,  ^  [p'—p")  will 
be  the  weight  of  the  metallic  iron. 

It  is  more  easy  to  make  the  assay  by  the  dry  way,  under  the  most 
favourable  conditions.  Experiment  has  shown  that  the  cast-iron 
most  readily  separates,  and  a  well-fused  slag,  nearly  entirely  free 
from  oxide  of  iron,  is  obtained  when  the  gangue  is  composed  of  clay 
and  carbonate  of  lime,  in  such  proportions  that  the  latter 
should  be  two-thirds  of  the  clay.  An  addition  of  chalk  or 
kaolin  to  10  gm.  of  powdered  ore  is  then  made,  until  the 
mixture  resembles  the  composition  just  indicated  ;  which, 
after  being  well  ground  in  an  agate  mortar,  is  introduced 
into  the  cavity  abc  of  a  crucible  covered  with  damp  char- 
coal* (fig.  516).  The  ore  is  inserted  in  a  heap  m  into 
the  cavity  made  with  a  glass  rod,  and  the  crucible  is 
filled  with  damp  charcoal.  The  lid  is  luted  with  clay, 
and  the  crucible  itself,  being  set  on  fire-bricks,  or  pieces  of  burnt 

earth,  and  secured  with  clay,  is  heated 
in  an  air-furnace,  or  in  a  forge.  Fi- 
gure 517  represents  the  construction 
of  an  air-furnace  very  suitable  for  test- 
ing iron-ores  ;  it  resembles  the  furnace 
for  melting  steel  (§  856),  but  is  smaller. 
Four  crucibles  may  be  arranged  in  this 
furnace,  and  4  tests  made  at  once.  Tlie 
fuel  used  is  a  mixture  of  equal  parts  of 
charcoal  and  coke,  taking  care  to  raise 
the  temperature  gradually,  so  that  the 
crucibles  may  dry  slowly,  while  the 
register  r  regulates  the  draught.  Dur- 
ing the  last  quarter  of  an  hour  the 
temperature  is  raised  as  high  as  pos- 
sible. The  operation  lasts  in  all  an 
hour  and  a  quarter,  after  which  the 
crucibles  are  removed  and  allowed  to 

*  The  preparation  of  a  "brasqued"  crucible  requires  some  precautions,  whicli 
it  may  be  worth  while  to  indicate.  "  Brasque"  is  composed  of  Charcoal,  powdered 
and  sifted,  moistened  with  water  so  as  to  give  it  a  certain  degree  of  consistency, 
and  introduced  into  a  crucible  of  refractory  clay,  into  which  it  is  rammed  with  a 
wooden  stamper.  This  requires  several  additions  of  the  material,  as  it  becomes 
compressed  by  pounding.  Before  adding  a  new  layer,  the  surface  of  the  preceding 
must  be  made  rough,  as  otherwise  it  would  not  incorporate  itself  with  the  succeed- 
ing stratum,  and  the  two  layers  might  separate  during  the  heating,  causing  cracks 
to  form,  through  which  the  liquid  substances  might  escape. 

When  the  crucible  is  filled  and  the  charcoal  well^heaped  in,  a  part  of  the 
"brasque"  is  removed  with  a  knife,  so  as  to  form  a  rounded  cavity  abc  (fig.  516), 
the  material  taken  from  which  is  heaped  along  the  sides  of  the  crucible ;  and  the 
surfaces  are  then  rubbed  smooth  with  a  strong  glass  rod. 


m» 


IRON. 


cool.  The  fused  lump  taken  from  the  bottom  of  the  crucible  is 
composed  of  a  button  of  cast-iron,  surmounted  by  slag,  both  of 
which  are  weighed  together.  The  slag  is  then  broken  off  and 
pounded  to  pieces,  to  ascertain  that  it  contains  no  metallic  globules, 
and  the  button  and  globules  are  weighed. 

It  is  proper  to  remark  that  as  the  metal  weighed  is  in  the  state 
of  cast-iron,  that  is,  combined  with  a  certain  quantity  of  carbon, 
its  weight  is  consequently  rather  too  great;  but  at  the  same  time 
this  excess  of  weight  nearly  compensates  for  the  small  quantity 
of  iron  which  always  remains  in  the  state  of  oxide  in  the  slag. 

Instead  of  the  air-furnace  of  fig.  517,  which  is  found  only  in 
laboratories  where  such  tests  are  made  in  quantity,  an  ordinary 
blacksmith's  forge  may  be  used,  when  a  sort  of  hearth  can  con- 
veniently be  made  with  refractory  bricks,  in  the  midst  of  which 
the  crucible  is  to  be  placed. 

Pig.  518  represents  a  small  portable  furnace,  which  may  be  con- 
structed without  much  expense,  and  is  well 
adapted  for  testing  iron-ores.  It  is  made 
of  two  large  refractory  crucibles  ABcd^ 
ABEF,  the  upper  one  of  which,  forming  the 
lid,  has  a  large  opening  0,  through  which 
the  fuel  is  charged  and  the  air  escapes, 
while  the  lower  crucible  has  three  holes 
0,  o\  o"^  and  its  bottom  rests  on  a  cup  U 
of  baked  clay,  into  which  the  nozzle  a  of  a 
bellows  enters.  The  small  "brasqued"  cru- 
cible is,  in  order  to  place  it  in  the  middle 
of  the  furnace,  set  on  several  pieces  of 
brick  placed  on  each  other,  to  the  upper  one 
of  which  it  is  luted  with  clay.  The  fuel 
Fig.  518.  used  is  charcoal  or  a  mixture  of  charcoal 

and  coke. 

2.  When  the  ore  consists  of  anhydrous  peroxide  of  iron,  the 
proportion  of  siliceous  gangue  can  no  longer  be  determined  by 
acting  on  it  with  chlorohydric  acid,  because  the  native  peroxide  is 
unaffected  by  this  acid,  and  the  latter  therefore  dissolves  only  the 
carbonate  of  lime,  which  may  be  thus  determined: — In  order  to 
make  the  assay  in  the  furnace,  J  of  its  weight  of  a  fusible  silicate, 
white  glass,  for  example,  is  mixed  with  the  ore,  in  order  to  prevent 
the  too  siliceous  scoriae  from  retaining  oxide  of  iron.  If  this 
should  nevertheless  take  place,  which  would  be  known  by  the 
deep  green  colour  of  the  slag,  the  test  must  be  repeated,  but  with 
an  increased  proportion  of  carbonate  of  lime,  or  with  less  glass 
than  before. 

3.  As  even  the  most  concentrated  acids  act  with  difficulty  on 
native  magnetic  iron,  the  proportion  of  quartzose  gangue  by  which 
such  ores  are  accompanied  cannot  be  determined  by  chlorohydric 


TESTING    OF   IRON-ORES.  Ill 

acid,  and  the  assay  must  be  made  as  in  the  preceding  case,  that 
is,  the  ore  must  be  immediately  fused  in  a  forge-fire  with  an  ad- 
mixture of  white  glass  and  carbonate  of  lime. 

4.  Although  the  native  protocarbonate  of  iron  is  converted  by 
calcination  into  magnetic  oxide,  the  loss  of  weight  which  sparry 
ores  suifer  by  heat  does  not  exactly  represent  the  weight  of  the 
disengaged  water  and  carbonic  acid,  because  the  protoxide  of  iron 
absorbs  a  portion  of  the  oxygen  of  the  carbonic  acid  which  it 
decomposes.  By  treating  the  ore  with  weak  nitric  acid,  the  car- 
bonate of  lime  is  dissolved ;  but  a  certain  quantity  of  iron  being 
dissolved  at  the  same  time,  the  lime  cannot  be  determined  as  in 
the  first  case,  and  it  becomes  necessary  to  act  on  the  ore  with  con- 
centrated boiling  chlorohydric  acid,  in  order  to  convert  the  iron 
into  sesquioxide.  The  solution  is  evaporated  to  dryness  at  a  gentle 
heat  to  drive  oiF  the  excess  of  acid,  and  treated  with  water,  which 
leaves  the  quartzose  and  argillaceous  gangue  undissolved  ;  after 
which  the  sesquioxide  of  iron,  the  protoxide  of  manganese,  and  the 
lime  are  then  successively  separated  in  the  liquid  by  the  processes 
described  §  803. 

§  859.  When  the  oxide  of  iron  readily  dissolves  in  acids,  the 
quantity  of  iron  existing  in  an  ore  can  be  exactly  and  rapidly 
determined  by  boiling  3  grammes  of  the  finely  powdered  ore  with 
chlorohydric  acid,  until  the  solution  loses  its  colour,  evaporating 
to  drive  oiF  the  excess  of  acid,  and  treating  the  residue  with 
water.  The  latter,  which  consists  of  the  quartzose  and  argillaceous 
gangue,  is  collected  on  a  filter  and  weighed.  A  standard  solution 
of  permanganate  of  potassa  is  then  poured  into  the  liquid,  using 
the  precautions  indicated  (§  804),  until  the  liquid  assumes  a  perma- 
nent rose-colour,  and  the  quantity  of  metallic  iron  existing  in  the 
3  grammes  of  ore  is  determined  from  the  quantity  of  permanganate 
of  potassa  used. 

If  the  ore  be  specular  iron,  or  magnetic  oxide,  it  can  only  be 
acted  on  by  chlorohydric  acid,  after  being  heated  to  a  high  red- 
heat  in  a  platinum  crucible,  with  3  or  4  times  its  weight  of  car- 
bonate of  soda,  or  bisulphate  of  potassa.  The  peroxide  of  iron,  in 
this  way,  becomes  disaggregated  and  easier  soluble  in  chlorohydric 
acid. 

ANALYSIS  OE  CAST-IRON  AND  STEEL. 

§  860.  Cast-iron  is  a  compound  of  carbon  with  iron,  frequently 
containing,  in  addition,  a  certain  quantity  of  silicium,  sulphur, 
phosphorus,  and  manganese.  We  shall  proceed  to  describe  the 
mode  of  successively  determining  these  several  elements. 


112  IRON. 


Determination  of  Carbon, 

§  861.  Gray  cast-iron  can  be  easily  filed,  while  white  cast-iron 
and  fine  metal  are,  on  the  contrary,  very  hard,  but  when  the  file 
will  not  cut  them,  they  can  be  pounded  in  a  mortar.  Fig.  519 
represents  a  small  apparatus  of  cast-steel,  in  which 
the  pulverization  can  be  easily  effected.  It  is  com- 
posed of  a  steel  receiver  ahcd^  to  which  is  fitted  a 
cylinder  efgh^  exactly  filled  by  a  steel  piston  P.  Some 
pieces  of  white  cast-iron  are  placed  in  the  cylinder, 
the  piston  P  is  introduced,  and  resting  the  base  he 
on  an  anvil,  the  head  of  the  piston  is  struck  with  a 
hammer.  After  a  certain  number  of  blows,  tlie 
powdered  substance  is  removed,  and  passed  through 
a  silk  sieve ;  the  fragments  then  remaining  on  the 
sieve  being  again  broken  up  in  the  apparatus,  and 
this  process  repeated  until  the  whole  quantity  is  reduced  to  fine 
powder.  ' 

Five  grammes  of  powdered  cast-iron  are  then  mixed  with  100 
or  120  gm.  of  chromate  of  lead,  J  of  the  mixture  is  set  aside,  and 
with  the  remaining  f,  5  gm.  of  chlorate  of  potassa  are  inti- 
mately mixed,  when  the  whole  is  introduced  into  a  tube  closed  nt 
one  end,  resembling  those  used  for  the  combustion  of  organic  sub- 
stances with  oxide  of  copper;  and  on  it  the  mixture  containing 
no  chlorate  of  potassa  is  placed.  The  tube  is  rested  on  a  sheet- 
iron  grate,  whil^  a  tube  containing  chloride  of  calcium,  or  pumice- 
stone  soaked  in  concentrated  sulphuric  acid,  to  absorb  the  moisture 
given  ofi"  by  the  materials,  is  fitted  to  its  extremity,  and  the  whole 
apparatus  is  then  arranged  as  represented  in  fig.  279. 

The  anterior  part  of  the  combustion-tube,  which  does  not  con- 
tain chlorate  of  potassa,  is  first  heated,  and  the  coals  are  then 
slowly  approached  to  that  part  containing  the  chlorate.  The  cast- 
iron  burns,  partly  at  the  expense  of  the  oxygen  of  the  chromate 
of  lead,  and  partly  by  that  disengaged  by  the  chlorate,  and  car- 
bonic acid  is  formed  and  collected  in  the  globe  apparatus.  Fresh 
coals  are  added,  until  the  end  of  the  tube  is  reached.  The  excess 
of  oxygen  gas  arising  from  the  decomposition  of  the  chlorate  is  at 
the  same  time  disengaged  and  driven  through  the  apparatus ;  but 
a  little  experience  soon  teaches  how  to  avoid  any  danger  of  an 
explosion.  It  is  well  to  place  a  small  quantity  of  a  mixture  of 
chromate  of  lead  and  chlorate  of  potassa  at  the  end  of  the  com- 
bustion-tube, as  the  oxygen  disengaged  from  this  drives  the  last 
traces  of  carbonic  acid  through  the  globe  apparatus.  The  increase 
of  weight  of  the  latter  gives  very  exactly  the  carbonic  acid  arising 
from  the  carbon  of  the  cast-iron,  while  the  sulphur  it  may  contain 


ANALYSIS    OF   CAST-IRON.  113 

remains  in  the  combustion-tube  in  the  state  of  sulphate  of  lead, 
and  does  not  affect  the  result  of  the  experiment. 

It  is  important  to  keep  the  mixture  in  the  combustion-tube  so 
that  a  free  space  may  remain  in  the  upper  part  of  the  tube,  as 
otherwise  the  chromate  of  lead,  on  becoming  doughy  and  expanded, 
might  obstruct  the  tube  and  cause  an  explosion. 

The  same  process  necessarily  applies  to  the  determination  of 
the  carbon  which  exists  in  steel  and  in  soft  iron. 

The  carbon  contained  in  cast-iron  and  steel  may  also  be  exactly 
determined  by  causing  these  substances  to  react  slowly  on  chloride 
of  silver.  To  do  this,  30  or  40  grammes  of  chloride  of  silver  are 
fused  in  a  porcelain  capsule,  a  piece  of  iron  or  steel'  weighing 
about  5  gm.  and  exactly  weighed  is  placed  on  it,  and  then  water 
containing  a  few  drops  of  chlorohydric  acid  is  added.  The  chlo- 
ride of  silver  is  gradually  decomposed,  while  protochloride  of  iron 
is  formed  and  the  carbon  set  free ;  but  the  reaction  is  very  slow, 
and  often  requires  several  weeks  for  its  completion.  There  re- 
mains, at  last,  a  spongy  mass  of  carbon  and  silicic  acid,  from 
which  the  last  traces  of  iron  are  extracted  by  boiling  with  dilute 
chlorohydric  acid.  The  precipitate  is  collected  on  a  filter  and 
weighed  after  being  well  dried,  or  better  still,  after  a  calcination 
in  a  current  of  hydrogen  gas.  Its  weight  is  that  of  the  carbon 
and  silicic  acid  united ;  and  it  is  then  calcined  in  a  platinum  capsule, 
by  which  the  carbon  burns  off,  when  the  weight  of  the  silicic  acid 
remaining  can  be  directly  determined,  and  that  of  the  carbon  cal- 
culated by  the  difference. 

As  a  substitute  for  chloride  of  silver,  chloride  of  copper  may  be 
employed,  which  acts  more  rapidly  on  the  cast-iron,  but  always 
disengages  a  small  quantity  of  carburetted  gas,  so  that  the  weight 
of  the  carbon  found  is  rather  too  small. 

§  862.  We  have  seen  that  carbon  could  exist  in  cast-iron  in  two 
states :  1st,  in  that  of  combined  carbon,  as  in  white  cast-iron  and 
steel ;  2dly,  in  the  state  of  small  isolated  laminse,  as  in  gray  cast- 
iron.  It  is  of  the  highest  importance  to  distinguish  these  two 
states  of  carbon,  as  they  exert  a  remarkable  influence  over  the 
nature  of  the  cast-iron,  and  moreover  are  easily  determined  by 
analysis.  In  fact,  when  chlorohydric  acid  is  allowed  to  act  on  a 
white  cast-iron  or  steel,  the  metal  dissolves  and  evolves  a  very 
fetid  hydrogen  gas,  containing  a  considerable  quantity  of  gaseous 
carburetted  hydrogen,  and  vapours  of  certain  liquid  carburetted 
h^'drogens  which  have  been  not  yet  studied.  All  the  carbon  of 
the  cast-iron  disappears  in  these  hydrogenated  products,  and  the 
residue  is  composed  only  of  the  silicic  acid  produced  by  the  silicium 
of  the  cast-iron.  If,  on  the  contrary,  a  gray  cast-iron  be  treated 
with  chlorohydric  acid,  the  gas  evolved  is  still  fetid,  as  the  carbon 
which  was  in  intimate  combination  with  the  iron  is  converted  into 

Vol.  IL— 8 


114  IRON. 

gaseous  or  liquid  carburets  of  hydrogen,  but  the  isolated  carbon 
which  existed  in  it  in  the  state  of  graphite  remains  intact  with  the 
silicic  acid.  The  residue  is  collected  on  a  small  filter,  and,  after 
being  well  washed,  is  dried.  Some  ether  is  then  poured  over  the 
filter,  to  dissolve  any  oil  which  may  remain,  after  which  it  is  again 
dried  at  a  temperature  above  212°,  and  the  residue  weighed :  the 
weight  of  the  graphite  and  silicic  acid  united  is  thus  obtained. 
The  substance  is  heated  in  a  platinum  capsule  in  the  open  air,  or 
better  still,  in  a  current  of  oxygen,  by  which  the  graphite  burns, 
and  leaves  as  a  residue  only  silicic  acid,  which  can  be  determined 
by  weight.  By  subtracting  from  the  whole  weight  of  the  carbon 
obtained  by  the  combustion  of  the  cast-iron  the  weight  of  graphite 
first  obtained,  the  weight  of  the  combined  carbon  is  ascertained. 

Determination  of  Silicium. 

§  863.  The  silicium  of  cast-iron  is  determined  by  dissolving  the 
latter  in  chlorohydric  acid,  which  converts  the  silicium  into  gelati- 
nous silicic  acid.  The  liquid  is  evaporated  to  dryness  to  render 
the  silex  insoluble,  then  treated  with  water,  and  the  residue 
collected  on  a  filter.  The  silex  is  weighed,  after  having  been  cal- 
cined at  a  dull  red-heat,  and  the  weight  of  the  silicium  is  deduced 
from  it. 

Cast-iron  frequently  contains  particles  of  slag,  so  that  the  residue 
is  composed  not  only  of  the  silicic  acid  furnished  by  the  silicium 
of  the  cast-iron,  but  also  that  of  the  slag,  which  may  have  been 
more  or  less  altered  by  the  chlorohydric  acid.  The  slag  of  char- 
coal furnaces  generally  resists  this  acid,  while  that  of  coke  furnaces 
is  more  or  less  completely  acted  on  by  it.  By  treating  powdered 
cast-iron  with  weak  chlorohydric  acid,  the  iron  may  be  entirely 
dissolved,  without  sensibly  afiecting  the  slag,  while  the  residue 
consists  of  gelatinous  silex  and  slag,  and  is  treated  by  a  solution 
of  caustic  potassa,  which  dissolves  the  silex  and  leaves  the  slag. 
The  silicic  acid  which  has  been  furnished  by  the  silicium  of  the 
cast-iron  can  thus  be  exactly  ascertained. 

Determination  of  Sulphur. 
§  864.  The  cast-iron  is  acted  on  by  aqua  regia,  which  dissolves 
the  iron  as  perchloride,  and  converts  the  sulphur  into  sulphuric 
acid.  The  liquid  is  diluted  with  water,  and  the  sulphuric  acid  pre- 
cipitated by  chloride  of  barium  as  sulphate  of  baryta,  from  which 
the  weight  of  the  sulphur  in  the  cast-iron  may  be  deduced. 

Determination  of  Phosphorus, 
§  865.  The  cast-iron  is  acted  on  by  aqua  regia,  evaporated  to  dry- 
ness to  drive  ofi"  the  excess  of  acid,  and  then  treated  with  water.  The 
liquid,  containing  phosphorus  in  the  state  of  phosphoric  acid,  is 


ANALYSIS   OF    SLAGS.  llo 

then  allowed  to  digest  at  a  temperature  of  about  212°,  for  several 
hours,  with  an  excess  of  sulf  hydrate  of  potassium,  which  precipitates 
iron  and  manganese  in  the  state  of  sulphides.  After  separating 
these  by  filtration,  the  liquid  contains  phosphoric  acid  and  alkaline 
sulphides,  which  are  decomposed  by  a  slight  excess  of  chlorohy- 
dric  acid,  after  which  the  liquid  is  boiled  to  drive  oft*  the  sulf  hydric 
acid.  One  decigramme  of  piano-forte  wire  is  then  weighed  very 
exactly,  dissolved  in  aqua  regia,  and  added  to  the  solution  of  per- 
chloride  of  iron  obtained.  An  excess  of  ammonia  poured  into  the 
liquid  then  completely  precipitates  the  iron  added  in  the  state 
of  hydrated  sesquioxide,  and  carries  with  it  all  the  phosphoric  acid 
which  existed  in  the  liquid,  precipitated  as  a  basic  perphosphate 
of  iron.  This  precipitate  is  weighed  after  calcination  in  the  air ; 
and  if  from  it  0.143  gm.,  the  weight  of  the  sesquioxide  of  iron 
yielded  by  0.100  gm.  of  metallic  iron,  are  subtracted,  the  weight 
of  the  phosphoric  acid,  whence  that  of  the  phosphorous  in  the  cast- 
iron  may  be  deduced,  is  obtained. 

The  same  determination  may  be  made  in  the  following  manner: — 
After  having  dissolved  the  cast-iron  in  chlorohydric  acid,  the  liquid 
is  filtered  and  an  excess  of  acetate  of  soda  added,  the  acetic  acid 
of  which  is  set  free  and  chloride  of  sodium  is  formed.  Now,  as 
sesquioxide  of  iron  forms  with  phosphoric  acid  a  phosphate  Fe^O^ 
PhOg  insoluble  in  acetic  acid,  the  phosphoric  acid  combines  with 
the  proper  quantity  of  sesquioxide  of  iron  to  form  this  phosphate, 
which  is  precipitated,  collected  on  a  filter,  washed  with  boiling 
water,  and  weighed  after  calcination.  The  precipitate  may  also 
be  redissolved  in  chlorohydric  acid,  the  liquid  boiled  with  sulphite 
of  soda  to  bring  the  perchloride  of  iron  to  the  state  of  protochlo- 
ride,  and  the  standard  solution  of  permanganate  of  potassa  poured 
in  to  determine  the  quantity  of  iron  it  contains.  The  weight  of 
phosphoric  acid  is  thence  easily  deduced,  and,  consequently,  that 
of  the  phosphorus  contained  in  the  cast-iron. 

Determination  of  Manganese. 

§  866.  The  manganese  contained  in  cast-iron  is  easily  ascertained 
by  the  processes  described  §  803. 

ANALYSIS  OP  SLAGS  AND  FURNACE  SCORIiB. 

§  867.  Slag  is  composed  chiefly  of  silicates  of  alumina  and  lime, 
but  often  contains,  in  addition,  small  quantities  of  the  silicates  of 
iron  and  manganese.  The  various  scoriae  arising  from  the  refining 
of  cast-iron  are  composed  of  silicates  of  iron  and  manganese,  but 
may  also  contain  small  quantities  of  silicates  of  alumina,  lime,  and 
potassa,  arising  from  the  ashes  of  the  fuel  used.  Forge  scoriae  are 
readily  acted  on  by  concentrated  chlorohydric  acid,  by  which  the  ma- 


116  IBON. 

jority  of  slags  is,  however,  not  attacked.  These  products  are  ana- 
lyzed by  the  processes  described  in  the  analysis  of  glass  (§  704), 
except  that,  in  the  case  of  forge  scorise,  it  is  useless  to  employ  car- 
bonate of  soda  and  fluohydric  acid,  as  the  substance  is  acted  on 
immediately  by  chlorohydric  acid. 

REMARKS  ON  THE  COMPOSITION  OF  IRON,  STEEL,  AND  CAST-IRON. 

§  868.  By  the  hardness  of  wrought-iron  is  understood  the  resist- 
ance it  presents  when  filed,  cut,  bored,  or  struck  with  a  hammer 
while  it  is  cold,  which  properties  vary  greatly  in  the  different  kinds 
of  iron  manufactured  in  different  furnaces.  Iron  which  when  cold 
readily  takes  the  impression  of  the  hammer,  is  commonly  flexible 
and  tough,  but,  although  of  an  excellent  quality,  cannot  be  univer- 
sally applied, — that  which  is,  at  the  same  time,  hard  and  tough  being 
preferred.  The  best  iron  is  that  which  is  very  hard,  without  being 
brittle,  that  is,  without  breaking  easily  under  the  hammer. 

Iron  which  breaks  or  splits  easily  when  heated  is  said  to  be 
short ;  a  defect  which  is  produced  by  a  small  quantity  of  sulphur : 
:^  part  of  sulphur  will  make  iron  slightly  short. 

When  iron  contains  0.5  per  cent,  of  phosphorus,  it  is  brittle  when 
cold,  while  a  smaller  quantity  only  renders  the  metal  harder,  still 
giving  iron  of  good  quality. 

Wrought-iron  may  contain  0.25  per  cent,  of  carbon,  without  pos- 
sessing the  property  of  remarkably  hardening  by  tempering,  which 
is  regarded  as  characteristic  of  steel  (§  857).  When  the  carbon  rises 
to  0.60  per  cent,  the  metal  becomes  too  steely,  and  strikes  fire  with 
a  flint  after  tempering.  The  quantity  of  carbon  which  renders  iron 
steely,  varies  with  the  purity  of  the  metal ;  for  very  pure  iron,  for 
example,  a  larger  proportion  than  for  that  containing  smaller  quan- 
tities of  sulphur  and  phosphorus  is  required. 

Steel,  refined  by  fagoting,  and  which  is,  at  the  same  time,  suffi- 
ciently hard  and  tough  for  cutting  instruments,  contains  from  1.0 
to  1.5  per  cent,  of  carbon.  When  the  proportion  of  the  latter  is 
greater,  the  steel  becomes  harder,  but  loses  in  toughness  and  par- 
ticularly in  the  property  of  being  welded.  Steel  containing  1.75 
per  cent,  of  carbon  cannot  be  welded  at  any  temperature. 

When  iron  is  combined  with  2  per  cent,  of  carbon,  it  cannot  be 
forged  under  the  hammer.  This  property  may  be  regarded  as  dis- 
tinguishing steel  from  cast-iron,  the  compounds  of  iron  with  a 
greater  proportion  of  carbon  than  1.9,  consequently,  being  no 
longer  steel,  but  cast-iron. 

Cast-steel  which  contains  from  1.9  to  2  per  cent,  of  carbon, 
cannot  be  forged,  but  it  never  parts  with  its  graphite,  even  by 
very  slow  cooling.  Graphite  separates  by  slow  cooling,  only  when 
the  iron  is  combined  with  at  least  2.5  per  cent,  of  carbon. 


PROPERTIES    OF   CAST-IRON.  117 

The  properties  of  cast-iron  do  not  depend  so  much  on  the  whole 
quantity  of  carbon  contained,  as  on  that  with  which  it  is  intimately 
combined.  Gray  cast-iron  most  frequently  contains  only  2  or  2.5 
per  cent,  of  combined  carbon,  the  rest  of  this  substance  being  scat- 
tered through  it  in  the  form  of  graphitous  spangles.  Gray  cast- 
iron  requires  a  higher  temperature  for  fusion  than  white  cast-iron, 
and  passes  almost  suddenly  from  the  liquid  to  the  solid  state,  while 
white  iron  passes  through  an  intermediate  doughy  state ;  on  which 
account,  probably,  white  cast-iron  is  more  easily  refined  than  gray 
iron  containing  the  same  quantity  of  carbon.  Therefore,  it  is 
always  endeavoured  to  obtain  white  cast-iron  for  refining,  when 
the  purity  of  the  ore  and  the  fuel  will  allow  it ;  for  we  have  already 
said  (§  826)  that  with  impure  ores  and  fuels,  the  temperature  of  a 
blast  furnace  producing  gray  cast-iron  must  be  greatly  elevated, 
unless  the  gray  iron  be  suddenly  cooled  on  leaving  the  furnace. 

Gray  cast-iron  is  converted  into  white  cast  iron  by  sudden  cool- 
ing, while  the  white  passes  into  the  gray  state  at  a  higher  tem- 
perature, and  by  slow  cooling. 


118 


CHROMIUM. 

Equivalent  =  26.7;  (333.75,0  =  100.) 

§  869.  Chromium*  is  obtained  combined  with  a  certain  quantity 
of  carbon,  bj  heating,  in  a  "brasqued"  crucible,  an  intimate  mix- 
ture of  sesquioxide  of  chromium  and  15  or  20  per  cent,  of  carbon 
in  a  forge-fire,  when  the  carburetted  metal  remains  in  the  form  of 
a  porous  lump,  as  the  heat  was  not  sufficient  to  fuse  it.  This 
metallic  mass  is  finely  powdered  in  a  steel  mortar,  intimately  mixed 
with  a  few  hundredths  of  the  green  oxide  of  chromium,  and  the 
mixture  heaped  in  a  porcelain  crucible  accurately  covered  by  its 
lid,  which  is  then  placed  in  a  second  earthen  crucible,  likewise 
*'brasqued,"  and  heated  to  the  highest  temperature  of  a  forge-fire. 
The  carbon  of  the  carburetted  chromiun^  is  burned  by  the  oxygen 
of  the  oxide,  and  a  purer  metal  is  obtained,  in  the  form  of  a  gray 
agglutinated  mass.  This  metal  is  brittle,  but  may  be  polished, 
and  then  displays  a  brilliant  metallic  lustre.  It  is  very  hard  and 
scratches  glass  readily,  and  its  specific  gravity  is  about  6.0.  It 
does  not  oxidize  in  dry  air  at  the  ordinary  temperature,  but  com- 
bines rapidly  with  oxygen  when  heated  to  a  dull  red-heat.  It 
dissolves  in  chlorohydric  and  dilute  sulphuric  acid  with  evolution 
of  hydrogen  gas. 

Pure  metallic  chromium  is  obtained,  in  the  form  of  a  dark-gray 
powder,  by  decomposing  the  violet  sesquichloride  of  chromium  by 
potassium.  The  pulverulent  metal  has  so  powerful  an  affinity  for 
oxygen,  that  it  ignites  before  it  reaches  a  dull  red-heat,  and  is 
converted  into  green  oxide  of  chromium  when  heated  in  contact 
with  the  air. 

COMPOUNDS  OF  CHROMIUM  WITH  OXYGEN. 

§  870.  Chromium  forms  many  compounds  with  oxygen : 

1.  The  protoxide  CrO,  isomorphous  with  protoxide  of  iron  FeO. 

2.  The  sesquioxide  Cr^Og,  isomorphous  with  alumina  and  ses- 
quioxide of  iron  Fe^Og. 

3.  An  oxide  CrgO^,  intermediate  between  the  first  two,  and  cor- 
responding to  magnetic  oxide  of  iron  FeOjFcaOg;  so  that  its 
formula  should  be  written  CrO,Cr203. 

4.  Chromic  acid  CrOg,  corresponding  to  ferric  acid  FeOg,  and 
manganic  acid  MnOg. 

5.  An  intermediate  oxide  CrO^,  which  should,  however,  rather 

*  Discovered  in  1797  by  Vauquelin. 


OXIDES    OF   CHROME.  119 

be  considered  as  a  combination  of  chromic  acid  with  protoxide  of 
chromium :   CrOjCrOg. 

6.  Lastly,  a  perchromic  acid  CraOy,  corresponding  to  permanganic 
acid  MngOy. 

Protoxide  of  Qhromium,  CrO. 

§  871.  Protoxide  of  chrome  is  obtained  by  adding  caustic  potassa 
to  a  solution  of  protochloride  of  chromium,  when  a  deep  brown 
precipitate  of  hydrated  protoxide  is  formed.  But  this  substance 
has  so  great  an  affinity  for  oxygen  that  it  decomposes  water  as 
soon  as  it  is  set  free,  disengaging  hydrogen,  and  being  converted 
into  a  tobacco-coloured  powder,  which  is  the  hydrate  of  a  definite 
oxide  CrgO^,  corresponding  to  magnetic  oxide  of  iron,  and  which 
should  consequently  assume  the  formula  CrOjCraOg.  The  trans- 
formation takes  place  very  rapidly,  at  the  temperature  of  boiling 
water.  The  hydrate  of  the  oxide  of  chrome  CrOjCr^Og,  heated  in 
a  closed  tube,  is  converted  into  the  green  oxide  Cr^Oa,  with  the 
evolution  of  hydrogen  gas. 

The  composition  of  protoxide  of  chrome  has  never  been  directly 
ascertained,  but  has  been  inferred  from  the  analysis  of  protochlo- 
ride of  chrome.     This  oxide  contains 

1  eq.  chromium 26.7  or  333.7 78.53 

1  "    oxygen 8.0       IQO.Q ..21.47 

1  «   protoxide 34.0       433.7 100.00 

Sesquioxide  of  Chromium  Qrfi^, 

§  872.  Sesquioxide  of  chromium  is  prepared  in  several  ways  : 

1.  By  heating  protochromate  of  mercury  Hg30,Cr03;  when 
oxygen  is  disengaged,  the  mercury  distils,  and  sesquioxide  of 
chrome  remains  in  the  form  of  a  deep-green  powder : 

2(Hg,0,Cr03)=Cr,03+4Hg+60. 

2.  By  heating  in  a  crucible  a  mixture  of 

1  part  of  bichromate  of  potassa, 

IJ  "         sal  ammoniac, 

1     "         carbonate  of  potassa, 

when  chloride  of  potassium  and  oxide  of  chrome  are  formed,  while 
the  oxygen  given  off  by  the  chromic  acid  combines  with  the  hy- 
drogen of  the  ammonia : 

K0,2Cr03+K0,C0,+2(NH3,HCl)  =  2KC1  +  CrA+5H0+N+ 

NH3,C0,. 

By  treating  the  substance  with  water,  the  chloride  of  potassium  is 
dissolved,  leaving  the  sesquioxide  of  chrome  in  a  state  of  purity. 

3.  By  heating  at  a  suitable  temperature,  in  an  earthen  crucible 


120  CHROMIUM. 

or  in  a  retort,  2  parts  of  bichromate  of  potassa,  and  1  part  of 
sulphur;  when  the  sulphur  forms,  with  the  oxygen  given  off  by  the 
chromic  acid,  sulphuric  acid,  which  combines  with  the  potassa : 

K0,2Cr03+S=Cr,03+K0,S03. 

But  an  excess  of  sulphur  is  necessary,  as  a  portion  of  this  sub 
stance  is  volatilized  without  reacting  on  the  chromate.  By  treat 
ing  it  with  water,  the  oxide  of  chrome  often  remains  mixed  with  a 
small  quantity  of  sulphur,  which  may  be  expelled  as  sulphurous 
acid  by  heating  it  in  contact  with  the  air. 

4.  By  calcining  bichromate  of  potassa  in  a  "brasqued"  crucible, 
when  carbonate  of  potassa,  which  is  removed  by  water,  and  sesqui- 
oxide  of  chrome  are  formed: 

2{KO,2Cr03)+3C=2(KO,COJ+C03+2Cr,03. 

5.  By  heating  bichromate  of  potassa  to  a  high  white-heat,  when 
half  of  the  chromic  acid  is  decomposed  into  sesquioxide  of  chrome 
and  oxygen,  and  a  neutral  chromate  of  potassa  is  formed,  which 
is  removed  by  water  : 

2(KO,2Cr03)=Cr,034-30+2(KO,Cr03). 

In  this  case  the  sesquioxide  of  chrome  assumes  the  form  of  crys- 
talline lamellae. 

6.  By  heating  chromate  of  potassa  to  a  red-heat,  in  a  current 
of  chlorine,  when  chloride  of  potassium  is  formed,  and  the  chromic 
acid  is  decomposed  into  sesquioxide  of  chrome  and  oxygen : 

2(KO,Cr03)+2Cl=2KCl+Cr,03+30. 

Sesquioxide  of  chrome,  thus  prepared,  appears  in  the  form  of 
green  crystalline  lamellae. 

7.  Lastly,  sesquioxide  of  chrome  is  obtained,  in  the  form  of 
small  rhombohedral  crystals,  isomorphous  with  native  crystallized 
alumina  or  corundum,  by  passing  through  a  heated  tube  a  red 
volatile  liquid  of  the  formula  CrOgCl,  which  we  shall  describe 
under  the  name  of  chlorochromie  acid. 

2CrO,Cl=Cr,03+2Cl+0. 

The  crystals  which  are  deposited  on  the  sides  of  the  tube  are 
often  1  or  2  millimetres  in  size,  very  brilliant,  and  of  so  deep  a 
green  colour  as  to  appear  black.  They  are  as  hard  as  corundum 
and  readily  scratch  glass.     Their  specific  gravity  is  5.21. 

Sesquioxide  of  chrome  cannot  be  decomposed  by  heat.  Hydrogen 
even  does  not  reduce  it  at  the  highest  temperature  of  our  labora- 
tory furnaces ;  but  charcoal  decomposes  it  in  a  forge-fire,  when  it 
is  intimately  mixed  with  the  oxide.  Vapour  of  sulphur  does  not 
act  on  it  at  a  white-heat,  while  sulphide  of  carbon  decomposes  it 
at  this  temperature,  and  converts  it  into  sulphide  of  chromium. 

Sesquioxide  of  chrome  imparts  a  green  colour  to  fluxes,  and  we 
have  already  seen  that  this  oxide  is  used  for  painting  on  glass  and 


SESQUIOXIDE    OF    CHKOME.  121 

porcelain.  A  red  colour,  called  pinh-colour,  is  also  prepared  with 
chrome,  and  was  first  used  on  porcelain  by  the  English.  It  is 
obtained  by  heating  to  redness  an  intimate  mixture  of  100  parts 
of  stannic  acid,  34  of  chalk,  and  3  or  4  of  chromate  of  potassa, 
and  then  treating  the  powdered  material  with  chlorohydric  acid 
until  it  has  acquired  a  beautiful  rosy  tinge.  The  colouring  prin- 
ciple of  this  substance  is  probably  an  oxide  of  chrome  superior  to 
the  sesquioxide. 

Strongly  calcined,  it  combines  with  the  acids,  even  when  they 
are  concentrated,  only  with  great  diflficulty;  the  hydrate  must 
therefore  be  dissolved  when  salts  of  the  oxide  are  to  be  prepared. 

In  order  to  prepare  the  hydrated  sesquioxide  of  chrome,  a  solu- 
tion of  the  sesquichloride  is  precipitated  by  ammonia,  when  a 
gelatinous  bluish-gray  precipitate  is  formed,  which  must  be  washed 
with  boiling  water.  The  sesquichloride  of  chrome  used  in  this 
preparation  is  obtained  by  decomposing  bichromate  of  potassa  by 
sulphurous  acid,  in  the  presence  of  an  excess  of  chlorohydric  acid. 
To  effect  this  a  current  of  sulphurous  acid  gas  is  passed  through  a 
concentrated  hot  solution  of  bichromate  of  potassa,  mixed  with 
chlorohydric  acid,  when  the  liquid  soon  changes  in  colour,  be- 
coming first  brown,  and  subsequently  assuming  a  beautiful  emerald 
green  hue.  The  reaction  is  terminated  when  the  liquid  still  exhales 
a  strong  smell  of  sulphurous  acid,  after  having  been  left  to  itself 
for  several  hours  in  a  well-corked  bottle. 

Hydrated  sesquioxide  of  chrome  dissolves  readily  in  acids. 
Moderately  heated,  it  loses  its  water,  still  preserving  the  property 
of  easily  combining  with  acids ;  but  if  the  temperature  be  further 
elevated,  the  substance  suddenly  becomes  incandescent  before 
reaching  a  red-heat,  and,  after  incandescence,  the  oxide  is  nearly 
insoluble  in  acids. 

§  873.  Sesquioxide  of  chrome  can  combine  with  powerful  bases, 
and  one  of  these  compounds,  found  in  nature,  acquires  great  im- 
portance from  being  the  ordinary  chrome  ore.  It  consists  of  ses- 
quioxide of  chrome  and  protoxide  of  iron,  combined  according  to 
the  formula  FeO,Cr303:  in  mineralogy,  it  is  called  chromate  of 
iron,  or  chromic  iron.  Chromic  iron  has  sometimes  been  found 
crystallized  in  regular  octahedrons,  presenting,  therefore,  the  same 
form  as  magnetic  oxide  of  iron  FeO,Fe303,  and  spinell  MgO,Ala03, 
which  have  similar  formulae.  Most  frequently,  chromic  iron 
forms  considerable  masses,  of  a  deep  gray  colour  and  a  greasy 
lustre ;  and  its  bearings  resemble  those  of  magnetic  oxide  of  iron. 
The  principal  mines  of  chromic  iron  are  in  Sweden,  the  Ural, 
and  near  Baltimore  in  the  United  States.*     It  has  been  found  in 

*  The  most  extensive  and  important  locality  by  far,  is  that  of  Lancaster  and 
Chester  counties,  Pennsylvania,  which  now  supplies  both  the  United  States  and 
Europe.  A  considerable  part  of  the  ore  is  now  obtained  by  simply  washing  the 
Bands  of  brooks. —  W.  L.  F. 


182  CHROMIUM. 

France,  in  the  department  of  Var,  but  the  mine  appears  nearly 
exhausted. 

Chromic  Acid  CrOg. 

§  874.  In  order  to  prepare  chromic  acid,  one  and  a  half  times 
its  volume  of  sulphuric  acid  is  added  gradually  and  in  small  quan- 
tities to  a  solution  of  bichromate  of  potassa,  saturated  at  a  tem- 
perature of  from  130°  to  140°,  when  bisulphate  of  potassa  is 
formed,  which  remains  in  solution,  and  the  liquid  deposits  on  cool- 
ing long  red  needles  of  chromic  acid.  When  the  solution  is  cooled 
and  the  acid  liquid  decanted  off,  the  crystals  are  allowed  to  drain 
in  a  funnel  stopped  with  asbestus,  and  are  then  spread  upon  un* 
burnt  porcelain,  which  absorbs  the  remaining  water.  In  order  to 
purify  them,  their  aqueous  solution  is  treated  with  a  small  quantity 
of  chromate  of  baryta,  which  combines  with  the  sulphuric  acid, 
and  the  filtered  liquid  is  evaporated  in  vacuo. 

Chromic  acid  is  of  a  beautiful  red  colour  at  the  ordinary  tem- 
perature, but  becomes  almost  black  when  heated.  It  decomposes 
before  attaining  a  red-heat  into  sesquioxide  of  chrome  and  oxygen, 
and  is  deliquescent  and  very  soluble,  with  an  orange-yellow  colour. 

Chromic  acid  is  a  very  powerful  oxidizing  agent :  a  few  drops 
of  absolute  alcohol  thrown  on  it,  instantly  convert  it  into  sesqui- 
oxide, with  so  great  an  evolution  of  heat  that  the  alcohol  some- 
times ignites.  Hot  concentrated  sulphuric  acid  decomposes 
chromic  acid,  disengaging  oxygen  and  forming  sesquisulphate  of 
chrome.  Oxygen  is  sometimes  prepared  in  the  laboratory  by 
heating  together  equal  weights  of  bichromate  of  potassa  and  con- 
centrated sulphuric  acid.  Chlorohydric  acid  converts  chromic 
acid  into  sesquichloride  of  chrome,  with  disengagement  of  chlo- 
rine: 

2Cr03+6HCl=Cr,Cl3-f6HO+3Cl. 

§  875.  Chromic  acid  appears  to  be  able  to  combine  in  several 
proportions  with  sesquioxide  of  chromium.  If  a  solution  of  bichro- 
mate of  potassa  be  treated  with  sulphurous  acid  until  it  assumes  a 
brown  colour,  and  at  that  moment  ammonia  be  added  to  the  liquid, 
an  ochreous  precipitate  is  obtained,  which  hot  water,  after  some 
time,  decomposes  into  chromic  acid  which  dissolves,  and  hydrated 
sesquioxide  of  chrome  which  remains.  A  similar  compound  is 
obtained  by  decomposing  nitrate  of  chrome  by  a  suitable  degree 
of  heat,  when  a  brown  spongy  mass  remains,  of  which  the  compor 
sition  is  represented  by  CrOg,  but  to  which  the  formula  Cr^Og, 
CrO„  has  been  assigned. 

PercTiromic  Acid, 
§  876.    By  treating   chromic   acid  with   oxygenated   water,  a 
beautiful  blue  solution  is  obtained,  which,  when  shaken  with  ether, 
loses  its  colour,  and  imparts  the    blue  compound  to  the  ether. 


PROTOSALTS   OF   CHROME.  123 

Xhis  compound,  which  is  not  very  stable,  has  not  yet  been  ob- 
tained in  an  isolated  state,  nor  has  it  been  combined  with  the 
mineral  bases.     Its  formula  is  supposed  to  be  Cr207. 

^  SALTS   FORMED  BY  PROTOXIDE    OF  CHROME. 

§  877.  Protoxide  of  chrome  CrO  is  a  powerful  base,  but  never- 
theless has 'been  combined  with  only  a  small  number  of  acids,  on 
account  of  the  difficulty  of  obtaining  it  pure,  and  the  ready  sus- 
ceptibility of  change  of  the  salts  themselves,  which  rapidly  absorb- 
ing the  oxygen  of  the  air,  are  converted  into  sesquisalts.  The 
acetate  and  the  double  sulphate  of  protoxide  of  chrome  and  potassa 
only  are  known ;  but  in  order  to  ascertain  the  distinctive  charac- 
ters of  the  protosalts  of  chrome,  the  protochloride  must  be  resort- 
ed to.  These  compounds  are  known  by  the  following  reactions  : — 
Caustic  potassa  at  first  affords  a  deep  brown  precipitate  of  hy- 
drated  protoxide,  but  which  is  immediately  changed  into  a  clear 
brown  hydrated  magnetic  oxide,  with  the  evolution  of  hydrogen 
gas.  Sulfhydric  acid  does  not  precipitate  them,  while  sulfhydrates 
yield  a  black  precipitate.  Bichloride  of  mercury  gives  a  white 
precipitate  of  protochloride  of  mercury.  Lastly,  oxidizing  reagents, 
such  as  chlorine,  nitric  acid,  etc.,  immediately  convert  the  proto- 
salts of  chromium  into  sesquisalts. 

SALTS  FORMED  BY  SESQUIOXIDE  OF  CHROME. 

§  878.  Sesquioxide  of  chrome  is  a  feeble  base,  analogous  to  ses- 
quioxide  of  iron.  The  salts  formed  by  this  oxide  may  exist  under 
two  different  modifications,  which  are  distinguished  by  their  co- 
lours, the  first  being  violet,  while  the  second  is  green.  Several 
acids  produce  both  modifications ;  but  with  others  only  one  of  the 
colours  has  hitherto  been  obtained. 

A  green  and  a  violet  sulphate  are  known.  Ammonia  forms  in 
the  solutions  of  these  two  salts  precipitates  which  are  distinguished 
by  their  shades  of  colour ;  the  precipitate  of  the  green  sulphate 
being  bluish  gray,  and  producing  a  green  solution  with  sulphuric 
acid,  while  that  furnished  by  the  violet  modification  is  of  a  greenish 
gray,  but  also  produces  a  green  solution  when  treated  with  sul- 
phuric acid. 

Potassa  and  soda  yield  bluish-gray  or  greenish-gray  precipi- 
tates, which  dissolve  in  an  excess  of  alkali,  forming  a  green  liquid, 
which  loses  its  colour  by  boiling,  as  the  hydrated  oxide  is  again 
precipitated. 

The  alkaline  carbonates  give  a  greenish  precipitate,  perceptibly 
soluble  in  an  excess  of  the  reagent. 

Sulfhydric  acid  does  not  precipitate  the  sesquisalts  of  chrome, 
but  the  sulfhydrates  precipitate  those  of  the  hydrated  sesquioxide. 

The  sesquisalts  of  chrome  produce,  like  the  protosalts,  a  glass 


124  CHROMIUM. 

of  a  characteristic  green  colour  when  fused  with  borax.  Fused 
with  the  alkaline  carbonates,  or  better  still,  with  the  nitrates,  they 
form  alkaline  chromates,  which  are  recognised  by  the  yellow  solu- 
tions they  produce,  and  by  their  great  colouring  power. 

Sesquinitrate  of  Qhrome, 

§  879.  Hydrated  sesquioxide  of  chrome  dissolves  immediately 
in  nitric  acid,  furnishing  a  green  solution  which  leaves,  after  eva- 
poration, a  very  soluble  green  salt,  readily  decomposable  by  heat. 
At  a  moderate  temperature,  it  yields  a  brown  substance,  which  is 
regarded  as  a  sesquichromate  of  chrome  CraOgjCrOg. 

Sesquisulphates  of  Chrome. 

§  880.  The  neutral  sesquisulphate  of  chrome  CrgOgjSSOg  has 
been  obtained  with  three  different  colours,  violet,  green,  and  red, 
which  appear  to  correspond  to  three  modifications  of  the  salt. 

The  violet  sulphate  is  obtained,  by  leaving  for  several  weeks,  in 
a  badly-corked  bottle,  8  parts  of  hydrated  sesquioxide  of  chrome, 
dried  at  212°,  and  8  or  10  parts  of  concentrated  sulphuric  acid. 
The  solution,  which  is  at  first  green,  gradually  becomes  blue,  and, 
after  some  time,  a  greenish-blue  crystalline  mass  is  deposited. 
With  an  aqueous  solution  of  this  substance,  alcohol  gives  a  violet- 
blue  crystalline  precipitate,  which,  after  having  been  dissolved  in 
very  weak  alcohol,  is  left  to  itself.  After  some  time,  the  liquid 
deposits  small  regular  octohedrons  of  the  formula  Cr303,3S03+ 
15H0. 

The  green  sulphate  is  prepared  by  dissolving  sesquioxide  of 
chrome,  at  a  temperature  of  120°  to  140°,  in  concentrated  sul- 
phuric acid,  or  by  boiling  the  solution  of  the  violet  sulphate.  The 
liquid,  when  rapidly  evaporated,  yields  a  green  crystalline  salt, 
having  the  same  composition  as  the  violet  sulphate.  The  green 
sulphate  readily  dissolves  in  alcohol  with  a  blue  colour,  while 
the  violet  sulphate  is  insoluble  in  it.  The  violet  and  green  sul- 
phates are  also  distinguished  by  several  chemical  reactions ;  thus, 
the  cold  solution  of  the  green  sulphate  is  not  completely  decom- 
posed by  the  soluble  salts  of  baryta,  and  the  decomposition  is 
complete  only  when  the  liquid  is  boiled,  while  all  the  sulphuric 
acid  of  the  violet  solution  may,  on  the  contrary,  be  precipitated 
when  cold  by  salts  of  baryta. 

If  the  violet  or  green  sulphate  be  heated  to  a  temperature  of 
392°,  with  an  excess  of  sulphuric  acid,  a  clear  yellow  mass  is 
obtained,  which  leaves  as  a  residue  the  red  neutral  sulphate  of 
chrome,  after  the  evaporation  of  the  excess  of  acid.  This  anhy- 
drous sulphate  is'  insoluble  in  water,  and  dissolves  with  difficulty 
even  in  acid  liquids. 


CHROMIC   ALUMS.  125 

Ohromie  Alums. 

§  881.  Sesquisulphate  of  chrome  is  isomorphous  with  sulphate 
of  alumina,  and  may  take  the  place  of  the  latter  in  the  alums.  The 
crystallizable  chromic  alums  contain  the  violet  modification  of 
sulphate  of  chrome.  Three  of  these  alums  are  known,  affording 
beautiful  crystals  : 

Potassic  alum Cr,033S03+KO,S03+24HO. 

Sodic  alum Cr,03,3S03+NaO,S03+24HO. 

Ammoniacal  alum Cr,03,3S03+(NH3,H0)S03+24H0. 

Potasso-chromic  alum  is  prepared  by  heating  slightly  a  mixture 
of  bichromate  of  potassa  and  sulphuric  acid  dissolved  in  water,  with 
a  reducing  substance,  such  as  sugar,  alcohol,  etc. ;  or  by  passing  a 
current  of  sulphurous  acid  through  the  liquid.  The  solution  depo- 
sits by  spontaneous  evaporation,  or  even  on  cooling,  if  it  be  suffi- 
ciently concentrated,  large  regular  octahedrons,  like  those  of  ordi- 
nary alum,  of  a  deep  violet  red.  They  dissolve  readily  in  water, 
with  a  dirty  violet  colour,  but  are  insoluble  in  alcohol.  Heated  to 
176°,  the  solution  becomes  green,  and  deposits  by  evaporation  red 
crystals  of  alum,  but  leaves  as  a  residue  an  uncrystallized  mass, 
which  is  still  a  double  sulphate  of  potassa  and  chrome,  but  which 
no  longer  presents  any  of  the  characters  of  potassa-chromic  alum. 
The  solutions  of  the  green  sulphates  of  chromium  give  the  same 
green  product  when  they  are  evaporated  with  sulphate  of  potassa. 

CHROMATES. 

§  882.  Chromic  acid  combines  with  nearly  all  the  bases,  forming 
with  the  alkalies  salts  which  crystallize  perfectly,  and  are  isomor- 
phous with  the  corresponding  sulphates.  The  chromates  of  stron- 
tian,  lime,  and  magnesia  are  soluble,  while  the  other  metallic  chro- 
mates are  insoluble,  or  nearly  so. 

Chromic  acid  forms  with  the  alkalies  two  series  of  salts :  neutral 
chromates  and  bichromates,  the  former  of  which  are  of  a  bright 
yellow  colour,  while  the  bichromates  are  orange-red.  The  soluble 
chromates  are  easily  distinguished :  first,  by  their  colour,  which  is 
very  decided,  even  in  very  dilute  solutions ;  and  also,  by  the  cha- 
racteristic colours  of  the  precipitate  they  yield  with  various  metallic 
salts.  They  form  a  yellow  precipitate  with  the  salts  of  lead  .and 
bismuth,  a  bright  red  one  with  those  of  mercury,  and  a  deep  red 
one  with  those  of  silver.  The  chromates,  heated  with  concen- 
trated chlorohydric  acid,  give  a  green  solution  of  sesquichloride 
of  chrome. 

Chromates  of  Potassa. 

§  883.  The  compounds  of  chromic  acid  with  potassa  are  the  most 
important  products  of  chrome,  as  large  quantities  of  them  are  used 
in  dyeing  and  calico-printing.     They  are  obtained  directly  from 


126  CHROMIUM. 

chrome-ore,  that  is,  from  chromic  iron.  The  chrome-ore,  which 
even  when  purified  by  washing  always  contains  a  certain  quantity 
of  quartzose  and  aluminous  minerals,  is  heated,  finely  powdered,  in 
a  reverberatory  furnace,  with  carbonate  of  potassa,  to  which  some 
nitrate  of  potassa  is  frequently  added,  and  the  material  is  constantly 
stirred  to  facilitate  its  oxidation.  Chromate  of  potassa,  but  at  the 
same  time,  a  certain  quantity  of  silicate  and  aluminate  of  potassa, 
are  formed,  to  separate  which  the  roasted  substance  is  treated  with 
water,  which  dissolves  the  soluble  alkaline  salts,  after  which  acetic 
acid  is  added  to  the  liquid  until  it  assumes  an  acid  reaction,  which 
is  a  sign  that  the  neutral  chromate  of  potassa  is  converted  into  a 
bichromate  and  that  the  silicic  acid  is  deposited.  The  bichromate, 
being  much  less  soluble  than  the  neutral  salt,  is  easily  separated 
by  crystallization,  and  purified  by  recrystallization. 

Bichromate  of  potassa  forms  beautiful  red  crystals,  which  fuse 
without  change  before  attaining  a  red-heat,  but  decompose  at  a 
higher  temperature  into  neutral  chromate,  sesquioxide  of  chrome, 
and  oxygen  which  is  given  ofi".  This  salt  contains  no  water  of 
crystallization,  and  is  soluble  in  10  parts  of  cold  and  in  a  much  less 
quantity  of  boiling  water. 

Neutral  chromate  of  potassa  is  obtained  by  adding  chromate  of 
potassa  to  a  solution  of  the  bichromate  until  the  latter  assumes  a 
clear  yellow  colour,  and  evaporating  the  liquid,  when  yellow  anhy- 
drous crystals  are  obtained,  presenting  exactly  the  same  form  as 
sulphate  of  potassa.  The  neutral  chromate  is  very  soluble,  as  cold 
water  dissolves  more  than  double  its  weight  of  it,  and  hot  water 
still  more.  The  solution  of  the  neutral  chromate  of  potassa  turns 
the  red  tincture  of  litmus  blue. 

The  neutral  chromate  of  soda  is  very  soluble  in  water,  and,  during 
cooling  from  a  hot  saturated  solution,  forms  crystals  corresponding 
to  the  formula  NaO,CrO3+10HO,  and  is  isomorphous  with  sul- 
phate of  soda  NaO,SO3+10HO. 

Bichromate  of  Chloride  of  Potassium^  or  Chloroohr ornate  of  Potassa, 
§  884.  If  a  solution  of  bichromate  of  potassa  be  boiled  with  chlo- 
rohydric  acid  until  chlorine  begins  to  be  evolved,  a  brown  liquid 
is  obtained,  which  on  cooling  deposits  beautiful  orange-coloured 
crystals  of  a  salt  which  may  be  regarded  as  a  bichromate  of  chlo- 
ride of  potassium  KCl,2Cr03.  This  substance  may  also  be  con- 
sidered as  a  bichromate  of  potassa,  in  which  one  of  the  equivalents 
of  chromic  acid  is  replaced  by  1  equiv.  of  chlorochromic  acid, 
CrOaCl;  but  then  its  formula  should  be  written,  K0(Cr03+Cr0aCl.) 

Chlorochromic  Acid, 
§  885.  A  chlorochromic  acid  CrOgCl  may  be  obtained  isolated, 
by  fusing  in  an  earthen  crucible  10  parts  of  sea-salt  and  17  parts 
of  bichromate  of  potassa.     The  liquid  matter  is  run  on  a  sheet-iron 


COMPOUNDS   OF   CHROMIUM.  127 

plate,  and,  when  cool,  broken  into  fragments,  which  are  introduced 
into  a  glass  retort  with  30  parts  of  concentrated  sulphuric  acid. 
Reaction  commences  immediately,  a  gentle  heat  is  subsequently 
applied,  and  a  blood-red  liquid  condenses  in  the  receiver,  which 
should  be  cooled  with  ice.  The  density  of  this  liquid  is  1.71 ;  it 
boils  at  248°.  By  contact  with  water  it  is  decomposed  into  chromic 
and  chlorohydric  acids:  Cr0,Cl+H0=Cr03+HCl.  It  should  be 
kept  in  glass  tubes  hermetically  sealed. 

COMPOUND  OF  CHROMIUM  WITH  SULPHUR. 
§  886.  If  sulphide  of  carbon  in  vapour  be  passed  through  a  heated 
porcelain  tube  containing  sesquioxide  of  chrome,  the  latter  is  con- 
verted into  crystalline  spangles  of  sulphide  of  chromium  Cr^Sg,  re- 
sembling native  graphite. 

COMPOUND  OF  CHROMIUM  WITH  NITROGEN. 

§  887.  A  compound  of  chromium  with  nitrogen  is  obtained  by 
heating  sesquichloride  of  chrome  in  a  current  of  dry  ammoniacal 
gas.  This  substance  then  presents  the  form  of  a  brown  powder, 
which  is  unchangeable  in  the  atmosphere  at  the  ordinary  tempera- 
ture, but  readily  ignites  and  is  converted  into  sesquioxide  when 
heated  in  the  air. 

COMPOUNDS  OF  CHROMIUM  WITH  CHLORINE. 

§  888.  Chromium  forms  two  compounds  with  chlorine :  a  proto- 
chloride  CrCl,  corresponding  to  the  protoxide  CrO ;  and  a  sesqui- 
chloride CrgClg,  corresponding  to  the  sesquioxide  Grfi^,  and  capable 
of  existing  under  two  different  modifications. 

Protochloride  of  chrome  CrCl  is  obtained  by  passing  hydrogen 
gas  over  anhydrous  sesquichloride  heated  to  redness  in  a  porcelain 
tube.  Protochloride  of  chrome  is  white,  dissolves  in  water,  yield- 
ing a  blue  solution,  which  absorbs  rapidly  the  oxygen  of  the  air, 
thus  converting  the  protochloride  into  an  oxychloride  CrgClaO. 
The  solution  of  protochloride  of  chrome  readily  absorbs  deutoxide 
of  nitrogen,  like  the  protochloride  and  protosulphate  of  iron. 

§  889.  Anhydrous  sesquichloride  of  chrome  is  prepared  by  heat- 
ing an  intimate  mixture  of  sesquioxide  of  chrome  and  charcoal  in 
a  current  of  dry  chlorine,  the  process  otherwise  exactly  resembling 
that  for  the  preparation  of  chloride  of  aluminum  (§  604).  The 
sesquichloride  is  deposited  in  the  anterior  part  of  the  tube,  in  the 
form  of  small  spangles  of  a  peach-blossom  colour.  Anhydrous 
sesquichloride  of  chrome  may  be  brought  in  contact  with  water 
without  being  dissolved  by  it  in  the  slightest  degree,  but  boiling 
water  dissolves  it  after  some  time,  giving  a  green  solution.  If  a 
very  small  quantity  of  protochloride  of  chrome  CrCl  be  added  to 
cold  water,  sesquichloride  immediately  dissolves  with  evolution  af 
heat,  and  yields  a  green  solution  identical  with  that  obtained  by 


128  CHROMIUM. 

dissolving  hydrated  sesquioxide  of  chrome  in  chlorohydric  acid. 
The  smallest  quantity  of  protochloride  of  chrome,  -^^^  is  sufficient 
to  produce  this  remarkable  effect. 

By  dissolving  hydrated  sesquioxide  of  chrome  in  chlorohydric 
acid,  a  green  solution  is  obtained,  which  yields,  on  evaporation,  a 
deliquescent  green  mass,  the  formula  of  which,  when  evaporated 
in  dry  air,  is  CrClg+OHO.  Heated,  it  evolves  water  and  chloro- 
hydric acid,  while  oxychlorides  remain.  Some  chemists  regard 
this  body  as  resulting  from  the  direct  combination  of  chlorohydric 
acid  with  sesquioxide  of  chromium,  as  a  chlorohydrate  of  sesqui- 
oxide of  chrome,  and  give  it  the  formula  CrgOgjSHCl  +  GHO.  If 
the  hydrated  sesquichloride  be  heated  in  a  current  of  chlorohydric 
acid  gas,  it  only  loses  its  water,  and  is  converted  into  a  violet  anhy- 
drous sesquichloride. 

By  pouring  chloride  of  barium  into  a  solution  of  violet  sulphate 
of  chrome,  sulphate  of  baryta  is  precipitated,  and  there  remains  in 
the  liquid  a  violet  sesquichloride  of  chrome,  presenting  the  same 
composition  as  the  green  sesquichloride.  These  two  modifications 
are  observed  in  several  chemical  reactions ;  thus  nitrate  of  silver 
only  precipitates  when  cold  f  of  the  chlorine  of  the  green  chloride, 
while  the  violet  sesquichloride  immediately  parts  with  the  whole 
of  it  at  the  boiling  point.  The  violet  chloride  is  rapidly  trans- 
formed into  the  green  chloride. 

DETERMINATION  OF  CHROME ;  AND  ITS  SEPARATION  FROM  THE 
METALS  PREVIOUSLY  STUDIED. 

§  890.  Chrome  is  always  determined  in  the  state  of  green  oxide. 
To  do  this,  the  chrome  is  converted  into  chloride  or  sulphate  of 
sesquioxide,  and  the  boiling  solution  is  precipitated  by  ammonia. 
The  gelatinous  precipitate  of  the  hydrate  is  collected  on  a  filter, 
and,  after  being  well  washed,  is  calcined  in  a  closed  platinum 
crucible.* 

*  A  much  more  exact  method  is  the  alkalimetrical  determination  of  chrome, 
which  depends  on  the  same  principle  as  that  of  peroxide  of  manganese,  described 
in  the  note  to  ^  765.  The  chrome  must  first  be  converted  into  chromic  acid,  unless 
it  be  already  in  that  state,  by  a  fusion  with  caustic  potassa  and  chlorate  of  potassa. 
Chlorohydric  acid  being  added  to  the  solution  of  the  chlorate  formed,  the  latter  is 
then  reduced  by  a  protosalt  of  iron   according  to  the  formula, 

6FeO-|-2Cr03= 3Fe  A4-Cr,03. 

Now,  if  a  certain  quantity  of  a  protosalt  of  iron  has  been  added,  and  the  surplus 
of  this  be  determined  by  permanganate  of  potassa,  according  to  ^  804,  the  quantity 
of  chromic  acid  or  oxide  may  be  found  by  the  above  formula  ;  as  six  equivalents  of 
the  protoxide  of  iron  found  by  subtracting  the  quantity  determined  from  the 
whole  quantity  added,  correspond  exactly  to  two  equivalents  of  chromic  acid,  or 
to  one  of  sesquioxide  of  chrome. 

The  protosalt  of  iron  employed  is  the  protosulphate  of  iron  and  ammonia,  of 
which  a  standard  solution  is  kept  for  the  determination  of  peroxide  of  manganese. 

The  methods  of  determining  chrome  by  weight  are  inexact ;  as  sesquioxide  of 
chrome  cannot  entirely  be  freed  from  a  part  of  the  fixed  alkali  used  for  its  pre- 


CHROME.  129 

When  chrome  exists  in  solution  as  chromic  acid,  nitrate  of  mer- 
cury is  added,  and  the  precipitate  of  chromate  of  mercury  formed 
IS  calcined  in  a  platinum  crucible,  leaving  sesquioxide  of  chrome, 
which  is  weighed.  Chromic  acid  may,  also,  be  converted  into  ses- 
quichloride  of  chrome,  by  heating  the  liquid  with  chlorohydric  acid, 
and  passing  a  current  of  sulphurous  acid  gas  through  it,  when  oxide 
of  chrome  may  be  precipitated  by  ammonia. 

When  the  oxide  of  chrome  exists  in  the  state  of  a  salt  mixed 
with  alkaline  or  alkalino-earthy  salts,  it  is  precipitated  when  hot 
by  caustic  ammonia,  which  only  precipitates  the  oxide  of  chrome, 
and  is  filtered  rapidly,  so  as  to  avoid,  as  much  as  possible,  the  con- 
tact of  the  air,  in  order  that  the  carbonic  acid  of  the  air  may  not 
precipitate  the  alkaline  earths.  If  the  liquid  contains  manganese, 
an  ammoniacal  salt  must  first  be  added  in  sufiicient  quantity  to 
prevent  the  magnesia  from  being  precipitated  by  the  ammonia. 
The  oxides  of  chrome  and  the  alkaline  earths  may  also  be  precipi- 
tated by  an  alkaline  carbonate,  but  the  mixture  must  then  be  fused 
in  a  platinum  crucible  with  carbonate  of  soda,  when  chromate  of 
soda  is  formed  which  is  dissolved  in  water.  The  chrome  is  then 
precipitated  by  the  processes  described. 

Oxide  of  chrome  is  separated  from  alumina  by  boiling  the  hy- 
drated  oxides  with  caustic  potassa,  which  dissolves  only  the  alumina. 

Oxide  of  chrome  is  separated  from  oxide  of  manganese  by  adding 
to  the  liquid  containing  the  two  oxides  a  quantity  of  ammoniacal 
salt  sufficient  to  prevent  the  oxide  of  manganese  from  being  pre- 
cipitated by  the  ammonia.  The  liquid,  is  then  boiled,  and  an  ex- 
cess of  ammonia  added,  which  completely  precipitates  the  oxide  of 
chrome.* 

In  order  to  separate  oxide  of  chrome  from  the  oxides  of  iron,  the 
substance  must  be  heated  with  caustic  potassa  in  a  silver  crucible, 
when  chromate  of  potassa  is  formed,  which  is  dissolved  in  water, 
leaving  the  peroxide  of  iron  isolated. 

cipitation,  and  ammonia  does  not  precipitate  it  perfectly ;  and  the  other  method, 
not  mentioned  in  the  text,  of  precipitating  chromic  acid  by  acetate  of  lead,  and 
weighing  the  chromate  of  lead  formed,  has  the  disadvantage  that  chromate  of  lead 
is  not  absolutely  insoluble  in  water. —  W.  L.  F. 

*  By  far  the  best  method  of  separating  chrome  from  manganese  is  to  precipi- 
tate the  former  as  sesquioxide  by  carbonate  of  baryta,  which  leaves  the  manga- 
nese in  solution. —  W.  L.  F. 


Vol.  II.— 9 


130 


COBALT. 

Equivalent  =  29.5  (369.0;  0  =  100). 

§  891.  Pure  metallic  cobalt*  is  obtained  by  reducing  its  oxides 
in  a  current  of  hydrogen  gas ;  but  the  metal  is  then  in  the  form 
of  a  black  powder  which  is  pyrophoric,  like  oxide  of  iron  under 
the  same  circumstances :  it  becomes  incandescent  when  projected 
in  contact  with  the  air.  The  metal  is  obtained  in  a  more  aggre- 
gated and  less  oxidizable  form,  by  making  the  reduction  by  hydro- 
gen at  a  higher  temperature,  in  a  porcelain  tube  heated  in  a  rever- 
beratory  furnace.  The  oxides  of  cobalt,  like  those  of  iron,  are 
easily  reduced  by  cementation  in  contact  with  charcoal.  If  oxide 
of  cobalt  be  heaped  in  a  "brasqued"  crucible,  and  heated  in  a 
forge-fire,  precisely  as  in  the  assay  of  iron,  a  fused  metallic  lump 
of  carburetted  cobalt  is  obtained,  which  is  gray,  possessing  a  lustre 
resembling  that  of  cast-iron ;  but  it  has  but  little  malleability,  and 
breaks  under  the  hammer.  Pure  fused  metallic  cobalt  may  be 
obtained  by  adopting  a  process  which  does  not  succeed  for  iron. 
Oxalate  of  cobalt  is  heaped  in  a  porcelain  tube  closed  at  one  end, 
so  as  to  introduce  as  great  a  quantity  as  possible ;  and  this  tube, 
closed  with  a  lid,  is  placed  iji  an  earthen  crucible,  and  the  whole  is 
then  heated  in  a  strong  forge-fire,  after  the  interstices  have  been 
filled  with  clay.  The  oxalate  of  cobalt  is  decomposed  with  evolu- 
tion of  carbonic  acid,  according  to  the  reaction, 
CoO,CA=Co+2CO„ 

when  the  metallic  cobalt  alone  remains,  and,  if  the  temperature  be 
sufficiently  high,  fuses  into  a  button.  The  cobalt  thus  obtained  is 
of  a  steel-gray  colour,  susceptible  of  a  fine  polish,  and  of  the  spe- 
cific gravity  8.5.     Cobalt  is  nearly  as  magnetic  as  iron. 

Cobalt  is  less  aff"ected  by  damp  air  than  iron,  but  after  some 
time  becomes  covered  with  a  brownish-black  rust.  Heated  in  the 
air,  it  is  converted  into  an  oxide. 

Cobalt  dissolves  in  chlorohydric  and  dilute  sulphuric  acids,  with 
disengagement  of  hydrogen  gas ;  but  the  solution  is  effected  more 
slowly  than  that  of  iron  or  zinc. 

COMPOUNDS  OF  COBALT  WITH  OXYGEN. 

§  892.  Cobalt  forms  two  well  defined  oxides :  a  protoxide  con- 
taining 21.32  per  cent,  of  oxygen,  and  a  sesquioxide  containing 
for  the  same  quantity  of  metal  one  and  a-half  times  more  oxygen. 

*  Cobalt  was  first  obtained  in  the  metallic  state  bj  Brandt,  in  1733. 


SALTS    OF    COBALT.  131 

The  equivalent  of  cobalt,  deduced  from  the  composition  of  these 
oxides  by  giving  to  the  protoxide  the  formula  CoO,  is  29.5. 

Hydrated  protoxide  of  cobalt  is  obtained  by  adding  caustic  pO- 
tassa  to  the  solution  of  a  salt  of  cobalt,  a  sulphate  or  a  nitrate  for 
example.  The  gelatinous  precipitate,  of  a  lavender-blue  colour, 
should  be  well  washed  with  boiling  water  to  remove  the  last  traces 
of  potassa,  and  calcined  protected  from  the  air.  The  protoxide  is 
also  prepared  by  calcining  carbonate  of  cobalt  in  a  close  crucible. 
Protoxide  of  cobalt  is  a  powder  of  a  deep  ash-gray  colour,  which, 
when  heated  in  the  air,  absorbs  oxygen,  and  appears  to  be  con- 
verted into  an  oxide  C0O4-C03O3,  corresponding  to  magnetic  oxide 
of  iron.  It  is  a  powerful  base,  which  forms  red  salts,  isomorphous 
with  those  yielded  by  the  other  metallic  oxides  of  the  same  formula. 

Sesquioxide  of  cobalt  is  obtained  by  passing  a  current  of  chlorine 
through  water  containing  hydrated  protoxide  in  suspension  ;  when 
the  liquid  becomes  rosfe-coloured  and  a  black  precipitate  is  formed. 
Under  these  circumstances,  a  portion  of  the  protoxide  is  changed 
into  a  chloride,  which  dissolves,  and  parts  with  its  oxygen  to  an- 
other portion  of  the  protoxide,  which  is  changed  into  sesquioxide : 

3CoO+Cl=CoA+CoCl. 

The  whole  of  the  protoxide  may  be  converted  into  sesquioxide 
by  precipitating  the  dissolved  protochloride  by  potassa,  and  again 
passing  chlorine  through  the  liquid ;  which  is  the  same  as  imme- 
diately treating  the  hydrated  protoxide  by  a  solution  of  an  alkaline 
hypochlorite. 

SALTS  FORMED  BY  PROTOXIDE  OF  COBALT. 

§  893.  The  protosalts  of  cobalt  are  generally  of  a  currant-red 
or  peach-blossom  colour.  Their  solutions  are  of  a  currant-red ; 
but  some  of  them,  principally  that  of  the  protochloride,  are  red 
only  when  diluted,  and  change  to  a  bright  blue  when  concen- 
trated, owing  to  a  dehydration  of  the  salt,  or  to  an  isomeric  modi- 
fication. It  also  occurs  when  the  temperature  is  elevated.  Crys- 
tals of  chloride  of  cobalt,  when  cold,  are  rose-coloured,  but  when 
slightly  heated,  assume  a  beautiful  blue,  without  perceptibly  losing 
any  water ;  for  they  return  to  the  rose  colour  on  cooling.  Charac- 
ters written  upon  paper  with  a  dilute  solution  of  chloride  of  cobalt, 
disappear  after  the  evaporation  of  the  water,  because  the  chloride 
of  cobalt  is  then  in  its  rose-coloured  modification ;  but  if  the  paper 
be  brought  near  to  the  fire,  the  chloride  is  transformed  by  the  ele- 
vation of  temperature  into  its  blue  modification,  by  which  the 
characters  become  apparent,  as  the  colour  of  this  modification  is 
deeper.  As  the  paper  cools,  the  characters  disappear  again  en- 
tirely, unless  the  paper  has  been  too  highly  heated. 

This  property  of  chloride  of  cobalt  has  given  it  some  celebrity 
as  a  sympathetic  ink. 


132  -  COBALT. 

The  characters  only  become  blue  if  the  chloride  of  cobalt  used 
is  very  pure ;  but  when  it  contains  a  small  quantity  of  nickel  they 
turn  green  :  the  purity  of  the  liquid  may  thus  be  ascertained. 

Salts  of  cobalt  yield,  with  potassa  and  soda,  lavender-blue  pre- 
cipitates. Ammonia  does  not  precipitate  the  solutions  containing 
an  excess  of  acid,  as  a  double  ammoniacal  salt,  not  decomposable 
by  an  excess  of  ammonia,  is  then  formed. 

The  alkaline  carbonates  produce  a  rose-coloured  precipitate  of 
carbonate  of  cobalt,  while  the  alkaline  phosphates  and  arseniates 
throw  down  peach-blossom  coloured  precipitates  readily  soluble  in 
an  excess  of  acid.  Yellow  prussiate  of  potash  gives  a  dirty-green 
precipitate.  When  the  salts  of  cobalt  contain  an  excess  of  acid 
they  are  not  precipitated  by  sulphuric  acid.  The  alkaline  sulf- 
hydrates  afford  a  black  hydrated  sulphide. 

Sulphate  of  cobalt  is  obtained  by  dissolving  the  oxide  in  sulphu- 
ric acid,  and  crystallizes,  at  the  ordinary  temperature,  with  7 
equivs.  of  water  CoOjSOg+THO,  in  the  same  form  as  sulphate  of 
iron.  The  formula  of  the  crystals  formed  between  68°  and  86° 
is  CoO,S03+6HO,  and  they  are  isomorphous  with  sulphate  of 
magnesia. 

Nitrate  of  cobalt  is  obtained  by  dissolving  the  metal,  or  the 
oxide,  in  nitric  acid.  The  nitrate  is  easily  decomposed  by  heat, 
and  leaves,  when  subjected  to  a  moderate  temperature,  the  oxide 
CoOjCOgOg  as  a  residue. 

Oxalate  of  cobalt  is  deposited  in  small  rose-coloured  crystals, 
when  oxalic  acid  is  added  to  a  solution  of  sulphate  of  cobalt.  The 
salt  is  but  slightly  soluble  in  water. 

The  alkaline  carbonates  produce  in  solutions  of  the  salts  of  cobalt 
a  pale  rose-coloured  precipitate  of  the  hydrocarbonate 
2(CoO,CO,)+3(CoO,HO.) 

COMPOUND  OF  COBALT  WITH  SULPHUR. 

§  894.  Sulphide  of  cobalt  is  prepared  by  heating  the  oxide  with 
an  alkaline  poly  sulphide  :  if  the  calcination  be  carried  to  a  white- 
heat,  a  bronze-coloured  metallic  button  is  obtained. 

COMPOUND  OF  COBALT  WITH  CHLORINE. 

§  895.  Chloride  of  cobalt  is  prepared  by  dissolving  the  oxide  in 
chlorohydric  acid.  We  have  already  said  that  this  chloride  exists 
under  two  modifications,  as  a  rose-coloured,  and  as  a  blue  com- 
pound. 

COMPOUNDS  OF  COBALT  WITH  ARSENIC. 

§  896.  Two  crystallized  arseniurets  of  cobalt  are  found  in  nature ; 
but  these  minerals  generally  contain  at  the  same  time  arseniurets 
of  nickel  and  iron.     Cobalt  is  also  found  in  combination,  at  the 


ANALYTIC   DETERMINATION.  133 

same  time,  with  arsenic  and  sulphur,  in  the  state  of  a  sulfarseniuret 
CoASa+CoSg :  mineralogists  call  it  gray  cobalt.  Its  most  ordinary 
crystalline  form  is  the  cuho-octahedral.  The  gray  cobalt  worked 
at  Tunaberg,  in  Sweden,  which  is  very  pure,  is  mostly  used  in  labo- 
ratories to  obtain  the  products  of  cobalt.  To  effect  this,  the  pow- 
dered ore  is  first  roasted  in  the  muffle  of  a  cupelling-furnace,  with 
a  gentle  heat  at  the  commencement,  in  order  to  avoid  the  fusion 
of  the  material,  when  the  sulphur  burns  to  sulphurous  acid,  a 
large  portion  of  the  arsenic  is  changed  into  arsenous  acid  which  is 
disengaged  in  white  fumes,  and  another  portion  of  the  arsenic  is 
transformed  into  arsenic  acid  which  remains  in  combination  with 
the  oxidized  cobalt,  forming  arseniate  of  cobalt.  When  white 
fumes  are  no  longer  disengaged,  a  small  quantity  of  powdered 
charcoal  is  thrown  on  the  material,  and  the  whole  is  mixed ;  after 
which  the  door  of  the  muffle  is  closed,  when  the  charcoal  reduces 
the  arseniate  to  the  state  of  an  arseniuret ;  and,  if  air  be  admitted, 
the  roasting  recommences  and  removes  an  additional  quantity  of 
arsenic.  As  this  substance,  however,  cannot  be  entirely  separated 
in  this  way,  the  whole  must  be  roasted  with  carbonate  of  soda  and 
a  small  quantity  of  nitre,  and  then  heated  in  a  crucible,  when  the 
last  portions  of  arsenic  combine  with  the  soda,  forming  arseniate 
of  soda,  w^hich  is  removed  by  treating  the  material  with  boiling 
water.  The  cobalt  remains  in  the  state  of  an  oxide,  generally  con- 
taining a  small  quantity  of  peroxide  of  iron,  which  is  separated  by 
dissolving  in  nitric  acid,  evaporating  to  drive  ofi*  the  excess  of  acid, 
and  then  treating  with  water.  A  few  drops  of  carbonate  of  soda 
added  to  the  liquid  precipitate  hydrated  peroxide  of  iron.  Lastly, 
the  oxide  of  cobalt  is  obtained  by  adding  caustic  potassa ;  or,  when 
metallic  cobalt  is  to  be  prepared,  the  oxalate  intended  for  this  pur- 
pose is  obtained  by  an  addition  of  oxalic  acid. 

The  powdered  ore  may  also  be  immediately  fused  with  a  mixture 
of  carbonate  of  soda  and  sulphur,  when  a  sulfarseniate  of  sodium  and 
sulphide  of  cobalt  are  formed,  which  collect  at  the  bottom  of  the 
crucible  in  the  form  of  a  ball.  This  sulphide,  heated  with  dilute 
sulphuric  acid,  dissolves  by  disengaging  sulfhydric  acid,  yielding 
a  solution  of  sulphate  of  cobalt. 

DETERMINATION  OF  COBALT ;  AND  ITS  SEPARATION  FROM  THE 
METALS  PREVIOUSLY  STUDIED. 

§  89T.  Cobalt  is  determined  either  as  protoxide  or  in  the  me- 
tallic state.  It  is  generally  precipitated  from  its  solutions  by 
caustic  potassa,  when  the  precipitate,  being  washed  with  boiling 
water  and  calcined  at  a  strong  red-heat  in  a  close  platinum  crucible, 
leaves  protoxide  of  cobalt ;  but  it  is  always  to  be  feared  that  a  por- 
tion of  the  cobalt  may  remain  in  the  state  of  sesquioxide.  It  is, 
therefore,  best  to  place  the  oxide  in  a  glass  bulb  A  (fig.  520),  and 
heat  it  in  a  current  of  hydrogen  gas,  thus  restoring  the  oxide  to 


134 


COBALT. 


the  state  of  metallic  cobalt,  which  is  weighed  as  such.     When  the 

liquid  contains  ammonia- 
cal  salts,  it  must  be  eva- 
porated to  dryness  with 
excess  of  potassa  to  drive 
ofPthe  ammonia,  and  then 
treated  with  water.  Co- 
balt may  also  be  precipi- 
tated as  sulphide  by  sulf- 
hydrate  of  ammonia;  but 
^'f  ^^^'   ^  the  sulphide  must  then 

be  redissolved  in  nitric  acid,  and  the  oxide  precipitated  by  potassa. 
§  898.  Cobalt  is  separated  from  the  alkaline  and  alkalino-earthy 
metals  by  sulf  hydrate  of  ammonia,  which  precipitates  the  cobalt 
alone  as  sulphide.  If  the  solution  contains  magnesia,  care  must 
be  taken  to  add  an  ammoniacal  salt,  to  prevent  the  precipitation 
of  this  substance. 

The  separation  of  the  oxides  of  cobalt  and  alumina  is  easily  ef- 
fected by  caustic  potassa  in  excess,  which  dissolves  the  alumina 
and  precipitates  the  oxide  of  cobalt. 

It  is  very  difficult  satisfactorily  to  separate  cobalt  from  manga- 
nese. The  best  method  is  to  heat  the  two  oxides,  first  in  a  current 
of  chlorohydric  acid  gas,  which  transforms  them  into  chlorides,  and 
then  in  a  current  of  hydrogen,  which  restores  the  chloride  of  cobalt 
to  the  metallic  state,  but  does  not  decompose  the  chloride  of  man- 
ganese ;  when,  by  treatment  with  water,  the  latter  chloride  only  is 
dissolved. 

In  order  to  separate  cobalt  from  iron,  the  iron  is  brought  to  the 
state  of  peroxide,  and  enough  sal-ammoniac  added  to  prevent  the 
precipitation  of  the  cobalt  by  an  excess  of  ammonia,  which  throws 
down  only  the  sesquioxide  of  iron :  the  cobalt  is  then  precipitated 
in  the  filtered  liquid  by  sulf  hydrate  of  ammonia. 

SMALT,  AZURE,  OR  ZAFFRE. 

§  899.  Oxide  of  cobalt  readily  combines  with  fusible  silicates, 
producing  beautiful  blue  glasses,  which  find  an  extensive  use  in  por- 
celain-painting, and  are  -highly  valued  for  their  property  of  resist- 
ing the  highest  temperatures,  provided  no  deoxidizing  substances 
be  present. 

A  blue  glass  containing  oxide  of  cobalt  is  technically  prepared, 
which,  when  finely  powdered,  is  used  for  colouring  wall  and  writing 
paper,  and  for  bluing  linen.  This  glass,  called  smalt,  or  azure,  is 
manufactured  in  large  quantities,  from  the  native  sulfarseniuret  of 
cobalt,  in  Saxony  and  other  parts  of  Germany.  The  ore  is  roasted 
in  a  reverberatory  furnace,  in  which  the  vapours  of  arsenious  acid 
condense  in  the  pipes  just  below  the  return-chimney.  The  ore, 
properly  roasted,  is  mixed  with  white  sand  and  very  pure  carbonate 


SMALT.  135 

of  potassa,  in  determinate  proportions,  and  fused  in  glass-house 
pots.  A  metallic  button,  which  is  called  speiss,  composed  chiefly 
of  arseniurets  of  nickel  and  iron,  is  often  deposited  at  the  bottom 
of  the  pot.  The  vitreous  substance,  which  has  an  intense  blue 
colour,  is  pounded  after  cooling,  and  then  ground  to  a  fine  powder, 
which  is  then  suspended  in  water,  when  the  grosser  particles  are 
first  deposited,  and  must  again  be  ground.  The  supernatant  muddy 
waters  are  decanted  after  some  time,  and  poured  into  buckets,  where 
they  gradually  deposit  finer  and  finer  powder.  The  clearness  of  the 
blue  colour  depends  on  the  fineness  of  the  particles. 

COBALT-BLUE,  OR  THENARD'S  BLUE. 

§  900.  Oxide  of  cobalt  also  enters  as  a  colouring  principle  into 
another  colour  used  in  painting,  and  called  eobalt-blue,  or  Thenard's 
blue.  This  colouring  matter  is  prepared  as  follows : — A  solution 
of  sulphate  or  nitrate  of  cobalt  is  precipitated  by  phosphate  of 
potassa ;  and,  on  the  other  hand,  a  solution  of  alum  is  treated  with 
carbonate  of  soda.  The  two  gelatinous  precipitates  of  alumina 
and  phosphate  of  cobalt  are  intimately  mixed,  in  the  proportion 
of  3  volumes  of  phosphate,  and  from  12  to  15  parts  of  alumina ; 
when  the  mixture,  dried  and  calcined  in  a  crucible,  changes  into  a 
beautiful  blue  powder.  It  is  important  to  prevent  the  combustible 
vapours  of  the  furnace  from  entering  the  crucible,  as  they  would 
seriously  injure  the  shade.  This  inconvenience  is  avoided  with 
certainty  by  placing  at  the  bottom  of  the  crucible  a  small  quantity 
of  oxide  of  mercury,  which  produces  an  atmosphere  of  oxygen  gas, 
and  preserves  the  oxide  of  cobalt  from  reduction. 


136 


NICKEL. 
Equivalent  =  29.6  (370.0 ;  0  =  100.) 

§  901.  Metallic  nickel*  is  obtained  in  precisely  the  same  manner 
as  cobalt.  Oxide  of  nickel,  reduced  by  oxygen  at  a  low  tempera- 
ture, yields  a  pulverulent  metal,  which  becomes  incandescent  in  the 
air,  and,  when  reduced  in  a  "  brasqued"  crucible  in  a  forge-fire, 
produces  a  well-fused  carburetted  metal.  Pure  melted  metallic 
nickel  is  obtained  by  heating  oxalate  of  nickel  in  a  closed  vessel 
in  a  strong  forge-fire. 

Nickel  is  a  slightly-grayish  white  metal,  which  is  so  much  more 
malleable  than  cobalt,  that  it  can  be  hammered  and  drawn  out  into 
fine  wire.  Its  density  is  about  8.8.  It  is  nearly  as  magnetic  as 
iron,  but  loses  this  property  when  heated  to  about  400°.  Nickel 
bears  pretty  well  the  contact  of  a  damp  atmosphere,  but  by  heating 
in  the  air  is  converted  into  an  oxide.  It  dissolves  in  chlorohydric 
and  dilute  sulphuric  acids,  with  disengagement  of  hydrogen  gas. 

COMPOUNDS  OF  NICKEL  WITH  OXYGEN. 

§  902.  Nickel  forms  two  oxides ; 

A  protoxide  composed  of.....  Nickel 78.72 

Oxygen 21.28 

100.00 

and  a  sesquioxide  composed  of.....  Nickel 71.13 

Oxygen 28.87   • 

100.00 

From  this  the  equivalent  of  nickel  is  29.6,  differing  by  only  one 
decimal  from  that  of  cobalt. 

Protoxide  of  nichel  is  obtained  in  the  hydrated  state  by  treating 
a  solution  of  sulphate  of  nickel  with  caustic  potassa,  when  an  apple- 
green  precipitate  forms,  which,  when  well-washed  in  boiling  water, 
and  then  calcined  and  protected  from  the  air,  yields  anhydrous 
oxide  as  an  ash-gray  powder.  It  is  also  obtained  by  the  calcina- 
tion of  the  hydrocarbonate.  Although  calcined  nitrate  of  nickel 
leaves  some  oxide,  the  temperature  must  be  very  high  to  convert  it 
entirely  into  protoxide. 

Sesquioxide  of  nickel  is  prepared  by  subjecting  hydrated  prot- 
oxide suspended  in  water  to  the  action  of  chlorine,  or  treating  it 

*  Recognised  as  a  peculiar  metal,  in  1751,  by  Cronstedt  and  Bergmann. 


SALTS   OP   NICKEL.  137 

by  an  alkaline  chlorite.     This  oxide  forms  a  black  powder,,  which 
dissolves  in  hydrochloric  acid  with  disengagement  of  chlorine. 

SALTS  FORMED  BY  PROTOXIDE  OF  NICKEL. 

§  903.  The  hydrated  salts  of  nickel  are  of  a  beautiful  green 
colour,  the  majority  of  them  becoming  yellow  by  losing  their  water 
of  crystallization,  while  their  solutions  are  of  a  beautiful  emerald 
green.  From  the  salts  of  nickel  the  fixed  alkalies  throw  down  an 
apple-green  gelatinous  precipitate,  while  ammonia  does  not  preci- 
pitate highly  acid  solutions,  and  gives  only  a  partial  precipitation 
with  neutral  solutions,  as  an  excess  of  the  reagent  redissolves  the 
precipitate,  and  the  liquid  turns  blue.  The  carbonates  of  soda  and 
potassa  produce  bright-green  precipitates  of  the  hydrocarbonate 
Ni0,C03+Ni0,H0,  while  the  alkaline  phosphates  and  arseniates 
throw  down  pale-green  precipitates.  Prussiate  of  potash  gives  a 
greenish-white  precipitate.  The  acid  solutions  of  salts  of  nickel 
are  not  affected  by  sulf hydric  acid,  but  are  partially  precipitated 
when  neutral,  especially  if  the  acid  of  the  salt  is  feeble  ;  while  the 
alkaline  sulfhydrates  give  a  black  precipitate  of  hydrated  sulphide 
soluble  in  an  excess  of  the  precipitant. 

§  904.  Sulphate  of  nickel  is  generally  obtained  from  the  nickel-ore, 
which  is  the  metallic  speiss  deposited  in  the  bottom  of  the  crucible 
in  the  manufacture  of  smalt.  It  is  principally  composed  of  arseni- 
urets  of  nickel  and  iron,  but  frequently  contains  some  traces  of 
cobalt;  in' which  case,  the  powdered  speiss  is  fused  with  a  small 
quantity  of  alkaline  glass,  to  which  a  little  nitre  is  added,  when  the 
oxide  of  cobalt  passes  into  the  vitreous  scoriae,  and  the  purified 
nickel  is  concentrated  in  the  lump  of  arseniuret,  because  cobalt  is 
more  oxidizable  than  nickel,  which  has,  on  the  contrary,  a  greater 
affinity  for  arsenic.  The  arseniuret  of  nickel  is  then  roasted  to 
drive  off  the  arsenic  as  completely  as  possible,  and  the  residue  of 
basic  arseniate,  after  being  heated  in  a  crucible  with  a  mixture  of 
carbonate  of  soda  and  a  small  quantity  of  nitre,  is  treated  with  hot 
water,  which  dissolves  the  alkaline  salts  containing  all  the  arsenic 
acid  in  the  state  of  arseniate  of  soda.  The  oxide  of  nickel  remain- 
ing is  dissolved  in  sulphuric  acid,  the  small  quantity  of  persulphate 
of  iron  which  the  sulphate  thus  formed  always  contains  being  easily 
removed  by  boiling  the  liquid  with  carbonate  of  lime,  which  preci- 
pitates only  the  peroxide  of  iron,  and  introduces  no  foreign  salts 
into  the  liquid,  as  sulphate  of  lime  is  very  slightly  soluble. 

Sulphate  of  nickel  crystallizes  at  the  ordinary  temperature  with 
7  equiv.  of  water,  but  may  be  obtained  combined  with  6  equiv. 
by  crystallization  from  a  hot  solution. 

Crystals  of  sulphate  of  nickel  with  7  equiv.  of  water  often  attain 
a  very  large  size,  and  exhibit  a  remarkable  phenomenon  of  molecu- 
lar movement :  on  leaving  a  large  crystal  to  itself  for  some  days, 
especially  if  exposed  to  solar  light,  it  preserves  its  outward  form, 


138  NICKEL. 

but  loses  its  transparency ;  and,  if  it  be  then  broken,  will  be  found 
filled  with  cavities,  the  walls  of  which  are  lined  with  brilliant  crys- 
tals of  quite  another  form,  and  in  which  the  molecules  are  grouped 
in  a  completely  different  manner,  while  the  substance  has  not  be- 
come liquid. 

By  adding  oxalic  acid  to  a  solution  of  sulphate  of  nickel,  no 
precipitate  is  immediately  formed,  while,  after  some  time,  a  crys- 
talline powder  of  oxalate  of  nickel  is  deposited,  and  only  a  very 
small  quantity  of  the  metal  remains  in  solution. 

COMPOUND  OF  NICKEL  WITH  SULPHUR. 

§  905.  Sulphide  of  nickel  is  prepared  by  heating  a  mixture  of 
oxide  of  nickel,  carbonate  of  soda,  and  sulphur,  when  the  sulphide 
fuses  into  a  bronze-yellow  button,  if  the  temperature  is  sufficiently 
elevated. 

COMPOUND  OF  NICKEL  WITH  CHLORINE. 

§  906.  Chloride  of  nickel  is  obtained  by  dissolving  the  oxide,  or 
metallic  nickel,  in  concentrated  chlorohydric  acid,  when  the  solu- 
tion deposits  green  crystals,  which,  when  heated  in  a  tube  pro- 
tected from  the  air,  part  with  their  water,  and  yield  a  volatile 
anhydrous  chloride,  which  sublimes  on  the  sides  of  the  tube  in  the 
form  of  gold-coloured  spangles. 

COMPOUNDS  OF  NICKEL  WITH  ARSENIC. 

§  907.  Nickel  is  found  in  nature  combined  with  arsenic,  in  the 
state  of  arseniurets,  NiAs  and  NiAsg  and  also  occurs  as  a  sulf- 
arseniuret  NiS^-fNiASg.  The  native  arseniurets  are  sometimes 
used  for  the  extraction  of  nickel,  but  generally  the  speiss  arising 
from  the  manufacture  of  smalt  js  preferred  for  that  purpose. 

GERMAN  SILVER,  ARGENTAN,  OR  MAILLECHORT. 

§  908.  Nickel  is  technically  used  for  making  an  alloy  capable  of 
a  high  polish  and  the  lustre  of  silver.  This  alloy,  which  is  com- 
posed of  100  parts  of  copper,  60  of  zinc,  and  10  of  nickel,  is  known 
in  commerce  by  the  various  names  of  G-erman  silver^  maillechort, 
packfong,  argentan.  Various  ornamental  objects  are  made  of  it, 
but  it  is  chiefly  used  for.  spurs,  for  carriage  and  harness  mount- 
ings, etc.*  It  has  been  proposed  for  kitchen  utensils,  but  this  use 
would  be  dangerous,  as  the  alloy  readily  oxidizes,  particularly  when 
in  contact  with  acid  liquids,  and  produces  very  poisonous  salts.f 

*  In  England. 

f  German  silver  finds  much  more  extensive  use  in  Great  Britain  and  the  United 
States,  being  now  a  substance  almost  universally  employed  for  the  manufacture 
of  all  articles  for  useful  and  ornamental  purposes  which  are  to  be  electro-plated. 
At  Birmingham  alone,  hundreds  of  tons  are  annually  fashioned  into  plate  of  every 
description,  and  subsequently  coated  with  silver  or  gold  by  the  galvanic  process. — 
W.  L.  F. 


ANALYSIS.  189 


DETERMINATION  OF  NICKEL,  AND  ITS  SEPARATION  FROM  THE 
METALS  PREVIOUSLY  STUDIED. 

§  909.  Nickel  is  precipitated  from  its  solutions  by  caustic  po- 
tassa,  or  bj  sulf  hydrate  of  ammonia,  and  is  determined  in  the  state 
of  protoxide,  like  cobalt,  after  having  been  highly  calcined  ;  but,  as 
is  the  case  with  cobalt,  the  degree  of  oxidation  of  the  oxide  which 
remains  is  uncertain.  In  exact  analyses,  it  is  preferable  to  reduce 
the  oxide  by  hydrogen  and  weigh  the  nickel  in  the  metallic  state. 

§  910.  As  nickel  is  separated  from  the  metals  previously  studied, 
by  the  same  processes  as  those  described  for  cobalt,  we  shall  refer 
the  reader  to  them  (898),  and  proceed  to  examine  only  the  separa- 
tion of  cobalt  and  nickel. 

Nickel  and  cobalt  are  frequently  found  associated,  and  their 
separation,  which  presents  some  difficulties,  becomes  necessary. 
One  of  the  most  simple  processes  consists  in  pouring  oxalic  acid 
into  the  solution  which  contains  the  two  oxides,  after  which  the  two 
oxalates,  which  precipitated  together,  are  redissolved  in  ammonia, 
and  the  ammoniacal  liquid  is  left  in  an  uncorked  bottle,  when  the 
ammonia  is  slowly  disengaged,  and,  as  its  quantity  diminishes,  the 
liquid  loses  more  and  more  its  power  of  dissolving  the  oxalates. 
Now,  the  two  salts  not  being  equally  soluble  in  the  ammoniacal 
liquid,  a  moment  arrives  at  which  the  latter  does  not  contain  enough 
ammonia  to  hold  the  oxalate  of  nickel  in  solution,  which  is  the  less 
easily  soluble  salt,  but  at  which  it  can  still  dissolve  the  oxalate  of 
cobalt :  the  oxalate  of  nickel  is  then  deposited,  and  the  liquid  as- 
sumes a  deeper  red  tinge.  When  a  bright  currant-colour  is  attained, 
the  liquid  is  decanted,  and  then  contains  only  cobalt.  The  small 
quantity  of  cobalt  which  the  precipitate  of  oxalate  of  nickel  always 
contains,  is  separated  by  again  dissolving  the  oxalate  of  ammonia, 
and  allowing  the  liquid  to  evaporate. 

Another  process  consists  in  pouring  alternately  chlorohydric  acid 
and  ammonia  into  the  solution  which  contains  the  two  oxides,  until 
the  liquid  yields  no  precipitate  with  an  excess  of  ammonia,  when  a 
sufficient  quantity  of  ammoniacal  salt  has  formed  to  constitute,  with 
the  metallic  salts,  double  salts  which  are  indecomposable  by  ammo- 
nia. The  liquid  is  bottled,  and  caustic  potassa  added  to  it,  which 
does  not  decompose  the  double  ammoniacal  salt  of  cobalt,  while 
that  of  nickel  parts  with  the  oxide  of  nickel,  which  is  precipitated. 
The  contact  of  the  air  must  be  avoided  during  this  experiment,  as 
otherwise  the  cobalt  would  absorb  oxygen  and  be  precipitated  in 
the  state  of  hydrated  sesquioxide.  The  cobalt  which  remains  in 
the  liquid  is  then  precipitated  by  an  alkaline  sulphide. 

These  metals  may  also  be  separated  very  accurately  by  dissolv- 
ing them  in  an  excess  of  chlorohydric  acid,  and  diluting  with  a 
large  quantity  of  water,  after  which  the  liquid  is  saturated  with 
chlorine  gas,  and  carbonate  of  baryta  in  excess  added.    The  liquid 


140  NICKEL. 

is  then  allowed  to  rest  for  18  hours  without  being  heated,  when 
the  whole  of  the  cobalt  is  precipitated  as  sesquioxide,  while  the 
nickel  remains  in  solution.  The  precipitate,  which  consists  of 
sesquioxide  of  cobalt  and  the  excess  of  carbonate  of  baryta,  is  col- 
lected on  a  filter,  and,  after  being  well  washed  with  cold  water,  is 
dissolved  in  concentrated  chlorohydric  acid,  after  which  the  baryta 
is  precipitated  by  sulphuric  acid,  and  then  the  oxide  of  cobalt  by 
potassa.* 

*  Since  the  author  has  published  the  above  methods,  a  still  better  one  has 
become  known,  which  is  the  discovery  of  Liebig  and  Wohler,  and  consists  in  the 
following  operations : — The  two  oxides  intended  to  be  separated  are  dissolved  in 
pure  cyanide  of  potassium,  and  the  red  solution  obtained  is  boiled  to  expel  the 
excess  of  prussic  acid ;  when  hydrogen  is  at  the  same  time  evolved,  and  the 
cyanide  of  cobalt  changes  to  cobaltidcyanide  of  potassium  Co3Cy3,3KCy,  while  the 
nickel  remains  as  potasso-cyanide  nickel  NiCy,2KCy.  An  addition  of  pure  oxide 
of  mercury,  suspended  in  water,  then  precipitates  all  the  nickel  as  a  mixture  of 
oxide  and  cyanide,  while  the  mercury  replaces  the  nickel  in  the  double  cyanide ; 
after  which  the  precipitate,  consisting  of  oxide  and  cyanide  of  nickel,  and  the  ex- 
cess of  oxide  of  mercury  added,  is  washed  and  calcined,  when  pure  oxide  of  nickel 
remains,  and  is  weighed.  The  cobalt,  which  still  exists  in  the  solution  as  cobaltid- 
cyanide of  potassium,  is  then  precipitated  by  protonitrate  of  mercury,  after 
having  neutralized  the  liquid  with  nitric  acid ;  when  a  heavy  white  precipitate  is 
formed,  containing  all  the  cobalt  as  cobaltidcyanide  of  mercury,  which,  by  calcina- 
tion in  the  air,  is  converted  into  pure  oxide  of  cobalt,  which  is  weighed. —  W.  L.  F. 


141 


ZINC. 

Equivalent  =  32.6  (407.5 ;  0  =  100). 

§  911.  Zinc  is  now  technically  employed  in  a  great  number  of 
different  ways.  That  found  in  commerce  is  not  perfectly  pure, 
while  the  sheet-zinc  more  nearly  approaches  perfect  purity,  be- 
cause the  presence  of  the  smallest  quantity  of  foreign  matter  con- 
siderably diminishes  the  malleability  of  the  metal  and  renders  it 
unfit  for  rolling.  Zinc  fuses  at  a  temperature  of  about  930°,  and 
boils  at  a  white-heat,  when  it  may  be  purified  by  distillation ;  to 
effect  which,  commercial  zinc  is  placed  in  an  earthen  retort,  which 
is  arranged  in  a  reverberatory  furnace,  while  below  the  open  neck 
of  the  retort  a  vessel  containing  water  is  placed  to  receive  the  zinc. 
Another  and  more  suitable  apparatus  for  this  distillation  consists 
of  a  clay  crucible  A  (fig.  521),  the  bottom  of  which  is  perforated, 
and  rests  on  a  clay  disk,  or  cheese  (froraage) 
B,  pierced  likewise  with  a  hole.  A  clay  pipe 
ah,  the  upper  end  of  which  reaches  the  top 
of  the  crucible,  being  hermetically  fastened  in 
both  apertures,  the  zinc  to  be  distilled  is 
placed  in  the  crucible,  which,  after  the  lid  is 
luted  on,  is  arranged  in  a  furnace  so  that 
the  pipe  may  pass  through  the  grate,  beneath 
which  is  placed  a  pan  C  filled  with  water. 
When  the  temperature  rises  in  the  furnace, 
the  zinc  first  fuses,  and  then  boils,  when  its 
vapour,  descending  through  the  pipe  and  there 
^^'       '  condensing,  allows  the  liquid  metal  to  run  into 

the  pan.     This  process  is  called  distillatio  per  deseensum. 

The  distillation  of  zinc  does  not  free  it  entirely  from  the  metals 
with  which  it  is  combined,  since  the  very  high  temperature  at  which 
the  distillation  takes  place,  causes  a  small  portion  of  the  other  me- 
tals to  be  carried  over  with  the  vapours  of  the  zinc. 

Zinc  is  of  a  bluish-white  colour,  and  its  fresh  fracture  exhibits 
large  and  very  brilliant  crystalline  laminae.  While  it  is  brittle  at  the 
ordinary  temperature,  it  becomes  malleable  at  a  few  degrees  above 
212°,  and,  when  heated  to  392°,  again  becomes  so  brittle  that  it 
may  be  pounded  in  a  mortar.  Ignorance  of  these  remarkable  pro- 
perties of  zinc  for  a  long  time  prevented  its  extensive  technical  use, 
and  formerly  it  was  only  employed  for  making  alloys.  It  is  now 
rolled  into  thin  sheets  for  roofing  houses,  and  making  bathing-tubs 
and  other  vessels  of  great  capacity.    Zinc  vessels  must  not  be  used 


142  ZINC. 

for  the  preparation  of  food,  because  the  metal  readily  oxidizes  in 
contact  with  the  air,  when  in  presence  of  even  the  weakest  acids, 
and  produces  poisonous  salts. 

The  density  of  zinc  varies  from  6.86  to  7.20,  according  as  the 
metal  has  been  cast,  or  rolled. 

§  912.  Zinc  is  a  very  oxidizable  metal,  as  its  surface  soon  tar- 
nishes by  superficial  oxidization  in  a  damp  atmosphere,  while,  when 
heated  in  contact  with  the  air  at  a  temperature  above  its  melting 
point,  it  becomes  incandescent  and  burns  with  a  dazzling  white 
flame,  the  brilliancy  of  which  is  owing  to  the  vapour  of  zinc,  which, 
by  burning  in  the  air,  forms  oxide  of  zinc,  a  perfectly  fixed  com- 
pound, of  which  the  particles,  heated  to  whiteness,  communicate  a 
bright  lustre  to  the  flame.  Zinc  dissolves  readily  in  chlorohydric 
and  dilute  sulphuric  acid,  and  disengages  hydrogen;  and  the  metal, 
when  impure,  dissolves  more  rapidly  than  perfectly  pure  zinc.  It 
decomposes  aqueous  vapour  with  disengagement  of  hydrogen,  and 
is  converted  into  an  oxide,  the  reaction  commencing  at  a  tempera- 
ture a  little  above  212°,  when  the  metal  exists  in  a  very  finely 
divided  state. 

Zinc  also  dissolves  with  disengagement  of  hydrogen  in  a  boiling  so- 
lution of  potassa  and  soda,  and  forms  soluble  alkaline  zincates.  When 
an  iron  blade  is  at  the  same  time  dipped  into  the  alkaline  solution, 
the  water  is  decomposed  even  when  cold,  while  the  zinc  alone  dis- 
solves, the  iron  acting  only  by  producing  with  the  zinc  a  voltaic 
current,  in  which  the  latter  metal  becomes  the  positive  element, 
and  thus  acquires  an  affinity  for  oxygen  sufficiently  great  to  de- 
compose water  at  the  ordinary  temperature  in  the  presence  of 
potassa.  The  decomposition  of  water  in  the  presence  of  potassa, 
is  effected  very  remarkably  by  plates  of  galvanized  iron,  when  very 
brilliant  small  crystals,  consisting  of  a  hydrated  ozide  of  zinc 
ZnO-fHO  are  deposited  on  the  sides  of  the  vessel. 

COMPOUND  OF  ZINC  WITH  OXYGEN. 
§  913.  Only  one  oxide  of  zinc,  a  very  powerful  base,  is  known, 
the  salts  of  which  are  isomorphous  with  those  of  magnesia  and  with 
the  protosalts  of  iron,  cobalt,  and  nickel.  The  oxide  is  obtained  by 
heating  the  metal  in  contact  with  the  air  until  it  ignites,  when  a 
white  flocculent  substance,  of  which  a  portion  is  carried  off"  by  the 
current  of  air,  is  deposited  on  the  edges  of  the  crucible.  The  old 
chemists  called  it  lana  philosophica,  or  pompholix.'^  The  oxide  thus 
obtained  always  contains  particles  of  the  metal,  which  it  may  be 
freed  from  by  levigation.  When  pure  oxide  of  zinc  is  to  be  prepared, 
it  is  better  to  decompose  by  heat  either  nitrate  of  zinc  or  the  hy- 
drocarbonate  which  is  obtained  by  adding  an  alkaline  carbonate  to 
the  solution  of  a  salt  of  zinc.    When  caustic  potassa  is  poured  into 

*  It  also  bore  the  curious  name  oi  nihil  album,  "  white  nothing." 


SALTS   OF   ZINC.  143 

a  salt  of  zinc,  a  white  precipitate  of  hydrated  oxide  of  zinc  is 
obtained,  which  retains  a  certain  quantity  of  alkali  with  great 
obstinacy. 

Anhydrous  oxide  of  zinc  is  white,  and  assumes  a  yellow  shade 
on  the  application  of  heat,  which  disappears  on  cooling. 

Oxide  of  zinc  is  formed  of 

Zinc 81.5 

Oxygen 18.5 

100.0 
whence  the  equivalent  of  zinc  is  32.6. 

Oxide  of  zinc,  when  mixed  with  drying  oils,  produces  a  white 
paint,  which  may  be  substituted  for  white-lead,  or  ceruse,  and  has 
been  recently  manufactured  on  a  large  scale.*  It  has  the  advan- 
tage of  not  being  blackened  by  sulphurous  gases,  and  not  exposing 
the  workmen  to  the  same  dangerous  affections. 

SALTS  FORMED  BY  OXIDE  OF  ZINC. 

§  914.  The  salts  of  zinc  are  colourless  when  the  acid  is  not 
coloured.  Their  solutions  yield,  with  potassa,  soda,  and  ammonia, 
white  precipitates  which  dissolve  in  an  excess  of  the  reagent ;  and 
the  alkaline  carbonates  throw  down  a  white  precipitate,  which  also 
takes  place  with  prussiate  of  potash  and  the  alkaline  phosphates 
and  arseniates.  Sulfhydric  acid  does  not  precipitate  the  salts  of 
zinc  when  they  contain  an  excess  of  acid,  but  the  sulf  hydrates  give 
white  precipitates. 

Sulphate  of  Zinc. 

§  915.  The  sulphate,  which  is  the  most  important  of  the  salts 
of  zinc,  is  readily  prepared  in  the  laboratory  by  dissolving  metallic 
zinc  in  dilute  sulphuric  acid.  It  crystallizes  at  the  ordinary  tem- 
perature with  7  equiv.  of  water,  of  which  6  are  easily  driven  off  by 
subjecting  the  salt  to  a  temperature  above  212°.  Crystallized 
sulphate  of  zinc  dissolves  in  two  or  three  times  its  weight  of  water, 
at  the  ordinary  temperature,  while  at  212°  its  solubility  may  be 
said  to  be  infinite,  as  it  melts  in  its  water  of  crystallization. 

Sulphate  of  zinc  is  prepared  on  a  large  scale  by  roasting  blende 
in  heaps,  when  a  portion  of  the  sulphur  is  disengaged  in  the  state 
of  sulphurous  acid,  while  the  greater  part  of  the  blende  is  con- 
verted into  sulphate  of  zinc,  provided  the  temperature  does  not 
rise  above  a  certain  point.  The  roasted  matter  is  treated  with 
water,  and  the  solution  evaporated  to  crystallization ;  and  in  order 
to  render  the  salt  easily  transportable,  it  is  generally  melted  in  its 
water  of  crystallization,  and  poured  into  square  moulds  of  the  size 

*  It  is  extensively  manufactured  at  Vieille  Montague,  and  also  in  New  Jersey, 
from  the  red  oxide  occurring  near  Franklin. 


144  ZINC. 

of  a  common  brick.     The  salt  is  called  in  commerce  white  vitriol, 
and  is  used  in  the  manufacture  of  calico. 

Carbonate  and  Hydrocarhonate  of  Zinc, 
§  916.  When  an  alkaline  carbonate  is  poured  into  a  solution  of 
sulphate  of  zinc,  a  precipitate  is  obtained,  which  is  not  a  carbonate, 
but  a  hydrocarhonate  of  zinc  (2ZnO,C024-3ZnO,HO).  Anhydrous 
carbonate  of  zinc  is  found  in  nature,  constituting  a  mineral  called 
calamine^  which  acquires  great  importance  from  being  the  ordinary 
ore  of  zinc.  Most  frequently,  calamine  exists  in  compact  masses, 
and  more  rarely  exhibits  distinct  crystals  belonging,  like  carbonate 
of  lime,  to  the  rhombohedric  system. 

COMPOUND  OF  ZINC  WITH  SULPHUR. 

§  917.  Zinc  in  the  state  of  filings  is,  when  heated  with  flowers 
of  sulphur,  converted  into  a  sulphide  ;  but  it  is  difficult  thus  to  ob- 
tain a  perfect  sulphuration.  It  is  better  to  heat  a  very  intimate  mix- 
ture of  oxide  of  zinc  and  flowers  of  sulphur,  when  sulphurous  acid 
is  disengaged,  and  sulphide  of  zinc  ZnS,  in  the  form  of  a  yellowish- 
white  powder,  remains.  Sulphide  of  zinc  is  found  abundantly  in 
nature,  forming  a  brownish-yellow  translucid  mineral,  crystallized 
in  regular  octahedrons,  or  cubo-octahedrons,  and  called  blende, 

COMPOUND  OF  ZINC  WITH  CHLORINE. 

§  918.  Zinc  is  easily  acted  on  by  gaseous  chlorine,  and  converted 
into  a  white,  butyrous,  very  fusible  substance,  which  distils  only 
at  a  red-heat.  This  chloride  is  obtained  in  solution  in  water,  by 
treating  zinc  with  chlorohydric  acid,  when  the  solution,  on  being 
evaporated  and  cooled,  becomes  crystalline.  Chloride  of  zinc  is 
soluble  in  water  and  in  alcohol  to  such  an  extent,  that  when  an 
aqueous  solution  of  the  salt  is  concentrated  by  ebullition,  the  tem- 
perature rises  continually  to  482°,  at  which  point  the  chloride 
becomes  anhydrous,  but  still  preserves  its  liquid  state.  This  pro- 
perty suggests  the  use  of  a  solution  of  chloride  of  zinc  instead  of 
oil,  for  baths  in  which  substances  are  to  be  heated  to  a  high  but 
certain  temperature. 

DETERMINATION  OF  ZINC,  AND  ITS  SEPARATION  FROM  THE  METALS 
PREVIOUSLY  STUDIED. 

§  919.  Zinc  is  generally  precipitated  from  its  solutions  by  car- 
bonate of  soda,  after  which  the  liquid  is  boiled,  and  the  gelatinous 
precipitate  of  hydrocarhonate  of  zinc  washed  with  boiling  water, 
when  it  is  determined  in  the  state  of  oxide  after  calcination.  If 
the  liquid  contains  much  ammoniacal  salt,  it  must  be  evaporated  to 
dryness  with  an  excess  of  carbonate  of  soda,  and  then  treated  with 
water. 


DETERMINATION   OF   ZINC.  145 

Zinc  IS  frequently  precipitated  as  sulphide  by  sulfhydrate  of 
ammonia ;  when  the  precipitate  is  washed  with  water  containing  a 
small  quantity  of  the  sulfhydrate,  in  order  to  prevent  the  forma- 
tion of  sulphate  of  zinc  by  contact  with  the  air.  The  hydrated 
sulphide  is  redissolved  in  chlorohydric  acid,  and  the  zinc  precipi- 
tated by  carbonate  of  soda  as  carbonate. 

§  920.  In  general,  zinc  is  separated  from  the  alkalies  and  alka- 
line earths  by  means  of  sulfhydrate  of  ammonia,  which  precipitates 
the  zinc  only  as  sulphide ;  but  it  is  more  readily  separated  from 
baryta  by  means  of  sulphuric  acid.  Lime  may  also  be  separated 
from  oxide  of  zinc  by  adding  to  the  liquid  containing  the  two 
bases  an  excess  of  ammonia,  and  some  oxalate  of  ammonia,  which 
precipitates  only  the  lime  in  the  state  of  oxalate  of  lime,  while  the 
oxide  of  zinc  remains  in  solution  in  the  excess  of  ammonia. 

The  separation  of  oxide  of  zinc  from  magnesia  is  effected  by 
means  of  sulfhydrate  of  ammonia,  the  precaution  being  used  first 
to  add  an  ammoniacal  salt  in  sufficient  quantity  to  the  liquid  to 
prevent  the  precipitation  <jf  the  magnesia  by  ammonia. 

Oxide  of  zinc  is  separated  from  alumina  by  ammonia  in  excess, 
which  dissolves  the  former  and  precipitates  the  alumina,  while  a 
perfect  separation  is,  however,  difficult,  as  alumina  is  slightly  so- 
luble in  ammonia. 

Oxide  of  zinc  is  separated  from  oxide  of  manganese  by  caustic 
potassa,  which  redissolves  the  former  and  leaves  the  oxide  of  man- 
ganese, especially  if  the  liquid  is  left  exposed  to  the  air  for  some 
time,  so  that  the  protoxide  of  manganese  may  be  changed  into  ses- 
quioxide.  The  separation  is,  however,  rarely  effected  perfectly,  the 
oxide  of  manganese  always  retaining  some  oxide  of  zinc  ;  and  the 
precipitate  must  be  redissolved  in  chlorohydric  acid  and  precipi- 
tated anew  by  an  excess  of  potassa. 

In  order  to  separate  zinc  from  iron,  the  latter  metal  is  first 
brought  to  the  state  of  a  sesquisalt  by  means  of  nitric  acid  or 
chlorine,  and  then  ammonia  in  excess  is  added,  which  redissolves 
the  oxide  of  zinc  and  precipitates  only  the  hydrated  sesquioxide 
of  iron.  It  is  well  to  redissolve  the  oxide  of  iron  in  an  acid  and 
precipitate  it  a  second  time  by  ammonia  in  excess,  as  the  small 
quantities  of  oxide  of  zinc,  which  in  the  first  precipitation  had  been 
carried  down  with  the  sesquioxide  of  iron,  are  thus  separated. 

The  separation  of  zinc  from  cobalt  and  nickel  is  more  difficult. 
The  best  plan  consists  in  precipitating  the  metals  together  by  car- 
bonate of  soda,  and  weighing  them  in  the  state  of  oxides  after  cal- 
cination. The  mixture  of  oxides  is  then  placed  in  a  glass  globe  D 
(fig.  522),  terminating  in  a  curved  end  hcd^  which  descends  to  the 
level  of  a  small  quantity  of  water  in  the  bottle  E,  and  a  current  of 
dried  chlorohydric  acid  gas  is  passed  through  the  tube  a5,  while  the 
globe  D  is  heated  by  an  alcohol-lamp.  The  oxides  are  thus  changed 
into  chlorides,  when  the  chloride  of  zinc,  being  very  volatile,  distils 

Vol.  II.— 10 


146 


ZINC. 


Fig.  522. 

over,  and  condenses  in  the  tube  bed  and  in  the  water  in  the  bottle. 
The  chlorides  of  cobalt,  or  nickel,  on  the  contrary,  remain  in  the 
globe  D.  At  the  close  of  the  operation,  the  tube  bed  is  detached 
and  thrown  into  the  bottle  E,  when  all  the  chloride  of  zinc  is  dis- 
solved ;  while,  on  the  other  hand,  the  globe  D  is  heated  with  acidu- 
lated water.  The  metals,  being  thus  separately  dissolved,  are  pre- 
cipitated in  the  ordinary  manner. 


METALLURGY  OF  ZINC. 

§  921.  Calamine  is  the  principal  ore  of  zinc.  Silicate  of  zinc  is 
frequently  mixed  with  calamine,  but,  as  it  yields  very  little  metal- 
lic zinc,  should  not  be  regarded  as  a  true  ore.  A  certain  quantity 
of  zinc  is  extracted  from  blende.  The  principal  mines  of  zinc  are 
those  of  Tarnowitz,  in  Silesia,  Vieille  Montague,  near  Liege,  and 
several  counties  in  England. 

The  theory  of  the  metallurgic  treatment  of  calamine  is  very 
simple  : — The  ore  is  calcined,  by  which  process  its  carbonic  acid  is 
driven  off  and  it  is  rendered  friable,  after  which  it  is  powdered  in 
mills  with  edge-stones,  and  the  powder,  mixed  with  charcoal,  is 
heated  in  earthen  retorts  in  a  furnace  to  a  strong  white-heat.  The 
oxide  of  zinc  is  reduced  by  the  charcoal,  while  carbonic  oxide  gas 
is  disengaged,  and  the  metallic  zinc  condenses  in  allonges  fitted  to 
the  retorts. 

§  922.  The  ore  of  Vieille  Montague  is  a  mixture  of  silicate  and 
carbonate  of  zinc,  being  sometimes  compact  and  sometimes  crys- 
tallized. The  gangue  consists  exclusively  of  clay,  in  amorphous 
masses,  scattered  through  the  fragments  of  calamine.  The  ore  is 
exposed  to  the  air  for  several  months,  to  allow  the  clay  to  rot, 
after  which  it  is  easily  separated ;  while  sometimes  it  is  washed, 
and  the  clay  in  this  manner  almost  entirely  removed.  Two  classes 
of  ore  are  distinguished,  according  to  their  aspect  and  chemical 
composition,  the  white  ore  and  red  ore,  the  latter  of  which  con- 
tains more  iron  than  the  first,  and  is  less  rich  in  zinc,  but  more 


METALLURGY   OF   ZINC.  147 

easily  worked.     The  following  is  the  average  composition  of  these 
two  kinds  of  ore : 


Oxide   of  zinc 


White  ore. 

Zinc 46.6  , 

^  Oxygen 11.7  . 

Silex  and  clay.,. 14.0  . 

Water  and  carbonic  acid 22.7  . 

Sesquioxide  of  iron 5.0  . 

100.0 


Red  ore. 

.  83.6 

,  8.4 

.  20.0 

,  20.0 

,  18.0 

100.0 


The  washed  ore  is  calcined  in  conical  kilns  (fig.  523),  resembling 
limekilns,  and  heated  by  two  lateral  fui-- 
naces,  covered  by  an  arch,  and  terminating 
in  a  canal  which  opens  into  the  kiln  by  20 
working-holes  o,o,o,  arranged  in  4  or  5  rows, 
each  opening  being  four  inches  square.  At 
the  lower  part  of  the  furnace  are  two  rec- 
tangular openings  A,  intended  for  the  re- 
moval of  the  roasted  ore,  while  two  cast-iron 
plates  /,  /,  having  an  inclination  of  45°, 
divide  the  descending  column  of  ore,  and 
Fig.  523.  facilitate  its  escape  from  the  kiln.      The 


Fig.  524. 


Fig.  525. 


148  ZINC. 

calcination  is  continuous,  and  the  ore  is  charged  from  above,  the 
large  and  small  pieces  being  so  mixed  as  to  allow  an  easy  passage 
for  the  flame.  The  ore  loses  during  the  calcination  its  water  and 
carbonic  acid ;  the  loss  being  about  25  per  cent.  The  kilns  are 
heated  with  pit-coal. 

The  calcined  ore  is  finely  powdered  in  edge-stone  mills,  sifted, 
and  then  sent  to  the  reducing  furnace. 

The  furnace  is  composed  of  four  kilns  joined  together,  the  shape 
of  each  being  that  of  a  cylindrical  cradle  A  (figs.  524  and  525), 
the  upper  edge  of  which  is  about  8.5  feet  above  the  floor.  The 
posterior  part  of  the  furnace  is  made  by  a  wall  hd,  inclined  back- 
ward, while  the  anterior  part  ac  is,  on  the  contrary,  entirely  open. 
The  hearth  F  is  below  the  floor  of  the  furnace,  into  which  the  flame 
enters  by  4  holes  o,  o,  and  at  the  top  of  the  wall  are  two  flues  U, 
U,  which  open  into  a  chimney  in  the  centre  of  the  building.  The 
chimney,  which  serves  for  the  4  kilns,  is  divided  into  4  compart- 
ments, each  having  its  own  register  T.  In  each  furnace  42  retorts 
of  refractory  clay  are  arranged,  consisting  of  long  earthen  pipes  bd 
(fig.  526),  closed  at  one  end  d,  3.4  feet  long,  with  an  internal  dia- 
meter of  5.9  inches.  Into  each  tube  a  conical  cast-iron  pipe  cd 
(fig.  527)  is  inserted,  which  acts  as  a  condenser,  and  to  which  is 


Fig.  526.  Fig.  627.  Fig.  528. 

fitted  a  second  conical  sheet-iron  pipe  ef  (fig.  528),  having  at  /  an 
opening  of  only  0.8  inch.  The  earthen  pipes  are  arranged  in 
the  kiln  in  8  rows  above  each  other,  their  closed  ends  resting  on  8 
projecting  edges  built  in  the  back  wall  hd  of  the  oven  (fig.  524). 
On  the  front  wall  ae,  which  is  open,  are  arranged  8  cast-iron  plates, 
supported  by  bricks,  and  intended  for  the  reception  of  the  anterior 
part  of  the  tubes,  which  are  slightly  inclined  forward.  The  kilns 
are  kept  burning  for  2  months,  after  which  they  generally  need 
repairing. 

In  order  to  start  a  new  furnace,  the  open  face  of  the  kiln  is  first 
closed  with  brickbats  and  broken  tubes,  and  cemented  with  mortar, 
after  which  it  is  heated  for  several  days,  at  first  gradually,  and  then 
to  a  white-heat.  After  4  days  of  preliminary  heating,  the  tubes  are 
introduced  by  removing  the  anterior  part  of  the  furnace  and  ar- 
ranging them  after  they  have  been  previously  heated ;  the  inter- 
stices between  the  tubes  and  the  anterior  compartment  through 
which  they  pass  being  luted  with  mortar;  and  lastly,  the  conical 
allonge  being  adapted  to  each  tube. 

When  the  crucibles  are  arranged  in  the  furnace,  a  small  quantity 
of  ore  and  charcoal  is  first  introduced,  these  charges  being  succes- 
sively increased  until,  after  several  days,  the  regular  work  of  the 


METALLURGY   OF   ZINC.  149 

furnace  begins.     This  period  of  the  operation  is  that  which  will 
alone  occupy  our  attention. 

The  ore  is  brought  in  a  wooden  box,  where  it  is  mixed  with  char- 
coal, and  a  little  water  added.  The  charge  of  a  furnace  consists 
of  10  cwt.  of  calcined  calamine,  and  5  cwt.  of  dried  pulverized  pit- 
coal,  which  substances  are  intimately  mixed  with  an  iron  shovel. 
The  residue  of  the  preceding  distillation  is  removed  from  each 
tube,  which  then,  with  its  cast-iron  receiver,  is  cleaned  by  means 
of  an  iron  rod.  The  lower  tubes  are  first  charged.  The  mixture 
is  introduced  by  means  of  semi-cylindrical  sheet-iron  shovels  (fig. 
529),  fastened  to  an  iron  handle ;  and  when  the  charging  is  com- 


Fig.  529. 

pleted  the  fire  is  blown  up.  A  large  quantity  of  carbonic  oxide  is 
soon  disengaged,  and  burns  with  a  blue  flame  at  the  openings  of 
the  cast-iron  receivers,  while  in  a  short  time  this  flame  becomes 
more  brilliant,  of  a  greenish-white  colour,  and  evolves  white  fumes, 
which  is  a  sign  that  the  distillation  of  the  zinc  has  commenced,  and 
that  it  is  time  to  fit  the  sheet-iron  allonges  to  the  tubes.  Whatever 
care  maybe  taken  to  obtain  a  uniform  temperature,  the  heat  is  always 
greater  in  some  parts  of  the  kiln  than  in  others ;  for  which  reason 
the  upper  tubes  are  charged  only  with  the  red  ore,  as  being  the 
most  easily  reduced,  while  the  white  is  introduced  into  the  lower 
ones.  After  2  hours'  firing,  the  workman  detaches  the  sheet-iron 
allonges,  and  shakes  them  over  a  sheet-iron  receiver,  when  a  dust 
of  zinc  and  oxide  of  zinc,  called  cadmie^  falls  down,  which  is  added 
to  the  ore  in  the  succeeding  operations.  An  assistant  then  holds  a 
large  sheet-iron  spoon  (fig.  530),  called  a  poelon,  near  the  opening 
of  each  cast-iron  receiver,  while  the  master  workman  introduces  an 
iron  rake,  with  which  he  draws  out  the  distilled  zinc,  which  has  ac- 
cumulated in  a  liquid  state  at  the  bottom  of  the 
allonge,  and  in  the  same  way  detaches  the  drops 
.  adhering  to  its  sides.     The  liquid  zinc  collected 

^^'  *  in  the  poelons  is  covered  with  metallic  scum,  con- 
sisting chiefly  of  oxide  of  zinc,  which  is  carefully  removed,  and  the 
zinc  run  into  rectangular  moulds,  in  pieces  weighing  from  60  to 
70  lbs.  The  sheet-iron  allonges  are  immediately  replaced  and  the 
fire  continued.  In  2  hours  a  second  drawing  is  made,  and  so  on 
until  5  o'clock  p.  M.,  when  the  operation  is  generally  terminated. 
The  tubes  are  then  cleaned,  and  new  ones  substituted  for  those 
destroyed  in  the  preceding  operation.  Two  operations  are  thus 
made  in  24  hours,  producing  together  about  6  cwt.  of  zinc  and  30 
to  50  lbs.  of  metallic  dust ;  so  that  by  this  treatment,  calamine 
yields  about  31  per  cent,  of  zinc,  about  10  per  cent,  remaining  in 
the  residue.  The  metal  contained  in  the  residue  existed  in  the 
Btate  of  silicate  of  zinc,  which  is  not  reduced  by  the  charcoal. 


150 


ZINC. 


The  greater  part  of  manufactured  zinc  being  used  in  the  shape 
of  rolled  zinc,  it  is  necessary  again  to  melt  the  ingots,  which  is 
done  in  a  reverberatory  furnace  with  an  elliptical  floor  of  refrac- 
tory clay  and  slightly  inclined  backward.  At  the  lowest  part  of 
the  floor  is  a  hemispherical  crucible  in  which  the  melted  zinc  col- 
lects, and  from  which  it  is  dipped  out  and  run  into  moulds  of  a 
suitable  form  for  rolling.  The  plates  are  being  reheated  in  a 
second  furnace  adjoining  the  first,  by  means  of  the  hot  gases  of  the 
former,  and,  when  they  have  reached  a  temperature  not  exceeding 
212°,  are  passed  between  cast-iron  rollers.  When  they  are  of 
suitable  size,  they  are  cut  into  rectangular  sheets  of  the  dimen- 
sions required,  the  clippings  being  again  fused.  Formerly,  zinc 
was  fused  in  large  cast-iron  pots,  which,  however,  soon  became 
perforated,  while  the  zinc  lost  many  of  its  qualities  by  being  com- 
bined with  a  small  quantity  of  iron. 

§  923.  The  furnaces  and  distilling  apparatus  used  in  Silesia  dif- 
fer essentially  from  those  in  Belgium.      Fig.  531  gives  a  view  of  a 


Fig.  631. 


Fig.  532. 

Silesian  furnace,  of  which  fig.  532  is  a  vertical  section.  The  distilla- 
tion is  effected  in  muffles  of  baked  clay  M  (figs.  533  and  534),  about 
3  feet  in  length  and  1.5  feet  in  height,  the  anterior  part  of  which 
has  2  openings :  the  lower  opening  a,  through  which  the  residue 
of  distillation  is  withdrawn,  is  closed  during  the  operation  by  a  clay 


METALLURGY    OF    ZINC. 


151 


tloor,  tightly  luted,  while  into  the  upper  opening  a  right  angled 
olay  tube  hod,  closed  at  d,  is  introduced.  The  ore  is  charged  with 
a  shovel  through  a  hole  c,  which  is  closed  during  the  distillation 


Fig.  533. 


Fig.  534. 


with  a  baked-clay  stopper.  Six  or  ten  muffles  are  arranged  in  two 
rows  in  a  kiln,  the  side  walls  of  which  have  apertures  for  their  pas- 
sage, which  are  closed  by  sheet-iron  doors,  preventing  too  sudden 
a  cooling  of  the  allonges  bed.  The  kiln  is  heated  with  pit-coal 
burned  on  the  grate  G,  and  they  are  charged  with  a  mixture  of  equal 
parts  of  calcined  calamine  and  charcoal  cinders,  which,  having 
fallen  through  the  grate,  are  immediately  extinguished  in  water 
placed  beneath.  No  pulverized  pit-coal  is  used,  lest  any  coal-dust, 
carried  by  the  current  of  gas,  should  obstruct  the  allonges ;  and 
the  calamine  itself  is  reduced  to  the  size  of  a  pea.  The  zinc  runs 
through  the  opening  d  of  the  allonge,  and  is  collected  in  the  spaces 
t  of  the  furnace.  Although  the  operation  lasts  only  24  hours,  the 
muffles  are  not  emptied  until  after  three  operations,  when  a  half- 
fused  greenish  mass  is  extracted  as  a  residue.  The  calamine  is 
roasted  in  reverberatory  furnaces  heated  by  the  waste  flame  of  the 
reducing  furnace.  Silesia  furnishes  the  greater  portion  of  the  zinc 
which  is  brought  into  commerce. 

§  924.  In  the  Belgian  and  Silesian  processes,  the  distillation  of 
the  zinc  is  eifected  per  ascensum,  while  the  process  employed  in 

England  furnishes  an  example  of  distilla- 
tion per  descensum.  The  reducing  fur- 
naces, resembling  very  much  the  ordi- 
nary glass-furnace,  being  circular  (fig. 
535),  and  having  the  hearth  F  in  the 
middle,  at  a  certain  distance  below  the 
floor  of  the  furnace.  The  ore,  mixed 
with  charcoal,  is  charged  in  the  crucibles 
c,  which  are  arranged  around  the  hearth, 
and  introduced  through  several  apertures 
in  the  arched  roof.  There  is  a  hole  in 
the  bottom  of  each  crucible,  into  which 
an  iron  tube  tt,  passing  through  an  aper- 
ture in  the  floor  of  the  furnace,  and  open- 
ing externally,  is  introduced.  The  upper 
opening  of  the  tube  is  closed,  before  the 
charging,  with  a  wooden  stopper,  which, 
by  becoming  carbonized  during  the  operation,  is  sufficiently  porous 


152  ZINC. 

to  allow  the  gaseous  zinc  to  escape,  while  the  ore  is  still  retained ; 
and  each  pot  is  covered  with  a  lid  accurately  luted  with  clay.  The 
distilled  zinc  condenses  in  the  iron  pipe  tt,  and  drops  into  a  sheet- 
iron  receptacle  beneath,  an  iron  rod  being,  from  time  to  time,  in- 
troduced to  detach  the  zinc  which  may  have  become  solid,  and 
might  ultimately  choke  the  tubes. 

§  925.  A  certain  quantity  of  zinc  is  also  extracted  from  blende, 
which  is  found  in  large  quantities  in  several  localities,  after  roast- 
ing the  blende  as  perfectly  as  possible,  first  in  heaps,  by  which  the 
greater  portion  of  the  sulphur  is  removed  and  the  ore  is  rendered 
very  friable,  and  then  in  a  reverberatory  furnace,  by  which  the 
oxidation  of  the  zinc  is  completed.  The  roasted  ore,  which  con- 
sists of  oxide  and  sulphate  of  zinc,  is  reduced  by  charcoal  in  a  dis- 
tilling apparatus,  in  the  same  manner  as  calamine. 


153 


CADMIUM. 
Equivalent  =  56  (700 ;  0  =  100). 

§  926.  Cadmium*  is  a  metal  still  more  volatile  than  zinc :  it 
distils  at  a  red-heat,  and  the  distillation  may  be  eiFected  in  glass 
retorts  which  are  difficult  of  fusion.  In  order  to  obtain  pure  cad- 
mium, a  mixture  of  oxide  or  carbonate  of  cadmium  and  charcoal  is 
heated  in  a  retort,  when  the.  cadmium  sublimes  and  condenses  in 
drops  in  the  neck  of  the  retort.  The  small  drops  often  crystallize 
on  solidifying,  the  crystalline  form  of  the  metal  belonging  to  the 
regular  system. 

Cadmium  is  a  white  metal,  rather  more  gray  than  tin,  and  pos- 
sessing a  considerable  degree  of  malleability  and  ductility.  Its 
density  is  8.7,  and  it  fuses  long  before  reaching  a  red-heat.  Cad- 
mium does  not  oxidize  appreciably  at  the  ordinary  temperature, 
but  on  being  heated,  its  vapour  ignites  and  burns  with  brilliancy. 
Chlorohydric  and  dilute  sulphuric  acid  dissolve  it  with  the  evolu- 
tion of  hydrogen  gas. 

COMPOUND  OF  CADMIUM  WITH  OXYGEN. 

§  927.  The  only  oxide  of  cadmium  known  is  obtained  either  by 
heating  the  metal  in  the  air  or  by  treating  it  with  nitric  acid,  and 
then  decomposing  the  nitrate  by  heat.  The  oxide  forms  a  brown 
powder,  which  resists  the  highest  temperature  without  volatilizing 
or  melting,  and  which  readily  combines  with  acids,  forming  colour- 
less salts,  unless  the  acid  itself  is  coloured.  Caustic  potassa  or 
soda  effects  a  white  precipitate  with  salts  of  cadmium,  consisting 
of  hydrated  oxide  of  cadmium. 

Oxide  of  cadmium  is  composed  of 

Cadmium 87.5 

Oxygen 12.5 

100.0 
whence  its  equivalent  is  inferred  to  be  56, 

SALTS  FORMED  BY  OXIDE  OF  CADMIUM. 

§  928.  The  salts  of  cadmium,  the  greater  number  of  which  readily 
crystallize,  are  colourless.  The  fixed  alkalies  precipitate  them 
from  their  solutions  as  gelatinous  hydrated  oxide,  which  does  not 
redissolve  in  an  excess  of  the  reagent.    Ammonia  affords  the  same 

*  Discovered  in  1818,  by  Hermani;  aaad  Stromeyer. 


154  CADMIUM. 

precipitate,  but  an  excess  of  ammonia  easily  redissolves  it.  The 
alkaline  carbonates  yield  a  white  precipitate  of  neutral  carbonate 
of  cadmium  CdO,COa,  insoluble  in  an  excess  of  the  reagent.  Sulf- 
hydric  acid  throws  down,  even  in  the  presence  of  a  considerable  ex- 
cess of  acid,  a  very  beautiful  yellow  precipitate,  while  the  alkaline 
sulfhydrates  afford  the  same  precipitate,  which  is  insoluble  in  an 
excess  of  sulfhydrate.  A  blade  of  zinc,  dipped  into  a  solution  of 
a  salt  of  cadmium,  precipitates  the  metal  in  the  form  of  crystalline 
spangles. 

Sulphate  of  cadmium  crystallizes  with  4  equiv.  of  water. 

COMPOUND  OF  CADMIUM  WITH  SULPHUR. 

§  929.  Sulphide  of  cadmium  is  found  crystallized  in  nature,  but 
is  a  rare  mineral.  It  is  obtained  artificially  by  passing  a  current 
of  sulf hydric  acid  gas  through  a  solution  of  a  salt  of  cadmium. 
The  beautifully  yellow  precipitate  thrown  down  is  used  in  paint- 
ing. Sulphide  of  cadmium  is  also  prepared  in  the  dry  way,  by 
heating  oxide  of  cadmium  with  sulphur.  The  sulphide  is  not  at- 
tacked by  dilute  chlorohydric  acid,  but  dissolves  in  the  concen- 
trated acid  with  the  evolution  of  hydrogen  gas. 

COMPOUND  OF  CADMIUM  WITH  CHLORINE. 

§  930.  Chloride  of  cadmium  is  obtained  by  heating  the  metal  in 
a  current  of  chlorine,  when  a  white  fusible  substance  is  formed, 
which  sublimes  when  further  heated.  By  dissolving  cadmium  in 
chlorohydric  acid,  or  in  aqua  regia  with  an  excess  of  chlorohydric 
acid,  a  solution  of  hydrated  chloride  is  obtained,  which  crystallizes 
readily,  and  loses  its  water  by  heat,  without  being  decomposed. 

DETERMINATION  OF  CADMIUM,  AND  ITS  SEPARATION  FROM  THE 
METALS  PREVIOUSLY  STUDIED. 

§  931.  Cadmium  is  determined  in  the  state  of  calcined  oxide  of 
cadmium,  and,  when  it  exists  in  solution,  is  precipitated  by  car- 
bonate of  soda  at  the  boiling  point.  The  precipitation  is  complete, 
even  when  the  liquid  contains  ammoniacal  salts. 

Cadmium  is  easily  separated  from  all  the  metals  we  have  hither- 
to studied,  by  passing  a  current  of  sulf  hydric  acid  gas  through 
the  solutions,  which  must  be  slightly  acidulated  by  a  mineral  acid. 
The  precipitate  of  sulphide  of  cadmium  formed  is  washed  with 
water  containing  a  small  quantity  of  sulfhydric  acid,  and  then  re- 
dissolved  in  nitric  acid,  and  the  hot  solution  precipitated  by  car- 
bonate of  soda. 

EXTRACTION  OF  CADMIUM. 

§  932.  Cadmium  occurs  in  nature  as  oxide,  or  carbonate,  spar- 
ingly scattered  through  calamine,  and  is  most  abundantly  found  in 
that  of  Silesia.   When  zinc  is  extracted  from  this  ore,  the  cadmium 


CADMIUM.  155 

is  reduced  at  the  same  time,  and,  as  it  is  much  more  volatile  than 
zinc,  is  first  disengaged,  and  burns  in  the  air  with  the  first  portions 
of  zinc  that  are  liberated,  when  a  more  or  less  brownish  dust  is 
formed,  composed  of  oxide  of  zinc  and  5  or  6  per  cent,  of  oxide  of 
cadmium.  This  oxide  is  mixed  with  J  of  its  weight  of  charcoal, 
and  then  heated  to  redness  in  iron  tubes,  when  the  greater  part  of 
the  zinc  remains  in  the  residue,  because  the  temperature  is  not  suf- 
ficiently high  to  volatilize  it,  while  the  cadmium  distils  with  a  por- 
tion of  the  zinc,  and  condenses  in  a  second  sheet-iron  tube  which 
acts  as  a  receiver.  By  subjecting  the  product  to  another  precisely 
similar  operation,  cadmium,  containing  only  a  few  hundredths  of 
zinc,  is  obtained.  Its  purity  is  ascertained  by  striking  it  with  a 
hammer :  a  very  small  quantity  of  zinc  deprives  it  of  its  mallea- 
bility. The  purification  of  the  metal  is  completed  by  dissolving  it 
in  chlorohydric  acid,  and  thea  precipitating  it  by  a  blade  of  zinc. 


156 

TIN. 

Equivalent  =  58  (725.0 ;  0  =  100). 

§  933.  Common  commercial  tin  is  never  absolutely  pure,  as  it 
always  contains  small  quantities  of  arsenic  and  other  foreign  me- 
tals; but  Malacca  tin  is  nearly  perfectly  pure.  In  order  to  obtain 
chemically  pure  tin,  the  metal  of  commerce  is  treated  with  nitric 
acid,  which  converts  it  into  an  insoluble  white  powder  consisting 
of  stannic  acid,  and  which  oxidizes  foreign  substances.  The  stannic 
acid  is  reduced  to  the  metallic  state  by  heating  it  iA  a  "brasqued" 
crucible,  after  being  washed  with  weak  chlorohydric  acid  to  remove 
more  certainly  the  foreign  substances. 

Tin  is  a  white  metal,  resembling  silver  in  its  appearance  and 
lustre,  and  possessing  a  certain  characteristic  taste  and  smell,  par- 
ticularly when  held  for  some  time  between  the  fingers.  It  is  very 
malleable,  and  may  be  beaten  into  exceedingly  thin  sheets,  its  mal- 
leability being  greater  at  212°  than  at  the  ordinary  temperature ; 
but  its  tenacity  is  very  feeble,  for  a  wire  of  2  millimetres  breaks 
under  a  weight  of  24  kilogs.  On  bending  a  bar  of  tin  a  peculiar 
noise  is  heard,  called  the  cry  of  tin,  which  is  owing  to  the  inter- 
nal crystalline  texture  of  the  metal.  The  crystalline  particles 
rub  upon  each  other  when  the  bar  is  bended,  while  the  latter  be- 
comes heated  at  the  point  of  this  internal  friction ;  and  if  the 
bending  is  repeated  several  times  at  the  same  spot,  the  evolution 
of  heat  becomes  sensible  to  the  hand. 

Tin  fuses  at  442.4°,  giving  off  at  a  white-heat  appreciable  va- 
pours of  very  feeble  tension,  for  the  metal  suffers  but  a  slight  loss 
at  the  temperature  of  a  forge-fire.  Tin  has  a  great  tendency  to  crys- 
tallization, and  its  crystalline  texture  is  easily  demonstrated  by 
attacking  its  surface  by  an  acid  which  removes  the  outer  pellicle. 

The  surface  of  the  metal  then  appears  to  be  watered,  in  conse- 
quence of  the  unequal  and  various  reflections  of  light  by  the  edges 
of  the.  crystalline  laminae  exposed  by  the  acid.  Tin  may  be  crys- 
tallized by  fusion,  by  melting  several  pounds  of  the  metal  in  a  ves- 
sel, and  allowing  it  to  cool  slowly  over  a  heated  sand-bath.  When  a 
solid  crust  has  formed  on  the  surface,  it  is  pierced  with  a  burning 
coal  and  the  liquid  portion  evacuated,  when  quite  large  crystals  of 
tin,  which,  however,  are  rarely  well-defined,  are  often  found  on  the 
Bides  of  the  vessel. 

By  precipitating  tin  by  means  of  the  galvanic  current,  it  may  be 
obtained  in  long  brilliant  prismatic  crystals,  the  form  of  which  has 
not  yet  been  exactly  determined.  For  this  purpose  a  concentrated 
Bolution  of  protochloride  of  tin  is  poured  into  a  glass,  and  above  it 


PROPERTIES   OP   THE   METAL.  157 

a  stratum  of  fresh  water  is  carefully  placed ;  after  which  a  blade 
of  tin,  which  traverses  both  strata,  is  introduced  into  the  glass, 
when  the  blade  of  tin  soon  becomes  covered  with  very  Williant 
metallic  crystals. 

The  density  of  tin  is  7.29,  and  is  not  sensibly  increased  by  the 
hammering  of  the  metal. 

Tin  is  too  malleable  to  be  pulverized  in  a  mortar,  for  which 
reason  tin  filings,  or  the  tin-leaf  employed  to  wrap  bonbons  and 
chocolate,  must  be  taken  when  the  metal  is  to  be  used  in  a  finely 
divided  state.  Finely  divided  tin  may  also  be  obtained  by  a  pecu- 
liar process,  consisting  in  beating  the  metal,  when  fused  in  a  cap- 
sule, rapidly  with  a  large  brush  until  it  is  entirely  cool,  when  it  is 
reduced  into  very  small  globules,  which  may  be  separated  into 
globules  of  various  sizes  by  a  kind  of  levigation. 

Tin  does  not  sensibly  change  in  the  air  at  the  ordinary  tempera- 
ture, but  at  its  fusing  point  becomes  quickly  covered  with  a  gray 
pellicle,  which  is  a  mixture  of  protoxide  of  tin  and  stannic  acid. 
Oxidation  takes  place  much  more  rapidly  at  a  higher  temperature, 
and  at  a  white-heat  the  metal  burns  with  a  white  flame.  Tin  de- 
composes aqueous  vapour  at  a  red-heat,  and  is  converted  into  stan- 
nic acid. 

Concentrated  chlorohydric  acid  dissolves  tin  with  the  disengage- 
ment of  hydrogen  gas.  Dilute  sulphuric  acid  also  act^  on  it,  when 
hot,  with  the  evolution  of  hydrogen,  but  the  metal  oxidizes  very 
slowly.  Concentrated  hot  sulphuric  acid  attacks  tin  rapidly:  sul- 
phurous acid  is  disengaged,  and  the  metal  is  changed  into  proto- 
sulphate.  Dilute  nitric  acid  oxidizes  tin  readily  and  converts  it  into 
stannic  acid,  while  the  concentrated  acid  causes  a  copious  evolu- 
tion of  deutoxide  of  nitrogen.  If  the  acid  is  very  dilute,  the  tin  is 
converted  into  stannic  acid  without  disengagement  of  gas,  the  water 
and  nitric  acid  being  simultaneously  decomposed  and  nitrate  of 
ammonia  formed  (§  122) ;  but  when  the  acid  is  at  its  maximum  of 
concentration,  that  is,  in  the  state  of  monohydrate  NO^+HO, 
it  does  not  attack  tin  at  all,  and  the  metal  preserves  its  bril- 
liancy. But,  if  a  few  drops  of  water  be  poured  into  the  acid, 
the  reaction  takes  place  with  extreme  violence,  and  the  liquid  is 
frequently  extravasated  by  the  rapid  and  sudden  disengagement 
of  gas. 

Aqua  regia  dissolves  tin  readily,  while,  if  chlorohydric  acid  pre- 
dominates in  the  mixture,  a  soluble  perchloride  of  tin  is  formed. 

Tin  decomposes  water  in  the  presence  of  the  fixed  alkalies,  and 
disengages  hydrogen  when  heated  with  a  concentrated  solution  of 
potassa  or  soda,  while  an  alkaline  stannate  is  formed. 

COMPOUNDS  OF  TIN  WITH  OXYGEN. 

§  934.  Two  well-defined  compounds  of  tin  with  oxygen  are 
known ; 


158  TIN. 

Protoxide  of  tin  SnO. 
Binoxide  of  tin  SnOg,  or  stannic  acid. 

These  two  oxides  can  combine  with  each  other  and  produce  seve- 
ral intermediate  compounds. 

Protoxide  of  Tin,  SnO. 

§  935.  Protoxide  of  tin  is  prepared  by  precipitating  a  solution 
of  the  protochloride  SnCl  by  carbonate  of  ammonia,  when  car- 
bonic acid  is  disengaged,  and  a  white  precipitate  of  hydrated  prot- 
oxide is  thrown  down.  If  the  liquid  be  boiled  with  the  precipi- 
tate, the  latter  gives  off  its  water  of  combination,  and  is  converted 
into  a  blackish-gray  powder,  consisting  of  anhydrous  protoxide, 
which  has  great  affinity  for  oxygen,  as  it  oxidizes  rapidly  in  the 
air,  and  is  converted  into  stannic  acid.  The  oxide  is  obtained  in 
a  state  of  greater  aggregation,  and  consequently  more  fixed,  by 
precipitating  protochloride  of  tin  by  caustic  potassa;  when  the 
oxide  is  first  separated  in  the  hydrated  state,  and  combines  with 
the  excess  of  potassa  to  form  a  true  salt,  in  which  it  acts  the  part 
of  an  acid.  But,  by  boiling  the  liquid,  this  combination  is  de- 
stroyed, and  the  oxide  is  precipitated  in  the  anhydrous  state, 
in  the  form  of  small  black  crystals,  which,  after  being  washed 
and  dried  in  the  air,  remain  unchanged  for  any  length  of  time. 
When  this  substance  is  he^-ted  in  an  oil-bath  to  about  482°,  it 
suddenly  decrepitates,  increases  considerably  in  volume,  and  is 
converted  into  a  number  of  small  brown  laminae,  which  are  soft 
to  the  touch.  The  oxide  has  not  changed  in  weight  during  the 
transformation,  and  has  only  passed  into  an  isomeric  modifica- 
tion ;  so  that  this  phenomenon  must  be  attributed  to  a  molecular 
movement,  caused,  probably,  by  a  change  in  the  crystalline  sys- 
tem. The  brown  modification  of  protoxide  of  tin  is  immediately 
obtained  by  precipitating  a  solution  of  protochloride  of  tin  by  an 
excess  of  ammonia,  and  boiling  the  liquid,  when  it  is  evaporated  in 
vacuo.  The  solution  of  the  protoxide  in  potassa  deposits  black 
crystals  of  the  first  modification  of  the  oxide ;  while  if,  on  the  con- 
trary, a  solution  of  the  protoxide  of  tin  in  potassa  be  highly  con- 
centrated by  rapid  boiling,  the  oxide  is  decomposed  into  metallic 
tin  which  is  separated,  and  stannic  acid  which  remains  combined 
with  the  potassa : 

2(KO,SnO)  =  Sn+KO,SnO,+KO. 

Lastly,  protoxide  of  tin  maybe  obtained  in  the  form  of  a  red  pow- 
der, by  decomposing  the  protochloride  by  ammonia,  boiling  the  liquid 
a  few  moments,  and  then  evaporating  it  at  a  gentle  heat ;  the  prot- 
oxide of  tin  is  converted  into  small  grains  of  a  beautiful  red  colour, 
under  the  influence  of  the  sal-ammoniac  formed  during  the  reaction. 
The  red  oxide  is  changed  into  the  brown  modification  by  simple 
friction  with  a  hard  body. 


OXIDES.  159 

Protoxide  of  tin  ignites  like  tinder  when  heated  in  contact  with 
the  air,  and  is  changed  into  stannic  acid. 
Protoxide  of  tin  is  composed  of 

Tin 87.88 

Oxygen 12.12 

100.00 
The  equivalent  of  tin  is  therefore  58. 

Stannic  Acid  SnOg. 

§  936.  Stannic  acid  may  be  obtained  under  two  isomeric  modifi- 
cations, which  are  clearly  distinguished  from  each  other  by  chemi- 
cal properties.  The  first  modification,  called  metastannic  acid,  is 
the  white  powder  obtained  by  treating  tin  by  nitric  acid ;  while  the 
second,  to  which  the  name  of  stannic  acid  is  given,  is  prepared  by 
decomposing  perchloride  of  tin  SnClg,  by  water,  or  a  soluble  stan- 
nate  by  an  acid. 

Metastannic  acid  is  found  crystallized  in  nature  in  some  of  the 
old  rocks,  forming  very  beautiful,  brilliant  crystals,  generally  of  a 
deep  brown  colour,  and  yielding  a  yellowish  powder.  The  same 
substance  is  obtained  by  oxidizing  tin  by  nitric  acid,  when  a  white 
powder,  which  is  a  hydrate,  is  formed,  but  which  changes  by  calci- 
nation into  anhydrous  metastannic  acid.  Hydrated  metastannic 
acid,  such  as  is  formed  by  the  action  of  nitric  acid  on  metallic  tin, 
has,  when  dried  in  the  air,  the  formula  SnOa-f-2HO.  It  loses 
one-half  of  its  water  at  212°,  and  then  presents  the  composition 
SnO^+HO,  while  it  loses  all  its  water  at  a  higher  temperature. 

Metastannic  acid  is  not  decomposed  by  heat  alone,  but  is  readily 
converted  into  metallic  tin  by  contact  with  charcoal  and  the  com- 
bustible gases.  It  is  insoluble  in  water  and  in  dilute  nitric  and 
sulphuric  acid,  while  concentrated  sulphuric  acid  dissolves  it  in 
considerable  proportions.  The  compound  formed  is  not  destroyed 
by  adding  water  to  the  liquid  ;  but  by  boiling,  the  metastannic  acid 
separates  in  the  state  of  hydrate  Sn03+2HO.  Chlorohydric  acid 
dissolves  it,  and  transforms  it  into  perchloride  of  tin  SnClg. 

Metastannic  acid  forms  crystallizable  salts  with  the  alkalies.  It 
dissolves  readily,  when  cold,  in  a  solution  of  potassa,  and,  if  frag- 
ments of  potassa  be  added  to  the  liquid,  its  solvent  power  is  so  far 
weakened  as  to  cause  the  metastannate  of  potassa  to  be  deposited 
in  the  form  of  a  crystalline  crust,  which  is  separated  and  spread  on 
a  plate  of  unglazed  porcelain,  when  the  mother  liquid  which  moist- 
ens them  is  thus  absorbed.  Analysis  has  proved  the  formula  of 
this  salt  to  be  KO,5SnOa+4HO ;  and  as  that  of  the  metastannate 
of  soda  is  similar,  the  conclusion  follows  that  the  equivalent  of 
stannic  acid  which  combines  with  1  equiv.  of  the  base  is  not  SnOg, 
but  rather  Sn^OjQ.  Metastannate  of  potassa  dissolves  in  water 
without  change,  and  the  liquid  leaves  after  evaporation  a  gummy^ 


160  TIN. 

uncrystalline  residue.  Heating  to  redness  destroys  the  compound, 
and  the  metastannic  acid  becomes  anhydrous  and  insoluble,  so  that 
water  will  only  remove  pure  potassa.  An  acid,  poured  into  a  solu- 
tion of  an  alkaline  metastannate,  precipitates  the  metastannic  acid 
in  the  form  of  a  gelatinous  substance,  which  appears  to  contain  more 
water  than  the  hydrate  Sn^Ojo+lOHO,  and  which  is  soluble  in  am- 
monia, while  the  hydrate  Sn^Ojo+lOHO  is  not.  A  slight  elevation 
of  temperature,  inferior  even  to  that  of  boiling  water,  causes  the 
gelatinous  acid  to  pass  into  the  state  of  the  hydrate,  which  is  inso- 
luble in  ammonia. 

Stannic  acid  is  obtained  by  decomposing  perchloride  of  tin  by 
ammonia,  or  a  soluble  stannate  by  an  acid.  It  is  a  white  gela- 
tinous precipitate,  insoluble  in  water,  but  readily  dissolving  in 
dilute  nitric  and  sulphuric  acid,  while  metastannic  acid  is  insoluble 
under  the  same  circumstances.  The  formula  of  stannic  acid,  dried 
in  vacuo,  is  SnO^jHO.  A  slight  elevation  of  temperature  causes 
it  to  pass  into  the  metastannic  modification,  even  without  losing  its 
water. 

Stannic  acid  dissolves  readily  in  alkaline  solutions,  and  the  liquid, 
"When  evaporated  in  vacuo,  yields  beautiful  colourless  and  transpa- 
rent crystals,  of  the  formula  K0,Sn03+4H0.  It  will  hence  be 
seen  that  stannic  acid  saturates  four  times  as  much  base  as  meta- 
stannic acid.  The  same  salt  is  obtained  by  heating  metastannic 
acid  with  an  excess  of  potassa  in  a  silver  crucible,  when  the  meta- 
stannic is  converted  into  stannic  acid.  The  completeness  of  the 
transformation  may  easily  be  ascertained  by  dissolving  a  small 
quantity  of  the  substance  in  water,  and  adding  an  excess  of  nitric 
acid ;  when  the  stannic  acid,  which  at  first  is  precipitated,  is  redis- 
Bolved  in  the  acid  liquid,  which  would  not  take  place  if  metastannic 
acid  were  still  present.  Stannate  of  potassa  is  not  decomposed  by 
heat  like  the  metastannic,  but  loses  its  water,  while  it  redissolves 
in  water  without  change. 

§  937.  Several  oxides  of  tin,  intermediate  between  the  protoxide 
and  stannic  acid,  are  known.  By  digesting  hydrated  metastannic 
acid  with  a  concentrated  solution  of  protochloride  of  tin,  the  liquid 
becomes  strongly  acid,  and  the  metastannic  acid  is  converted  into 
a  yellowish  powder,  which  may  be  considered  as  a  compound  of 
metastannic  acid  and  protoxide  of  tin,  having  the  formula  SnO, 
Sn30jo+4HO.  Another  intermediate  oxide  of  tin  is  obtained  by 
mixing  hydrated  sesquioxide  of  iron  with  a  solution  of  protochlo- 
ride of  tin,  when  a  yellowish  precipitate  is  formed,  which  may  be 
considered  as  a  stannate  of  tin  SnO,SnOa. 

PROTOSALTS  OF  TIN. 

§  938.  Only  a  small  number  of  gaits  formed  by  protoxide  of  tin 
is  known.  The  protosulphate  is  obtained  by  saturating,  when 
hot,  dilute  sulphuric  acid  with  recently  prepared  and  moist  hy- 


SULPHIDES.  161 

drated  protoxide  of  tin.  The  oxide  is  dissolved,  and,  on  cooling, 
small  crystalline  lamellae  of  protosulphate  of  tin  SnOjSOg  are  de- 
posited. This  salt  readily  dissolves  without  change  in  cold  water, 
while  heat  decomposes  it  in  its  solution,  and  precipitates  a  sub- 
sulphate.  Protosulphate  of  tin  forms  with  the  alkaline  sulphates 
double  sulphates,  which  are  more  fixed  than  the  simple  sulphate 
of  tin,  and  may  be  obtained  crystallized. 

Protonifrate  of  tin  is  prepared  by  dissolving  hydrated  protoxide 
in  weak  nitric  acid,  when  the  salt  remains  in  solution ;  but  it  is 
decomposed  when  the  liquid  is  evaporated,  while  stannic  acid  is 
formed. 

SALTS  FORMED  BY  STANNIC  AND  METASTANNIC  ACID  ACTING  THE 
PART  OF  A  BASE. 

§  939.  It  has  been  shown  that  metastannic  acid  combines  with 
concentrated  acids,  and  that  stannic  acid  dissolves  even  in  dilute 
acids.  True  salts,  in  which  these  bodies  act  the  part  of  bases,  are 
thus  formed ;  but  they  have  been  too  little  studied  to  require  our 
further  consideration. 

COMPOUNDS  OF  TIN  WITH  SULPHUR. 

§  940.  Tin  forms  two  compounds  with  sulphur :  a  protosulphide 
SnS  corresponding  to  the  protoxide,  and  a  bisulphide  SnSg  cone- 
sponding  to  stannic  acid. 

Protosulphide  of  tin  is  prepared  by  heating  a  mixture  of  tin  filings 
and  sulphur  to  redness  in  an  earthen  crucible,  pulverizing  the  product 
of  this  first  operation  and  reheating  it  with  an  additional  quantity 
of  sulphur,  when  a  mass  of  a  deep  gray  colour,  with  very  brilliant 
large  crystalline  lamellae,  is  obtained.  The  same  sulphide  is  pre- 
cipitated as  a  deep  brown,  nearly  black  powder,  in  a  hydrated  state, 
when  a  current  of  sulf  hydric  acid  gas  is  passed  through  a  solution 
of  protochloride  of  tin.  Concentrated  chlorohydric  acid  dissolves 
protosulphide  of  tin  with  the  disengagement  of  sulf  hydric  acid, 
while  the  presence  of  a  small  excess  of  the  former,  in  a  dilute  solu- 
tion of  tin,  does  not  prevent  the  salt  from  being  completely  preci- 
pitated by  sulfhydric  acid. 

Perchloride  of  tin  SnClg  yields  with  sulfhydric  acid  a  yellow 
precipitate  of  hydrated  bisulphide  of  tin  SnSg.  If  sulfhydric 
acid  gas  and  vapour  of  anhydrous  perchloride  of  tin  be  passed 
through  a  tube  heated  to  a  dull  red,  bisulphide  of  tin  is  deposited 
in  the  form  of  very  brilliant  crystalline  lamellae,  of  a  beautiful 
golden-yellow  colour,  which  substance  is  technically  prepared  in 
the  dry  way,  and  is  used,  under  the  name  of  mosaic  gold,  for  bronz- 
ing wood.  This  product  is  obtained  as  follows : — An  amalgam  of 
12  parts  of  cin  and  6  parts  of  mercury,  pulverized  in  a  mortar,  is 
mixed  with  7  parts  of  flowers  of  sulphur  and  6  parts  of  sal-ammo- 
niac, and  heated  in  a  long-necked  matrass  in  a  sand-bath,  the  tern- 

Vol.  XL— 11 


162  TIN. 

perature  of  which  is  gradually  raised  to  a  dull  red.  Sulphur,  sal- 
ammoniac,  sulphide  of  mercury,  and  protochloride  of  tin  condense 
in  the  globe  and  in  the  neck  of  the  matrass,  while  mosaic  gold 
remains  at  the  bottom  in  the  form  of  a  very  light,  gilded  mass, 
formed  by  the  union  of  a  large  quantity  of  small  crystalline  la- 
mellae. The  theory  of  this  operation  is  quite  complicated :  finely 
divided  tin,  when  heated  with  sulphur  at  a  low  temperature,  is 
changed  into  an  amorphous  bisulphide,  which  does  not  present  the 
gilded  spangles  which  alone  give  it  a  technical  value.  By  being 
still  further  heated  it  parts  with  one-half  of  its  sulphur,  and  passes 
into  the  state  of  monosulphide,  which  the  sal-ammoniac  added  to 
the  mixture  prevents,  because,  by  becoming  volatile  below  a  dull 
red-heat,  it  absorbs  a  considerable  quantity  of  latent  caloric ;  but 
it  facilitates  at  the  same  time  the  sublimation,  and,  consequently, 
the  crystallization  of  the  mosaic  gold  which  is  carried  over  by  the 
vapour. 

COMPOUNDS  OF  TIN  WITH  AKSENIC. 

§  941.  Tin  and  arsenic  combine  readily,  and  in  all  proportions, 
forming  very  brittle  crystalline  compounds.  The  arseniurets  of 
tin  disengage  mixtures  of  pure  hydrogen  and  arseniuretted  hydro- 
gen by  treatment  with  chlorohydric  acid. 

COMPOUNDS  OF  TIN  WITH  CHLORINE. 

§  942.  Tin  forms  two  compounds  with  chlorine  :  a  protochloride 
SnCl,  corresponding  to  the  protoxide,  and  a  bichloride  SnCl^,  cor- 
responding to  stannic  acid. 

Protochloride  of  tin  is  obtained  by  dissolving  tin  in  concentrated 
boiling  chlorohydric  acid,  when  hydrogen  gas  is  evolved.  This  salt 
is  used  in  dyeing,  and  is  prepared  on  a  large  scale  by  heating  curved 
bars  of  tin  in  large  retorts  with  concentrated  chlorohydric  acid, 
after  which  the  saturated  liquid  is  decanted,  and  the  protochloride 
bf  tin  separated  by  evaporation  in  the  form  of  hydrated  crystals, 
of  the  formula  SnCH-2H0. 

Protochloride  of  tin  dissolves  without  alteration  in  a  small  quan- 
tity of  water,  while  a  large  quantity  of  this  liquid  decomposes  it, 
and  precipitates  an  insoluble  oxychloride  SnCl+SnO. 

Crystallized  protochloride  of  tin  can  be  freed  from  its  water  by 
heating  in  a  retort,  while  a  small  quantity  of  the  chloride  is  always 
decomposed  during  this  desiccation,  and  chlorohydric  acid  is  disen- 
gaged ;  but  if  the  temperature  be  raised  to  redness,  the  protochlo- 
ride distils  over  unaltered.  Protochloride  of  tin  combines  readily 
with  the  alkaline  chlorides,  and  yields  easily  crystallizable  double 
chlorides. 

Protochloride  of  tin  has  such  an  affinity  for  oxygen  that  it  readily 
absorbs  this  gas  from  the  air,  and  abstracts  it  from  a  great  number 
of  oxides,  which  it  reduces  to  an  inferior  degree  of  oxidation,  or 


CHLORIDES.  163 

even  to  the  metallic  state.  It  readily  precipitates  mercury,  gold, 
and  silver  from  their  solutions  in  the  metallic  state,  and  reduces 
the  salts  of  sesquioxide  of  iron  and  protoxide  of  copper  CuO  to  the 
minimum  of  oxidation. 

§  943.  Perehloride  of  tin  is  readily  obtained  by  treating  tin 
by  an  excess  of  chlorine.  The  affinity  of  these  two  bodies  is  so 
great  that  tin  filings  ignite  when  thrown  into  a  bottle  filled  with  dry 
chlorine.  In  order  to  prepare  any  quantity  of  perehloride,  some 
tin  is  placed  in  a  tubulated  glass  retort,  furnished  with  a  well- 
cooled  receiver,  and  a  current  of  chlorine  is  passed  through  the 
tubulure,  when  the  tin  immediately  combines  with  the  chlorine ; 
and,  if  the  retort  be  gently  heated,  a  liquid  distils  over  and  con- 
denses in  the  receiver.  This  liquid,  which  is  generally  tinged  with 
yellow  by  the  chlorine  it  contains  in  solution,  is  purified  by  shaking 
it  with  tin  filings  or  protochloride  of  tin  and  redistilling  it.  This 
substance  may  also  be  prepared  by  heating,  in  a  glass  retort,  a  mix- 
ture of  1  part  of  tin  filings  and  5  parts  of  chloride  of  mercury  or 
corrosive  sublimate. 

Perehloride  of  tin  forms  a  colourless  liquid  of  the  specific  gravity 
2.28,  and  which  boils  at  248°,  the  density  of  its  vapour  being  9.2. 
It  gives  ofi^  very  thick  white  fumes  when  in  contact  with  the  air, 
owing  to  the  immediate  combination  of  the  vapour  of  the  anhy- 
drous chloride,  the  tension  of  which  is  very  high  at  the  ordinary 
temperature,  with  the  aqueous  vapour  contained  in  the  atmosphere, 
and  the  resulting  formation  of  a  hydrate  which  has  no  sensible  ten- 
sion, and  is,  consequently,  precipitated.  If  a  few  drops  of  water 
be  added  to  the  anhydrous  perehloride,  a  noise  resembling  that 
produced  by  plunging  a  red-hot  iron  in  water  is  heard,  and  the 
perehloride  then  combines  with  the  water  with  great  evolution  of 
heat,  giving  rise  to  a  hydrated  chloride  of  the  formula  SnCl^-f  5H0, 
which  is  deposited  in  beautiful  crystals. 

The  same  hydrated  perehloride  of  tin  may  be  obtained  by  dis- 
solving tin  in  aqua  regia  containing  an  excess  of  chlorohydric  acid, 
or  by  passing  chlorine  through  a  solution  of  protochloride  of  tin. 
The  hydrated  perehloride  dissolves  in  a  small  quantity  of  water, 
and  in  any  quantity  whatever  of  this  liquid  when  it  is  sufficiently 
acidulated  with  chlorohydric  acid,  while  an  addition  of  a  quantity 
of  fresh  water  again  decomposes  it,  and  causes  the  precipitation 
of  hydrated  stannic  acid. 

Hydrated  perehloride  of  tin  is  decomposed  by  heat,  when  chlo- 
rohydric acid  is  disengaged  and  metastannic  acid  remains.  Heated 
with  anhydrous  phosphoric  acid,  or  with  concentrated  sulphuric 
acid,  it  imparts  its  water  to  them,  and  the  anhydrous  perehloride 
distils  over. 

The  anhydrous  perehloride  of  tin  was  called  by  the  old  chemists 
the  fuming  liquid  of  Lihavius. 


164  TIN. 

Perchloride  of  tin  combines  with  a  great  number  of  metallic 
chlorides,  forming  readily  crystallizable  double  chlorides,  which  all 
consist  of  1  equiv.  of  perchloride  of  tin  and  1  equiv.  of  the  other 
metallic  chloride.  The  anhydrous  perchloride  combines  with  sulf- 
hydric  acid,  and  also  forms  with  phosphuretted  hydrogen  gas  a 
compound  of  the  formula  PHajSnClg. 

DISTINCTIVE  CHARACTERS  OF  THE  SOLUBLE  COMPOUNDS  OF  TIN. 

§  944.  Tin  forms  two  series  of  soluble  compounds :  1st,  those 
which  correspond  to  the  protoxide  SnO,  such  as  the  protochloride 
and  the  soluble  salts  formed  by  the  protoxide;  and  2dly,  com- 
pounds corresponding  to  stannic  acid  ;  that  is,  perchloride  of  tin 
and  the  soluble  compounds  of  stannic  acid  with  the  acids.  These 
two  series  present  different  reactions,  which  it  is  necessary  to  ex- 
amine separately. 

Characters  of  the  Protosalts  of  Tin, 

§  945.  The  salts  of  the  protoxide  of  tin  are  free  from  colour 
when  the  acid  is  itself  colourless,  and  always  strongly  redden  tinc- 
ture of  litmus.  A  small  quantity  of  water  in  most  cases  dissolves 
them,  while  a  greater  quantity  of  this  liquid  decomposes  them, 
forming  a  white  precipitate,  which  is  generally  a  basic  salt.  This 
precipitation  is  avoided  by  acidulating  the  water  with  a  certain 
quantity  of  chlorohydric  acid. 

The  caustic  alkalies  throw  down  a  white  precipitate,  which  is 
soluble  in  an  excess  of  the  reagent,  while,  by  boiling  the  liquid,  an- 
hydrous protoxide  of  tin  separates  in  the  form  of  a  black  powder. 
Ammonia  also  throws  down  a  white  precipitate,  which  is,  however, 
insoluble  in  an  excess  of  ammonia. 

The  alkaline  carbonates  likewise  yield  white  precipitates,  which 
are  insoluble  in  an  excess  of  the  reagent,  and  become  black  by 
boiling  the  liquid. 

Sulf  hydric  acid  precipitates  them  as  a  deep-brown  powder,  while 
the  alkaline  sulfhydrates  throw  down  a  dirty-white  precipitate, 
which  dissolves  in  a  great  excess  of  the  reagent. 

Prussiate  of  potash  yield  a  white  precipitate. 

Salts  of  mercury  are  reduced  by  the  protosalts  of  tin,  a  gray 
precipitate  of  very  finely  divided  metallic  mercury  being  formed, 
which  collects  in  globules  by  trituration. 

Chloride  of  gold  gives  a  precipitate  which  is  purple  when  the  so- 
lutions of  protoxide  of  tin  are  very  dilute,  and  brown  when  they 
are  more  concentrated. 

A  blade  of  iron  or  zinc  precipitates  tin  in  the  form  of  gray  crys- 
talline  spangles,  which  assume  under  the  burnisher  the  ordinary 
colour  and  lustre  of  tin. 


ANALYTIC    DETERMINATION.  165 

Characters  of  the  Soluble  Compounds  of  Tin^  corresponding  to 
Stannic  Acid. 

§  946.  The  characters  about  to  be  indicated  all  refer  to  the  per- 
chloride,  which  is  the  only  soluble  compound  corresponding  to 
stannic  acid  which  has  been  properly  studied. 

A  solution  of  perchloride  of  tin  always  has  a  strong  acid  reac- 
tion, and  is  decomposed  by  a  large  quantity  of  water,  affording  a 
white  precipitate  of  hydrated  stannic  acid. 

Potassa,  soda,  and  ammonia  yield  a  white  precipitate,  which  dis- 
solves in  an  excess  of  the  reagent ;  but  the  liquid  does  not  throw 
down  a  black  precipitate  on  being  boiled,  as  is  the  case  with  the 
compounds  of  the  protoxide. 

The  alkaline  carbonates  disengage  carbonic  acid,  and  give  a 
white  precipitate,  which  is  neither  soluble  in  an  excess  of  the  re- 
agent nor  turns  black  by  ebullition. 

Prussiate  of  potash  gives  a  white  precipitate,  which  does  not  form 
until  after  sometime. 

Sulf  hydric  acid  gives  a  dirty-yellow  precipitate,  which  also  does 
not  appear  immediately,  and  which,  when  formed  by  alkaline  sulf- 
hydrates,  is  soluble  in  an  excess  of  the  reagent. 

Chloride  of  gold  throws  down  no  precipitate  from  a  solution  of 
perchloride  of  tin,  which  reaction  clearly  distinguishes  the  per- 
chloride from  the  compounds  of  the  protoxide  of  the  metal.  Per- 
chloride of  tin  does  not  precipitate  mercury  from  its  solutions  in 
the  metallic  state. 

Iron  and  zinc  precipitate  metallic  tin. 

DETERMINATION  OF  TIN,  AND  ITS  SEPARATION  FROM  THE  METALS 
PREVIOUSLY  STUDIED. 

§  947.  Tin  is  always  determined  in  the  state  of  calcined  stannic 
acid.  Sometimes  it  is  precipitated  as  sulphide,  which  is  converted 
into  stannic  acid  by  roasting  in  a  platinum  crucible ;  taking  care 
to  add  a  few  drops  of  nitric  acid  before  the  calcination,  in  order  to 
prevent  the  separation  of  metallic  tin,  which  would  soon  attack 
the  crucible.  After  the  roasting,  the  crucible  is  allowed  to 
cool,  a  small  quantity  of  carbonate  of  ammonia  added,  and  it  is 
again  heated  to  drive  off  more  readily  the  last  traces  of  sulphuric 
acid. 

Tin  is  easily  separated  from  all  the  metals  which  we  have  hitherto 
studied,  except  from  cadmium,  by  means  of  sulf  hydric  acid.  The 
substances  are  dissolved  in  chlorohydric  acid,  so  that  the  tin  may 
exist  in  the  state  of  a  protochloride,  and  a  current  of  sulf  hydric  acid 
is  passed  through  the  liquid,  in  which  a  large  excess  of  chlorohy- 
dric acid  is  left.  When  the  liquid  contains  an  excess  of  sulf  hy- 
dric acid,  the  bottle  is  loosely  corked,  and  left  to  stand  for  several 
hours  at  a  temperature  of  from  120°  to  140°.      The  precipitate  is 


166  TIN. 

then  collected  on  a  filter,  and,  if  it  is  composed  only  of  sulphide 
of  tin,  is  converted  into  stannic  acid  by  means  of  nitric  acid. 

If  the  substance  contains  tin  and  cadmium,  these  metals  are  pre- 
cipitated together  by  sulfhydric  acid,  and  the  two  sulphurets  are 
treated  with  nitric  acid,  which  converts  the  tin  into  insoluble  stan- 
nic acid,  and  dissolves  the  cadmium,  which  is  then  precipitated  from 
its  solution  by  the  processes  indicated  in  §  931. 

METALLURGY  OF  TIN. 

§  948.  The  binoxide,  which  is  the  only  tin-ore,  originally  occurs 
only  in  the  oldest  rocks,  forming  small  veins,  or  irregular  threads, 
in  the  granitic  formations ;  but  it  is  sometimes  also  found  in  the  dis- 
aggregated sands  arising  from  the  destruction  of  these  rocks.  The 
principal  localities  of  tin  are  in  Saxony,  Bohemia,  in  Cornwall  in 
England,  and  in  the  East  Indies.  The  sands  containing  tin  found 
in  Brittany  are  too  poor  to  be  worked  with  advantage.  The  crushed 
stanniferous  rocks  and  the  stanniferous  sands  are  washed,  in  order 
to  separate  the  gangue  mechanically,  which  is  an  easy  operation, 
as  the  oxide  of  tin  is  much  heavier  than  the  gangue,  and,  as  it  is 
very  hard,  yields  but  little  dust  under  the  stamper.  Sands  con- 
taining only  J  per  cent,  of  tin  may  yet  be  advantageously  concen- 
trated by  washing. 

The  washed  ores,  which  consist  of  a  mixture  of  oxide  of  tin  and 
some  very  heavy  metalliferous  minerals,  such  as  the  crystallized 
sulphides,  sulfarseniurets,  and  oxides  of  iron,  etc.,  are  roasted  in 
heaps  or  in  kilns,  when  the  oxide  of  tin  remains  unaltered,  while 
the  sulphides  and  sulfarseniurets  become  partially  oxidized  and  dis- 
aggregated, so  that  if  the  ore  be  again  subjected  to  the  stampers, 
the  roasted  substances  are  pulverized,  while  the  oxide  of  tin  re- 
mains nearly  in  its  original  condition.  By  another  washing  the 
roasted  and  stamped  sand  is  easily  freed  from  the  substances  which 
have  been  altered  by  roasting,  and  a  very  rich  ore  is  obtained, 
yielding  often  more  than  50  per  cent,  of  metallic  tin. 

In  Saxony,  the  ore  is  fused  in  a  cupola-furnace  of  about  9  feet 
in  height  (figs.  536  and  537).  The  sides  of  the  oven  A  are  made 
of  slabs  of  granite,  while  the  bottom  consists  of  a  single  stone  D, 
called  the  sole-stone,  which  is  properly  hewn,  and  rapidly  inclines 
toward  the  anterior  part  of  the  furnace,  called  the  breast.  The 
fused  materials  constantly  run  into  an  exterior  crucible  B,  made 
of  slabs  of  granite  lined  with  damp  charcoal.  At  the  lower  part 
of  this  furnace  is  a  hole  which  opens  over  a  cast-iron  pot  C. 

The  furnace  is  charged  by  alternate  layers  of  ore  and  charcoal, 
the  combustion  being  fed  by  a  blowing-machine,  the  nozzle  of  which 
passes  through  the  twyer  o. 

The  oxide  of  tin  is  reduced  by  the  carbonic  oxide  which  is  pro- 
duced by  its  contact  with  the  fuel.  The  gangue  itself,  being  gene- 
rally very  fusible,  yields  a  doughy  scoriae,  which  flows  with  the  tin 


METALLURGY   OF  TIN. 


167 


into  the  basin  B,  whence  it  is  removed  from  time  to  time.     When 

the  basin  B  is  filled  with  melted  metal, 
the  stopper  is  removed  from  the  hole, 
and  the  metal  runs  into  the  cast-iron 
pot  C,  where  it  is  stirred  with  a  stick 
of  green  wood,*  which,  by  being  par- 
tially carbonized  in  the  hot  liquid,  causes 
a  bubbling,  produced  by  the  disengage- 
ment of  gas,  which  raises  the  dross  which 
is  scattered  through  the  metal  to  the 
surface  of  the  bath,  while  it,  at  the 
same  time,  reduces  the  oxide  of  tin 
beneath  to  the  metallic  state.  When 
the  temperature  of  the  metal  is  only  a 
few  degrees  above  that  of  its  fusion,  it 
is  allowed  to  rest,  and  is  then  removed 
with  iron  ladles  and  run  into  moulds. 
The  upper  strata  furnish  the  purest 
metal,  while  those  at  the  bottom  con- 
tain the  greater  portion  of  foreign  sub- 
stances. 

As  the  scoriae  do  not  become  per- 
fectly fluid,  they  always  contain  a  quan- 
^^S*  ^^^'  tity  of  grains  of  tin,  for  which  reason 

the  richest  are  added  to  the  ore  and  fused  with  the  next  charge, 
while  the  poorest  are  stamped  and  the  metallic  grains  separated 
by  washing.  The  greater  part  of  the  scoriae  is,  however,  smelted 
separately  in  tlie  same  furnace,  by  increasing  the  blast  and  quan- 
tity of  fuel,  by  which  more  fluid  scoriae  are  obtained,  from  which 
the  tin  separates  more  readily,  but  is  gained  only  in  inferior 
quality. 

§  949.  In  England,  the  ore  of  the  stanniferous  sands  is  treated 
nearly  in  the  same  manner,  the  furnaces  being  only  much  higher. 
The  tin  furnished  by  the  upper  strata  of  the  crucible  is  alone  run 
into  bars,  while  the  balance  is  again  melted,  The  bars  of  tin  are 
sometimes  heated  to  above  212°  and  allowed  to  fall  from  a  certain 
height,  when  the  metal,  which  is  very  brittle  at  this  temperature, 
breaks  into  small  crystalline  fragments,  and  is  then  called  grain-tin. 
The  ore  taken  from  the  veins  is  much  less  pure  than  that  of  the 
sands.  After  the  primary  stamping  and  washing,  it  is  roasted  in 
a  reverberatory  furnace,  when  sulphates  of  iron  and  copper  are 
formed,  which  are  washed  out  and  separated  by  crystallization. 
The  ore  is  then  again  washed,  and  the  sludge  arising  from  it  is 


*•  This  process,  which  is  called  poling,  is  effecied  in  the  Cornish  tin- works  by- 
boiling  billets  of  green  wood  in  the  melted  tin,  where  they  are  kept  under  the  sur- 
face by  means  of  an  iron  frame. —  W.  L.  F. 


168  TIN. 

heated  on  the  hearth  of  a  reverberatory  furnace  with  powdered 
charcoal,  to  which  lime  is  added  to  hasten  the  fusion  of  the  gangue. 
The  scoriae  are  ladled  out  from  time  to  time,  and  the  tin  is  run 
into  moulds. 

The  tin  obtained  by  this  process  is  refined  by  heating  the  metal 
slowly  on  the  hearth  of  a  reverberatory  furnace,  when  the  pure  tin 
melts  first,  and  runs  out  of  the  furnace,  as  the  hearth  is  inclined 
toward  the  tap-hole,  leaving  on  the  hearth  an  alloy  of  tin  with 
foreign  substances.  This  method  of  refining  is  called  liquation. 
Frequently,  two  successive  liquations  are  necessary  in  order  to  ob- 
tain very  pure  tin. 

§  950.  Tin  is  used  in  the  manufacture  of  various  articles,  such 
as  kitchen  utensils,  cotton  machinery,  etc.,  etc. ;  a  small  quantity 
of  lead  being  often  added  to  it  to  render  it  less  brittle.  The  alloy 
generally  employed  contains  18  per  cent,  of  lead. 

Tin  is  also  made  in  very,  thin  sheets,  called  tin  foily.a,nd  used 
either  for  tinning  glass  or  for  wrapping  bonbons,  chocolate,  etc. 
Tin  foil  is  manufactured  by  beating,  only  the  best  tin  being  used. 
It  is  first  run  into  plates,  which  are  hammered  until  their  thickness 
is  reduced  to  about  1  millimetre,  after  which  8  or  10  plates  are 
laid  on  each  other,  and  the  hammering  continued  until  they  are 
sufficiently  thin,  when  they  are  cut  in  half,  and  again  laid  on  each 
other  and  beaten,  which  process  is  repeated  until  a  hundred  sheets, 
of  the  thickness  required,  are  obtained. 

One  of  the  most  important  applications  of  tin  is  that  of  tinning 
sheet-iron,  as  was  fully  described  in  §  847. 


169 


TITANIUM. 
Equivalent  ==  25  (312.5 ;  0  =  100). 

§  951.  Titanium*  has  been  found  combined  with  oxygen  in  several 
minerals :  rutile  is  nearly  pure  titanic  acid,  and  titanic  iron  is  a 
mixture,  or  a  compound  of  titanic  acid  and  oxide  of  iron.  Certain 
iron-ores  contain  a  very  small  quantity  of  these  titanic  minerals ; 
and  metallic  titaniumf  is  often  found  in  the  products  of  the  blast- 
furnaces in  which  such  ores  are  smelted.  It  is  especially  met  with 
in  the  metallic  masses  which  adhere  to  the  sides  of  the  furnace, 
toward  the  close  of  the  blast,  when  this  process  is  beginning  to 
slacken,  and  then  appears  under  the  form  of  small,  very  brilliant 
cubic  crystals  of  a  copper-red  colour,  scattered  through  a  mass 
of  half-refined  metal,  slag,  and  frequently  sulphide  of  iron.  These 
masses  are  treated  with  chlorohydric  acid,  which  dissolves  the  iron 
and  does  not  attack  the  titanium ;  by  which  a  large  portion  of  the 
little  crystals  are  detached,  while  they  still  remain  mixed  with  par- 
ticles of  slag,  from  which  they  are  easily  separated  by  levigation, 
their  density  being  5.3,  while  that  of  the  slag  is  much  lower.  These 
crystals  are  hard  enough  to  scratch  quartz,  and  are  unafi"ected  by 
concentrated  acids,  except  by  aqua  regia,  which,  however,  requires 
a  long  time  to  act  on  them. 

When  titanic  acid  is  heated  in  a  forge-fire  in  a  "brasqued"  cru- 
cible, it  is  converted  into  an  aggregated  black  mass,  which  is  an 
inferior  oxide  of  titanium,  while  the  portions  in  immediate  contact 
with  the  charcoal  are  still  more  reduced,  having  passed  into  the 
state  of  metallic  titanium,  which  forms  a  pellicle  of  a  copper-red 
colour  around  the  mass. 

The  best  method  of  preparing  metallic  titanium  in  the  labora- 
tory consists  in  decomposing  by  heat  perchloride  of  titanium,  which 
is  a  volatile  liquid,  in  a  retort  of  hard  glass  placed  in  a  furnace, 
and  through  which  a  current  of  dry  ammoniacal  gas  is  passed ; 
when  the  ammonia  immediately  combines  with  the  perchloride  of 
titanium,  which  is  converted  into  a  white  powder.  The  retort  is 
then  surrounded  by  burning  coals  and  the  current  of  ammoniacal 
gas  kept  up  ;  when  a  large  quantity  of  sal-ammoniac  is  sublimed 
and  condensed  on  the  globe  and  in  the  neck  of  the  retort,  the  me- 
tallic titanium  remaining  at  the  bottom  in  the  form  of  very  bril- 

*  Discovered  in  1791,  by  W.  Gr^gor. 

t  This  product  is  not  metallic  titanium,  as  was  erroneously  supposed,  but  a 
combination  of  nituret  and  cyanide  of  titanium,  according  to  the  formula 
Ti,C,N-f  3Ti,N.— IT.  L.  F. 


170  TITANIUM. 

liant  small  spangles  of  a  purple-red  colour.  The  retort  is  allowed 
to  cool,  still  maintaining  the  gaseous  current,  and  the  titanium  is 
then  removed. 

The  titanium  thus  prepared  is  more  easily  attacked  by  acids  than 
that  of  the  blast-furnaces,  and  nitric  acid  readily  converts  it  into 
titanic  acid.  Heated  in  the  air  it  becomes  incandescent,  and  is 
changed  into  a  white  powder  of  titanic  acid. 

COMPOUNDS  OF  TITANIUM  WITH  OXYGEN. 

§  952.  Three  compounds  of  titanium  with  oxygen  are  known : 

A  protoxide     TiO. 

A  sesquioxide  T\fi^, 

Titanic  acid      TiOg. 

Titanic  acid,  which  is  the  most  important  compound,  occurs  in 
nature  in  the  form  of  brownish-yellow  opake  crystals,  called  rutile 
by  mineralogists.  Rutile,  which  is  not  pure  titanic  acid,  but  gene- 
rally contains  one  or  two  hundredths  of  oxide  of  iron,  is  isomor- 
phous  with  native  binoxide  of  tin.  Other  minerals,  formed  by 
sesquioxide  of  titanium  combined  with  protoxide  of  iron,  and  called 
titanic  irons,  appear  to  be  analogous  to  magnetic  oxide  of  iron. 
Lastly,  the  mineral,  called  anatase,  which  forms  crystals  of  a  beau- 
tiful blue  colour,  is  composed  of  nearly  pure  titanic  acid.  Rutile 
is  attacked  neither  by  acids  nor  alkaline  solutions,  but  is  acted  on, 
at  a  red-heat,  by  the  alkalies  and  alkaline  carbonates.  Titanic 
acid  may  be  obtained  in  a  gelatinous  state^  in  which  it  combines 
with  the  acids  by  heating  finely  powdered  rutile  with  two  or  three 
times  its  weight  of  chloride  of  barium  in  a  strong  forge-fire.  The 
powdered  substance  is  calcined  and  treated  with  hot  water,  to  dis- 
solve the  chloride  of  barium  which  has  been  left  unchanged,  when 
the  residue  is  composed  of  titanate  of  baryta  and  oxide  of  iron.  It 
is  heated  in  a  porcelain  saucer  with  concentrated  sulphuric  acid, 
and  the  temperature  elevated  sufficiently  to  drive  off  the  greater 
part  of  the  excess  of  sulphuric  acid ;  after  which  it  is  again  treated 
with  water,  when  a  residue  of  sulphate  of  baryta  remains,  which  is 
separated  by  filtering.  An  excess  of  ammonia  added  to  the  liquid, 
which  contains  sulphates  of  titanium  and  iron  dissolved  in  an  ex- 
cess of  sulphuric  acid,  precipitates  the  titanic  acid  and  oxide  of 
iron,  after  which  a  small  quantity  of  sulfhydric  acid  is  passed 
through  to  convert  the  oxide  of  iron  into  a  sulphide.  When  the 
gelatinous  precipitate  has  become  black,  a  portion  of  the  superna- 
tant liquid  is  decanted  and  replaced  by  a  solution  of  sulphurous 
acid,  which  dissolves  the  sulphide  of  iron  by  transforming  it  into  a 
hyposulphite.  When  the  precipitate  is  completely  discoloured,  it 
is  collected  on  a  filter  and  washed  with  boiling  water. 

Gelatinous  titanic  acid  dissolves  in  the  acids,  and  by  boiling  its 
dilute  solutions  the  greater  part  of  the  titanic  acid  is  again  depo- 


CHLORIDE    OF   TITANIUM.  171 

sited.  When  subjected  to  heat,  a  moment  arrives  at  which  the 
substance  suddenly  becomes  incandescent,  remaining  so  only  for  a 
moment,  after  which  the  titanic  acid  becomes  insoluble  in  acids. 
Titanic  acid  forms  no  crystallized  compounds  with  the  acids,  while 
it  forms  substances  which  assume  a  crystalline  texture  on  cooling 
by  fusion  with  potassa  or  soda.  But  these  substances  are  decom- 
posed by  treatment  with  water,  and  while  an  insoluble  residue  of 
titanate  with  a  large  excess  of  acid  remains,  the  alkaline  liquid 
contains  but  little  titanic  acid. 

Titanic  acid,  heated  in  a  forge-fire  in  a  brasqued  crucible,  is 
converted  into  a  black  substance,  which  some  chemists  regard  as  a 
protoxide  TiO,  but  the  existence  of  this  substance  is  not  sufficiently 
proved. 

By  heating  it  to  a  high  temperature  in  a  current  of  hydrogen 
gas,  the  titanic  acid  is  converted  into  a  black  powder,  the  compo- 
sition of  which  very  nearly  approaches  that  of  the  oxide  Ti^Og. 
The  existence  of  a  sesquioxide  of  titanium  is,  moreover,  placed 
beyond  doubt  by  that  of  the  sesquichloride  Ti^Clg,  from  which  it 
may  be  obtained.  In  fact,  on  adding  ammonia  to  a  solution  of 
fcesquichloride  of  titanium,  a  brown  precipitate  of  hydrated  sesqui- 
oxide is  obtained,  which,  on  being  left  to  itself  in  water,  becomes 
first  black,  and  then  blue,  and  at  last  is  converted  into  white 
titanic  acid,  with  the  evolution  of  hydrogen  gas.  By  treating  ses- 
quichloride of  titanium  with  sulphuric  acid,  a  sesquisulphate  of 
titanium,  which  crystallizes  with  difficulty,  is  obtained. 

COMPOUNDS  OF  TITANIUM  WITH  CHLORINE. 

§  953.  Two  chlorides  of  titanium  are  known :  a  sesquichloride 
TijClg,  and  a  bichloride  TiClg,  corresponding  to  titanic  acid  TiOg. 

Bichloride  of  titanium  is  prepared  by  decomposing  an  intimate 
mixture  of  titanic  acid  and  charcoal,  heated  to  a  strong  red-heat, 
by  dry  chlorine,  for  which  purpose  the  apparatus  described  for  the 
preparation  of  chloride  of  silicium  (§  245),  and  represented  in  fig. 
638,  is  used. 

A  mixture  of  charcoal  and  rutile,  reduced  to  an  impalpable 
powder,  is  made  into  a  consistent  paste  with  a  certain  quantity  of 
oil,  and  calcined  to  redness  in  an  earthen  crucible  in  the  shape  of 
small  balls.  The  balls,  which  preserve  their  form,  and  consist  of  an 
intimate  and  porous  mixture  of  titanic  acid  and  charcoal,  are  intro- 
duced into  an  earthen  retort  C,  into  the  tubulure  a  of  which  a  por- 
celain tube  ab  is  introduced,  descending  to  the  bottom  of  the  retort. 
After  placing  the  retort  in  a  furnace  and  fitting  a  condensing  ap- 
paratus to  its  neck,  a  current  of  dry  chlorine  is  passed  through  the 
tubulure  ab  ;  and,  when  the  apparatus  has  become  filled  with  the 
gas,  the  retort  is  heated  to  a  strong  red-heat,  while  the  current  of 
chlorine  is  continued ;  when  the  bichloride  of  titanium  condenses 
in  the  refrigerating  apparatus,  and  may  be  obtained  in  large  quan- 


TITANIUM. 


Fig.  538. 

titles.  The  bichloride  of  titanium  thus  obtained  is  yellow,  from  a 
certain  quantity  of  chlorine  it  contains  in  solution,  and  is  also 
yet  impurified  by  some  sesquichloride  of  iron.  It  is  obtained  pure 
by  shaking  it  with  a  small  quantity  of  mercury,  which  combines 
with  the  dissolved  chlorine,  and  then  distilling  in  a  glass  retort  to 
separate  it  from  the  sesquichloride  of  iron.  • 

Bichloride  of  titanium  is  a  colourless  liquid,  giving  off  thick 
white  fumes  in  the  air.  Its  density  at  32°  is  1.761,  and  it  boils 
at  276.8°,  when  the  density  of  its  vapour  is  6.836.  It  behaves 
with  water  like  bichloride  of  tin,  which  it  closely  resembles  in  its 
physical  and  chemical  properties.  It  combines  with  a  small  quan- 
tity of  water  and  forms  a  crystallized  compound;  but  a  large 
quantity  of  water  decomposes  it  by  forming  a  white  precipitate  of 
titanic  acid,  while  the  liquid  contains  bichloride  of  titanium  dis- 
solved in  a  great  excess  of  chlorohydric  acid.  The  precipitate 
itself  dissolves  when  treated  with  chlorohydric  acid,  but  again 
gives  off  titanic  acid  by  boiling  the  diluted  liquid  for  some  time, 
when  the  latter  passes  into  a  modification  in  which  it  is  extremely 
insoluble  in  acids. 

By  passing  hydrogen,  saturated  at  the  temperature  of  212°  with 
vapour  of  bichloride  of  titanium,  through  a  porcelain  tube  heated  to 
redness,  crystalline  spangles  of  a  deep  violet  colour,  consisting  of 
sesquichloride  of  titanium^  are  condensed  in  the  cold  portions  of 
the  reducing  tube.  This  compound  is  deliquescent,  and  dissolves 
readily  in  water,  producing  a  violet-red  solution,  which  is  one  of 
the  most  powerful  reducing  agents.  It  precipitates  gold,  silver, 
and  mercury  in  a  metallic  state  from  their  solutions,  and  reduces 


COMPOUNDS    or   TITANIUM.  173 

the  salts  of  iron  and  copper  to  their  minimum  of  oxidation.    It  even 
decomposes  sulphurous  acid,  by  setting  free  the  sulphur. 

The  equivalent  of  the  metal  and  the  composition  of  titanic  acid 
have  been  inferred  from  the  analysis  of  the  bichloride  of  titanium. 

COMPOUND  OF  TITANIUM  WITH  SULPHUR. 

§954.  A  compound  of  titanium  with  sulphur  is  known,  corre- 
sponding to  titanic  acid,  and  closely  resembling  the  bisulphide  of 
tin,  or  mosaic  gold.  Bisulphide  of  titayiium  TiSg  is  obtained  by 
passing  a  current  of  sulfhydric  acid  gas,  saturated  at  212°  with 
vapour  of  bichloride  of  titanium,  through  a  tube  heated  to  redness  ; 
when  the  inside  of  the  tube  becomes  covered  with  a  thick  coating 
of  bisulphide  of  titanium,  in  the  form  of  scales  having  a  metallic 
lustre  and  the  colour  of  brass. 

DISTINCTIVE  CHARACTERS  OF  THE  COMPOUNDS  OF  TITANIUM. 

§  955.  The  combinations  of  titanium  are  recognised  by  the  above 
indicated  properties  of  titanic  acid,  and  by  the  following  distinctive 
reaction : — Titanic  acid  affords  with  borax,  in  the  oxidizing  flame 
of  the  blowpipe,  a  colourless  glass,  which  assumes  a  deep  blue 
colour  in  the  reducing  flame.  Titanium  is  also  recognised  by  the 
properties  of  its  bichloride,  and  by  the  red  metallic  dust  which  the 
latter  leaves  when  decomposed  by  ammonia  under  the  influence  of 
heat. 

The  combinations  of  titanium  may  be  easily  confounded  with 
those  of  tin,  on  account  of  the  close  resemblance  of  the  salts  of 
these  two  metals ;  while  they  may  readily  be  distinguished  by  means 
of  the  blowpipe,  as  stannic  acid,  when  heated  with  charcoal  and 
some  carbonate  of  soda,  yields  metallic  tin,  which  can  be  imme- 
diately recognised. 

DETERMINATION  OF  TITANIUM;  AND  ITS  SEPARATION  FROM  THE 
METALS  PREVIOUSLY  STUDIED. 

§  956.  Titanium  is  always  determined  in  the  state  of  calcined 
titanic  acid.  Its  separation  from  the  metals  we  have  hitherto 
studied  is  effected  either  by  the  insolubility  of  calcined  titanic 
acid  in  acids,  or  by  the  volatility  of  the  bichloride.  Titanic  acid 
dissolved  in  an  excess  of  chlorohydric  acid  is  not  precipitated  by 
sulfhydric  acid,  which  property  allows  its  separation  from  the 
heavy  metals,  such  as  cadmium,  tin,  lead,  bismuth,  copper,  mer- 
cury, gold,  silver,  platinum,  etc.,  which,  under  the  same  circum- 
stances, are  all  precipitated. 


174 


TANTALUM  OR  COLUMBIUM,  NIOBIUM,  PELOPIUM, 

ILMENIUM. 

§  957.  These  names  have  been  given  to  four  new  metals*  found 
some  few  years  since  in  minerals,  called  tantalites  and  yttro-tan- 
talites  ;  but  their  properties  are  not  yet  sufficiently  known  to  de- 
mand description  in  this  work. 


LEAD. 
Equivalent  =  103.7  (1296.25 ;  0  =  100). 

§  958.  The  lead  of  commerce  is  often  tolerably  pure,  and  then 
possesses  a  great  degree  of  flexibility  and  malleability.  Chemically 
pure  lead  is  obtained  by  calcining  in  a  brasqued  crucible  the  oxide 
obtained  by  calcining  the  crystallized  nitrate  of  lead.  Lead  is  a 
bluish-gray  metal,  possessing  a  bright  metallic  lustre  when  freshly 
cut.     Its  density  is  11.445. 

Lead  is  so  soft  as  to  be  easily  cut  with  a  knife,  and  leaves  me- 
tallic-gray marks  on  paper.  Being  very  malleable  when  cold,  it 
can  be  beaten  into  very  thin  sheets,  and  drawn  out  into  fine  wire, 
which  is  so  extremely  flexible  that  it  can  be  tied  in  knots  like 
a  hempen  string ;  but,  on  the  other  hand,  possesses  so  little  tenacity 
that  a  leaden  wire  of  2  millimetres  in  diameter  breaks  under  a 
weight  of  9  kilogs. 

Lead  fuses  at  a  temperature  of  about  335°,  giving  off  appreciable 
vapours  at  a  red-heat,  without  being,  however,  sufficiently  volatile 
to  be  distilled.  It  may  be  crystallized  by  fusion,  by  the  same  pro- 
cess as  that  indicated  for  sulphur  and  bismuth,  and  the  crystals, 
although  rarely  well  defined,  may  be  seen  to  be  regular  octa- 
hedrons. 

Lead  soon  tarnishes  in  the  air  at  the  ordinary  temperature,  an 
extremely  superficial  layer  being  formed  on  it,  which  is  supposed  to 

^  Tantalum  was  discovered  in  1801,  by  Hatchett,  in  an  American  mineral,  for 
which  reason  he  called  it  columbium ;  while  in  the  following  year  it  was  again  dis- 
covered in  a  Swedish  mineral  by  Ekeberg,  who  gave  to  it  the  name  of  tantalum. 

Niobium  and  pelopium  were  discovered  in  1846,  by  H.  Rose. 

Ilmenium  was  recognised  as  a  peculiar  metal  in  1847,  by  Hermann.  [The  ex- 
istence of  ilmenium  is  yet  a  matter  of  dispute,  as  some  chemists,  and  especially 
Rose,  regard  the  ilmenic  acid  found  in  samarskite  as  an  impure  niobic  acid. — 
W.  L.  F.-^ 


OXIDES.  175 

be  the  suboxide  Vhfi  ;  and  when  maintained  in  a  state  of  fusion  in 
the  air  oxidizes  very  rapidly.  During  the  first  few  moments  it  is 
covered  with  an  iridescent  pellicle,  which  soon  changes  into  a  yel- 
low pulverulent  dust,  while  at  a  red-heat  oxidation  advances  rapidly. 
The  oxide  PbO  then  comes  into  fusion,  and  must  be  run  off  in  order 
that  the  oxidation  should  continue. 

Lead  oxidizes  in  damp  air  and  the  vapour  of  acids,  even  in  that  of 
carbonic.  Distilled  water,  likewise,  under  these  circumstances,  acts 
the  part  of  an  acid,  in  consequence  of  the  afiinity  of  water  for  the 
oxide  of  lead ;  and  a  sheet  of  lead  dipped  into  distilled  water  be- 
comes covered  with  a  pellicle  of  white  hydrated  oxide,  or  hydro- 
carbonate,  which  sonietimes  forms  small  crystalline  spangles,  visible 
with  a  lens.  The  water  itself  contains  a  quantity  of  hydrated 
oxide  of  lead,  sufficient  to  be  detected  by  being  blackened  by  sulf- 
hydric  acid.  The  presence  of  a  small  quantity  of  some  salts,  chiefly 
sulphate  of  lime,  prevents  the  oxidation  of  lead,  for  which  reason 
the  effects  described  are  not  observed  in  common  spring  or  well 
water. 

Concentrated  boiling  chlorohydric  acid  acts  but  very  feebly  on 
lead,  and  dilute  sulphuric  acid  attacks  it  only  wlien  the  air  has 
access  to  it ;  while  hot  concentrated  sulphuric  acid  converts  it  into 
sulphate  with  disengagement  of  sulphurous  acid.  Nitric  acid,  which 
is  the  best  solvent  of  lead,  acts  on  it  at  the  ordinary  temperature 
with  the  evolution  of  reddish  vapours,  and  forms  soluble  nitrate 
of  lead. 

COMPOUNDS  OF  LEAD  WITH  OXYGEN. 

§  959.  Three  compounds  of  lead  with  oxygen  are  known : 

A  suboxide  PbgO. 

A  protoxide  PbO. 

A  binoxide  PbOa,  or  plumbic  acid. 

Again,  protoxide  of  lead  and  plumbic  acid  can  combine  in  various 
proportions,  forming  several  intermediate  oxides,  called  miniums, 
of  which  red-lead  is  the  most  important. 

Suboxide  of  Lead  Pb<p. 

§  960.  Suboxide  of  lead  is  a  black  powder  obtained  by  heating 
the  oxalate  to  a  temperature  of  572°  in  an  oil-bath,  until  gaseous 
carbonic  acid  and  oxide  are  no  longer  disengaged.  The  reaction  is 
represented  by  the  following  equation  : 

2(PbO,  C.O^) =Pb,0  -f  3C0,+  CO. 

The  opinion  of- some  chemists,  who  regarded  suboxide  of  lead  as 
an  intimate  mixture  of  metallic  lead  with  protoxide,  is  shown  to 
be  erroneous  by  the  following  reactions: — When  the  suboxide  is 
rubbed  with  mercury,  the  latter  dissolves  absolutely  nothing; 
but  solution  would  take  place  if  any  metallic  lead  existed  in  the 
mixture.     Again,  by  treating  the  suboxide  with  an  aqueous  solu- 


176  LEAD. 

tion  of  sugar,  no  protoxide  of  lead  is  dissolved,  showing  that  none 
exists  in  the  suboxide,  as  else  it  would  immediately  dissolve. 

But  by  treating  suboxide  of  lead  with  strong  acids,  even  when 
they  are  dilute,  it  is  converted  into  protoxide  PbO  which  dissolves, 
and  into  metallic  lead.  A  temperature  above  750°  immediately 
effects  the  same  decomposition ;  when  the  calcined  substance  parts 
with  its  lead  to  mercury,  and  with  its  protoxide  of  lead  to  a  solu- 
tion of  sugar  in  water. 

Suboxide  of  lead  heated  in  the  air  burns  like  tinder,  and  is  con- 
verted into  protoxide  of  lead  PbO. 

Protoxide  of  Lead  PbO. 

§  961.  Protoxide  of  lead  is  obtained  by  the  calcination  of  nitrate 
or  carbonate  of  lead  in  the  form  of  a  yellow  powder,  which  fuses  at 
a  red-heat,  and  yields,  on  cooling,  a  mass  composed  of  crystalline 
lamellae,  in  which  state  it  is  called  litharge^  while  the  name  of  mas- 
sicot is  given  to  the  pulverulent  oxide.  Well-defined  rhombohedral 
crystals  of  protoxide  of  lead  are  sometimes  found  in  the  fissures 
of  lead  furnaces.  Litharge,  when  fused  in  an  earthen  crucible, 
readily  acts  on  the  latter  by  combining  with  silicic  acid  and  per- 
forating the  crucible. 

Hydrated  oxide  of  lead  is  obtained  by  adding  ammonia  to  a  cold 
solution  of  a  salt  of  lead,  when  a  white  precipitate  forms,  which 
readily  dissolves  in  a  solution  of  potassa,  soda,  or  ammonia.  On 
evaporating  the  liquid,  the  oxide  of  lead  is  deposited  in  the  anhy- 
drous state,  in  the  form  of  brownish-yellow  lamellae,  resembling 
those  of  litharge.  Solutions  of  baryta  and  caustic  lime  may  be 
substituted  for  those  of  the  alkalies.  By  adding  a  concentrated 
solution  of  a  salt  of  lead  to  milk  of  lime,  previously  heated  to  ebul- 
lition, the  oxide  of  lead  is  precipitated  in  the  form  of  small  and 
very  heavy  crystals  of  a  beautiful  red  colour,  which  are  more 
easily  procured  by  boiling  a  concentrated  solution  of  caustic  soda 
with  an  excess  of  protoxide  of  lead  and  allowing  the  liquid  to  cool. 
The  red  crystals  of  protoxide  of  lead  retain  their  colour  when  they 
are  slowly  cooled  after  the  application  of  heat,  but  turn  yellow 
when  the  cooling  is  sudden.  Thus,  protoxide  of  lead  may  assume 
very  difi'erent  colours,  all  varieties  of  which  are  found  in  the 
litharge  of  commerce. 

Protoxide  of  lead  acts  the  part  of  a  true  acid  with  powerful 
bases,  and  its  solution  in  alkalies  should  be  considered  as  saline. 
The  compound  of  oxide  of  lead  with  lime  has  even  been  obtained 
crystallized.  A  solution  of  oxide  of  lead  in  lime  is  sometimes  used 
for  dyeing  hair  black  ;  which  effect  is  produced  by  the  oxide  of  lead 
reacting  on  the  sulphur  contained  in  the  organic  matter,  when 
black  sulphide  of  lead  is  formed.  The  same  solution  is  also  used 
in  the  manufacture  of  artificial  tortoise-shell. 


OXIDES.  177 

Protoxide  of  lead  contains 

Lead 92.83 

Oxygen 7.17 

100.00 

The  well-ascertained  isomorphism  of  several  compounds  of  lead 
■with  the  analogous  compounds  of  baryta  and  lime,  leaves  no  doubt 
as  to  the  formula  of  the  protoxide,  and  it  is  written  PbO,  whence 
the  equivalent  of  lead  is  deduced  as  103.7. 

Binoxide  of  Lead^  or  Plumbic  Acid  PbOg. 

§  962.  Binoxide  of  lead,  often  called  also  puce-coloured  oxide  of 
lead  on  account  of  its  colour,  is  prepared  by  treating  heated  red 
lead  with  dilute  nitric  acid,  which  dissolves  the  protoxide  and 
leaves  the  plumbic  acid  in  the  form  of  a  brown  powder.  The 
nitric  acid  must  be  renewed  until  no  more  oxide  of  lead  is  dis- 
solved ;  after  which  the  plumbic  acid  is  dried  at  a  temperature 
below  212°,  Plumbic  acid  is  also  obtained  by  treating  finely  di- 
vided protoxide  of  lead  suspended  in  water  by  chlorine  in  excess ; 
or  by  adding  a  solution  of  an  alkaline  hypochlorite  to  a  boiling  solu- 
tion of  acetate  of  lead.  A  certain  quantity  of  chloride  of  lead, 
which  in  the  latter  case  is  precipitated  with  the  plumbic  acid,  is 
removed  by  boiling  the  precipitate  several  times  with  water,  in 
which  the  chloride  is  quite  soluble. 

Plumbic  acid  contains 

1  equiv.  of  lead 103.7  88.47 

1      "         oxygen 16.0  11.53 

119.7  100.00 

Heat  readily  decomposes  plumbic  acid,  by  driving  off  half  of  its 
oxygen  and  converting  it  into  protoxide  of  lead.  Plumbic  acid 
does  not  combine  with  the  acids,  but  gives  ofi*  a  portion  of  its  oxy- 
gen to  those  which  are  susceptible  of  superoxidation ;  when  salts 
of  protoxide  of  lead  are  formed.  It  rapidly  absorbs  sulphurous 
acid  with  an  elevation  of  temperature,  and  forms  protosulphate  of 
lead ;  which  property  of  plumbic  acid  is  often  applied  to  the  sepa- 
ration of  sulphurous  acid  gas  when  mixed  with  other  gases.  It  also 
loses  one-half  of  its  oxygen  when  heated  with  concentrated  sul- 
phuric acid,  and  is  converted  into  the  protosulphate.  With  chlorohy- 
dric  acid  it  evolves  chlorine  and  yields  protochloride  of  lead  PbCl. 

Binoxide  of  lead  readily  combines  with  bases  forming  several  crys- 
tallizable  salts,  for  which  reason  it  has  been  called  plumbic  acid, 
Plumbate  of  potassa  is  obtained  by  heating  a  mixture  of  caustic 
potassa  and  binoxide  of  lead  entirely  freed  from  protoxide.  The 
binoxide  of  lead  is  placed  in  a  silver  crucible,  and  intimately  mixed 
with  a  highly  concentrated  solution  of  caustic  potassa ;  after  which 
it  is  slowly  and  gently  heated,  while,  from  time  to  time,  a  small 

VoL.II.-12 


178  '  LEAD. 

quantity  of  the  substance  is  dissolved  in  a  little  water  and  decom- 
posed by  nitric  acid.  When  a  copious  deposit  of  plumbic  acid 
ensues,  the  combination  may  be  considered  as  effected.  A  small 
quantity  of  water  is  then  poured  into  the  crucible,  and  rapidly  de- 
canted while  it  is  still  hot ;  when  the  solution  deposits,  on  cooling, 
colourless  and  transparent  octahedral  crystals  of  plumbate  of  po- 
tassa,  of  the  formula  K0,Pb03-f  3H0.  The  alkaline  liquid  float- 
ing above  the  crystals  contains  no  plumbic  acid,  because  plumbate 
of  potassa  is  nearly  insoluble  in  cold  alkaline  solutions.  It  is  de- 
composed by  solution  in  fresh  water. 

Plumbates  of  baryta  and  lime  are  obtained  as  insoluble  com- 
pounds by  heating  in  the  air  a  mixture  of  these  bases  and  minium. 

Intermediate  Oxides  of  Lead,  Miniums. 

§  963.  By  heating  finely  powdered  protoxide  of  lead,  or  mas- 
sicot, in  the  air  at  a  properly  regulated  temperature,  it  absorbs 
oxygen  and  is  converted  in  a  beautiful  orange-red  powder,  called 
minium."^  The  composition  of  this  substance  varies  according  to 
the  prolongation  of  the  roasting ;  and  by  continuing  it  until  the 
minium  no  longer  increases  in  weight,  the  product  is  found  to  pre- 
sent a  composition  corresponding  to  the  formula  2PbO,PbOj,.  It 
has  been  accidentally  found  crystallized  in  the  fissures  of  a  furnace 
used  for  the  preparation  of  minium,  and  presenting  the  characters 
of  a  well-defined  compound,  the  composition  of  which  corresponded 
to  the  formula  3PbO,Pb03.  Protoxide  of  lead  and  plumbic  acid 
may  very  probably  form  several  definite  compounds ;  but  minium 
should  not  be  considered  as  a  peculiar  oxide  of  lead,  as  it  behaves 
in  all  its  chemical  reactions  like  a  compound  of  the  two  oxides  just 
mentioned.  When  treated  with  nitric  or  acetic  acid,  the  protoxide 
of  lead  is  dissolved,  while  the  plumbic  acid  is  set  free ;  which  reac- 
tion is  generally  employed  for  the  preparation  of  the  latter  sub- 
stance. 

Minium  may  be  obtained  in  the  humid  way,  by  adding  a  solu- 
tion of  plumbate  of  potassa  to  an  alkaline  solution  of  litharge ;  when 
a  yellow  precipitate  of  hydrated  minium  is  formed,  which  is  con- 
verted by  desiccation  into  a  red  powder  of  anhydrous  minium. 

A  large  quantity  of  minium  is  used  in  the  manufacture  of  crys- 
tal glass  (§  686).   - 

In  order  to  prepare  minium,  powdered  litharge  is  oxidized  in  a 
reverberatory  furnace  at  a  temperature  which  should  not  exceed 
570°,  the  massicot  being  generally  prepared  from  very  pure  lead 
expressly  for  the  purpose..  The  furnaces  have  two  stories,  in  the 
lower  one  of  which,  where  the  temperature  is  highest,  the  lead  is 
converted  into  massicot,  always  taking  care  that  the  temperature 

*  We  distinguish  commercially  two  kinds  of  minium  :  orange  mineral,  the 
colour  of  -Nvhich  is  indicated  by  the  name ;  and  red-Lead,  which  presents  a  fine 
vermilion  hue. —  W.  L.  F. 


RED-LEAD.  179 

does  not  rise  suffioiently  high  to  fuse  the  oxide  of  lead,  because  the 
converting  of  litharge  which  is  not  in  the  state  of  powder  into 
minium  by  roasting  is  eifected  only  with  great  difficulty.  The 
massicot  arising  from  this  operation  is  generally  subjected  to  levi- 
gation,  to  free  it  from  the  particles  of  metallic  lead  it  may  contain ; 
after  which  it  is  placed  in  the  upper  furnace,  which  is  heated  only 
by  the  waste  heat  of  the  lower.  It  is  sometimes  simply  spread  in  a 
thin  layer  over  the  floor  of  the  second  furnace,  its  surface  being 
renewed  from  time  to  time  by  stirring  it  with  an  iron  rod ;  while, 
at  other  times,  it  is  placed  in  sheet-iron  boxes  arranged  in  the  fur- 
nace. In  some  manufactories,  only  one  furnace  is  used  for  the 
roasting  of  the  lead  and  the  conversion  of  the  massicot  into  minium. 
The  lead  is  first  oxidized  to  litharge,  which,  after  being  powdered 
and  levigated,  is  disposed  in  flat  sheet-iron  dishes,  which  are  piled 
up  in  the  hot  furnace.  The  doors  are  then  closed,  and,  during  the 
slow  cooling  of  the  furnace,  the  greater  part  of  the  massicot  is  con- 
verted into  minium.  Red-lead  of  a  good  quality  is  then  obtained 
by  repeating  the  operation. 

A  certain  quantity  of  minium  is  also  prepared  by  decomposing 
carbonate  of  lead,  commonly  called  ceruse  or  white-lead,  in  the  air; 
when  a  product  of  a  paler  colour  than  that  of  red-lead,  namely, 
orange  mineral,  is'  obtained. 

SALTS  FORMED  BY  THE  PROTOXIDE  OF  LEAD. 

§  964.  The  protoxide  is  the  only  oxide  of  lead  which  acts  the 
part  of  a  base  with  acids.  It  is  a  powerful  base,  the  affinities  of 
which  are  scarcely  inferior  to  those  of  baryta  and  lime.  It  is  dis- 
tinguished among  the  metallic  bases  by  its  tendency  to  form  basic 
salts,  which  often  present  all  the  characters  of  definite  compounds, 
the  solutions  of  which  turn  the  red  tincture  of  litmus  blue.  The 
salts  of  lead  are  poisonous:  in  small  doses  they  occasion  colic  and 
pains  in  the  intestines.  Workers  in  lead,  particularly  house  painters, 
are  highly  exposed  to  the  disease  called  lead  or  painter  s  colic ; 
the  best  treatment  of  which  consists  in  administering  drinks  con- 
taining a  small  quantity  of  sulphuric  acid,  or  sulphate  of  soda,  in 
order  to  convert  the  oxide  of  lead  into  an  insoluble  sulphate. 

Sulphate  of  Lead. 

§  965.  Sulphate  of  lead  being  insoluble  in  water,  is  easily  pre- 
pared by  pouring  an  alkaline  sulphate  into  the  solution  of  a  soluble 
salt  of  lead.  A  large  quantity  of  this  product  is  obtained  in  tlie 
drying-sheds  where  alum  is  decomposed  by  acetate  of  lead  in  order 
to  obtain  acetate  of  alumina  in  solution.  Although  the  sulphate  is 
nearly  insoluble  in  fresh  water,  it  readily  dissolves  in  acid  liquids, 
and  particularly  in  an  excess  of  sulphuric  acid.  Attention  must 
be  paid  to  this  solubility  in  chemical  analyses ;  in  which  case  the 
lead  remaining  in  the  liquid  is  separated  by  a  current  of  sulFhydric 


180  LEAD. 

acid,  which  precipitates  it  as  sulphide.  Concentrated  chlorohydrio 
acid  decomposes  sulphate  of  lead,  especially  at  the  boiling  point, 
and  transforms  it  into  crystalline  spangles  of  chloride  of  lead; 
which  reaction  proves  that  in  a  liquid  containing  an  excess  of  hy- 
drochloric acid,  the  chloride  of  lead  is  more  insoluble  than  the 
sulphate. 

Sulphate  of  lead  cannot  be  decomposed  by  heat ;  being  the  only 
sulphate,  among  those  of  the  metals  of  the  fourth  class  which  we 
have  now  studied  which  possesses  this  stability.  When  heated  to 
a  high  temperature  in  an  earthen  crucible,  the  sulphate  is  never- 
theless decomposed  near  the  sides  of  the  vessel,  by  forming  silicate 
of  lead  by  contact  with  the  silex  of  the  crucible.  Sulphate  of  lead 
is  easily  reduced  by  charcoal,  the  products  of  decomposition  vary- 
ing with  the  temperature  and  proportion  of  charcoal  used.  If  the 
charcoal  be  present  in  excess  and  heat  applied  suddenly,  the  sul- 
phate is  transformed  into  a  protosulphide  PbS ;  but  if,  on  the  con- 
trary, the  temperature  be  slowly  raised,  a  considerable  quantity 
of  sulphurous  acic}  is  disengaged,  and  the  subsulphide  of  lead 
PbgS  is  formed.  When  only  the  quantity  of  charcoal  absolutely 
necessary  to  convert  the  sulphuric  into  sulphurous  acid  and  to 
reduce  the  oxide  of  lead  is  used,  perfectly  pure  metallic  lead  re- 
mains ;  while  with  only  one-half  of  this  quantity  of  charcoal,  the 
protoxide  PbO  is  obtained. 

By  heating  1  equiv.  of  sulphate  and  1  equiv.  of  protosulphide  of 
lead  together  in  an  earthen  crucible,  sulphurous  acid  is  disengaged, 
and  2  equiv.  of  metallic  lead  remain : 

PbO,S03+PbS=2SO,+2Pb. 

But  by  heating  a  mixture  of  2  equiv.  of  sulphate  and  1  equiv. 
of  sulphide,  the  sulphur  is  again  disengaged  in  the  state  of  sul- 
phurous acid,  but  oxide  of  lead  remains  with  the  metallic  lead ; 

2(PbO,S03)+PbS=3SO,+2PbO+Pb. 

These  two  reactions  are  applied  in  the  metallurgy  of  lead. 

Iron  and  zinc  decompose  sulphate  of  lead  by  placing  the  metala 
in  acidulated  water  containing  sulphate  of  lead  in  suspension ; 
when  the  lead  separates  in  the  metallic  state. 

By  boiling  solutions  of  the  alkaline  carbonates,  sulphate  of  lead 
is  decomposed  and  converted  into  carbonate.  The  decomposition 
is  much  more  easily  effected  by  the  dry  way. 

Nitrate  of  Lead. 

§  966.  Nitrate  of  lead  is  prepared  by  dissolving  litharge,  or  white- 
lead,  or  also  metallic  lead,  in  an  excess  of  nitric  acid,  taking  care 
in  the  latter  case  to  keep  the  acid  in  excess.  The  hot  solution, 
when  saturated,  deposits  regular  octahedrons  of  nitrate  of  lead  on 
cooling,  which  are  sometimes  transparent  and  sometimes  opake, 


SALTS.  '  181 

but  in  each  case  anhydrous.  Cold  water  dissolves  only  about  4  of 
its  weight  of  nitrate  of  lead,  while  it  is  much  more  soluble  in  hot 
water.  Crystals  of  nitrate  of  lead  decrepitate  on  hot  coals,  and 
feed  the  combustion,  like  all  the  nitrates.  Nilrate  of  lead  is  de- 
composed by  heat  into  hyponitric  acid  which  is  disengaged,  and 
protoxide  of  lead  which  remains.  We  have  seen  (§  118)  that  this 
decomposition  is  applied  in  the  laboratory  to  the  preparation  of 
hyponitric  acid. 

By  boiling  a  solution  of  nitrate  of  lead  with  the  oxide  or  car- 
bonate of  lead,  a  liquid  is  obtained  which  deposits,  on  cooling,  large 
crystals  of  a  basic  nitrate  2PbO,N05-f-HO. 

A  nitrate  of  lead  possessing  still  higher  basic  properties  is  ob- 
tained by  treating  the  nitrate,  or  bibasic  nitrate,  with  ammonia, 
when  a  white  precipitate  of  the  formula  4PbO,N05-f-3HO  is  formed. 
A  large  excess  of  ammonia  decomposes  the  precipitate  and  leaves 
hydrated  oxide  of  lead. 

Nitrites  of  Lead. 

§  967.  When  thin  sheets  of  metallic  lead  are  digested  with  the 
application  of  heat  in  a  solution  of  nitrate  of  lead,  a  great  portion 
of  the  lead  is  reduced  without  any  disengagement  of  gas,  and  the 
liquid  assumes  a  yellow  colour,  and  deposits  crystals  on  cooling, 
which,  when  treated  with  an  acid,  disengage  copious  nitrous  fumes. 
Several  different  salts  may  be  obtained  by  varying  the  proportions 
of  metallic  lead.  By  digesting,  at  a  temperature  of  from  140°  to 
176°,  1  equiv.  of  nitrate  of  lead  dissolved  in  a  large  quantity  of 
water  with  1  equiv.  of  metallic  lead,  until  the  lead  is  entirely  dis- 
solved, a  yellow  solution  is  obtained,  which,  on  cooling,  deposits 
large  yellow  crystalline  lamellae  of  the  formula  2PbO,NOj-f  HO. 
The  reaction  producing  them  is  expressed  by  the  following  equa- 
tion: 

PbO,NO,+Pb+HO=2PbO,NO,+HO. 

The  crystals  are  readily  decomposed,  even  when  cold,  by  a  solu- 
tion of  carbonate  of  potassa ;  when  carbonate  of  lead  is  precipi- 
tated, and  the  liquid,  when  allowed  to  evaporate,  deposits  succes- 
sively crystals  of  nitrate  and  nitrite  of  potassa.  It  is  probable 
from  this  that  the  yellow  crystals  contain  no  ready  formed  hypo- 
nitric acid,  for  this  does  not  appears  to  be  able  to  produce  true 
saline  compounds,  but  that  they  contain  at  the  same  time  nitrite 
and  nitrate  of  lead.  Their  formula  may,  therefore,  be  written 
2PbO,NO,+2PbO,NO,+2HO. 

By  digesting  3  equiv.  of  metallic  lead  with  a  solution  of  2  equiv. 
of  nitrate  of  lead,  until  the  former  is  completely  dissolved,  a  liquid 
is  obtained  which  deposits  small  orange-coloured  crystals,  much  less 
soluble  than  the  yellow  lamellge.  The  formula  of  these  crystals  is 
7PbO,2N04+3HO:  they  are  also  decomposed  by  the  alkaline  car- 


182  '  LEAD. 

boiiates,  and  the  solution  which  results  from  the  reaction  yields,  on 
evaporation,  alkaline  nitrate  and  nitrite.  By  considering  this 
compound  as  containing  nitrate  and  nitrite  of  lead,  we  may  write 
its  formula  4PbO,N03+3PbO,N03+3HO.  The  same  compound 
is  obtained  by  boiling  a  solution  of  the  yellow  salt  with  oxide  of 
lead. 

Lastly,  by  boiling  for  a  long  time  with  an  excess  of  metallic  lead, 
either  a  solution  of  nitrate  of  lead,  or  of  the  yellow  or  orange- 
coloured  salts  just  described,  small  rose-coloured  crystals  of  the 
formula  4PbO,N03-|-HO  are  obtained,  which  are,  consequently,  a 
quadribasic  nitrite  of  lead.  The  neutral  nitrite  of  lead  is  easily 
prepared  with  the  basic  salt,  by  suspending  the  latter  in  water  and 
passing  through  it  a  current  of  carbonic  acid  gas ;  when  5  equiv. 
of  oxide  of  lead  are  precipitated  as  carbonate,  while  the  liquid,  on 
being  evaporated  in  vacuo,  deposits  yellow  prismatic  crystals  of 
anhydrous  neutral  nitrite  PbOjNO^.  By  means  of  this  neutral 
nitrite  of  lead,  the  soluble  neutral  nitrites  are  easily  prepared  by 
double  decomposition,  by  adding  to  its  solution  that  of  the  car- 
bonate or  sulphate  of  the  base  which  it  is  desired  to  obtain  in 
combination  with  the  nitrous  acid. 

Phosphates  of  Lead, 

§  968.  Several  compounds  of  oxide  of  lead  with  phosphoric  acid 
are  known,  corresponding  to  the  modifications  of  phosphoric  acid 
described  §  842.  By  pouring  a  solution  of  ordinary  phosphate  of 
soda  (2NaO  +  HO)P05+24HO,  into  a  solution  of  nitrate  of  lead, 
a  white  insoluble  precipitate  is  obtained,  which,  however,  dissolves 
readily  in  an  excess  of  acid  or  alkali.  The  formula  of  the  preci- 
pitate is  (2PbO  +  HO)P05:  it  melts  readily  before  the  blowpipe 
into  a  yellow  globule,  assuming  crystalline  fticets  on  solidifying ; 
which  character  is  sometimes  used  as  a  blowpipe  reaction  for 
phosphates. 

A  basic  phosphate  SPbOjPO^  is  obtained  by  treating  the  pre- 
ceding salt  with  ammonia.  The  other  phosphates  have  been  but 
little  studied. 

A  phosphate  of  lead  combined  with  a  certain  quantity  of  chloride 
of  lead,  which  occurs  in  nature,  and  is  called  phosphate  of  lead, 
crystallizes  in  regular  6-sided  prisms,  belonging  to  the  rhombohe- 
dric  system.  Its  colour  is  a  more  or  less  greenish  yellow,  and  its 
formula  is  3(3PbO,P03)+PbCl. 

Silicates  of  Lead, 

§  969.  Oxide  of  lead  and  silicic  acid  combine  in  all  proportions, 
and  form,  after  fusion,  vitreous  substances,  which  have  a  yellow 
tinge  when  the  proportion  of  oxide  of  lead  is  considerable.  The 
silicates  of  lead  enter  into  the  composition  of  glass,  and  have  been 
treated  of  under  this  head  (§  669). 


ACETATES.  183 

Aluminate  of  Lead, 
§  970.  A  compound  of  oxide  of  lead  with  alumina  occurs  in 
nature,  in  which  the  latter  substance  plays  the  part  of  an  acid: 
the  formula  of  the  mineral  is  PbO,2Ala03-}-6HO. 

Chromates  of  Lead, 

§  971.  The  neutral  chromate  of  lead  PbOjCrOg  is  obtained  in  the 
form  of  a  beautiful  yellow  powder  by  adding  a  solution  of  neutral 
acetate  of  lead  to  one  of  neutral  chromate  of  potassa.  The  salt  is 
used  in  oil-painting,  under  the  name  of  chrome  yellow^  and  also 
finds'application  in  dyeing.  The  shade  of  chromate  of  lead  varies 
with  the  more  or  less  perfect  neutrality  of  the  salts  used  in  preci- 
pitation, and  according  to  the  greater  or  less  dilution  and  the  tem- 
perature of  the  liquids.  Neutral  chromate  of  lead  is  found  in 
nature,  forming  beautiful  red  prismatic  crystals,  which  yield  a 
yellow  powder. 

A  bibasic  chromate  of  lead  2PbO,Cr03  is  obtained  by  fusing 
neutral  chromate  of  lead  with  nitrate  of  potassa;  when  beautiful 
red  crystals  are  deposited  at  the  bottom  of  the  crucible.  The 
supernatant  nitrate  of  potassa  is  decanted,  and  the  crystals  of 
bibasic  chromate  of  lead  are  washed  as  quickly  as  possible. 

Acetates  of  Lead. 

§  972.  Neutral  acetate  of  lead,  which  is  extensively  used  in  dye- 
ing, is  prepared  by  treating  litharge  with  acetic  acid  or  vinegar, 
taking  care  to  have  an  excess  of  acid,  to  prevent  the  formation  of 
basic  acetates.  The  liquid,  evaporated  slowly,  yields  large  crystals, 
of  which  the  formula  is  PbO,C^H303+3HO.  (The  formula  of 
acetic  acid,  at  its  maximum  of  concentration,  is  C4Hg03+ HO.) 
The  solution  of  acetate  of  lead  is  perfectly  neutral,  and  absorbs 
a  small  quantity  of  carbonic  acid  from  the  air ;  when  the  sides  of 
the  vessel  become  covered  with  a  thin  deposit  of  carbonate  of  lead, 
while  the  solution  manifests  a  slight  acid  reaction.  Crystals  of 
neutral  acetate  of  lead  part  with  their  water  in  a  dry  vacuum,  and 
when  heated.  After  melting  in  their  water  of  crystallization, 
which  they  lose  entirely  at  a  temperature  of  212°,  they  undergo 
the  igneous  fusion  at  about  374°  ;  and,  when  heated  still  further, 
lose  a  portion  of  their  acetic  acid,  which  is  partially  decomposed 
by  disengaging  carbonic  acid,  while  a  basic  acetate  3PbO,2C4H303 
remains,  which  is  itself  decomposed  at  a  higher  temperature. 
Acetate  of  lead  has  a  sweet  taste,  which  becomes  astringent  and 
metallic ;  and  it  dissolves  in  ^  of  its  weight  of  cold  water. 

By  boiling  a  solution  of  neutral  acetate  of  lead  with  a  quantity 
of  litharge  equal  to  one-half  of  that  which  the  acetate  contains,  a 
liquid  is  obtained  which,  after  evaporation,  deposits  crystals  of  a 
basic  acetate  of  lead  of  the  formula  3PbO,2C^H303+HO.     By 


184  LEAD. 

boiling  the  same  solution  with  a  quantity  of  oxide  of  lead  equal  to 
that  which  the  neutral  acetate  contains,  a  liquid  results  which  yields 
crystals  of  a  still  more  basic  salt,  and  of  which  the  formula  is 
8PbO,C,H303+HO. 

Lastly,  by  boiling  the  solution  of  the  last  basic  salt  with  an  ex- 
cess of  oxide  of  lead,  a  very  slightly  soluble  compound  is  obtained, 
which  is  almost  entirely  deposited  on  cooling.  Its  formula  is 
6PbO,C,H303. 

In  medicine,  a  solution  of  basic  acetate  of  lead  is  employed, 
under  the  name  of  extractum  saturni,  or  liquor  plumhi  subacetatis, 
which  is  obtained  by  dissolving  2  parts  of  neutral  acetate  of  lead 
and  1  part  of  litharge  in  3J  parts  of  water,  and  may,  therefore, 
be  considered  as  containing  a  mixture  of  the  two  sub-acetates 
3PbO,2C,H303+HO  and  3PbO,C,H303+HO.  The  solutions  of 
the  sub-acetates  of  lead  have  a  very  decided  alkaline  reaction,  and 
turn  blue  the  red  tincture  of  litmus.  Carbonic  acid  decomposes 
them,  and  precipitates  carbonate  of  lead,  while  the  liquid  contains 
neutral  acetate  mixed  with  a  certain  quantity  of  free  acetic  acid. 

Carbonate  of  Lead. 

§  973.  Carbonate  of  lead  is  found  crystallized  in  nature,  form- 
ing beautiful  and  highly  refracting  transparent  crystals,  belonging 
to  the  fourth  system  of  crystallization,  and  isomorphous  with  arra- 
gonite.  The  salt  is  prepared  by  double  decomposition  by  pouring 
an  alkaline  carbonate  into  the  solution  of  a  soluble  salt  of  lead, 
when  a  white  precipitate  is  formed,  which  is  the  anhydrous  neutral 
carbonate,  nearly  insoluble  in  water. 

Carbonate  of  lead  is  used  in  oil-painting,  under  the  name  of 
white-lead,  or  ceruse.  It  is  prepared  by  several  processes  appa- 
rently very  different  from  each  other,  but  all  consisting  in  the  de- 
composition of  sub-acetate  of  lead,  produced  by  various  reactions, 
by  carbonic  acid. 

One  of  these  processes,  called  the  process  of  Clichy,  from  its 
having  been  first  employed  at  Clichy,  near  Paris,  consists  in  dis- 
solving litharge  in  acetic  acid  so  as  to  obtain  a  solution  of  a  basic 
acetate  containing  a  large  quantity  of  oxide  of  lead,  and  decom- 
posing it  by  the  carbonic  acid  produced  by  combustion  in  the 
furnace  which  serves  to  heat  the  kettles  in  which  acetic  acid  is 
saturated  with  the  oxide  of  lead.  To  effect  this,  the  air  driven 
across  the  grate  of  the  furnace  by  a  blowing-machine,  is  conveyed 
by  pipes  into  the  solution  of  sub-acetate  of  lead  to  be  decomposed. 
In  some  localities  the  carbonic  acid  arising  from  the  earth  is  used 
(§  253).  Nearly  the  whole  of  the  oxide  of  lead  is  precipitated  in 
the  state  of  carbonate,  while  the  liquid  contains  all  the  acetic  acid, 
which  is  used  to  dissolve  an  additional  quantity  of  oxide  of  lead, 
and  the  fresh  solution  is  again  subjected  to  the  action  of  carbonic 
acid.     The  same  acid  may  thus  serve  for  the  transformation  of  an 


>      WHITE-LEAD.  185 

indefinite  quantity  of  oxide  of  lead  into  white-lead ;  but,  a  certain 
quantity  of  it  being  invariably  wasted  in  the  various  manipulations, 
a  small  quantity  must  be  added  each  time. 

In  England,  litharge  moistened  with  acetic  acid,  or  with  a  solu- 
tion of  neutral  acetate  of  lead,  is  exposed  to  a  current  of  carbonic 
acid  gas,  produced  by  the  combustion  of  charcoal ;  by  which  means 
the  litharge  is  in  a  short  time  converted  into  the  carbonate  of 
lead. 

The  greater  part  of  the  white-lead  used  in  France  is  prepared 
in  the  Department  of  the  North,  by  a  process  first  adopted  in  Hol- 
land, and  called,  for  this  reason,  the  Dutch  process.  Sheets  of 
lead,  of  from  0.12  m.  to  0.15  m.  wide,  and  from  0.6  m.  to  1.0  m. 
long,  coiled  up  into  a  cylinder  Z  (fig.  539),  are  placed  each  in  a 
^  glazed  earthen  pot,  having  two  little  projections  b,  h, 
on  which  the  roll  of  lead  rests.  Each  pot  contains  at 
the  bottom  a  small  quantity  of  common  vinegar,  made 
from  fermented  beer,  and  is  covered  with  a  leaden 
plate  mn  which  closes  it  imperfectly.  A  large  num- 
ber of  pots  being  arranged  in  several  rows  on  a  layer 
of  stable  manure,  are  covered  with  straw,  and  a  second 
Fig.  539.  YOYf  is  placed  on  them,  with  another  layer  of  manure ; 
"which  process  is  continued  until  5  or  6  rows  of  pots  are  thus  ar- 
ranged. Lastly,  the  whole  is  covered  with  manure,  held  together 
by  means  of  boards,  so  as  to  allow  the  air  to  permeate  slowly  the 
whole  mass. 

The  vinegar  in  the  pots  yields  vapour  of  water  and  acetic  acid, 
which,  by  their  contact,  rapidly  oxidize  the  metal  and  cover  its 
surface  with  sub-acetate  of  lead.  On  the  other  hand,  by  the  fer- 
menting action  of  the  manure,  carbonic  acid  is  disengaged  and 
the  temperature  elevated  internally,  so  that  the  acid  vapours  are 
more  and  more  copiously  evolved.  The  carbonic  acid  then  decom- 
poses the  sub-acetate  of  lead  and  transforms  it  into  carbonate, 
while  the  acetic  acid  set  free  effects  the  formation  of  a  fresh  quan- 
tity of  sub-acetate,  which,  in  its  turn,  is  converted  into  a  carbonate, 
and  so  on.  In  15  days  the  operation  is  terminated,  and  the  disks 
of  lead  covering  the  pots  are  nearly  entirely  converted  into  car- 
bonate. The  leaden  rolls,  which  are  more  or  less  deeply  corroded, 
are  unrolled,  beaten  to  detach  the  carbonate,  and  then  placed  in 
other  pots  until  they  have  completely  disappeared.  The  white- 
lead  is  finely  powdered,  purified  by  levigation,  and  placed  to  dry 
in  porous  earthen  pots. 

^  A  certain  quantity  of  sulphate  of  baryta,  or  chalk,  is  often  mixed 
with  white-lead,  to  discover  the  presence  of  which  the  mixture  is 
treated  with  nitric  acid,  which  dissolves  the  carbonate  of  lead  and 
lime  and  leaves  the  sulphate  of  baryta.  On  evnporaling  the  solu- 
tion of  the  nitrates  and  treating  with  alcohol,  the  nitrate  of  lime  is 
dissolved,  while  the  nitrate  of  lead  remainci  as  a  residue. 


186  LEAD. 

DISTINCTIVE  CHARACTERS  OF  THE  SALTS  OF  LEAD. 

§  974.  The  neutral  salts  formed  by  the  protoxide  of  lead  are  co- 
loui'less  when  the  acid  is  free  from  colour,  while  the  basic  salts,  on 
the  contrary,  are  frequently  yellow.  The  soluble  salts  have  a  sweet 
taste. 

Caustic  potassa  and  soda  yield,  when  cold,  white  precipitates  of 
hydrated  protoxide  of  lead,  which  dissolves  in  an  excess  of  the  re- 
agent. 

The  alkaline  carbonates  throw  down  a  white  precipitate  of  car- 
bonate of  lead,  insoluble  in  an  excess  of  the  reagent. 

Sulf  hydric  acid  and  the  alkaline  sulf  hydrates  produce  a  black 
precipitate  of  sulphide  of  lead,  even  when  the  liquid  does  not  con- 
tain a  great  excess  of  acid,  which  does  not  dissolve  in  an  excess  of 
alkaline  sulf  hydrates. 

Solutions  of  lead  yield  with  the  soluble  sulphates  a  white  preci- 
pitate, insoluble  in  water,  which  at  first  might  be  confounded  with 
sulphate  of  baryta,  but  which  is  easily  distinguished  from  the  latter 
by  being  blackened  by  sulf  hydric  acid. 

Prussiate  of  potash  throws  down  a  white  precipitate  with  salts  of 
lead. 

By  adding  chlorohydric  acid,  or  a  soluble  chloride,  to  a  slightly 
concentrated  and  hot  solution  of  a  salt  of  lead,  a  white  precipitate 
of  chloride  of  lead  is  obtained,  which  changes,  on  cooling,  into  small 
crystalline  lamellae  of  a  peculiar  aspect.  If  an  iodide  be  substituted 
for  the  chloride,  gold-coloured  yellow  spangles,  which  are  equally 
characteristic,  are  obtained. 

Iron,  zinc,  and  tin  precipitate  lead  from  its  solutions  in  the  me- 
tallic state. 

Lastly,  the  salts  of  lead  are  easily  recognised  in  the  blowpipe, 
because,  when  heated  with  carbonate  of  soda  on  charcoal,  in  the 
reducing  flame,  they  yield  a  globule  of  metallic  lead,  easily  recog- 
nised as  such  by  its  physical  and  chemical  properties. 

COMPOUNDS  OF  LEAD  WITH  SULPHUR. 

§  975.  The  sulphide  of  lead  PbS  corresponding  to  the  protoxide 
PbO,  found  in  nature  in  the  form  of  beautiful  bluish-gray  and  bril- 
liant crystals,  which  mineralogists  call  galena.  It  is  the  most  com- 
mon ore  of  lead,  and  also  the  most  important,  as  it  furnishes  nearly 
all  the  lead  of  commerce.  The  sulphide  is  obtained  directly  by 
fusing  grain  lead  with  sulphur,  when  the  combination  takes  place 
with  incandescence ;  but  to  obtain  a  pure  sulphide,  the  substance 
must  be  pulverized  and  heated  a  second  time  with  sulphur.  The 
black  precipitate  effected  by  a  current  of  sulf  hydric  acid  in  a  solu- 
tion of  a  salt  of  lead  is  very  finely  divided  protosulphide. 

Sulphide  of  lead  fuses  at  a  red-heat,  and,  if  allowed  to  cool  very 
slowly,  the  mass  presents  after  its  solidification  a  crystalline  texture, 
in  which  the  cubic  cleavage  is  easily  distinguished.      Sulphide  of 


SULPHIDE.  187 

lead  is  slightly  volatile,  and  may  be  sublimed  in  a  porcelain  tube  in 
a  current  of  gas ;  when  the  colder  parts  of  the  tube  become  coated 
with  small,  but  extremely  brilliant  cubic  crystals  of  sulphide. 

Sulphide  of  lead  reacts  readily  in  the  air,  the  products  varying 
with  the  temperature  and  marteer  of  conducting  the  operation ;  and 
while  a  great  deal  of  sulphate  and  oxide  of  lead  is  generally  formed, 
a  large  quantity  of  metallic  lead  may  also  be  obtained.  We  have 
seen  (§  965)  that  by  heating  1  equiv.  of  sulphate  with  1  equiv.  of 
sulphide  of  lead,  2  equiv.  of  metallic  lead  are  obtained  with  disen- 
gagement of  sulphurous  acid ;  and  again,  by  heating  1  equiv.  of  sul- 
phide with  2  equiv.  of  protoxide,  sulphurous  acid  is  disengaged,  and 
3  equiv.  of  metallic  lead  remain  : 

PbS+2PbO=3Pb+SO,. 

As  will  easily  be  conceived,  these  various  reactions  may  occur 
during  the  roasting  of  sulphide  of  lead ;  and  we  shall,  in  fact,  meet 
with  examples  of  this  in  the  metallurgy  of  lead. 

Sulphide  of  lead  ,is  not  appreciably  acted  on  by  chlorohydric  or 
by  dilute  sulphuric  acid ;  but  concentrated  boiling  sulphuric  acid 
converts  it  into  sulphate  with  disengagement  of  sulphurous  acid. 
Nitric  acid,  even  when  diluted,  acts  readily  on  galena ;  and,  when 
the  acid  is  mixed  with  a  sufficient  quantity  of  water,  the  sulphur  is 
set  free,  while  the  lead  dissolves  in  the  state  of  nitrate.  Fuming 
nitric  acid  converts  the  sulphide  into  sulphate ;  and  lastly,  nitric 
acid  in  a  state  of  medium  concentration,  transforms  a  great  portion 
of  the  sulphide  into  sulphate,  while  the  remaining  sulphide  yields 
free  sulphur  and  lead  which  dissolves  in  the  state  of  nitrate. 

By  heating  1  equiv.  of  sulphide  of  lead  with  1  equiv.  of  metallic 
lead,  a  subsulphide  of  lead  PbgS  is  obtained,  which  is  constantly 
met  with  in  the  metallurgy  of  lead,  where  it  forms  what  are  called 
leaden  matts.  Sulphide  of  lead  appears  to  possess  the  property  of 
combining  with  larger  quantities  of  lead. 

COMPOUND  OF  LEAD  WITH  SELENIUM. 

Selenide  of  lead  has  been  found  in  some  mines  of  galena, 
chiefly  in  the  Hartz  mountains,  forming  crystalline  masses,  with 
cubic  cleavage,  closely  resembling  galena.  Selenium  is  extracted 
from  this  mineral,  by  heating  in  a  crucible  an  intimate  mixture  of 
powdered  selenide  of  lead,  nitrate,  and  carbonate  of  soda,  and  treat- 
ing the  fused  mass  with  boiling  water ;  when  a  solution  is  obtained 
containing  seleniate  of  soda,  which  is  separated  by  crystallization. 
The  seleniate  is  then  boiled  with  an  excess  of  chlorohydric  acid, 
which  converts  the  selenic  into  selenious  acid ;  and,  lastly,  the  sele- 
nium is  precipitated  by  sulphuroils  acid. 

COMPOUNDS  OF  LEAD  WITH  ARSENIC. 

§  976.  Lead  and  arsenic  combine  readily,  and  produce  very  brittle 
crystalline  compounds. 


188  LEAD. 


COMPOUND  OF  LEAD  WITH  CHLORINE. 

§  977.  .Lead  is  easily  acted  on  by  chlorine,  yielding  but  one  com- 
pound, the  protochloride  of  lead  PbCl.  Chloride  of  lead  is  readily 
prepared  by  heating  litharge  with  chlorohydric  acid,  by  which  the 
oxide  is  transformed  into  a  white  crystalline  powder,  formed  of  small 
acicular  crystals,  or  small  spangles.  The  chloride  is  but  slightly 
soluble,  especially  in  cold  water ;  and  is  deposited  from  a  hot  satu- 
rated solution,  on  cooling,  in  the  form  of  small  crystals,  only  a  small 
proportion  remaining  in  the  mother  liquid.  Chloride  of  lead  fuses 
without  decomposition  before  attaining  a  red-heat,  and  congeals  into 
a  substance  resembling  horn,  and  divisible  by  a  knife ;  while,  at  a 
higher  temperature,  it  gives  off  copious  fumes.  It  may  be  prepared 
by  double  decomposition,  by  pouring  a  solution  of  sea-salt  into  a 
concentrated  solution  of  a  salt  of  lead. 

Chloride  and  oxide  of  lead  combine  in  several  proportions,  pro- 
ducing oxychlorides,  which  crystallize  readily  by  fusion,  and,  on 
account  of  their  beautiful  yellow  colour,  are  used  in  painting,  under 
the  names  of  mineral  yellow^  Cassel  yellow,  Turner's  yellow.  Cas^ 
sel  yellow,  which  is  prepared  by  fusing  together  10  parts  of  red- 
lead  and  1  part  of  sal-ammoniac,  consists  of  large  crystalline  lamel- 
lae, of  the  formula  PbCH-7PbO.  Turner's  yellow  is  obtained  by 
allowing  a  paste  made  with  7  parts  of  litharge,  1  part  of  sea-salt, 
and  a  certain  quantity  of  water,  to  rest  for  several  days,  and  sub- 
sequently removing  the  soda  by  treatment  with  water,  and  fusing 
the  residue  in  a  crucible. 

COMPOUND  OF  LEAD  WITH  IODINE. 

§  978.  On  adding  a  solution  of  iodide  of  potassium  to  a  hot  and 
sufficiently  dilute  solution  of  a  salt  of  lead,  the  liquid  deposits,  on 
cooling,  yellow  crystalline  spangles  of  iodide  of  lead  Pbl,  having 
the  lustre  of  gold. 

DETERMINATION  OF  LEAD,  AND  ITS  SEPARATION  FROM  THE  METALS 
PREVIOUSLY  STUDIED. 

§  979.  Lead  is  determined  in  the  state  of  anhydrous  protoxide, 
or  as  sulphate.  It  is  frequently  precipitated  from  its  solutions  in 
the  state  of  carbonate,  and  converted  into  protoxide  by  calcining  to 
redness ;  but  it  is  important  not  to  calcine  the  substance  with  the 
filter,  as  a  portion  of  the  lead  would  then  be  reduced  to  the  metal- 
lic state,  and  attack  the  platinum  crucible,  if  the  experiment  were 
made  in  a  vessel  of  this  metal.  Care  must  therefore  be  taken  to 
separate  the  substance  from  the  filter,  and  drop  it  into  the  crucible, 
after  which  the  filter  is  burned  at  the  end  of  a  platinum  wire  held 
over  the  crucible,  so  that  the  calcined  matter  may  fall  into  it.  The 
crucible  is  then  heated  to  redness  over  an  alcohol  lamp ;  while,  for 
the  sake  of  greater  certainty,  the  substance  is  moistened  with  a  few 


ALLOYS   OF   LEAD.  189 

drops  of  nitric  acid,  and  again  calcined.  Analogous  precautions 
must  be  observed  diiring  the  calcination  of  sulphate  of  lead,  the 
sulphate  being  reduced  to  sulphide  by  contact  with  organic  matter. 
Lead  is  separated  from  the  alkaline  metals  by  many  of  the  solu- 
ble carbonates  and  sulphates,  or  by  sulf  hydric  acid,  all  of  which 
reagents  precipitate  only  the  lead.  It  is  separated  from  magnesia, 
alumina,  the  oxides  of  manganese,  iron,  chrome,  cobalt,  nickel,  zinc, 
etc.,  by  the  alkaline  sulphates  or  sulf  hydric  acid;  and  from  cad- 
mium by  the  alkaline  sulphates,  which  precipitate  only  the  lead.  It 
is  separated  from  titanium  by  a  current  of  sulf  hydric  acid  passed 
through  the  strongly  acid  liquid,  by  which  the  lead  alone  is  precipi- 
tated. In  order  to  separate  lead  from  tin,  both  metals  are  precipi- 
tated together  by  an  alkaline  carbonate,  and  afterward  by  calcin- 
ing the  precipitate  and  treating  it  with  nitric  acid,  the  tin  is  con- 
verted into  stannic  acid,  and  the  oxide  of  lead  into  nitrate  of  lead ; 
the  latter  alone  is  dissolved  by  treating  again  with  water. 

TESTING  OF  LEAD  ORES  BY  THE  DRY  WAY. 

§  980.  Galena,  which  is  the  principal  ore  of  lead,  is  tested  by 
heating  to  a  strong  red-heat  in  an  earthen  crucible  a  mixtm-e  of 
20  gr.  of  pulverized  galena  with  30  gr.  t)f  black  flux  and  5  or  6  gr. 
of  small  iron  nails,  called  Paris  tacks  ;  when  the  galena  is  decom- 
posed, its  sulphur  combining  partly  with  the  iron  and  partly  with 
the  alkaline  matter  of  the  black  flux,  and  the  lead  separates  and 
forms  a  button  at  the  bottom  of  the  crucible.  After  cooling,  the 
leaden  ball  is  extracted  by  breaking  the  crucible,  and  flattened 
under  a  hammer,  to  see  that  it  contains  no  iron  nails,  and  then 
weighed.  The  small  quantity  of  lead  remaining  in  the  slag  is  of 
no  importance  in  ordinary  testing. 

ALLOYS. 

§  981.  Lead  forms  several  alloys  used  in  the  arts,  the  principal 
of  which  are,  type-metal,  composed  of  antimony  and  lead,  and  the 
alloys  of  lead  and  tin  used  for  soldering  and  in  the  manufacture  of 
tin  utensils. 

The  alloy  used  for  type-metal  corresponds  nearly  to  the  formula 
PbgSb,  and  is  composed  of 

Lead 76.2 

Antimony 23.8 

100.0 
A  small  quantity  of  bismuth  is  sometimes  added. 

This  alloy  is  analyzed  by  means  of  nitric  acid,  which  dissolves 
the  lead  in  the  state  of  nitrate,  and  converts  the  antimony  into 
antimonic  acid.  It  is  evaporated  to  dryness  to  drive  ofi"  the  excess 
of  acid,  after  which  water  dissolves  the  nitrate  of  lead,  and  leaves 
the  insoluble  antimony.     As  it  is  difficult  to  convert  the  whole  of 


190  LEAD. 

the  antimony  into  antimonic  acid  by  means  of  nitric  acid,  it  is  pre- 
ferable to  reduce  the  residue  to  the  state  of  metallic  antimony,  by 
heating  it  in  a  glass  tube  in  a  current  of  hydrogen  gas.  The  lead 
is  then  determined  either  differentially,  or  as  sulphate  by  precipi- 
tating the  solution  containing  it  by  an  alkaline  sulphate.  If  the 
alloy  contained  bismuth,  the  residue  obtained  by  evaporating  the 
nitric  solution  to  dryness  must  again  be  treated  with  water  acidu- 
lated with  nitric  acid,  in  order  to  dissolve  the  lead  and  bismuth ; 
after  which  the  liquid  is  carefully  saturated  with  ammonia,  which 
would  precipitate  the  bismuth  without  precipitating  the  lead,  unless 
a  great  excess  were  added.  The  perfect  separation  of  lead  and  bis- 
muth is  difficult. 

Lead  and  tin  combine  readily  in  all  proportions ;  and  the  fusi- 
bility of  the  alloys  formed  greatly  varies  according  to  the  propor 
tions  of  the  two  metals. 

Pure  lead  fuses  at 635.0° 

The  alloy  Pb3Sn  "    552.2° 

"        PbSn  "  465.8° 

"        PbSn^  "  384.8° 

"        PbSn3"  366.8° 

"        PbSn,"  372.2° 

"        PbSn,  "  381.2° 

Pure  tin  " 437.0° 

Thus  the  most  fusible  alloy  corresponds  to  the  formula  PbSug, 
and  fuses  at  a  temperature  lower  than  that  of  the  most  fusible  me- 
tal which  enters  into  its  composition.  These  alloys  are  easily 
destroyed  by  eliquation  (§315). 

For  tin-ware,  tin  is  alloyed  with  12  or  18  per  cent,  of  lead,  by 
which  the  metal  is  rendered  harder  and  more  easy  to  be  worked  in 
a  lathe. 

Plumber's  solder  is  composed  of 

Tin 1  part. 

Lead 2    " 

This  solder  fuses  at  about  527°. 
Tin-worker's  solder  contains 

Tin. 1  part. 

Lead 1    " 

The  alloys  of  tin  and  lead  are  easily  analyzed.  It  suffices  to 
attack  the  alloy  with  nitric  acid,  which  dissolves  the  lead  and  con- 
verts the  tin  into  insoluble  stannic  acid ;  when  the  tin  is  determined 
in  the  state  of  calcined  stannic  acid,  and  the  lead  differentially. 

METALLURGY  OF  LEAD. 

§  982.  A  great  number  of  minerals  containing  lead  are  found  in 
nature,  the  principal  of  which  are  sulphide  of  lead  or  galena,  the 
selenide,  carbonate,  chlorophosphate,  and  chromate.     The  sulphide 


METALLURGY   OF   LEAD.  191 

and  carbonate  of  lead  are  the  only  minerals  sufficiently  rich  to  be 
worked  to  advantage. 

Galena  is  generally  found  in  veins  traversing  the  primitive  and 
transition  rocks,  and  also  often  forms  pipe-veins  of  greater  or  less 
size  in  the  transition  rocks  and  the  lower  stage  of  the  secondary 
rocks.  Lastly,  certain  sandstones,  belonging  to  the  variegated 
sandstone  {hunter  sandstein)  formation,  are  impregnated  with  small 
grains  of  galena,  which  are  easily  separated  mechanically,  when  the 
sandstone  is  not  too  hard. 

Galena  always  undergoes  a  mechanical  preparation.  The  ore  is 
first  sorted  by  hand,  and  the  pieces  sufficiently  rich  are  smelted  im- 
mediately, while  the  remainder  is  crushed  between  cylinders  and 
sifted.  A  fresh  quantity  of  ore  fit  for  meltmg  is  thus  obtained, 
besides  an  ore  closely  mixed  with  gangue,  which  is  stamped,  and 
then  washed  in  boxes  or  on  tables.  These  preparations  yield  a 
sludge  of  greater  or  less  fineness  of  grain,  which  is  sent  to  the 
smelting-house. 

Galena  often  contains  enough  silver  to  allow  it  to  be  extracted 
with  advantage ;  and  its  metallurgic  treatnfent  is  then  directed  to 
the  extraction  of  both  the  lead  and  silver.  Some  galenas  are  mixed 
with  copper  pyrites,  and  then  yield  a  sufficient  quantity  of  copper 
to  make  them  valuable  for  the  extraction  of  that  metal. 

Carbonate  of  lead  forms  small  pipe-veins  in  the  secondary  rocks, 
and  exists  most  frequently  in  the  vicinity  of  the  galena-mines.  Its 
metallurgic  treatment  is  very  simple :  it  is  fused,  in  contact  with 
charcoal,  in  small  blast-furnaces,  called  elbow-furnaces ;  when  the 
lead  is  reduced  and  easily  separated  from  the  slag. 

The  most  common  gangue  of  lead-ore  is  quartz,  carbonate  of 
lime,  sulphate  of  baryta,  and  fluor-spar.  Care  must  be  taken  that 
the  melting-bed  contains  substances  essential  to  an  easy  fusion  of 
the  slag ;  for  which  reason  it  is  often  necessary  to  add  foreign 
substances,  in  order  to  obtain  more  fusible  scoriae. 

§  983.  The  metallurgic  processes  by  means  of  which  lead  is  ex- 
tracted from  galena  are  divided  into  two  classes : 

In  the  first,  the  ore  is  smelted  with  metallic  iron,  which  separates 
the  sulphur  from  the  lead  and  forms  a  fusible  sulphide  of  iron,  while 
the  lead  is  set  free.  Theoretically,  the  mixture  for  smelting  should 
be: 

1  equiv.  of  sulphide  of  lead 109.7 

1      "  "  iron 28.0 

147.7 

From  which  are  obtained 

1  equiv.  of  lead 103.7 

1     "  sulphide  of  iron 44.0 

iirr 


192  LEAD. 

The  second  method  is  founded  on  the  reactions  already  men- 
tioned (§  965). 

By  fusing  together  1  equiv.  of  sulphide  of  lead  and  2  equiv.  of 
oxide  of  lead,  3  equiv.  of  metallic  lead  are  obtained,  while  1  equiv. 
of  sulphurous  acid  is  disengaged  : 

PbS+2PbO=3Pb+SO,. 

By  melting  together  1  equiv.  of  sulphide  and  1  equiv.  of  sulphate 
of  lead,  2  equiv.  of  sulphurous  acid  are  disengaged,  while  2  equiv. 
of  metallic  lead  are  obtained. 

The  process  founded  on  the  reactions,  and  called  the  process  hy 
reaction,  consists  in  roasting  the  galena  in  a  reverberatory  furnace 
until  a  certain  quantity  of  oxide  and  sulphate  is  formed,  and  then 
giving  a  blast,  after  having  intimately  mixed  the  material  and 
closed  all  the  doors  of  the  furnace.  During  this  second  period  of 
the  operation,  the  reaction  between  the  sulphate  and  sulphide  takes 
place,  and  the  lead  is  separated. 

§  984.  The  reduction  of  galena  by  iron  is  used  especially  in  the 
case  of  ores  which  are  accompanied  by  a  very  siliceous  gangue,  and 
which  are  not  very  amenable  to  the  process  by  reaction,  because  a 
great  part  of  the  oxide  of  lead  combines  with  the  silex  and  no 
longer  reacts  on  the  sulphide.  The  process  by  iron  is  employed  to 
a  great  extent  on  the  Hartz  Mountains ;  and  the  following  is  the 
plan  adopted  in  the  smelting  works  of  Clausthal : 

A  melting-bed  is  made  of  sorted  ores  and  sludges,  which  are 
mixed  with  granular  cast-iron,  and  with  various  secondary  products 
of  the  further  treatment  of  the  ores,  the  origin  of  which  we  shall 
successively  explain.     The  charge  is  generally  composed  of 

34  cwt.  of  sorted  ore  and  sludge,  containing  24  cwt.  of  pure 
galena. 
4  to  5    "     of  the  debris  of  the  cupelling  furnaces,  which  is  strongly 
impregnated  with  litharge. 
1    "     of  scrapings  (ahstrich)  of  cupellation. 

39  "  of  slag  arising  from  a  first  fusion  of  the  ore,  or  yielded 
by  the  fusion  of  the  leaden  stones,  or  martts,  the  ob- 
ject of  which  addition  is  to  assist  the  fusion  of  the 
gangues. 

IJ    "     of  granular  cast-iron. 

The  fusion  is  effected  in  a  blast-furnace  (figs.  540,  541,  542,  and 
543),  about  18  or  20  feet  high,  and  measuring  3  feet  at  its  greatest 
width.  At  the  bottom  of  the  hearth  is  a  crucible  which  partly  pro- 
jects from  the  furnace,  the  base  of  which  is  formed  of  two  blocks  of 
sandstone,  making  a  gutter,  on  which  a  mixture  of  clay  and  char- 
coal* is  heaped,  so  as  to  form  a  cavity  which  extends  beyond  the 

*  Two  different  mixtures  of  clay  and  charcoal  are  employed  in  various  opera- 
tions occurring  in  the  German  methods  of  smelting:  one  consisting  of  2  parts  of 


METALLURGY   OF   LEAD. 


193 


furnace.  A  tap-hole  opening  at  the  lower  part  of  the  crucible  per- 
mits the  escape  of  the  liquid  products  which  have  there  accumulated ; 
and  they  are  led  into  a  second  crucible  E,  which  is  wholly  external. 
The  furnace  receives  the  blast  of  two  tuyers  arranged  on  the  oppo- 
site side  of  the  tymp. 


Fig.  540. 


Fig.  541. 


Fig.  542. 

The  ore  ,is  charged  on  the  side  of  the  tuyers,  and  the  fuel  on  that 
of  the  centre-vent.  As  slag  suddenly  cooled  by  the  cold  air  always 
adheres  around  the  tuyers,  the  workman  arranges  them  so  as  to 
form  a  canal  which  projects  for  about  6  inches  into  the  furnace,  and 
thus  makes  a  prolongation  of  the  tuyer,  which  he  calls  the  nose 

clay  and  1  of  charcoal,  called  schweres  gestuebbe;  and  one  containing  1  of  clay  and 
2  of  charcoal,  called  leichtes  gestuebbe.  The  first  I  shall,  in  the  following,  translate 
by  heavy  brasque,  and  the  second  by  light  brusque. 

To  the  "  leaden  stones"  {bleistein)  I  shall  give  the  French  name  of  matt. —  W.  L.  F. 
Vol.  II.— 13 


194 


LEAD. 


of  the  tuyer.  The  object  of  the  nose  is  to  convey  the  air  imme- 
diately upon  the  fuel,  and  prevent  it  from  first  passing  through  the 
ore,  which  would  be  thus  exposed  to  an  oxidizing  action,  and  part 
with  a  great  deal  of  oxide  of  lead  to  the  scoriae.  The  smelter  must 
also  be  careful  to  give  a  proper  shape  to  the  nose  of  the  tuyer,  and 
to  modify  it  according  to  the  blast  of  the  furnace. 

The  temperature  must  not  be  very  high  in  the  upper  part  of  the 
furnace,  as  otherwise  a  large  proportion  of  galena  would  be  vola- 
tilized. In  all  cases,  the  gases  pass,  on  leaving  the  throat  G,  and 
before  reaching  the  chimney  T,  several  condensing-chambers  ar- 
ranged above  the  smelting-furnace ;  where  a  plumbiferous  dust  is 
copiously  deposited,  which*  is  carefully  collected  and  thrown  into  the 
melting-beds. 

During  the  smelting,  the  scorise  flow  oif  continually,  an  assistant 
detaching  those  which  have  become  solid,  and  drawing  them  out 
with  a  hook.  When  the  inner  basin  is  full  of  metallic  products,  the 
canal  communicating  with  the  basins  D  and  E  is  opened ;  when  the 
substance  flows  into  the  external  crucible  E, 
and  there  divides  into  two  layers ;  the  infe- 
rior layer  being  metallic  lead,  and  the  upper 
stratum  consisting  of  subsulphide  of  lead 
PbgS,  mixed  with  other  metallic  sulphides 
which  existed  in  the  ore,  and  with  that  of 
iron  arising  from  the  reaction  of  the  metallic 
iron  on  the  galena.  This  substance,  which 
is  called  the  first  leaden  matt,  soon  solidifies, 
and  is  then  withdrawn  with  a  hook  and  set 
aside.  The  workman  then  removes  the  lead 
with  a  ladle,  and  runs  it  into  moulds  which 
give  it  the  shape  of  lenticular  disks.  The 
poorest  scoriae,  that  is,  those  least  rich  in  lead, 
are  rejected,  while  those  which  float  on  the 
matt  in  the  pot,  and  which  always  contain 
some  grains  of  lead,  are  set  aside  to  be  added  to  a  subsequent  charge ; 
though  poor  scoriae  are  sometimes  used  for  this  purpose  when  rich 
scoriae  are  wanting.  The  charges,  or  smelting-beds,  the  composi- 
tion of  which  we  have  just  indicated,  yield  19  cwt.  of  lead,  and  7 
or  8  cwt.  of  the  first  leaden  matt,  containing  from  2  to  2J  cwt.  of 
lead. 

§  985.  The  first  matts  are  collected  in  the  foundry,  and  when 
there  is  sufficient  quantity  of  them  to  be  worked  up,  they  are  roasted 
in  heaps  on  a  layer  of  fuel ;  when  a  large  portion  of  the  sulphur  is 
disengaged  in  the  state  of  sulphurous  acid.  The  roasting  lasts  for  3 
or  4  weeks ;  after  which  the  material  is  sorted,  and,  while  the  pieces 
sufficiently  roasted  are  considered  as  ready  for  smelting,  the  others 
are  again  roasted.  Four  successive  roastings  are  necessary  for  the 
proper  preparation  of  the  material. 


Fig.  543. 


METALLURGY   OF   LEAD. 


195 


A  charge  of  matt  is  composed  of 
32  cwt.  of  roasted  matt. 

32    "    of  rich  scoriee,  arising  from  the  smelting  of  the  ores. 
4  or  5    "    of  debris  of  cupellation. 
2    "of  scrapings,  {abstrich.) 

2    "    of  scoriae  arising  from  the  reduction  of  litharge. 
1    "of  granular  cast-iron. 

The  roasted  matts  are  smelted  in  an  elbow-furnace,  which  is  a 
small  blast-furnace  (figs.  544,  545,  and  546),  about  4.5  feet  in  height, 
widened  at  its  upper  part  C.  Fig.  546  represents  a  horizontal  sec- 
tion of  it  made  at  the  height  of  the  tuyer,  while  fig.  545  shows  a 
vertical  section  through  the  line  XY  of  the  plane  (fig.  546) ;  and 
lastly,  fig.  544  gives  an  anterior  view.     The  furnace  is  fed  by  a 


Fig.  544. 


Fig.  545. 


single  tuyer  T,  at  the  extremity  of  which  a  nose  of  4  inches  in 
length  is  allowed  to  form.  At  the  bottom  of  the  furnace  is  a 
brasqued  crucible  E,  projecting  partly  from  the  furnace,  and  com- 
municating, by  means  of  a  canal,  with  an  external  crucible  F,  placed 
on  a  lower  level. — Coke  is  the  fuel  used. 


196 


LEAD. 


By  the  roasting  of  the  matt,  a  large  portion  of  the  sulphide  of 
iron  has  passed  into  the  state  of  oxide,  which,  during  the  fusion  in 
the  elbow-furnace,  combines  with  the  silicates  of  the  scoriae  and 
with  the  ashes  of  the  fuel,  forming  very  fusible  scoriae,  which  flow 
constantly  from  the  furnace.  The  sulphide  of  lead  is  reduced  by 
the  metallic  iron,  and  a  fresh  quantity  of  lead  and  a  second  matt 
analogous  to  the  first  are  formed.  When  the  matt  is  solidified  it  is 
removed  and  set  aside  to  be  again  worked,  while  the  metallic  lead  is 
run  into  disks. 

A  smelting-bed  of  first  matt,  composed  as  we  have  indicated, 
yields  12  cwt.  of  lead  and  8  cwt.  of  second  matt. 

The  second  matts  are  subjected  to  a  similar  treatment,  being  sub- 
jected to  3  or  4  successive  roastings,  and  then  passed  through  the 
elbow-furnace,  with  additions  similar  to  those  of  the  first.  A  cer- 
tain quantity  of  metallic  lead  is  thus  obtained,  and  a  third  matt, 
which  is  roasted  in  its  turn  and  melted  in  the  elbow-furnace,  yield- 
ing an  additional  quantity  of  lead  and  a  fourth  matt. 

The  affinity  of  the  copper  existing  in  the  original  ore  for  sul- 
phur being  greater  than  that  of  the  lead,  the  former  passes  indefi- 
nitely into  the  matts ;  so  that  the  metal,  which  is  found  in  a  very 
small  quantity  in  the  original  ore,  is  concentrated  in  the  fourth  matt 
in  sufficient  quantity  to  make  it  a  very  rich  ore  of  copper,  and 
capable  of  being  advantageously  worked.  It  is  called  the  copper 
matt. 

§  986.  When  the  gangue  of  the  galena  is  but  slightly  siliceous, 
the  process  by  reaction  is  preferred.  It  is  adopted  in  England,  in 
Carinthia,  and  the  majority  of  the  lead-foundries  in  France,  par- 
ticularly at  PouUauen  in  Brittany,  and  Pont-Gibaud  in  Auvergne. 

The  ore  is  deposited  in  the  state  of  sludge  on  the  floor  of  a  rever- 
beratory  furnace  (figs.  547  and  548)  of  about  9  or  12  feet  in  length, 


Fig.  547. 

and  nearly  the  same  width,  formed  either  of  pulverized  scoriae  or 
of  a  slightly  siliceous  clay.    In  the  centre  there  is  an  excavation  B, 


METALLURGY   OF   LEAD. 


197 


in  which  the  fused  lead  collects,  and  whence  it  flows  through  a  small 
canal  into  cast-iron  pots  G.     The  charge  is  inserted  through  an 


Fig.  548. 

upper  aperture  T,  furnished  ^ith  a  hopper.  Three  lateral  open- 
ings 0,  0,  0  are  made  in  both  of  the  opposite  faces  of  the  furnace, 
and  serve  as  working-holes.  Pit-coal  is  burned  on  the  grate  F ; 
and  the  flame  and  current  of  hot  air,  after  having  passed  through 
the  furnace,  traverse  long  condensing  chambers,  in  which  they 
deposit  the  substances  carried  over  mechanically  or  by  volati- 
lization. 

The  quantity  of  ore  treated  in  the  furnace  at  a  time  varies  in 
difierent  foundries :  20  or  25  cwt.  are  used  in  England.  The  ore  is 
spread  evenly  over  the  floor,  and  roasted  from  2  to  4  hours  at  a  dull 
red-heat ;  when  sulphurous  acid  is  disengaged,  while  a  large  quan- 
tity of  oxide  and  sulphate  of  lead  is  formed.  The  workman  stirs 
it  frequently,  in  order  to  hasten  the  roasting,  at  the  end  of  which 
operation  the  working-doors  are  closed  and  a  blast  of  air  is  ad- 
mitted. The  unaltered  sulphide  of  lead  then  reacts  on  the  oxide 
and  on  the  sulphate ;  metallic  lead  and  also  the  subsulphide  Pb^S, 
which  forms  a  very  fusible  plumbeous  matt,  are  separated.  The 
fused  substances  collecting  in  the  inner  excavation  are  allowed  to 
run  out  after  some  time,  after  which  the  material  remaining  on  the 
floor  is  again  roasted  by  opening  the  working-doors,  and  stirring 
the  mass  with  iron  rods,  while  the  temperature  of  the  furnace  is  at 
the  same  time  allowed  to  fall.  The  doors  are  then  again  closed, 
and,  another  blast  of  air  being  admitted,  an  additional  quantity  of 
metaUic  lead  is  reduced.  These  alternate  operations  are  several 
times  repeated. 

In  some  works  small  quantities  of  lime  are  from  time  to  time 
thrown  on  the  floor,  in  order  to  lessen  the  fusibility  of  the  slag ; 
while  in  others  powdered  charcoal  is  added  at  a  certain  period,  in 
order  to  decompose  the  oxysulphides  of  lead  which  form,  and  retard 
the  roasting  when  it  progresses  too  rapidly.  Toward  the  close  of 
the  operation,  when  the  greater  part  of  the  lead  has  run  ofi",  there 
remains  on  the  hearth  a  scorifijed  slag,  impregnated  with  metallic 


198 


LEAD. 


Fig.  549. 


lead ;  a  large  portion  of  which  is  separated  by  admitting  a  blast, 
and  allowing  the  furnace  to  cool  slowly.  This  last  stage  of  the  ope- 
ration is  called  the  sweating.  The  whole  operation  requires  7  or  8 
hours  in  England,  and  12  or  16  in  France. 

The  matts  arising  from  the  reverberatory  furnace  are  added,  in 
the  English  works,  to  the  roasting  of  a  fresh  quantity  of  ore ;  while 
in  most  of  the  continental  works  they  are  passed  through  an  elbow- 
furnace. 

The  matts  are  frequently  roasted  in 
a  heap,  and  then  smelted,  after  a  pro- 
per addition  of  scoriae,  in  a  very  low 
i)  elbow-furnace,  called  a  Scotch  hearth, 
in  which  a  reaction  takes  place  between 
the  sulphate,  the  oxide,  and  sulphide  of 
lead,  while  metallic  lead,  a  matt,  and 
scoriae  are  obtained.     Fig.  550  repre- 
sents a  horizontal  section  of  a  Scotch 
furnace ;  and  fig.  549  shows  a  vertical 
cut  through  the  line  AB  in  fig.  550. 
The  furnace  is  only  3  feet 
in  height ;  and  the  blast  is 
furnished  by  a  single  tuyer 
T.     The  metallic  lead  and 
matt  are  collected  in  a  cast- 
iron  pot  M.     The  workman 
removes,  from  time  to  time, 
W;\  the  slag  which  accumulates 
f  at  the  bottom  of  the  fur- 

Fig.  650.  nace,   and   as  it  contains 

a   considerable   quantity   of    lead,    he   throws   it    back   into    the 
furnace. 

§  987.  The  lead  arising  from  these  different  processes  often  con- 
tains enough  silver  to  allow  the  extraction  of  the  latter  to  be  made 
to  advantage,  and  is  then  called  pig-lead,  (werkblei.)  The  silver  is 
separated  by  the  process  of  cupellation,  which  is  founded  on  the 
property  of  lead  to  oxidize  when  heated  in  contact  with  the  air, 
while  the  silver,  which  remains  unaltered,  concentrates  indefinitely 
in  the  lead  which  remains  in  the  metallic  state,  and  is  left  isolated 
at  the  end  of  the  operation,  when  all  the  lead  is  oxidized.  In  order 
to  accelerate  the  oxidation  of  the  lead,  the  litharge  formed  must  be 
removed  as  fast  as  it  is  produced,  for  which  purpose  the  tempera- 
ture is  kept  sufficiently  elevated  to  fuse  the  oxide  of  lead.  As  the 
melted  metal  forms  a  convex  surface,  the  litharge  flows  constantly 
into  the  space  between  the  metal  and  the  side  of  the  vessel,  and 
the  litharge  runs  off  as  it  is  formed,  without  the  loss  of  any  metal- 
lic lead,  through  little  gutters  cut  into  the  side  of  the  vessel,  which 
are  made  deeper  as  the  level  of  the  metal  sinks. 


METALLURGY    OF    LEAD. 


199 


Figs.  551,  552,  and 
553  represent  a  cu- 
pelling-furnace,  used 
at  Clausthal  in  the 
Hartz.  Fig.  552  gives 
a  horizontal  section, 
made  at  the  height  of 

Ythe  line  XYof  fig.  551; 

and  fig.  551  represents 
averticalsection  made 
throughthe  plane  pass- 
ing through  the  line 
Fig.  551.  ED  of  fig.  552.  Lastly, 

fig.  553  furnishes  an  interior  view  of  the  furnace.  The  cupelling- 
furnace  is  a  kind  of  reverberatory,  consisting  of  a  lateral  hearth  F, 
and  a  circular  one  A,  the  floor  of  which,  having  the  shape  of  a 
spherical  cap,  is  composed  of  bricks  r/,  placed  edgewise  on  a  base 
uu  of  scoriae.  It  is  lined  internally  with  a  layer  of  marl  mm, 
which  is  carefully  heaped,  and  renewed  at  each  operation,  and 
which  constitutes  the  cupel  properly  so  called.  The  arch  of  the 
oven  is  formed  of  a  riveted  sheet-iron  cover  C,  lined  with  clay,  and 
suspended,  by  means  of  chains,  to  a  crane  GG'G'',  by  which  it  can 
be  easily  raised  and  replaced. 

The  furnace  has  four  openings :  that  by  which  the  flame  from  the 
hearth  is  introduced ;  two  openings  a,  a,  which  receive  the  nozzles 

of  two  bellows  which 


constantly  drive  air 
over  the  surface  of  the 
bath,  and  assist  the 
oxidation,  while,  at  the 
same  time,  they  remove 
the  litharge  from  the 
surface ;  the  aperture 
P,  serving  for  the  in- 
troduction of  the  disks 
of  lead;  and  lastly,  the 
opening  o,  which  is 
F^g-5^2.  the   tap-hole   for   the 

litharge.  At  the  commencement  of  the  operation,  this  last  open- 
ing is  closed  by  the  cupel,  but  the  latter  is  gradually  notched,  so 
as  to  keep  the  spout  on  a  level  with  the  bath  of  metal.  The  litharge 
flowing  from  the  hole  o  accumulates  at  L  on  the  floor  of  the  foun- 
dry, where  it  solidifies. 

The  cupel  must  be  arranged  before  commencing  the  process,  for 
which  purpose  the  cover  is  removed,  and  the .  old  cupel,  being 
strongly  impregnated  with  litharge,  broken  into  pieces,  which  are 
added  to  the  charges  of  the  ores  and  matts,  as  stated  in  §§  984 


200 


LEAD. 


and  985.  The  brick  floor  ii  is  moistened  with  water,  and  sucbes- 
sive  layers  of  marl  are  beaten  down  upon  it  with  a  stamper.*  The 
cover  then  being  replaced,  all  the  joints  are  accurately  luted  with 
clay. 


Fig.  553. 

One  hundred  and  sixty  cwt.  of  lead  being  introduced  into  the 
furnace,  and  heat  applied,  the  metal  soon  comes  into  fusion ;  and 
the  bellows  then  being  gently  worked,  the  oxidation  commences,  and 
the  surface  of  the  bath  becomes  covered  with  a  black  dust  of  oxide 
of  lead,  mixed  with  foreign  substances.  The  dust,  which  is  infu- 
sible at  the  temperature  applied,  constitutes  the  scrapings,  (ah- 
strichs.)  The  workman  throws  from  time  to  time  a  small  quantity 
of  powdered  charcoal  on  the  bath,  and,  by  means  of  a  billet  of  wood 
placed  crosswise  at  the  end  of  an  iron  rod,  removes  the  abstrichs 
from  the  furnace.  After  some  time,  the  fused  litharge  begins  to 
appear ;  and  after  the  first  portions,  which,  being  impure,  are 
allowed  to  flow  off",  and  are  set  aside,  comes  •  the  pure  litharge, 
called  merchantable  litharge,  which  can  be  sold  in  this  state,  when 
it  is  not  mixed  with  the  former.  The  cupellation  is  continued,  the 
blast  being  gradually  increased  to  accelerate  the  oxidation,  until  all 
the  lead  is  converted  into  litharge,  and  the  silver  remains  isolated 
in  the  shape  of  a  disk. 

At  the  moment  when  the  oxidation  is  arrested,  and  consequently 
when  the  cupellation  is  finished,  a  peculiar  phenomenon  is  mani- 

*  A  layer  of  marl  about  an  inch  in  thickness  being  stamped  down,  its  surface 
is  again  loosened  by  means  of  an  iron  rake,  to  the  depth  of  about  half  an  inch, 
before  the  next  layer  is  heaped  on ;  as  without  this  precaution  the  layers  would 
form  successive  strata  by  the  heat  of  the  furnace,  and  not  a  consolidated 
W.  L.  F. 


METALLURGY   OF   LEAD.  201 

fested,  called  the  hrightning.  During  the  whole  period  of  oxida- 
tion, the  metallic  bath  appears  to  be  more  brilliant  than  the  sides 
of  the  furnace ;  and  its  temperature  is  in  fact  higher,  since  it 
shares  not  only  that  of  the  surrounding  space,  but  also  takes  ad- 
vantage of  all  the  heat  developed  by  the  chemical  combination  of 
the  lead  with  oxygen.  But  when  the  lead  is  completely  oxidized, 
the  second  source  of  heat  disappears,  the  small  disk  of  metallic  sil- 
ver falls  rapidly  to  the  temperature  of  the  oven,  and  its  original 
brilliancy  is  replaced  by  a  dull  colour.  On  the  other  hand,  at  the 
moment  when  the  last  traces  of  lead  are  oxidized,  there  exists  only 
on  the  brilliant  surface  of  the  metallic  bath  a  pellicle  of  melted 
litharge,  which  rapidly  grows  thinner,  presenting  the  rapid  succes- 
sion of  colours  of  a  soap-bubble,  and  at  last  tears  like  a  veil,  dis- 
playing the  surface  of  the  metal.  The  name  of  hrightning^  or  fulgu- 
ration,  is  given  to  this  rapid  succession  of  optical  phenomena. 

As  soon  as  the  hrightning  appears,  the  workman  pours  first  hot 
and  then  cold  water  on  the  hearth,  and  then  removes  the  cake  of 
solid  silver.  The  silver,  called  cupel  silver^  which  is  not  pure, 
but  contains  about  ^  of  lead,  is  afterwards  refined^  as  will  be  de- 
scribed when  treating  of  silver. 

A  cupellation  generally  lasts  30  hours,  including  the  time  neces- 
sary for  the  arrangement  of  the  cupel. 

The  cupellation  of  160  cwt.  of  pig-lead,  arising  from  the  smelting 
of  the  schlichs,  yields  at  Clausthal, 

K>Q  marcs  of  silver,  (a  marc  =  J  pound.) 
118  cwt.  of  litharge. 

21    "     of  debris  of  cupellation,  (German,  heerd,) 
15    "     of  scrapings. 
6    "     of  rich  litharge. 
The  rich  litharge,  which  is  that  obtained  during  the  last  stage  of 
cupellation,  is  not  mixed  with  the  rest  because  it  contains  a  consi- 
derable quantity  of  silver. 

160  cwt.  of  pig-lead,  arising  from  the  smelting  of  the  matts,  yield 
62  marcs  of  silver. 
112  cwt.  of  litharge. 
21    "     of  debris  of  cupellation. 
18    "     ofabstrich. 
9    "     of  rich  litharge. 
Wood  is  the  fuel  used  in  cupellation. 

The  litharge  arising  from  cupellation  is  reduced  to  metallic  lead, 
a  small  quantity  only  being  sold  as  litharge.  The  conversion  of 
litharge  into  metallic  lead,  which  is  called  the  revival  of  the  litharge, 
is  effected  by  smelting  the  litharge  in  contact  with  charcoal  in  an 
elbow-furnace,  furnished  with  an  outer  crucible.  The  scoriae  arising 
from  this  fusion  are  added  to  the  charges  of  ore,  and  the  lead,  after 
being  run  into  bars,  is  sent  to  market. 


202  LEAD. 

§  988.  Silver  can  be  advantageously  extracted  from  pig-lead  by 
direct  cupellation,  only  when  it  contains  at  least  ^  part  of  silver ; 
but  latterly,  much  poorer  lead  has  been  profitably  worked,  by  first 
subjecting  it  to  a  process  called  refining  hy  crystallizaton.'^  This 
operation,  which  separates  the  lead  into  very  poor  lead  and  into 
such  sufficiently  rich  for  cupellation,  is  based  on  the  following  prin- 
ciple : — By  allowing  a  large  quantity  of  melted  argentiferous  lead  to 
cool  slowly,  and  frequently  stirring  the  liquid  mass  with  an  iron 
spatula,  a  crystalline  powder  of  a  poor  lead  is  soon  formed,  which 
may  be  skimmed  off  as  fast  as  it  is  produced ;  and  by  thus  succes- 
sively separating  a  portion  of  the  lead  in  the  state  of  imperfect  crys- 
tals, the  greater  part  of  the  silver  is  left  in  the  metal  remaining 
fluid,  which  thus  becomes  much  richer.  By  properly  repeating  these 
operations,  either  on  the  mass  which  has  been  removed  in  the  solid 
state,  or  on  the  portion  poured  ofi"  in  the  liquid  state,  on  the  one 
hand  a  poorer  and  poorer  lead  is  obtained,  and  on  the  other,  lead 
which  is  more  and  more  rich  in  silver.  Only  that  lead  which  con- 
tains a  proper  quantity  of  silver  is  subjected  to  cupellation,  the  re- 
mainder being  sold. 

§  989.  Metallic  lead  is  technically  used  in  the  shape  of  sheet-lead^ 
for  roofing  houses,  lining  bathing-tubs,  making  gutters  and  spouts 
for  conveying  water,  etc.  etc.  In  the  manufacture  of  sheet-lead, 
the  melted  metal  is  allowed  to  run  over  a  marble  table  into  plates, 
the  size  of  which  is  regulated  by  wooden  rulers,  and  which  are  then 
passed  through  rollers. 

The  rolling-machine  is  composed  of  two  cast-iron  cylinders,  the 
lower  one  of  which  alone  is  tui^ned  by  machinery,  while  the  upper 
one  is  carried  round  simply  by  adhesion,  the  pressure  it  exerts  on 
the  sheet  of  lead  being  regulated  by  a  counter  weight.  Return 
screws,  which  fasten  the  upper  boxes  of  the  tw^o  gudgeons,  limit  the 
elevations  of  the  cylinder,  and  regulate  the  thickness  of  the  sheet ; 
and,  as  the  screws  work  independently  of  each  other,  the  side  on 
which  the  plate  is  least  rolled  may  be  tightened,  so  as  to  obtain  a 
uniform  thickness.  On  each  side  of  the  cylinders  are 
tables  furnished  with  iron  rails,  which  receive  and  guide 
the  sheets.  Five  or  six  sheets  are  rolled,  and  then  passed 
in  an  opposite  direction  between  the  cylinders,  their  mo- 
tion being  reversed ;  which  is  repeated  until  the  sheets 
have  acquired  the  requisite  thickness. 

Leaden  pipe  is  made  on  a  iron  mandrel  between  grooved 
cylinders,  after  having  been  run  into  a  cast-iron  mould, 
abed  (fig.  554),  in  the  axis  of  which  is  an  iron  mandrel 
e/,  of  the  proposed  diameter  of  the  leaden  pipe.  A  thick 
leaden-tube,  of  from  2.0  to  2.3  feet  in  length,  is  thus 
obtained,  and  is  then  fastened  on  an  iron  mandi^el  of 

*  Commonly  known  as  Patiinson's  process. —  W.  L.  F. 


LEAD.  203 

the  same  diameter  as  that  ef  of  the  mould,  after  which  the  whole  is 
drawn  out  between  cylinders  resembling  those  used  for  the  drawing 
of  iron-wire.  The  sides  of  the  pipe  are  thus  reduced  in  thickness 
until  it  attains  the  length  required.* 

MANUFACTURE  OF  LEAD-SHOT. 

§  990.  Lead  alloyed  with  0.3  to  0.8  per  cent,  of  arsenic  is  gene- 
rally used  in  the  manufacture  of  lead-shot ;  the  addition  of  this 
small  quantity  of  arsenic  giving  the  lead  the  property  of  forming 
perfectly  spherical  globules.  A  sheet-iron  sieve  is  used,  shaped  like 
a  spherical  cap,  and  pierced  with  holes  of  the  size  of  the  shot  to  be 
made.  The  dross  which  forms  on  the  fused  lead  is  first  pressed  into 
the  sieve,  so  as  to  completely  line  its  sides,  and  the  melted  metal, 
being  then  poured  in  by  small  quantities  with  a  spoon,  filters  throagh 
the  dross  and  drops  from  the  perforations.  The  drops,  which  should 
be  made  to  fall  from  a  great  height,  in  order  to  become  solid  during 
their  descent,  are  collected  in  a  reservoir  of  water ;  a  greater  eleva- 
tion being  required  according  to  the  size  of  the  shot.  The  shot, 
being  sorted  into  sizes  by  means  of  sieves,  is  polished  by  causing  it 
to  revolve  in  wooden  barrels  with  a  small  quantity  of  plumbago. 

*  The  new  method  of  making  lead-pipe  consists  of  a  powerful  press,  which 
forces  the  lead  in  a  heated  and  soft  state  out  of  an  opening  in  an  iron  reservoir, 
having  a  solid  and  short  mandrel  of  iron  in  the  centre  of  the  opening,  of  the  same 
diameter  as  the  interior  of  the  tube  to  be  made.  The  lead  is  perfectly  hard  when 
issuing  from  the  opening,  and  presents  a  tubing  of  a  fine  glaze  interiorly  and 
exteriorly.  By  this  machine  also  tubes  of  any  length  may  be  manufactured. — 
J.  C.  B. 


204 


BISMUTH. 
Equivalent  =  213  (2662.5 ;  0  =  100). 

§  991.  The  bismuth*  of  commerce  is  never  absolutely  pure ;  but, 
as  the  foreign  metals  with  which  it  is  alloyed  are  generally  more 
oxidizable  than  itself,  it  may  be  purified  by  heating  the  pulverized 
metal  with  y^  of  its  weight  of  nitre  in  an  earthen  crucible.  The 
temperature  should  be  gradually  raised  until  the  nitrate  is  decom- 
posed ;  when  the  foreign  metals  oxidize  and  combine  with  the  po- 
tassa  as  well  as  a  portion  of  the  bismuth,  the  remainder  of  the  latter 
being  left  as  a  button  at  the  bottom  of  the  crucible. 

In  order  to  obtain  bismuth  chemically  pure,  a  mixture  of  sub- 
nitrate  of  bismuth  and  black  flux  must  be  fused  in  a  crucible. 

Bismuth  is  a  grayish- white  metal,  having  at  the  same  time  a  very 
decided  reddish  shade,  which  is  easily  seen  by  placing  a  piece  of 
bismuth  alongside  of  a  specimen  of  a  white  metal,  such  as  zinc,  an- 
timony, etc.  Its  density  is  9.9.  It  presents  a  crystalline  fracture 
with  large  glittering  lamellse,  has  but  slight  malleability,  and  crys- 
tallizes readily  by  fusion.  Beautiful  crystals  may  be  obtained  by 
fusing  in  an  earthen  capsule  some  kilogrammes  of  bismuth  of  com- 
merce, purified  by  fusion  with  nitre,  and  allowing  to  cool  very  slowly. 
To  effect  this,  the  capsule  is  placed  on  a  bath  of  heated  sand,  and 
covered  with  a  sheet-iron  plate,  on  which  burning  charcoal  is  placed. 
In  a  short  time  a  hole  is  made  in  the  solid  crust  which  forms  on  the 
surface,  and  the  liquid  metal  is  allowed  to  run  off".  The  crust  being 
carefully  removed,  a  geode  of  very  beautiful  crystals,  frequently  of 
several  centimetres  in  diameter,  is  displayed.  These  crystals,  which 
are  cubes,  or  rather  pyramidal  figures  resembling  those  of  sea-salt 
(493),  exhibit  very  elegant  iridescent  colours,  produced  by  the  very 
thin  pellicles  of  oxide  which  form  on  the  surface  of  the  metal  as  it  is 
brought,  while  hot,  in  contact  with  the  air.  The  pellicles  present 
the  play  of  thin  scales  or  soap-bubbles. 

Bismuth  fuses  at  507.2° ;  and  a  thermometer  plunged  into 
melted  bismuth  marks  this  temperature  during  the  whole  period  of 
its  solidification.  Like  water,  bismuth  expands  at  the  moment  of 
solidifying,  and  is  therefore  lighter  when  solid  than  when  liquid. 
It  is  volatile  at  a  very  high  temperature,  but  nevertheless  difficult 
to  distil. 

Bismuth  remains  unchanged  in  a  dry  atmosphere,  but  when  ex- 
posed to  damp  air,  becomes  covered  with  a  very  thin  pellicle  of 

*  Bismuth  was  known  to  the  ancients,  who  often  confounded  it  with  lead  and 
tin.     Stahl  and  Dufay  first  proved  it  to  be  a  peculiar  metal. 


OXIDES.  205 

oxide  after  some  time.  Heated  in  the  air,  it  burns  with  a  small 
bluish  flame,  giving  ofi"  yellow  fumes.  Bismuth  decomposes  water 
onlj  at  a  very  high  temperature,  and  effects  no  decomposition  of 
cold  water  in  the  presence  of  powerful  acids.  Concentrated  chloro- 
hydric  acid  acts  on  it  with  difficulty,  while  sulphuric  acid  attacks  it 
only  when  concentrated  and  hot,  with  disengagement  of  sulphurous 
acid.  Nitric  acid  attacks  it  very  energetically,  and  dissolves  it 
completely. 

COMPOUNDS  OF  BISMUTH  WITH  OXYGEN 

§  992.  Bismuth  forms  two  compounds  with  oxygen : 

1.  An  oxide  BiOg ; 

2.  An  oxide  BiO^,  or  bismuthic  acid. 

An  intermediate  oxide  BiO^  is  known,  but  should  be  regarded  as 
a  compound  of  the  two  preceding,  and  its  formula  should  be  writ- 
ten BiOgjBiOg. 

Oxide  of  Bismuth  BiOg. 

§  993.  The  oxide  of  bismuth  BiOg,  which  is  obtained  by  roasting 
the  metal  in  the  air,  or  better  still,  by  decomposing  the  basic  nitrate 
of  bismuth  by  heat,  presents  the  appearance  of  a  bright-yellow  pow- 
der, fusible  at  a  red-heat,  and  producing  on  solidification  a  deeper 
yellow  glass,  which  readily  perforates  earthen  crucibles.  The  oxide 
of  bismuth  is  fixed,  and  its  density  is  8.45. 

The  oxide  can  be  obtained  hydrated  in  the  form  of  a  white  pow- 
der, by  decomposing  the  basic  nitrate  by  an  alkali,  or  by  ammonia. 
On  boiling  the  hydrate  in  a  solution  of  potassa,  it  parts  with  its 
water,  and  is  converted  into  a  yellow  crystalline  powder,  which  is 
the  anhydrous  oxide. 

The  chemical  composition  of  the  oxide  is, 

Bismuth 89.87 

Oxygen 10.13 

100.00 

Some  chemists,  regarding  this  oxide  as  formed  of  1  equiv.  of  the 
metal  and  1  of  oxygen,  write  its  formula  BiO,  and  adopt  for  the 
equivalent  of  the  metal  the  number  71,  which  is  given  by  the 
proportion : 

10.18  :  89.87  ::S:x,  whence  a;=71. 

But  as  this  hypothesis  is  contrary  to  all  analogy,  and  is  sustained 
by  no  example  of  isomorphism,  we  shall  assign  to  oxide  of  bismuth 
the  formula  BiOj,  and  the  equivalent  of  the  metal  will  be  deduced 
from  the  proportion : 

10.13 :  89.87  : :  24  :  x,  whence  a;=213. 


206  BISMUTH. 

Bismuthic  Acid  ^lO^. 

§  994.  Bismuthic  acid  BiO^  is  prepared  by  passing  a  current  of 
chlorine  through  a  concentrated  solution  of  potassa  in  which  very 
finely  divided  oxide  of  bismuth  is  suspended ;  or  by  heating  for  a 
long  time  in  the  air  a  mixture  of  potassa  and  oxide  of  bismuth ;  or 
better  still,  by  calcining  a  mixture  of  oxide  of  bismuth,  caustic  po- 
tassa, and  chlorate  of  potassa.  Bismuthic  acid  prepared  by  either 
of  these  processes  is  always  mixed  with  a  certain  quantity  of  oxide 
of  bismuth,  which  may  be  separated  by  treating  the  substance  with 
weak  nitric  acid,  which  dissolves  the  oxide  of  bismuth,  and,  when 
cold,  does  not  affect  the  bismuthic  acid.  Bismuthic  acid  is  a  bright- 
red  powder,  which  readily  parts  with  a  portion  of  its  oxygen  at  a 
temperature  slightly  above  212°,  and  is  then  converted  into  an  inter- 
mediate oxide  BiO^.  Concentrated  acids  also  decompose  it,  reducing 
it  to  the  state  of  oxide  BiOg,  which  combines  with  the  acid. 

Bismuthic  acid  can  combine  w^th  oxide  of  bismuth,  and  thus  pro- 
duce saline  oxides ;  but  these  compounds  have  not  yet  been  much 
studied.  They  are  obtained  by  heating  in  the  air  a  mixture  of 
oxide  of  bismuth  BiOg  and  caustic  potassa,  or  by  passing  a  current 
of  chlorine  through  a  solution  of  potassa  which  contains  oxide  of 
bismuth  in  suspension.  When  these  reactions  are  terminated,  bis- 
muthic acid  is  obtained,  while,  if  they  are  prematurely  arrested, 
brown  compounds  of  variable  proportions  result,  which  are  combi- 
nations of  bismuthic  acid  BiOg  with  oxide  of  bismuth  BiOg. 

SALTS  FORMED  BY  OXIDE  OF  BISMUTH, 

§  995.  Oxide  of  bismuth  is  a  feeble  base,  forming  with  acids  seve- 
ral crystallizable  salts,  which  water  decomposes  into  basic  salts  which 
are  precipitated,  and  into  very  acid  salts  which  remain  in  the  solu- 
tion. 

Nitrate  of  Bismuth. 

§  996.  The  nitrate,  which  is  the  most  important  of  the  salts  of 
bismuth,  is  obtained  by  dissolving  bismuth  in  nitric  acid.  The 
liquid,  when  evaporated,  yields  large,  colourless,  and  deliquescent 
crystals,  of  the  formula  Bi03,3N05+3H0.  It  dissolves  without 
decomposition  in  a  small  quantity  of  water,  particularly  when  acidu- 
lated with  a  few  drops  of  nitric  acid,  but  is  decomposed  if  the  quan- 
tity of  w^ater  is  greater,  a  white  precipitate  of  a  basic  nitrate  being 
formed,  which  is  known  by  the  name  of  pearl  powder.  This  sub- 
stance is  used  for  whitening  the  skin,  but  is  liable  to  the  objection 
of  being  blackened  by  sulf  hydric  acid.  Its  composition  varies  ac- 
cording to  the  quantity  of  water  used  in  the  precipitation,  the  tem- 
perature, and  duration  of  contact  of  the  basic  salt  with  the  water. 
Boiling  water  ultimately  removes  all  its  acid,  and  leaves  only 
hydrated  oxide. 


BINARY   COMPOUNDS.  207 

Sulphate  of  Bismuth, 

§  997.  By  heating  powdered  bismuth  with  concentrated  sulphuric 
acid,  sulphurous  acid  is  disengaged,  and  the  metal  is  converted  into 
a  white,  insoluble  powder  of  sulphate  of  bismuth  BiOgjSSOg.  This 
salt  is  decomposed  by  treatment  w^ith  water  into  a  very  acid  salt 
which  remains  in  solution,  and  an  insoluble  bi-basic  sulphate  BiOg, 
SO3+HO. 

Carbonate  of  Bismuth, 

§  998.  By  adding  carbonate  of  soda  to  an  acid  solution  of  nitrate 
of  bismuth,  a  white  precipitate  of  a  basic  carbonate  BiOgjCOg  is 
obtained,  which  is  easily  destroyed  by  heat,  leaving  a  residue  of 
oxide. 

COMPOUND  OF  BISMUTH  WITH  SULPHUR. 

§  999.  Bismuth  combines  directly  with  sulphur  when  assisted  by 
heat.  To  effect  the  combination,  it  is  sufficient  to  heat  together 
the  two  substances  in  the  state  of  fine  powder,  a  certain  quantity 
of  metallic  bismuth  always  remaining  mixed  or  dissolved  in  the 
sulphide.  In  order  to  obtain  the  latter  pure,  the  product  of  the 
first  fusion  must  be  reduced  to  a  fine  powder,  and  again  fused  in  a 
crucible  with  an  additional  quantity  of  sulphur.  The  sulphide  then 
appears  under  the  form  of  a  gray  ball,  possessing  a  metallic  lustre, 
and  evincing  in  its  fracture  a  fibrous  texture.  The  formula  of  the 
sulphide  is  BiSg.  It  has  been  found  crystallized  in  nature,  and 
appears  to  be  isomorphous  with  the  sulphide  of  antimony  to  which 
the  same  formula  is  assigned. 

Sulphide  of  bismuth  may  be  obtained  by  the  humid  way  in  the 
form  of  a  black  powder,  by  passing  a  current  of  sulf  hydric  acid 
through  a  solution  of  a  salt  of  bismuth. 

COMPOUNDS  OF  BISMUTH  WITH  CHLORINE. 

§  1000.  Bismuth  combines  directly  with  chlorine  with  disengage- 
ment of  heat,  and  even  of  light,  when  the  metal  is  very  finely 
divided.  If  a  current  of  chlorine  be  led  over  bismuth  heated  in  a 
tubulated  retort,  the  chloride  distils  over  and  condenses  in  the  form 
of  a  readily  fusible  white  substance.  The  same  substance  is  ob- 
tained by  distilling  in  a  small  retort  a  mixture  of  1  part  of  metallic 
bismuth  and  2  parts  of  bichloride  of  mercury.  Chloride  of  bismuth 
rapidly  attracts  the  moisture  of  the  air,  and  is  converted  into  a 
crystallizable  hydrated  chloride;  which  may  also  be  obtained  by 
dissolving  metallic  bismuth  in  aqua  regia,  and  evaporating  the 
liquid.  Chloride  of  bismuth  BiClg  dissolves  without  change  in 
water  acidulated  with  chlorohydric  acid,  but  is  decomposed  by  fresh 
water ;  when  a  portion  of  the  chloride  dissolves  by  means  of  the 
chlorohydric  acid  which  is  set  free,  while  a  white  precipitate  of 
oxychloride  of  bismuth  BiCl3+2(Bi03  4-3HO)  remains. 


208  BISMUTH. 

On  pouring  an  acid  solution  of  nitrate  of  bismuth  into  a  solution 
of  sea-salt,  a  white  precipitate  of  very  fine  crystalline  spangles  is 
formed,  which  is  an  oxy chloride  of  bismuth  of  the  formula  BiClg-f 
2(Bi03+3HO).  This  substance  is  used  for  whitening  the  skin,  and 
is  called  pearl-white, 

ALLOYS  OF  BISMUTH. 

§  1000  his.  By  alloying  bismuth  with  lead  and  tin,  very  fusible 
alloys  are  obtained,  which  are  used  for  taking  impressions,  making 
stereotype-plates,  etc.  The  alloy  composed  of  1  part  of  lead,  1 
part  of  tin,  and  2  of  bismuth  fuses  at  200°,  while  that  containing  5 
of  lead,  3  of  tin,  and  8  of  bismuth  fuses  at  about  208.4°.  By 
diminishing  the  proportion  of  bismuth,  the  fusing  point  of  the  alloys 
obtained  varies  between  212°  and  392°,  and  these  substances  ha^  e 
been  used  as  washers  for  the  safety-valves  of  the  boilers  of  high- 
pressure  steam-engines.  Their  composition  was  such  as  to  fuse  at 
a  point  slightly  above  the  temperature  corresponding  to  the  maxi- 
mum of  tension  which  the  steam  should  not  exceed.  When  the 
safety-valves  were  out  of  order  or  overloaded,  and  the  elastic  force 
of  the  steam  surpassed  the  maximum,  the  washers,  by  beginning  to 
fuse,  allowed  the  steam  to  escape.  This  means  of  safety  was  soon 
found  to  be  useless,  as  the  alloy,  being  kept  for  a  long  time  at  a 
temperature  approaching  its  melting  point,  underwent  a  kind  of 
eliquation — a  more  fusible  alloy  separated  from  it,  and  that  which 
remained  was  much  less  fusible  than  the  original  alloy.  For  this 
reason  the  use  of  fusible  washers  has  been  abandoned. 

DISTINCTIVE  CHARACTERS  OF  THE  SOLUBLE  COMPOUNDS  OF  BISMUTH. 

§  1001.  We  have  seen  that  all  the  compounds  of  bismuth,  being 
soluble  in  a  very  small  quantity  of  water,  are  decomposed  when 
treated  with  a  larger  quantity,  and  yield  white  precipitates  of  basic 
salts :  therefore,  one  of  the  distinctive  characters  of  solutions  of 
bismuth  is  to  become  cloudy  when  diluted  with  a  large  quantity 
of  water. 

The  caustic  alkalies  and  alkaline  carbonates  throw  down  white 
precipitates,  insoluble  in  an  excess  of  the  reagent. 

Sulf hydric  acid  and  the  sulf hydrates  afford  black  precipitates, 
which  do  not  redissolve  in  an  excess  of  sulf  hydrate. 

Iron,  zinc,  and  copper  precipitate  bismuth  in  the  form  of  a  black 
powder,  which  fuses  readily  on  charcoal  in  the  reducing  flame  of 
the  blowpipe  into  a  metallic  globule,  which  becomes  very  brittle 
after  cooling,  and  yields  a  powder  of  a  characteristic  rose-colour. 

DETERMINATION  OF  BISMUTH;  AND  ITS  SEPARATION  FROM  THE 
METALS  PREVIOUSLY  STUDIED. 

§  1002.  Substances  containing  bismuth  which  are  to  be  subjected 
to  chemical  analysis  are  always  dissolved  in  nitric  acid,  and  the 


METALLURGY   OF   BISMUTH.  209 

boiling  liquid  is  precipitated  by  an  excess  of  carbonate  of  ammonia. 
Tlie  precipitate  is  washed  on  the  filter,  and  then  calcined  in  a  small 
porcelain  capsule,  in  which  it  remains  in  the  state  of  the  oxide 
BiOg.  The  calcination  should  not  be  made  in  a  platinum  crucible, 
because  this  metal  is  easily  attacked  by  oxide  of  bismuth,  especially 
when  a  small  quantity  of  metallic  bismuth  can  be  produced  by  a 
reducing  action.  The  filter  should  be  calcined  separately,  its  ashes 
sprinkled  with  a  few  drops  of  nitric  acid,  and  then  recalcined  to 
decompose  the  nitrate  of  bismuth  which  is  formed. 

It  is  often  necessary  to  precipitate  bismuth  in  the  state  of  sul- 
phide by  means  of  sulf  hydric  acid,  as,  for  example,  when  the  metal 
exists  in  a  liquid  with  other  metals  which  are  precipitated  by  the 
alkalies  or  alkaline  carbonates,  but  not  by  sulf  hydric  acid.  It  is 
also  precipitated  as  sulphide  when  the  liquid  contains  chlorohydric 
acid,  because  the  precipitate  formed  by  the  alkaline  carbonates 
would  in  this  case  contain  chloride  of  bismuth,  which  is  difiicult  to 
decompose  by  an  excess  of  alkaline  carbonate.  The  bismuth  being 
in  the  state  of  sulphide  is  collected  on  a  filter,  dissolved  in  nitric 
acid,  and  then  reprecipitated  by  an  excess  of  carbonate  of  ammonia. 

Lastly,  bismuth  is  sometimes  precipitated  in  the  metallic  state  by 
a  blade  of  iron  or  zinc,  and  the  metallic  powder,  being  collected  on 
a  filter,  is  calcined  in  a  porcelain  capsule ;  after  which  a  few  drops 
of  nitric  acid  are  added,  it  is  recalcined,  and  the  bismuth  deter- 
mined in  the  state  of  oxide. 

Bismuth  is  easily  separated  by  sulf  hydric  acid  passed  through  an 
acid  liquid,  from  all  the  metals  we  have  hitherto,  studied,  with  the 
exception  of  cadmium,  tin,  and  lead.  It  is  separated  from  tin  by 
treating  the  sulphides,  immediately  after  their  being  precipitated, 
with  a  solution  of  sulf  hydrate  of  ammonia,  which  dissolves  only 
the  sulphide  of  tin.  In  order  to  separate  bismuth  from  lead,  both 
metals  are  dissolved  in  nitric  acid,  and  evaporated  with  an  excess 
of  sulphuric  acid  until  the  vapours  of  the  acid  begin  to  pass  over, 
after  which  they  are  treated  with  water,  which  dissolves  only  the 
sulphate  of  bismuth  by  means  of  the  excess  of  acid.  This  process 
does  not  efiect  a  very  accurate  separation.  No  method  of  sepa- 
rating bismuth  from  cadmium  is  yet  known.* 

METALLURGY  OF  BISMUTH. 

§  1003.  Bismuth  has  hitherto  been  found  only  in  a  small  number 
of  minerals,  the  only  one  of  which  sufficiently  abundant  and  rich  to 
be  used  as  an  ore  is  native  bismuth,  which  constitutes  metallic  veins 

*  A  perfect  separation  of  bismuth  from  cadmium  is  effected  by  adding  a  solu- 
tion of  cyanide  of  potassium  to  the  solution  of  the  two  oxides,  by  which  the  bis- 
muth is  precipitated,  while  the  cadmium  remains  in  solution  as  a  double  cyanide 
of  cadmium  and  potassium. 

Another  method  might  be  based  on  the  solubility  of  oxide  of  cadmium  in  am- 
monia, in  which  oxide  of  bismuth  is  insoluble. —  W.  L.  F. 
Vol.  IL— 14 


210 


BISMUTH. 


in  the  quartzose  rocks  of  the  old  formations.  All  the  bismuth  used 
in  the  arts  comes  from  Saxony,  and  is  extracted  by  a  very  simple 
process :  the  ore  being  heated  in  close  vessels,  the  bismuth  fuses, 
separates  from  the  gangue,  and  falls  to  the  bottom  of  the  vessel. 

The  fusion  is  effected  in 
sheet-iron  or  cast-iron  tubes 
hd  (fig.  555),  arranged  in  a 
furnace,  and  inclining  down- 
ward. The  ore  being  intro- 
duced through  the  opening 
dy  the  latter  is  closed,  while 
the  other  end  5  is  closed  by 
a  plate  having  a  hole  o, 
through  which  the  metal 
escapes.  It  is  received  in 
^^S-  555.  earthen  cups  «,  a,  heated  by 

charcoal  placed  in  the  space  K  beneath,  in  order  to  keep  the  metal 
fluid.     It  is  then  scooped  out  and  run  into  moulds. 

The  metal  thus  obtained,  which  always  contains,  besides  metallic 
sulphides  and  arseniurets,  some  foreign  metals,  is  purified  by  fusion 
with  y^  of  its  weight  of  saltpetre. 


^11 

ANTIMONY. 
Equivalent  =  129  (1612.5 ;  0  =  100). 

§  1004.  The  antimony*  of  commerce,  which  is  rarely  pure,  con- 
taining most  frequently  a  small  admixture  of  iron,  lead,  arsenic,  and 
sulphur,  is  purified  in  the  laboratory  by  mixing  it  intimately  with 
y\j  of  its  weight  of  nitre,  and  fusing  the  mixture  in  an  earthen  cru- 
cible ;  when  the  antimony  appears  in  the  form  of  a  metallic  button, 
composed  of  very  small  crystalline  lamellae.  The  fineness  of  the 
grain  of  antimony  is  an  index  of  its  purity. 

Antimony  is  a  metal  of  a  slightly  bluish,  very  brilliant,  silvery 
white  colour.  It  fuses  at  842°,  and  at  a  white-heat  gives  olF  appre- 
ciable vapours,  at  which  temperature  it  may  be  distilled  in  a  current 
of  hydrogen  gas ;  but  the  tension  of  its  vapour  being  still  very  feeble, 
the  distillation  is  slow.  Antimony  crystallizes  readily  from  fusion, 
and  its  fracture  presents  very  brilliant  surfaces  of  cleavage,  the 
disposition  of  which  leads  to  the  rhombohedron,  and  which  are  fre- 
quently of  great  extent.  The  tendency  of  the  metal  to  crystallize 
may  be  well  seen  in  the  cakes  of  commercial  antimony,  their  upper 
surfaces  often  exhibiting  a  beautiful  star,  the  rays  of  which  resemble 
the  fern-leaf.  It  is  a  very  brittle  metal  and  easily  reduced  to  pow- 
der in  a  mortar. 

Antimony  does  not  sensibly  alter  in  the  air  at  the  ordinary  tem- 
perature, while  it  readily  oxidizes  when  kept  in  a  fused  state  in 
contact  with  the  air.  Heated  to  a  high  temperature,  it  burns  with 
a  white  flame  and  gives  off  copious  fumes.  If  the  fused  metal, 
heated  to  redness,  be  thrown  from  a  certain  height  on  the  floor,  a 
very  brilliant  phenomenon  of  combustion  is  observed,  accompanied 
by  thick  white  fumes. 

Finely  powdered  antimony  dissolves  in  boiling  concentrated  chlo- 
rohydric  acid,  with  disengagement  of  hydrogen  gas,  but  does  not 
decompose  water  in  the  presence  of  sulphuric  acid,  which  will  not 
oxidize  it  except  when  concentrated  and  hot,  when  sulphurous  acid 
is  disengaged.  Nitric  acid,  even  when  dilute,  readily  attacks  it, 
converting  the  metal  into  an  insoluble  white  precipitate.  Aqua 
regia  transforms  antimony  into  a  chloride  which  dissolves  without 
change  in  an  excess  of  chlorohydric  acid. 

COMPOUNDS  OF  ANTIMONY  WITH  OXYGEN. 
§  1005.  Two  well-defined  compounds  of  antimony  with  oxygen 
are  known,  the  quantities  of  oxygen  contained  in  which  are  as  3  to  5. 

*  Although  the  ores  of  antimony  were  known  to  the  ancients,  Basil  Valentine 
was  the  first  who  made  mention  of  metallic  antimony. 


212  ANTIMONY. 

The  most  oxygenated  compound,  of  whicli  the  formula  is  SbO^,  and 
which  plays  the  part  of  an  acid,  is  antimonic  acid  ;  while  that  con- 
taining the  least  amount  of  oxygen,  and  is  expressed  by  the  formula 
SbOj,  acts  as  a  feeble  base.  We  shall  call  it  sesquioxide  of  anti- 
moni/,  or  simply  oxide  of  antimony/, 

A  third  oxide  SbO^,  which  by  some  chemists  is  regarded  as  an 
oxide  per  se,  and  called  antimonious  acid,  should  rather  be  consi- 
dered as  an  antimoniate  of  oxide  of  antimony,  SbOg-SbO^. 

Oxide  of  Antimony  SbOg. 

§  1006.  Oxide  of  antimony  is  formed  when  antimony  is  heated  in 
an  imperfectly  closed  crucible,  when  small  elongated  and  very  bril- 
liant prismatic  crystals,  which  have  been  called  argentine  flowers 
of  antimony,  are  deposited  on  the  sides  of  the  crucible  at  a  little 
distance  above  the  fused  metal.  But  as  it  is  difficult  to  prevent  the 
oxide  prepared  in  this  way  from  containing  some  antimoniate  of 
oxide  of  antimony,  a  better  method  of  obtaining  the  oxide  in  a  state 
of  purity  consists  in  pouring,  by  small  quantities  at  a  time,  a  solu- 
tion of  chloride  of  antimony  SbClg  into  a  boiling  solution  of  carbo- 
nate of  soda ;  when  the  oxide  of  antimony  separates  in  the  form  of 
small  crystals. 

Oxide  of  antimony,  the  colour  of  which  is  a  grayish  white,  fuses 
at  a  red-heat,  and  sublimes  at  a  higher  temperature.  It  readily 
absorbs  oxygen  when  heated  in  the  air,  and  is  converted  into  anti- 
moniate of  oxide  of  antimony,  while  it  is  indecomposable  by  heat 
alone,  but  is  easily  reduced  by  hydrogen  or  by  charcoal. 

The  oxide  of  antimony,  precipitated  when  cold  from  the  solution 
of  the  chloride  by  carbonate  of  soda,  which  is  hydrated,  and  has 
the  formula  SbOg 4- HO,  dissolves  readily  in  alkaline  liquids,  form- 
ing true  salts  in  which  it  acts  the  part  of  an  acid,      v 

Oxide  of  antimony  contains  : 

Antimony 84.31 

Oxygen 15.69 

100.00 

Its  formula  is  written  SbOg ;  and  consequently  the  equivalent  of 
antimony  is  obtained  from  the  proportion : 

15.68  :  84.32  : :  24  :  x,  whence  2^=129. 
Antimonic  Acid  SbOg. 

§  1007.  Antimonic  acid  is  obtained  by  attacking  antimony  by 
nitric  acid,  or  better  still,  by  aqua  regia  containing  an  excess  of 
nitric  acid,  when  an  insoluble  white  powder  of  hydrated  antimonic 
acid  is  formed,  which  loses  its  water  at  a  slightly  elevated  tem- 
perature, and  is  converted  into  anhydrous  antimonic  acid.  The 
hydrated  acid  is  also  obtained  by  decomposing  the  perchloride  of 


ANTIMONIC   ACID.  2l3 

antimony  SbCl^  by  water ;  but  the  hydrates  obtained  by  the;;e  twc 
processes  are  far  from  being  identical.  Their  capabilities  of  satu- 
ration with  bases  being  different,  they  in  this  respect  exhibit  a  phe- 
nomenon analogous  to  that  observed  in  stannic  acid,  and  which  was 
treated  of  (§  479  et  seq.)  when  speaking  of  phosphoric  acid,  which 
presents  the  same  feature.  The  product  obtained  by  attacking  an- 
timony by  nitric  acid,  and  to  which  the  name  of  antimonia  acid  has 
been  preserved,  only  saturates  1  equivalent  of  a  base,  producing 
neutral  salts  of  the  general  formula  ROjSbO^;  while  the  precipi- 
tate obtained  by  decomposing  perchloride  of  antimony  by  water 
saturates  2  equiv.  of  a  base,  and  forms  neutral  salts  of  the  formula 
2  ROjSbO^.     It  has  been  called  metantimonic  acid. 

Anhydrous  antimonic  acid  is  a  powder  of  a  yellowish-white  co- 
lour, which  is  decomposed  by  a  red-heat,  producing  antimoniate  of 
oxide  of  antimony  Sb03,Sb05.   . 

The  neutral  antimoniate  of  potassa  is  prepared  by  heating  in  an 
earthen  crucible  1  part  of  metallic  antimony  and  4  parts  of  nitrate 
of  potassa,  and  treating  the  powdered  mass  with  a  small  quantity 
of  tepid  water,  which  dissolves  the  potassa  in  excess  and  tl^e  unde- 
composed  nitrite  of  potassa.  The  residue  is  then  boiled  with  water 
for  several  hours,  by  which  the  anhydrous  antimoniate  of  potassa., 
which  is  insoluble,  is  converted  into  a  soluble  hydrated  antimoniate. 
An  insoluble  residue  remains,  which  is  the  bi-antimoniate  of  potassa 
K0,2Sb05 ;  and  the  liquid  leaves  after  evaporation  a  gummy  mass 
which  presents  no  appearance  of  crystallization,  and  the  formula  of 
which,  when  desiccated  in  dry  air,  is  KO,Sb05+5HO.  This  neu- 
tral antimoniate  KO,Sb05+5HO  is  converted  into  a  crystalline 
powder  of  bi-antimoniate  K0,2Sb05  by  passing  a  current  of  car- 
bonic acid  through  its  solution. 

By  heating  in  a  silver  crucible  antimonic  acid  or  neutral  antimo- 
niate of  potassa  with  a  large  excess  of  potassa,  a  fused  mass  which 
completely  dissolves  in  a  small  quantity  of  cold  water  is  obtained ; 
and  the  solution,  when  evaporated  in  vacuo,  deposits  small  crystala 
of  metantimoniate  of  potassa  2K0,Sb05.  ^^i^  salt  dissolves, 
without  apparent  decomposition,  in  a  small  quantity  of  cold  water 
to  which  a  certain  quantity  of  caustic  potassa  has  been  added,  while 
it  is  decomposed  by  pure  water  into  potassa  and  acid  metaantimo- 
niate  of  potassa  KOjSbO^+THO,  which  is  but  slightly  soluble  in 
cold  water.  Water  dissolves  it  more  freely  at  a  temperature  of 
105°  or  120°,  while  a  prolonged  contact  with  cold  water  transforms 
it  into  neutral  antimoniate  of  potassa;  which  transformation  is 
rapidly  effected  by  boiling  the  liquid.  The  solution  of  the  acid 
metantimoniate  of  potassa  possesses  the  property  of  precipitating 
the  salts  of  soda,  and  yielding  an  acid  metantimoniate  of  soda, 
which  is  almost  insoluble  in  water.  It  is  the  only  reagent  as  yet 
known  which  precipitates  soda  from  its  solutions ;  but  it  is  necessary 
to  use  freshly  prepared  acid  metantimoniate  of  potassa,  as  the  salt 


214  ANTIMONY. 

is  after  some  time  converted  into  the  common  antimoniate,  which 
does  not  precipitate  the  salts  of  soda. 

Antimoniate  of  Oxide  of  Antimony  Sb03,Sb03. 

§  1008.  By  heating  antimonic  acid  until  oxygen  is  no  longer 
given  off,  a  white  powder,  of  which  the  composition  is  SbO^,  but 
which  should  be  written  SbO^jSbOg,  remains.  This  product,  which 
is  sometimes  called  antimonious  acid,  is  also  formed  when  antimony 
is  roasted  in  the  open  air.  A  solution  of  tartaric  acid  or  bi-tartrate 
of  potassa  abstracts  its  oxide  of  antimony,  leaving  the  antimonic 
acid,  while  a  solution  of  caustic  potassa  dissolves,  on  the  contrary, 
the  antimonic  acid,  and  leaves  the  oxide  of  antimony ;  which  reac- 
tions render  the  existence  of  both  oxide  of  antimony  and  antimonic 
acid  in  this  body  very  probable.  Antimoniate  of  oxide  of  antimony 
is  infusible. 

SALTS  FORMED  BY  OXIDE  OF  ANTIMONY. 

§  1009.  Oxide  of  antimony  SbOs  is  a  feeble  base,  which  neverthe- 
less forms  several  salts  with  acids. 

A  nitrate  of  antimony  is  obtained  by  treating  cold  antimony  with 
fuming  nitric  acid,  in  the  shape  of  crystalline  spangles  of  the  for- 
mula 2Sb03,N03.  The  salt  is  decomposed  by  water,  and  trans- 
formed into  hydrated  oxide  of  antimony. 

Several  compounds  of  oxide  of  aiitimony  with  sulphuric  acid  are 
known,  and  present  the  following  composition : 

Sb03,4S03+HO 
Sb03,2S03 

Sb03,     SO3 

2Sb03,  SO3. 

We  do  not  find  among  these  salts  the  compound  Sb03,3S03, 
which  should  be  regarded  as  the  neutral  sulphate  of  antimony,^  from 
the  formula  SbOa  which  we  have  adopted  to  represent  oxide  of 
antimony. 

The  oxychloride  of  antimony  SbCl3,2Sb03-|-HO,  the  prepara- 
tion of  which  will  be  explained  hereafter,  is  converted  into  the 
sulphate  Sb03,4S034-HO  when  it  is  treated  with  concentrated 
sulphuric  acid,  while  the  sulphate  Sb03,2S03  is  obtained  by  treat- 
ing oxide  of  antimony  with  fuming  oil  of  vitriol,  (Nordhausen  sul- 
phui'ic  acid.)  Lastly,  the  sulphate  Sb03,4S03+HO  is  decomposed 
by  treatment  with  hot  water,  leaving  a  residue  of  the  formula 
2Sb03,S03. 

COMPOUND  OF  ANTIMONY  WITH  HYDROGEN. 

§  1010.  Antimony  forms  a  gaseous  compound  with  hydrogen, 
which  resembles  in  its  composition  that  of  arseniuretted  hydrogen 
and  phosphuretted  hydrogen  gas,  but  which  hitherto  has  not  been 


SULPHIDES.  215 

obtained  in  a  state  of  purity.  Bj  introducing  a  solution  of  proto- 
chloride  of  antimony  into  a  bottle  in  which  hydrogen  is  being  dis- 
engaged by  the  reaction  of  dilute  sulphuric  acid  on  zinc,  the  hydro- 
gen always  contains  a  certain  quantity  of  antimoniuretted  hydrogen 
gas,  which  is  easily  recognised  on  igniting  the  gas,  when  it  burns 
with  a  yellowish  flame  which  evolves  white  fumes,  and  which,  on 
being  allowed  to  play  on  a  cold  porcelain  capsule,  yields  glittering 
spots  of  metallic  antimony.  If  the  gas  be  passed  through  a  heated 
tube,  a  brilliant  ring  of  metallic  antimony  forms  on  the  sides  of  the 
tube,  in  front  of  the  heated  portion. 

COMPOUNDS  OF  ANTIMONY  WITH  SULPHUR. 

§  1011.  Two  combinations  of  antimony  with  sulphur  are  known ; 
and  while  the  formula  of  the  first,  which  we  shall  call  sulphide  of  an- 
timony^ is  SbSg  corresponding  to  the  oxide  SbOg,  the  second  cor- 
responds to  antimonic  acid,  and  its  formula  being  SbS^,  we  shall 
call  it  suJfantimonic  acid. 

Sulphide  of  antimony  is  found  in  nature,  and  is  the  only  ore  of 
antimony.  It  always  occurs  crystallized,  but  the  prismatic  crys- 
tals are  so  dovetailed  into  each  other,  that  it  is  often  difiicult  to 
ascertain  their  form.  It  is  sometimes  found  in  isolated  crystals, 
which  are  prisms  belonging  to  the  fourth  system.  Sulphide  of  anti- 
mony, which  is  of  a  deep  gray  colour,  and  a  very  decided  metallic 
lustre,  fuses  below  a  red-heat,  and  readily  crystallizes  on  cooling . 
from  a  white-heat.  It  exhales  copious  fumes,  and  may  be  distilled 
in  a  current  of  nitrogen  gas.  Its  density  is  4.62.  The  sulphide  is 
formed  by  the  direct  combination  of  antimony  with  sulphur,  by 
several  successive  fusions,  when  a  purer  sulphide  than  that  occur- 
ring in  nature  is  obtained,  which  always  contains  a  small  quantity 
of  other  metallic  sulphides. 

Sulphide  of  antimony  is  easily  roasted  in  the  air,  during  which 
operation  no  sulphate  is  formed,  but  only  oxide  of  antimony,  which 
combines  with  the  undecomposed  sulphide,  especially  under  the  in- 
fluence of  an  elevated  temperature.  Fusible  oxysulphides  are  thus 
formed,  which,  after  cooling,  yield  brown  vitreous  substances,  called 
in  commerce  glass  of  antimony^  liver  of  antimony,  or  crocus,  accord- 
ing to  the  proportions  of  the  substances  entering  into  their  compo- 
sition. Glass  of  antimony,  which  contains  about  8  parts  of  oxide 
and  1  of  sulphide,  is  transparent  and  of  a  reddish-yellow  colour, 
while  crocus,  which  contains  8  parts  of  oxide  and  2  of  sulphide,  is 
opake  and  reddish  yellow.  Liver  of  antimony  is  opake  and  of  a 
deep  brown  colour,  and  contains  nearly  4  parts  of  sulphide  for  8 
of  oxide. 

Hydrogen  decomposes  sulphide  of  antimony  at  a  red-heat  with 
disengagement  of  sulf  hydric  acid,  while  the  antimony  remains  in 
the  metallic  state ;  but  it  is  difiicult  to  prevent  a  small  quantity  of 
antimony  from  being  disengaged  in  the  state  of  antimoniuretted 


216  ANTIMONY. 

hydrogen  gas.  Charcoal  also  decomposes  sulphide  of  antimony 
at  a  high  temperature,  while  sulphide  of  carbon  is  disengaged, 
and  the  antimony  remains  in  the  metallic  state.  It  is,  however, 
difficult  by  these  methods  to  obtain  antimony  entirely  free  from 
sulphur. 

Iron,  zinc,  and  copper  decompose  sulphide  of  antimony  at  a  red- 
heat  ;  but  the  metallic  antimony  thus  obtained  always  contains  a 
certain  quantity  of  these  metals.  Concentrated  chlorohydric  acid 
readily  dissolves  sulphide  of  antimony  with  disengagement  of  sulf- 
hydric  acid,  which  reaction  is  sometimes  applied  in  the  laboratory 
to  the  preparation  of  sulf  hydric  acid  (§  149).  Boiling  concentrated 
sulphuric  acid  attacks  sulphide  of  antimony  and  evolves  sulphurous 
acid.  Nitric  acid  converts  it  into  an  insoluble  oxide  of  antimony 
and  sulphuric  acid. 

The  alkalies  and  alkaline  carbonates  decompose  sulphide  of  anti- 
mony both  in  the  dry  and  humid  way,  sulphide  of  antimony  and  a 
compound  of  oxide  of  antimony  with  potassa  being  formed.  When 
the  sulphide  of  antimony  is  in  excess,  there  is  formed  in  addition  a 
compound  of  sulphide  of  antimony  with  monosulphide  of  potassium, 
in  which  combination  the  sulphide  of  antimony  acts  the  part  of  an 
acid.  If  the  decomposition  be  effected  in  a  brasqued  crucible,  a 
portion  of  the  antimony  separates  in  the  metallic  state. 

The  sulphide  of  antimony  SbSg  may  be  prepared  in  the  hum'd 
way,  by  passing  a  current  of  sulf  hydric  acid  gas  through  a  solution 
of  chloride  of  antimony  SbClg  in  water  charged  with  chlorohydric 
acid,  when  an  orange-coloured  precipitate  of  hydrated  sulphide  is 
formed,  which  dissolves  readily  in  the  alkaline  sulphurets,  when  it 
plays  the  part  of  an  acid.  Acids  precipitate  anew  the  hydrated 
sulphide  from  solutions  of  the  sulphosalts.  Heat  easily  drives  off 
the  water  from  the  hydrated  sulphide,  which  then  is  converted  into 
a  gray  anhydrous  sulphide. 

In  medicine  the  hydrated  sulphide  is  used  either  mixed  or  com- 
bined with  oxide  of  antimony,  and  often  with  sulfantimonic  acid 
SbSg,  and  is  known  by  the  name  of  kermes  mineral^  golden  sul- 
phide of  antimony y  etc. 

Kermes  is  prepared  either  in  the  dry  or  humid  way. 

In  the  former  case,  a  mixture  of  5  parts  of  native  sulphide  of  an- 
timony and .  3  parts  of  dried  carbonate  of  soda  is  fused  in  an 
earthen  crucible,  and  the  fused  substance,  after  being  reduced  to 
powder,  is  boiled  with  a  large  quantity  of  water.  The  hot  liquid  is 
rapidly  filtered,  taking  care  that  it  does  not  cool  in  the  filter ;  when 
the  liquid,  which  is  nearly  colourless,  or  but  slightly  yellow,  deposits 
on  cooling  a  copious  brown  flaky  precipitate,  which  is  the  kermes. 
It  should  be  quickly  washed,  dried  at  a  low  temperature,  and  kept 
in  well-stoppered  bottles. 

It  is  obtained  in  the  humid  way  by  boiling  1  part  of  native  sul- 
phide of  antimony,  finely  powdered,  with  20  or  25  parts  of  dried 


CHLORIDES.  217 

carbonate  of  soda,  and  250  parts  of  water;   the  liquid,  which  is 
almost  colourless,  depositing  the  kermes  on  cooling. 

By  pouring  chlorohydric  acid  into  the  mother  liquid  from  which 
the  kermes  has  been  deposited,  a  precipitate  of  a  deeper  red  colour 
than  the  precipitate  is  obtained,  which  has  been  called  the  golden 
sulphide.  It  is  a  mixture  of  sulphide  of  antimony  SbSg,  sulfanti- 
monic  acid  SbS.,  and  oxide  of  antimony  SbOg. 

It  is  easy  to  ascertain  that  the  oxide  of  antimony  exists  only  as 
an  admixture  in  kermes  mineral  and  in  the  golden  sulphide ;  an 
examination  with  the  microscope  shows  the  oxide  of  antimony  in 
the  form  of  white  points  scattered  through  the  mass. 

Kermes  contains,  also,  a  small  quantity  of  sulphide  of  potassium 
combined  with  the  oxide,  or  with  a  portion  of  the  sulphide  of  an- 
timony. 

Sulfantimonic  acid  SbS^  is  obtained  by  passing  a  current  of 
sulf  hydric  acid  through  a  solution  of  per  chloride  of  antimony  SbCl^ 
in  dilute  chlorohydric  acid,  when  a  yellow  precipitate  is  formed, 
readily  dissolving  in  the  alkaline  sulphides,  and  forming  sulphosalta 
which  frequently  crystallize  with  great  facility.  For  medicinal 
purposes,  a  sulfantimoniate  of  sodium  is  often  prepared  by  mix- 
ing intimately  18  parts  of  very  finely  powdered  sulphide  of  anti- 
mony, 12  parts  of  dried  carbonate  of  soda,  13  of  lime  and  3 J  of 
sulphur,  and  allowing  the  mixture,  after  it  has  been  triturated  for' 
a  long  time,  to  digest  for  several  days  in  a  flask  filled  with  water, 
the  vessel  being  frequently  shaken.  The  liquid,  when  evaporated, 
first  by  heat,  and  then  under  the  receiver  of  an  air-pump,  yields 
large  crystals  of  a  pale  yellow  colour,  and  of  which  the  formula  is 
3NaS,SbS3+18HO. 

COMPOUNDS  OF  ANTIMONY  WITH  CHLORINE. 

§  1012.  Antimony  forms  two  compounds  with  chlorine,  SbClg  and 
SbCl,,  corresponding  to  the  oxide  of  antimony  SbOg  and  antimonic 
acidSbO^. 

The  chloride  of  antimony  SbClg  is  obtained  by  passing  chlorine 
slowly  through  a  tube  containing  antimony  in  excess,  while  the  per- 
chloride  SbCl^  would  be  formed  if  the  chlorine  be  in  too  great 
quantity.  The  chloride  is  also  obtained  by  distilling  in  a  glass 
retort  an  intimate  mixture  of  1  part  of  antimony  and  ^  parts  of  bi- 
chloride of  mercury ;  but  the  most  economical  method  of  preparing 
it  consists  in  dissolving  native  sulphide  of  antimony  in  chlorohydric 
acid,  and  evaporating  the  liquid  with  an  excess  of  acid.  In  the 
laboratory  the  residue  of  the  preparation  of  sulf  hydric  acid  is  used 
for  this  purpose. 

Chloride  of  antimony  SbClg  is  a  white,  readily  fusible  substance, 
which,  from  its  consistence  at  the  ordinary  temperature,  was  for- 
merly called  butter  of  antimony.  It  volatilizes  at  a  temperature 
below  a  red-heat.  ' 


218  ANTIMONY. 

The  protochloride  of  antimony  is  deliquescent  m  a  moist  atmo- 
sphere, and  dissolves  without  change  in  a  small  quantity  of  water, 
while  the  addition  of  chlorohydric  acid  is  necessary  for  its  solution 
in  larger  quantities  of  the  same  liquid ;  as  with  much  pure  water  de- 
composition would  ensue,  a  white  soluble  powder  of  an  oxychloride 
of  antimony  SbCl352Sb03+HO,  called  by  the  old  chemists  powder  of 
Algaroth,  being  formed.  By  treating  a  chlorohydric  solution  of  chlo- 
ride of  antimony  with  hot  water,  the  clear  liquid  deposits,  on  cool- 
ing, crystals  of  another  oxychloride  of  the  formula  SbClgySSbOg. 
Repeated  washings  decompose  the  oxychlorides  of  antimony  and 
leave  pure  oxide.  The  best  method  of  preventing  solutions  of  chlo- 
ride of  antimony  from  being  clouded  by  water  consists  in  the  addi; 
tion  of  a  certain  quantity  of  tartaric  acid. 

Anhydrous  chloride  of  antimony  combines  with  dry  ammoniacal 
gas,  yielding  a  compound  of  which  the  formula  is  NHgjSbClg.  With 
the  alkaline  chlorides  and  chlorohydrate  of  ammonia  it  forms  dou- 
ble crystallizable  chlorides. 

In  surgery,  chloride  of  antimony  is  used  to  cauterize  wounds. 
Gunsmiths  employ  it  for  bronzing  gun-barrels,  the  iron  of  which, 
being  thus  covered  with  a  very  thin  pellicle  of  metallic  antimony, 
is  preserved  from  rust. 

PereJdoride  of  antimony  SbCl^  is  prepared  by  heating  antimony 
in  a  current  of  dry  chlorine,  the  same  apparatus  being  used  as  that 
employed  for  the  preparation  of  the  perchloride  of  tin.  The  liquid 
collected  in  the  receiver,  which  always  contains  some  protochloride 
SbClg  in  solution,  must  be  completely  saturated  with  chlorine,  and 
then  distilled  in  a  small  retort.  The  first  portions  which  pass  over 
contain  a  considerable  quantity  of  dissolved  chlorine,  and  are  co- 
loured deeply  yellow,  while  the  subsequent  liquid,  being  nearly 
colourless,  is  collected  by  itself.  Perchloride  of  antimony  never- 
theless appears  to  decompose  at  the  temperature  of  its  ebullition 
under  the  ordinary  pressure  of  the  atmosphere,  as  it  always  disen- 
gages chlorine  when  subjected  to  distillation. 

DISTINCTIVE  CHARACTERS   OF  THE  SOLUBLE  COMPOUNDS  OP 
ANTIMONY. 

§  1013.  The  characteristic  reactions  of  solutions  of  antimony 
which  we  are  about  to  indicate  refer  to  the  protochloride  of  anti- 
mony and  to  emetic  tartar^  which  is  a  double  tartrate  of  antimony 
and  potassa.  They  will  serve  to  distinguish  antimony  in  all  cases, 
because  it  is  always  easy  to  convert  its  other  compounds  into  these 
two  products. 

Solutions  of  antimony  produce  with  potassa  and  soda  white  pre- 
cipitates, which  are  easily  redissolved  in  an  excess  of  alkali. 
Ammonia  throws  down  a  white  precipitate  insoluble  in  an  excess  of 
the  reagent. 

The  alkaline  carbonates  yield,  carbonic  acid  being  at  the  same 


ANALYTIC   DETERMINATIONS.  219 

time  evolved,  a  white  precipitate  of  the  hydrated  oxide,  which  does 
not  dissolve  in  an  excess  of  carbonate. 

Sulf  hydric  acid  and  sulf  hydrate  of  ammonia  yield  a  characteris- 
tic orange-coloured  precipitate,  which  dissolves  in  an  excess  of  sulf- 
hydrate. 

A  blade  of  iron  or  zinc  precipitates  antimony  in  the  form  of  a 
black  powder,  from  which,  by  fusion  on  charcoal  before  the  blow- 
pipe, metallic  antimony  is  obtained,  possessing  the  characteristic 
physical  properties  which  distinguish  it  from  tin,  this  metal  being 
analogous  to  it  in  its  chemical  reactions. 

DETERMINATION  OF  ANTIMONY;  AND  ITS  SEPARATION  FROM  THE 
METALS  PREVIOUSLY  STUDIED. 

§  1014.  Antimony  can  neither  be  determined  as  the  oxide  SbOg 
nor  as  antimonic  acid  SbO^,  as  the  purity  of  these  substances  would 
always  be  questionable.  It  is  precipitated  from  its  solution  by  sulf- 
hydric  acid,  a  sufficient  quantity  of  chlorohydric  acid  being  added 
to  prevent  the  liquid  from  being  clouded  by  water,  or  still  better, 
tartaric  acid,  when  the  addition  of  this  substance  does  not  interfere 
with  the  determination  of  the  remaining  substances.  The  liquid, 
after  being  saturated  with  sulf  hydric  acid  gas,  is  exposed  to  a 
gentle  heat  for  several  hours  in  an  imperfectly  closed  bottle,  in 
order  to  allow  the  greater  portion  of  the  sulf  hydric  acid  to  be  dis- 
engaged ;  when  the  precipitate  of  sulphide  of  antimony  is  collected 
on  a  filter,  and,  after  being  well  washed,  is  dried  on  the  filter  at  a 
temperature  of  212°.  The  filter,  with  the  substance  it  contains, 
being  weighed,  the  latter  is  separated  as  completely  as  possible, 
and  dropped  into  a  small  flask ;  when  the  weight  of  the  filter,  sub- 
tracted from  that  of  the  filter  and  substance  together,  gives  the 
weight  of  the  sulphide.  The  small  quantity  which  always  remains 
in  the  pores  of  the  filter  can  be  taken  into  account  by  incinerating 
the  paper  and  considering  the  residue  as  antimoniate  of  antimony 
SbOgjSbO^.  The  sulphide  of  antimony  being  now  treated  with 
hot  aqua  regia,  the  antimony  dissolves  as  perchloride,  and  the  sul- 
phur in  the  state  of  sulphuric  acid,  the  oxidation  of  the  sulphur 
being  accelerated  by  an  addition  of  a  small  quantity  of  chlorate  of 
potassa.  Chloride  of  barium  is  then  poured  into  the  liquid  pro- 
perly diluted  with  water,  while  a  small  quantity  of  tartaric  acid  is 
added  to  prevent  the  precipitation  of  oxychloride  of  antimony; 
when  sulphate  of  baryta  is  precipitated  and  weighed  after  calcina- 
tion. By  subtracting  from  the  weight  of  the  sulphide  of  antimony 
the  weight  of  sulphur  corresponding  to  the  sulphate  of  baryta,  the 
weight  of  the  metallic  antimony  is  obtained.* 

*  The  method  given  in  the  text  may  be  considerably  shortened,  by  collecting 
the  sulphide  of  antimony  on  a  weighed  filter,  which  has  been  previously  dried  at 
212°,  (a  balanced  filter;)  when  the  weight  of  the  filter  with  the  precipitate,  after 
being  dried  at  the  same  temperature,  minus  the  weight  of  the  filter,  gives  imme- 


220  ANTIMONY. 

The  sulphide  of  antimony  may  also  be  heated  in  a  current  of 
hydrogen  gas,  when  metallic  antimony  remains,  sulf  hydric  acid 
and  vapour  of  sulphur  being  disengaged.  For  this  purpose,  the 
sulphide  of  antimony  is  placed  in  a  small  porcelain  crucible,  through 
the  lid  of  which  a;  tube  passes  conveying  dry  hydrogen  to  the  bot- 
tom of  the  crucible,  and,  the  temperature  being  gradually  raised, 
the  reaction  is  maintained  until  the  crucible  no  longer  alters  in 
weight. 

In  no  case  can  antimony  be  weighed  in  the  state  of  sulphide,  its 
composition  always  being  a  matter  of  uncertainty. 

§  1015.  In  order  to  separate  antimony  from  the  metals  we  have 
previously  studied,  the  insolubility  of  antimonic  acid  in  nitric  acid 
is  sometimes  relied  on,  and  sometimes  its  precipitation  by  sulf  hy- 
dric acid,  and  the  solubility  of  sulphide  of  antimony  in  alkaline 
sulfhydrates.  Antimonic  acid  not  being  absolutely  insoluble  in 
nitric  acid,  it  is  always  necessary  to  test  for  antimony  in  the  liquid 
by  means  of  sulf  hydric  acid. 

In  order  to  separate  antimony  from  the  alkaline,  alkalino-earthy, 
and  earthy  metals,  chlorohydric  acid  is  added  to  the  liquid  to  pre- 
vent the  deposit  of  oxychloride  of  antimony,  and  sulf  hydric  acid 
gas  is  passed  through  it.  When  the  antimony  is  nearly  wholly  pre- 
cipitated, the  liquid  is  diluted  with  water,  because  sulphide  of  anti- 
mony is  slightly  soluble  in  chlorohydric  acid,  unless  the  latter  is 
very  dilute  ;  and  sulf  hydric  acid  is  again  passed  through  it.  The 
precipitate  of  sulphide  of  antimony  having  been  separated  on  a  fil- 
ter, the  substances  remaining  in  solution  may  be  determined  by  the 
ordinary  processes. 

Antimony  is  separated  from  manganese,  iron,  chrome,  cobalt, 
nickel,  and  zinc  by  passing  sulf  hydric  acid  through  the  liquid  acidu- 
lated with  chlorohydric  acid.  The  precipitation  of  oxychloride  of 
antimony  is  frequently  prevented  by  the  addition  of  tartaric  acid, 
in  which  case,  however,  the  other  metals  can  no  longer  be  com- 
pletely separated  from  their  solutions  either  by  ammonia  or  the 
alkaline  carbonates,  because  tartaric  acid  prevents  their  precipita- 
tion. The  liquid  then  being  saturated  with  ammonia,  the  metals 
axe  precipitated  by  sulf  hydrate  of  ammonia. 

Antimony  is  separated  from  cadmium,  lead,  and  bismuth  by 
saturating  the  chlorohydric  solution  with  ammonia,  and  adding  a 
large  excess  of  sulf  hydrate  of  ammonia  in  which  a  certain  quantity 
of  sulphur  has  been  dissolved.  The  bottle,  imperfectly  closed,  is 
exposed  for  several  hours  to  a  temperature  of  from  120°  to  140°  ; 
when  the  antimony  dissolves  in  the  state  of  sulphide,  while  the  sul- 
phides of  the  other  metals  are  precipitated.     By  decomposing  the 

diately  the  weight  of  all  the  antimony  as  sulphide  SbS„  -whence  that  of  the  me- 
tallic antimony  may  be  deduced.  The  antimony  having  been  in  the  state  of  proto- 
chloride  SbCl,,  is  precipitated  entirely  as  protosulphide  SbS„  in  all  cases  when 
the  antimonial  compound  has  not  been  dissolved  in  nitromuriatic  acid. —  W.  L.  F 


ANALYTIC   DETERMINATION.  221 

filtered  liquid  bj  dilute  chlorohydric  acid,  the  sulphide  of  antimony 
separates,  mixed  with  a  large  quantity  of  free  sulphur. 

Antimony  cannot  be  separated  from  tin  by  any  of  the  processes 
just  described.  The  reactions  of  these  metals  being  very  similar, 
their  separation  is  consequently  a  matter  of  some  difficulty.  Both 
metals  being  dissolved  in  aqua  regia,  are  precipitated  together  by  a 
blade  of  zinc,  and  the  metallic  precipitate  is  weighed.  It  is  then 
dissolved  in  aqua  regia  with  an  excess  of  chlorohydric  acid,  and  a 
blade  of  tin  dipped  into  the  liquid  when  properly  diluted,  by  which 
the  antimony  alone  is  precipitated,  and  perfectly,  if  care  be  taken  to 
keep  the  liquid  gently  heated,  with  a  slight  excess  of  chlorohydric 
acid. 

DETECTION  OF  ANTIMONY  IN  CASES  OF  POISONING. 

§  1016.  As  compounds  of  antimony  act  as  poisons  on  the  animal 
economy,  it  occasionally  falls  to  the  lot  of  the  medical  man  to  in- 
vestigate their  toxicological  effects,  the  subject  of  investigation 
being  sometimes  food  and  sometimes  portions  of  the  human  body. 
For  this  purpose,  the  suspected  matter  being  diluted  with  water,  a 
certain  quantity  of  pure  chlorohydric  acid  added,  and  the  liquid 
boiled,  20  gm.  of  chlorate  of  'potassa  for  every  100  parts  of  mat- 
ter are  thrown  into  it  by  small  quantities  at  a  time,  the  liquid  is 
filtered  while  boiling,  and  concentrated  by  evaporation.  It  is  then 
introduced  into  a  Marsh's  apparatus,  as  represented  in  fig.  260 ; 
when  a  glittering  ring  of  metallic  antimony  forms  in  the  tube  fg^  in 
which  all  the  characteristic  reactions  of  antimony  may  be  observed. 
A  blade  of  tin  may  also  be  plunged  into  the  filtered  liquid  after  it 
has  been  properly  concentrated,  when  the  antimony  is  deposited  on 
the  tin.  The  tin  is  dissolved  in  aqua  regia,  with  the  black  precipi- 
tate which  may  have  separated  from  it,  after  which  it  is  evaporated 
with  an  excess  of  chlorohydric  acid,  redissolved  with  the  same  acid 
in  .a  very  dilute  state,  and  the  solution  treated,  as  before,  in 
Marsh's  apparatus. 

ALLOYS  OF  ANTIMONY. 

§  1017.  Although  antimony  combines  with  a  great  number  of 
metals,  the  only  alloys  used  in  the  arts  are  those  of  antimony  and 
lead  for  printers'  types,  and  those  of  antimony  and  tin  for  various 
purposes. 

Antimony  combines  readily  with  potassium  and  sodium,  produc- 
ing alloys  which  decompose  water  at  the  ordinary  temperature  with 
disengagement  of  hydrogen  gas,  and  which  frequently  detonate  sud- 
denly when  moistened  with  a  small  quantity  of  water  or  exposed  tc 
a  damp  atmosphere.  An  alloy  of  antimony  and  fused  potassium  is 
prepared  by  heating  for  several  hours,  in  an  earthen  crucible,  a 
mixture  of  6  parts  of  tartar  emetic  and  1  of  nitre,  or  equal  parts 
of  metallic  antimony  and  black  flux;  when  the  metallic  button 


222 


ANTIMONY. 


found  at  the  bottom  of  the  crucible  will  decompose  water  at  the 
ordinary  temperature,  with  disengagement  of  hydrogen.  A  finely 
divided  alloy,  which  explodes  when  moistened  with  a  drop  of  water, 
is  obtained  by  heating  for  several  hours  in  an  earthen  crucible,  at 
a  high  temperature,  100  parts  of  tartar  emetic  and  3  parts  of  lamp- 
black. The  crucible  should  be  placed,  after  the  calcination,  under 
a  well-dried  bell-glass,  which  should  be  removed  only  when  it  is 
perfectly  cool.  This  substance  requires  the  most  careful  handling, 
as  it  frequently  gives  rise  to  fearful  accidents  by  detonating  spon- 
taneously. 

By  fusing  in  an  earthen  crucible,  at  a  strong  white-heat,  a  mix- 
ture of  70  parts  of  metallic  antimony  and  30  of  iron-filings,  a  very 
hard  metallic  globule  is  obtained,  which  on  being  filed  emits  sparks 
of  fire.  This  substance  is  known,  in  the  laboratory,  under  the  name 
of  RSaumur's  alloy, 

METALLURGY  OF  ANTIMONY. 

§  1018.  We  have  said  that  the  sulphide  is  the  only  ore  of  anti- 
mony. It  is  first  separated  from  its  gangue  by  simple  fusion,  for 
which  purpose  the  ore  is  placed  in  large  crucibles  P  (fig.  556),  ar- 
ranged in  two  rows  in  a  furnace. 
Each  crucible  has,  at  its  lower 
part,  an  aperture  corresponding 
to  an  opening  made  in  the  benches 
on  which  it  rests.  Under  the 
crucibles,  and  in  the  compart- 
ments I)  of  the  furnace,'  are 
earthen  pots  Q,  in  which  the 
fused  antimony  is  collected,  while 
pine  wood  is  burned  on  the 
grates  G.  Sometimes  the  ore  is 
heated  in  a  reverberatory  fur- 
nace, when  the  fused  sulphide 
runs  into  a  cavity  in  the  hearth, 
and  flows  outwardly  into  iron 
pots. 

The  sulphide  of  antimony  is 
then  roasted  in  a  reverberatory 
furnace,    where  it   is   converted 
iinto  oxysulphide  or  glass  of  an- 
„.     -gg  timony ;  after  which  the  roasted 

substance  is  pulverized,  and  then 
mixed  with  20  per  cent,  of  charcoal  soaked  in  a  strong  solution  of 
carbonate  of  soda.  This  mixture  being  calcined  in  crucibles,  the 
oxide  of  antimony  is  reduced  to  the  metallic  state,  while  a  portion 
of  the  sulphide  is  decomposed  by  the  carbonate  of  soda  and  yields 
an  additional  quantity  of  metal.     A  globule  of  antimony,  called 


ANTIMONY.  223 

regulus  of  antimony,  is  found  at  the  bottom  of  the  crucibles,  sur- 
mounted by  an  alkaline  dross  containing  sulphide  and  oxide  of 
antimony,  and  which  may  be  used  for  the  preparation  of  kermes 
mineral. 

Metallic  antimony  may  also  be  obtained  by  decomposing  sul- 
phide of  antimony  by  iron ;  but  its  quality  is  then  inferior,  as  it 
contains  a  large  proportion  of  iron ;  and  although  the  latter  may 
be  separated  by  subjecting  the  substance  to  a  partial  roasting,  a 
considerable  quantity  of  antimony  must  be  oxidized  in  order  to 
e£fect  a  complete  separation  of  the  iron. 


224 

URANIUM, 
Equivalent  =  60  (750.0;  0  =  100). 

§  1019.  Uranium*  is  prepared  in  the  same  way  as  magnesium  ; 
that  is,  by  decomposing  its  chloride  by  means  of  potassium,  for 
which  purpose  a  mixture  of  about  2  parts  of  protochloride  of  ura- 
nium and  1  of  potassium  is  gently  heated  in  a  platinum  crucible,  the 
lid  of  which  is  fastened  down  by  iron  wire.  When  the  reaction,  which 
ensues  with  lively  incandescence,  is  terminated,  the  crucible  is  again 
heated  in  order  to  volatilize  the  greater  portion  of  the  potassium  in 
excess,  after  which  the  crucible  is  allowed  to  cool,  and  the  substance 
treated  with  water,  which,  dissolving  the  chloride  of  potassium,  leaves 
the  uranium  in  the  form  of  a  black  powder.  Small  plates  of  ura- 
nium are  often  found  on  the  sides  of  the  crucible,  in  which  case  the 
metal  possesses  a  lustre  resembling  that  of  silv-er,  and  a  certain 
degree  of  malleability. 

Uranium  is  very  combustible :  it  ignites  in  the  air  when  heated 
above  392°,  burning  with  great  brilliancy,  and  being  transformed 
into  a  deep-green  oxide.  It  remains  unchanged  in  the  air  at  the 
ordinary  temperature,  and  does  not  decompose  cold  water.  It  dis- 
solves with  disengagement  of  hydrogen  in  the  dilute  acids,  and  pro- 
duces green  solutions.  It  unites  with  chlorine  with  great  disen- 
gagement of  heat  and  light,  forming  a  green  volatile  chloride. 
With  sulphur  it  combines  directly,  and  at  a  low  temperature. 

COMPOUNDS  OF  URANIUM  WITH  OXYGEN. 

§  1020.  Two  compounds  of  uranium  with  oxygen  are  known : 

A  protoxide  UO ; 

A  sesquioxide*  U3O3. 

Several  intermediate  oxides,  which  are  regarded  as  compounds  of 
the  first  two,  are  also  known. 

Protoxide  of  uranium  UO  is  prepared  by  decomposing  the  ses- 
quioxalate  of  uranium  Ua03,C303  by  hydrogen  at  a  red-heat,  when 
a  brown  powder  remains,  which  must  be  preserved  in  an  atmosphere 
of  hydrogen,  by  hermetically  sealing  the  ends  of  the  tube  in  which 
the  decomposition  has  been  effected.  The  oxide  is  very  pyrophoric, 
becoming  feebly  incandescent  in  the  air,  and  being  converted  into  a 
black  powder,  which  is  an  intermediate  oxide  U4O5,  and  the  for- 
mula of  which  should  probably  be  written  2U0,U303.  The  pro- 
toxide is  obtained  in  a  more  aggregated  form  by  decomposing  the 

*  Oxide  of  uranium  was  discovered  in  1 789,  by  Klaproth ;  while  metallic  ura- 
nium was  isolated  by  M.  P^ligot  only  as  late  as  1842. 


SALTS.  225 

double  chloride  of  uranium  and  potassium  by  hydrogen,  when  the 
protoxide  of  uranium  remains,  after  treatment  with  water,  in  the 
form  of  crystalline  spangles  which  do  not  change  in  the  air  at  the 
ordinary  temperature. 

Protoxide  of  uranium  may  also  be  obtained  in  the  hydrated  state 
by  decomposing  by  ammonia  the  green  solution  of  protochloride  of 
m*anium  UCl;  a  flaky,  reddish-brown  precipitate  being  formed, 
which  readily  dissolves  in  acids. 

By  heating  protoxide  of  uranium  in  the  air  to  a  dull  red-heat,  it 
is  converted  into  an  oxide  of  a  deep  olive  colour  and  a  velvety  ap- 
pearance, the  composition  of  which  is  UgO^,  or  moie  probably, 
UOjUgOg,  as  by  solution  in  acids  a  protosalt  and  a  sesquisalt  are 
formed.  At  a  higher  temperature  this  oxide  is  decomposed  and 
changed  into  a  black  oxide  2U0,U303.  The  oxide  of  uranium  has 
been  long  regarded  as  a  metal,  and  called  uranium. 

Sesquioxide  of  m'anium  U3O3,  which  is  the  base  of  the  yellow 
salts  of  uranium,  has  not  yet  been  isolated.  When  the  sesqui- 
nitrate  is  decomposed  by  a  properly  regulated  heat,  an  orange- 
coloured  basic  salt  is  fii'st  obtained,  while  on  still  increasing  the 
temperature  it  loses  a  portion  of  its  oxygen,  while  it  at  the  same 
time  parts  with  the  last  traces  of  its  acid.  By  precipitating  a  solu- 
tion of  a  yellow  salt  of  uranium  by  potassa  or  ammonia,  a  yellow 
precipitate  is  formed,  which  is  a  true  uranate  of  the  base  which 
efiected  the  precipitation.  Hydrated  sesquioxide  of  uranium  is 
prepared  as  follows : — A  solution  of  the  yellow  oxalate  of  uranium  is 
exposed  to  the  action  of  solar  heat,  which  effects  the  disengage- 
ment of  a  mixture  of  carbonic  acid  and  oxide,  while  a  flaky  preci- 
pitate of  a  violet-brown  colour  is  formed.  The  precipitate  rapidly 
absorbs  the  oxygen  of  the  air  while  it  is  being  collected  on  a  filter, 
and  is  converted  into  a  yellow  substance,  which  is  the  hydrated 
sesquioxide  U3O3+2HO. 

PROTOSALTS  OF  URANIUM. 

§  1021.  Only  a  small  number  of  protosalts  of  uranium  are  known, 
from  the  solutions  of  which  ammonia  and  the  alkalies  throw  down 
brownish  black  precipitates,  which  turn  yellow  by  exposure  to  the 
air,  being  then  converted  into  sesquioxide,  which  remains  in  com- 
bination with  the  alkali.  Sulf  hydric  acid  exerts  no  action  on  these 
salts,  while  the  sulf  hydrates  yield  black  precipitates.  The  green 
salts  of  the  protoxide  of  uranium  are  readily  converted  into  yellow 
salts  of  the  sesquioxide  by  oxidizing  reagents ;  and  nitric  acid  or 
chlorine  effect  the  same  change,  even  when  cold. 

Protosulphate  of  uranium  is  prepared  by  pouring  sulphuric  acid 
into  a  concentrated  solution  of  green  protochloride,  heat  being  ap- 
plied to  drive  off  the  chlorohydric  acid.  By  treatment  with  water 
a  liquid  is  obtained  which  deposits  green  crystals  of  the  protosul- 
phate, of  which  the  formula  is  U0,S03+4H0. 
Vol.  IL— 15 


226  URANIUM. 

By  adding  oxalic  acid  to  a  solution  of  the  green  protochldride,  a 
greenish-white  precipitate  is  obtained,  which  may  be  washed  in 
in  boiling  water  without  dissolving,  and  consists  of  protoxalate  of 
uranium,  with  the  formula  UOjCaOg+SHO. 

SESQUISALTS  OF  URANIUM. 

§  1022.  The  sesquioxide  of  uranium  U^Og  forms  a  great  number 
of  crystallizable  salts,  the  peculiarity  of  whose  composition  distin- 
guishes them  from  salts  formed  by  the  other  metallic  sesquioxides. 
We  have  seen  that,  in  all  the  neutral  salts  formed  by  a  same 
acid,  the  ratio  between  the  oxygen  of  the  base  and  that  of  the 
acid  is  constant ;  being  as  3 : 1  for  the  sulphates :  the  formula  of 
the  neutral  sulphates  are  therefore  R0,S03  for  the  protoxides,  and 
R203,3S03  for  the  sesquioxides.  The  ratio  being  as  5  : 1  for  the 
nitrates,  R0,N05  is  the  formula  of  the  protonitrates,  and  ^^03,3^05 
that  of  the  sesquinitrates.  But,  when  the  sulphate,  or  nitrate,  of 
the  sesquioxide  of  uranium  is  crystallized  in  any  excess  whatever  of 
its  respective  acid,  the  crystallized  salts  always  present  the  for- 
mula UaOgjSOg  and  11303,^05.  If,  therefore,  we  admitted  the 
general  application  of  the  law  of  composition  of  salts  first  laid  down, 
these  salts  would  be  tri-basic  salts,  which  would  be  very  remarkable, 
inasmuch  as  they  have  crystallized  in  presence  of  a  great  excess  of 
acid.  In  order  to  remove  this  anomaly,  several  chemists  have  sup- 
posed the  sesquioxide  of  uranium  to  be  a  true  protoxide,  formed  by 
the  combination  of  one  equivalent  of  oxygen  with  an  already  oxidized 
radical,  which  would  present  the  composition  of  protoxide  of  ura- 
nium, and  which  they  call  uranyle.  Sesquioxide  of  uranium  being 
therefore,  in  their  opinion,  a  protoxide  of  uranyle^  they  write  its 
formula  (2U0)0,  and  the  salts  of  the  sesquioxide  of  uranium  are 
neutral  salts  of  protoxide  of  uranyle  (2UO)0,S03,(2UO)0,N05, 
etc.  etc.  We  shall  have  occasion  to  meet  with  several  other  com- 
pounds of  uranium  which  may  be  cited  in  favour  of  this  opinion. 

Solutions  of  the  sesquisalts  of  uranium,  or  protosalts  of  uranyle, 
are  of  a  beautiful  yellow  colour,  and  throw  down  with  the  alkalies 
yellow  precipitates  of  uranates,  in  which  the  sesquioxide  of  uranium 
acts  the  part  of  a  weak  acid  with  powerful  bases.  The  alkaline 
carbonates  and  carbonate  of  ammonia  throw  down  granular  yellow 
precipitates,  which  are  double  carbonates  and  dissolve  in  an  excess 
of  the  reagent.  Sulf hydric  acid  exerts  no  action  on  solutions  of 
sesquisalts  of  uranium,  while  the  sulfhydrates  yield  a  brownish- 
yellow  precipitate.  Prussiate  of  potash  gives  a  brownish-red  pre- 
cipitate. 

Sesquinitrate  of  uranium,  which  is  the  most  important  of  all  the 
sa,lts  of  this  metal,  is  obtained  directly  from  the  ore  of  uranium. 
The  principal  minerals  containing  uranium  are  pitchblende  and 
uranite.  Pitchblende,  which  chiefly  consists  of  oxide  of  uranium 
UOyUaOa,  and  forms  compact  black  masses,  with  a  brilliant  frac- 


SALTS.  227 

ture,  resembling  pitch,  occurs  principally  in  Bohemia ;  while  uranite, 
which  is  a  double  phosphate  of  the  sesquioxide  of  uranium  and  lime 
(CaO,2U303)Ph05-f8HO,  and  forms  yellow  crystalline  lamellae, 
with  greenish  reflections,  is  found  in  most  abundance  in  the  envi- 
rons of  Autun. 

Bohemian  pitchblende  is  the  material  which  is  always  used  for 
the  preparation  of  the  compounds  of  uranium.  The  mineral,  being 
reduced  to  a  fine  powder,  is  levigated  to  separate  the  lighter  earthy 
matter,  and  then  treated  with  nitric  acid,  which  readily  attacks  it ; 
after  which  the  solution  is  evaporated  to  dryness  and  treated  with 
water,  which  leaves  undissolved  a  brick-red  residue,  consisting  of 
sulphate  of  lead  and  sesquioxide  of  iron  combined  with  a  certain 
quantity  of  arsenious  acid ;  while  the  liquid,  which  is  of  a  greenish- 
yellow  colour,  affords  after  suitable  evaporation  a  copious  and  con- 
fused crystallization  of  sesquinitrate  of  uranium.  The  sirupy  mother 
liquid  is  decanted,  and  the  crystals,  after  having  been  allowed  to 
drain,  are  redissolved  in  water  for  the  purpose  of  recrystallization. 
As  the  mother  liquid  still  contains  a  considerable  quantity  of  ses- 
quinitrate of  uranium  which  cannot  crystallize  on  account  of  the 
presence  of  foreign  salts,  it  is  diluted  with  water,  and  treated  with 
a  current  of  sulf  hydric  acid  gas  to  precipitate  the  sulphides  of  cop- 
per, lead,  and  arsenic,  after  which  the  filtered  liquid  is  again  evapo- 
rated to  dryness  and  treated  with  cold  water,  when  a  ferruginous 
deposit  remains.  The  liquid  then  yields  on  evaporation  an  addi- 
tional quantity  of  crystallized  sesquinitrate  of  uranium. 

The  nitrate  of  uranium  thus  prepared  undergoes  a  last  purifica- 
tion by  being  placed  in  a  flask  with  ether,  in  which  it  is  consider- 
ably soluble,  and  from  which,  by  evaporation  of  the  ether,  pure 
nitrate  of  uranium  is  deposited,  which,  after  being  redissolved  in 
water,  is  again  crystallized. 

Sesquinitrate  of  uranium  forms  beautiful,  often  very  large,  yellow 
crystals,  which  exhibit  green  reflections,  like  nearly  all  the  sesqui- 
salts  of  uranium.  Its  formula  is  U303,N05+6H0,  or  (2U0)0, 
NO5+6HO.  It  melts  in  its  water  of  crystallization,  with  which  it 
parts  nearly  wholly,  yielding  a  crystalline  mass  after  cooling.  This 
salt  is  used  for  the  preparation  of  all  the  other  compounds  of  ura- 
nium :  calcination  converts  it  into  oxide. 

Sesquisulphate  of  uranium,  which  is  prepared  by  decomposing 
the  nitrate  by  sulphuric  acid,  forms  several  crystallizable  double^ 
sulphates.    The  formula  of  the  double  sulphate  of  uranium  and  po- 
tassa  is  U203,S03+K0,S03+2H0,  and  will  be  seen  to  possess  no 
analogy  with  the  alums. 

Sesquioxalate  of  uranium,  being  but  slightly  soluble  in  water,  is 
precipitated  when  oxalic  acid  is  poured  into  a  solution  of  the  sesqui- 
nitrate. The  formula  of  the  salt  is  11303,0203+ 3H0,  which  should 
be  written  (2UO)0,Ca03-f  3H0,  if  the  hypothesis  of  uranyle  be 
admitted. 


228  URANIUM. 

Sesquioxide  of  uranium  communicates  a  clear  yellow  colour  with 
beautiful  green  reflections  to  vitreous  fluxes,  and  has  been  used  for 
several  years  for  colouring  glass. 

COMPOUNDS  OF  URANIUM  WITH  CHLORINE. 

§  1023.  Two  compounds  of  uranium  with  chlorine  are  known : 
The  protochloride  UCl  is  obtained  by  subjecting  a  mixture  of 
oxide  of  uranium  and  charcoal  to  the  action  of  chlorine.  The  mix- 
being  introduced  into  a  tube  of  hard  glass,  so  as  to  half  fill  it,  and 
dry  chlorine  passed  through  the  end  containing  the  mixture,  the 
latter  is  heated  to  redness,  when  the  protochloride  of  uranium  ap- 
pears in  the  form  of  red  vapours,  which  condense  in  the  cold  part 
of  the  tube  in  very  brilliant  and  nearly  black  octahedric  crystals. 
The  chloride,  which  is  very  susceptible  of  moisture,  dissolves  readily 
in  water,  and  produces  a  deep-green  solution. 

If  the  protochloride  be  heated  in  a  glass  tube  in  a  current  of  hy- 
drogen gas,  it  loses  a  portion  of  its  chlorine,  and  is  converted  into 
a  slightly  volatile,  deep  brown  product,  of  which  the  formula  is 
U4CI3.  This  chloride  dissolves  readily  in  water,  and  yields  a  purple 
solution,  which  soon  turns  green  by  disengaging  hydrogen  gas. 

Oxychloride  of  Uranium^  or  Chloride  of  Uranyle, 

§  1024.  By  heating  protoxide  of  uranium  in  a  current  of  chlorine, 
a  yellow,  very  fusible,  and  but  slightly  volatile  crystalline  compound 
is  formed,  which  shows  the  formula  UgO^Cl,  or  (2U0)C1,  if  it  be 
regarded  as  protochloride  of  uranyle.  When  heated  with  potassium 
it  loses  only  its  chlorine,  and  the  residue  consists  of  the  protoxide 
(2U0),  or  uranyle.  This  compound  is  soluble  in  water,  with  a  yel- 
low colour,  and  forms  crystallizable  compounds  with  chloride  of 
potassium  and  chlorohydrate  of  ammonia.  The  formulae  of  these 
double  chlorides  are  (2U0)C1+KC1+2H0  and  (2UO)CH-NH3, 
HC1+2H0. 

DETERMINATION  OF  URANIUM;  AND  ITS  SEPARATION  FROM  THE 
METALS  PREVIOUSLY  STUDIED. 

§  1025.  Uranium  is  determined  as  protoxide,  for  which  purpose 
the  superior  oxides  are  reduced  by  hydrogen  at  a  red-heat.  It  is 
sometimes  weighed  in  the  state  of  the  black  oxide  2UO,U303,  in 
which  case  it  is  sufficient  to  roast  the  oxides  in  the  air  and  calcine 
at  a  strong  red-heat.  Sesquioxide  of  uranium  is  generally  precipi- 
tated by  ammonia,  which  yields  a  yellow  precipitate  of  uranate  of 
ammonia ;  and  as  the  precipitate  is  apt  to  pass  through  a  filter,  this 
inconvenience  is  remedied  by  adding  a  certain  quantity  of  sal-am- 
moniac to  the  liquid. 

Sesquioxide  of  uranium  is  separated  from  the  alkalies  by  am- 
monia, and  from  baryta  by  sulphuric  acid,  which  precipitates  the 
latter  base ;  while  it  is  separated  from  lime  and  strontian  by  evapo- 


ANALYTIC   DETERMINATION.  229 

rating  the  liquid  with  sulphuric  acid,  and  treating  it  with  alcohol, 
which  dissolves  only  the  sesquisulphate  of  uranium.  In  order  to 
separate  iron  from  uranium,  the  former  is  brought  to  the  state  of 
sesquisalt,  and  a  large  excess  of  carbonate  of  ammonia  is  added, 
which,  precipitating  the  sesquioxide  of  iron,  maintains  the  uranium 
in  solution.  The  sesquioxide  of  uranium  may  be  separated  from 
alumina,  and  the  oxide  of  chrome  by  the  same  process. 

The  separation  of  uranium  from  magnesia  and  the  oxides  of 
manganese,  zinc,  cobalt,  and  nickel  is  founded  on  the  solubility  of 
sesquioxide  of  uranium  in  bicarbonate  of  potassa :  an  excess  of  bi- 
carbonate of  potassa  is  poured  into  the  acid  liquid,  when  a  soluble 
double  carbonate  of  sesquioxide  of  uranium  and  potassa  is  formed, 
while  the  carbonates  of  the  other  metals  are  precipitated. 

In  order  to  separate  uranium  from  cadmium,  tin,  lead,  bismuth, 
and  antimony,  it  suffices  to  pass  a  current  of  sulf  hydric  acid  gas 
through  the  acid  solution,  by  which  means  all  these  metals  are  pre- 
cipitated, while  the  uranium  alone  remains  in  the  liquid. 


230 


TUNGSTEN. 

Equivalent  =  95  (1187.5 ;  0  =  100). 

§  1026.  Tungsten*  is  obtained  by  heating  at  a  strong  red-heat 
tungstic  acid  in  a  current  of  hydrogen  gas  in  a  porcelain  tube, 
when  the  metal  remains  in  the  form  of  a  deep  gray  powder.  It  is 
obtained  in  a  more  aggregated  form  by  heating  tungstic  acid  in  a 
"brasqued"  crucible  in  a  forge-fire,  in  which  case  the  metal  is  in  a 
consistent,  but  not  fused  mass,  which,  when  filed,  assumes  a  metallic 
lustre.  Its  density  is  considerable,  being  about  17.5.  It  does  not 
oxidize  in  the  air  at  the  ordinary  temperature,  but  at  a  red-heat  is 
converted  into  tungstic  acid,  into  which  it  is  also  converted  when 
brought  at  a  red-heat  into  contact  with  w^ater,  which  it  decomposes. 
Chlorohydric  acid  does  not  act  sensibly  on  metallic  tungsten,  while 
nitric  acid  attacks  it  actively,  and  transforms  it  into  tungstic  acid, 
which  efiect  is  also  produced  by  sulphuric  acid,  when  concentrated 
and  hot. 

COMPOUNDS  OF  TUNGSTEN  WITH  OXYGEN. 

§  1027.  Tungsten  forms  two  well-defined  compounds  with  oxy- 
gen :  a  binoxide  WO^  and  tungstic  acid  WO3. 

Tungstic  acid,  which  is  the  most  important  of  these  compounds, 
is  used  in  the  preparation  of  the  other  compounds  of  tungsten. 
Tungsten  occurs  in  nature  as  tungstic  iron,  or  wolfram,'f  which  is 
a  double  tungstate  of  iron  and  manganese,  of  the  general  formula 
(FeO,MnO)W03 ;  the  formulae  of  the  minerals  from  the  various 
localities  which  have  hitherto  been  analyzed  being  2(reO,W03)  + 
3(MnO,W03),  or  4(FeO,W03)+MnO,W03.  Wolfram,  which  is 
found  in  large  blackish-brown  crystals  in  the  primitive  rocks,  in 
which  it  frequently  accompanies  oxide  of  tin,  is  found  in  many 
places,  particularly  in  the  environs  of  Limoges.  In  order  to  obtain 
tungstic  acid  from  wolfram,  the  mineral  is  treated  with  aqua  regia, 
which  dissolves  the  iron  and  manganese  as  chlorides,  while  the 
tungsten  remains  in  the  state  of  insoluble  tungstic  acid.  It  is  col- 
lected on  a  filter,  and,  after  being  well- washed,  is  treated  by  a  solu- 
tion of  ammonia ;  when  tungstate  of  ammonia  is  formed,  which  dis- 
solves and  separates  from  the  quartzose  gangue  and  the  untouched 
ore.     The  solution  yields  small  prismatic  crystals  of  tungstate  of 

*  Scheele  discovered  tungstic  acid,  while  the  brothers  Elhujart  first  separated 
the  metal  from  it. 

•j-  In  German,  the  metal  is  called  wolfram,  after  the  mineral ;  or  scheel,  after  its 
discoverer;  and  from  the  name  of  wolfram,  the  symbol  of  tungsten,  W,  is  derived. 
^W.L.F. 


OXIDES   AND    SALTS.  231 

ammonia,  which,  when  heated  in  the  air,  is  converted  into  tungstic 
acid. 

Tungstic  acid  is  a  bright-yellow  powder,  insoluble  in  water  and 
the  acids,  but  readily  soluble  in  alkaline  liquids  and  ammonia  when 
it  has  not  been  calcined. 

By  heating  tungstic  acid  at  a  moderate  temperature  in  a  cur- 
rent of  hydrogen  gas,  a  brown  powder  of  the  hinoxide  W0„  re- 
mains, the  best  method  of  preparing  which  consists  in  fusing  1  part 
of  wolfram  and  2  of  carbonate  of  potassa  in  a  platinum  crucible, 
and  treating  the  mass  with  water ;  after  which  the  filtered  liquid 
containing  tungstate  of  potassa  in  solution  is  evaporated  to  dryness 
with  a  J  part  of  sal-ammoniac.  The  calcined  matter  being  treated 
with  water,  the  oxide  of  tungsten  WO^  remains  in  the  form  of  a 
black  powder,  which  changes  readily  into  tungstic  acid  by  heating 
it  in  the  air.  When  heated  with  a  concentrated  solution  of  caustic 
potassa,  it  decomposes  water  and  is  converted  into  tungstic  acid. 

Binoxide  of  tungsten  forms  with  soda  a  compound  of  the  formula 
NaO,2W03,  which  is  obtained  by  heating  bi-tungstate  of  soda  in  a 
current  of  hydrogen  gas,  and  purified  by  treatment,  first  with  chlo- 
rohydric  acid,  and  then  with  a  solution  of  potassa,  which  removes 
the  tungstic  acid  in  excess.  The  substance  forms  small  cubic  crys- 
tals of  a  beautiful  golden  yellow  colour. 

When  tungstic  acid  is  subjected  to  a  partial  reduction,  a  blue 
oxide  is  obtained,  which  is  regarded  as  a  compound  of  the  two  pre- 
ceding oxides,  having  the  formula  W03,W03.  For  this  purpose, 
tungstate  of  ammonia  is  decomposed  in  a  close  tube,  or  a  blade  of 
zinc  is  plunged  into  a  liquor  containing  both  tungstic  and  chloro- 
hydric  acids. 

TUNGSTATES. 

§  1028.  No  salts  formed  by  a  combination  of  the  oxides  of  tung- 
sten with  acids  are  known,  while  tungstic  acid  has  been  obtained 
combined  with  powerful  bases.  The  tungstates  of  potassa,  soda, 
and  ammonia  are  soluble,  while  those  of  the  other  bases  are  inso- 
luble. These  salts  are  easily  recognised  by  the  residue  of  tungstic 
acid  which  they  leave  on  being  decomposed  by  acids ;  but  in  order 
to  obtain  a  perfect  decomposition  it  is  often  necessary  to  boil  the 
tungstate  with  concentrated  acid.  Sulphurous  acid  does  not  de- 
compose the  salts  of  tungsten,  and  they  are  not  precipitated  by 
sulf  hydric  acid  and  the  alkaline  sulf  hydrates. 

The  formulae  of  the  tungstates  of  potassa,  soda,  and  ammonia, 
obtained  by  dissolving  tungstic  acid,  prepared  in  the  humid  way, 
*n  alkaline  solutions,  are 

KO,W03+5HO,    NaO,W03+2HO,    (NHgHO^WOa. 

Tungstic  acid  appears  to  be  able  to  exist  under  several  modifica- 
tions, corresponding  to  different  degrees  of  saturation. 


232  TUNGSTEN. 

COMPOUNDS  OP  TUNGSTEN  WITH  SULPHUR. 

§  1029.  Non-calcined  tungstic  acid  dissolves  readily  in  the  sulf- 
hydrates  of  the  alkaline  sulphides,  forming  sulphotungstates  of  an 
alkaline  sulphide.  By  adding  an  acid  to  these  solutions,  sulpho- 
tungstic  acid  WSg  is  thrown  down  in  a  brown  precipitate. 

Sulphotungstic  acid  is  decomposed  by  heat,  leaving  as  a  residue 
bisulphide  of  tungsten  WS3,  in  the  form  of  a  black  powder,  which 
may  also  be  obtained  by  distilling  1  part  of  tungstic  acid  with  5  or 
6  times  its  weight  of  sulphide  of  mercury. 

COMPOUNDS  OF  TUNGSTEN  WITH  CHLORINE. 

§  1030.  Metallic  tungsten  unites  directly  with  chlorine,  with  dis- 
engagement of  light ;  and  if  the  experiment  be  made  in  a  heated 
glass  tube,  traversed  by  a  current  of  chlorine,  the  cold  portions  of 
the  tube  become  covered  with  small  deep-red  needles  of  bichloride 
of  tungsten  WC\^,  which  is  very  fusible  and  volatile.  Water  de- 
composes it  into  binoxide  of  tungsten  which  is  precipitated,  and 
chlorohydric  acid. 

By  heating  sulphotungstic  acid  in  a  current  of  chlorine,  a  tri- 
chloride of  tungsten  WCI3  is  obtained,  which  sublimes  in  the  form 
of  small  red  crystals.  This  chloride  is  decomposed  by  water  into 
tungstic  and  chlorohydric  acids. 

If  gaseous  chlorine  be  passed  over  tungstic  acid,  small  yellow 
needles,  of  the  formula  WO3CI3,  corresponding  in  composition  to 
chlorochromic  acid  (§  884),  sublime  in  the  cooler  parts  of  the  tube. 

DETERMINATION  OF  TUNGSTEN;  AND  ITS  SEPARATION  FROM  THE 
METALS  PREVIOUSLY  STUDIED. 

§  1031.  Tungsten  is  always  determined  in  the  state  of  tungstic 
acid. 

In  order  to  separate  it  from  other  metals,  either  the  insolubility 
of  tungstic  acid  in  water  and  the  acids,  or  its  solubility  in  the  alka- 
line sulf  hydrates,  is  relied  on. 

The  insolubility  of  tungstic  acid  in  dilute  acids  insures  its  sepa- 
ration from  the  alkaline,  alkalino-earthy,  and  earthy  metals,  from 
manganese,  iron,  chrome,  cobalt,  nickel,  zinc,  cadmium,  lead,  cop- 
per, mercury,  and  silver ;  while  its  solubility  in  ammonia  allows  its 
separation  from  iron,  chrome,  tin,  bismuth,  etc.  Lastly,  its  sepa- 
ration from  the  metals  the  sulphides  of  which  are  not  soluble  in  the 
sulf  hydrates ;  that  is,  from  iron,  zinc,  manganese,  copper,  lead, 
silver,  etc.  etc.,  is  effected  by  its  solubility  in  the  alkaline  sulf- 
hydrates. 


233 


MOLYBDENUM. 

Equivalent  =  46  (575.0 ;  0  =  100). 

§  1032.  Molybdenum*  is  obtained  by  heating  in  a  porcelain  tube 
any  oxide  of  the  metal  in  a  current  of  hydrogen  gas ;  when  the 
molybdenum  remains  in  the  form  of  a  gray  powder,  which,  when 
burnished,  assumes  a  metallic  lustre.  Molybdenum  is  obtained  in 
a  more  aggregated  form,  by  reducing  the  oxide  in  a  "brasqued" 
crucible  in  a  forge-fire ;  and  if  the  temperature  be  raised  as  high  as 
possible,  small  fused  masses,  having  a  dead  silvery  hue,  and  the 
density  of  which  is  then  8.62,  are  sometimes  obtained.  Molybde- 
num is  so  easily  oxidizable,  that  that  obtained  by  reduction  by  hy- 
drogen is  entirely  converted,  when  exposed  to  the  air  for  some 
time,  into  a  brown  powder  of  the  oxide ;  and  by  heating  the  metal 
in  the  air  it  becomes  incandescent,  and  is  transformed  into  molyb- 
dic  acid.  Chlorohydric  and  dilute  sulphuric  acid  do  not  attack 
molybdenum,  while  nitric  acid,  on  the  contrary,  acts  very  power- 
fully upon  it,  converting  it  into  molybdic  acid. 

COMPOUNDS  OF  MOLYBDENUM  WITH  OXYGEN. 

§  1033.  Molybdenum  forms  three  compounds  with  oxygen  :  the 
protoxide  MoO  and  the  binoxide  MoO^,  which  are  both  bases  form- 
ing salts ;  and  a  third  oxide  MoOg,  which  is  an  acid. 

Molyhdic  acid  MoO,,  which  is  the  most  important  compound  of 
molybdenum,  serves  for  the  preparation  of  the  other  combinations 
of  this  metal.  Molybdenum  is  chiefly  found  in  nature  in  the  state 
of  sulphide  MoSg,  forming  gray  spangles  of  a  metallic  lustre,,  and 
resembling  native  graphite,  like  which  substance  it  leaves  gray 
marks  on  paper.  It  occurs  in  the  granitic  rocks,  frequently  ac- 
companying ores  of  tin,  and  is  principally  found  in  Bohemia  and 
Sweden.  After  treating  the  sulphide  of  molybdenum  with  aqua 
regia,  which  converts  the  sulphur  into  sulphuric  acid,  and  the  mo- 
lybdenum into  molybdic  acid,  the  liquid  is  evaporated  to  dryness 
and  the  residue  treated  with  ammonia,  which  dissolves  the  molybdic 
acid  during  the  evaporation  of  the  liquid.  The  molybdate  of  am- 
monia, which  separates  in  crystals,  is  converted  into  molybdic  acid 
when  heated  in  the  air.  Molybdic  acid  may  also  be  separated  by 
pouring  chlorohydric  acid  into  a  solution  of  a  molybdate. 

Molybdic  acid  is  a  white  powder,  which  sublimes  at  a  strong  red- 
heat  in  white  crystalline  spangles ;  which  operation  can  be  well 

*  Discovered  by  Scheele,  in  1778. 


234  MOLYBDENUM. 

performed  only  in  a  current  of  gas.  Although  molyhdic  acid  is 
very  feebly  soluble  in  water  when  freshly  precipitated  by  an  acid, 
it  readily  dissolves  after  calcination.  It  is  easily  soluble  in  the 
acids. 

Protoxide  of  molyhdenum  MoO  is  obtained  by  pouring  chloro- 
hydric  acid  into  the  solution  of  an  alkaline  molybdate,  until  the 
molybdic  acid,  which  is  at  first  precipitated,  is  redissolved,  when  a 
Hade  of  zinc  is  plunged  into  the  liquid,  which  is  turned  black,  after 
passing  through  the  shades  of  blue  and  brownish-red  successively. 
Ammonia  is  then  carefully  added  to  the  liquid  containing  proto- 
chloride  of  molybdenum  and  chloride  of  zinc  ;  and,  as  the  protoxide 
of  molybdenum  is  precipitated  first,  the  addition  of  ammonia  is  ar- 
rested as  soon  as  the  liquid  becomes  clouded.  The  precipitate 
should  be  washed  rapidly,  and  protected  as  much  as  possible  from 
the  air,  because  it  is  a  great  absorbent  of  oxygen. 

Binoxide  of  molyhdenum  MoOgis  prepared  by  decomposing  molyb- 
date of  ammonia  by  heat,  protected  from  the  air,  or  by  calcining  a 
mixture  of  molybdate  of  soda  and  sal-ammoniac.  This  oxide,  a  red- 
dish-brown crystalline  powder,  forms  a  reddish-brown  hydrate, 
which  resembles  the  hydrate  of  sesquioxide  of  iron. 

By  adding  ammonia  to  the  blue  liquid  obtained  by  partially  re- 
ducing by  zinc  a  chlorohydric  solution  of  molybdic  acid,  a  blue  pre- 
cipitate is  formed,  which  is  a  saline  oxide  resulting  from  the  com- 
bination of  molybdic  acid  with  binoxide  of  molybdenum. 

SALTS  FORMED  BY  THE  OXIDES  OF  MOLYBDENUM. 

§  1034.  Both  the  protoxide  and  binoxide  of  molybdenum  form 
salts  by  combining  with  acids. 

These  two  classes  of  salts  present  the  following  reactions : — The 
alkalies  and  ammonia  yield  brown  precipitates,  while  the  alkaline 
carbonates  afford  the  same  coloured  precipitate,  which  dissolves 
in  a  large  excess  of  the  carbonate  of  ammonia.  Sulf  hydric  acid 
precipitates  them  completely  after  some  time  as  a  black  deposit, 
the  same  precipitate  being  formed  with  the  alkaline  sulf  hydrates ; 
in  an  excess  of  which  it  is  soluble.  The  salts  of  the  protoxide  im- 
part to  their  solutions  a  brown  colour  approaching  a  black,  while 
those  of  the  sesquioxide  produce  a  deep  red  colour. 

Molyhdates, 

§  1035.  Molybdic  acid  forms  two  series  of  salts :  neutral  molyb- 
dates  RO,Mo03  and  bimolybdates  RO,2Mo03;  the  former  of  which 
are  obtained  by  dissolving  molybdic  acid  in  an  excess  of  alkali,  and 
the  latter  by  boiling  a  solution  of  an  alkali  or  an  alkaline  carbonate 
with  an  excess  of  molybdic  acid.  The  bimolybdates  generally  crys- 
tallize during  the  cooling  of  the  liquid. 


VANADIUM.  235 

COMPOUNDS  OF  MOLYBDENUM  WITH  CHLORINE. 

§1036.  Metallic  molybdenum  combines  directly .  with  chlorine, 
yielding  at  a  high  temperature  a  red  vapour,  which  condenses  in 
the  form  of  crystals  closely  resembling  those  of  iodine.  The  for- 
mula of  the  chloride,  which  dissolves  freely  in  water,  is  MoCl^. 

A  protoehloride  of  molyhdenum  is  obtained  by  dissolving  the  hy- 
drated  protoxide  in  chlorohydric  acid. 

By  passing  chlorine  over  heated  binoxide  of  molybdenum,  small 
and  very  soluble  spangles  are  sublimed,  the  formula  of  which  is 
M0O2CI,  corresponding  to  chlorochromic  and  chlorotungstic  acids. 


VANADIUM. 

Equivalent  =  68.6  (857.5;  0  =  100). 

§  1037.  Vanadium*  is  an  exceedingly  rare  metal,  found  in  very 
small  quantities  in  certain  Swedish  iron-ores,  and  also  occur- 
ring in  the  state  of  vanadate  of  lead.  Vanadium  is  obtained  by 
heating  vanadic  acid  with  potassium  in  a  platinum  crucible ;  when 
active  reaction  takes  place,  after  which  the  substance  is  treated 
with  water  to  dissolve  the  potassa,  and  the  metal  remains  in  the 
form  of  a  black  powder.  It  may  also  be  prepared  by  decomposing 
chloride  of  vanadium  by  ammoniacal  gas  at  a  red-heat,  in  which 
case  it  presents  the  appearance  of  a  flaky,  silvery-white  mass. 

§  1038.  Vanadium  forms  three  compounds  with  oxygen :  the 
protoxide  VO,  the  binoxide  VO2,  and  vanadic  acid  VO3. 

Vanadic  acid  is  readily  obtained  from  the  native  vanadate  of 
lead,  by  heating  the  mineral  with  nitric  acid,  when  vanadic  acid  is 
set  free,  while  nitrate  of  lead  is  formed.  It  is  treated  with  water, 
which  leaves  the  vanadic  acid.  The  acid  is  dissolved  in  ammonia, 
and  the  vanadate  of  ammonia  crystallized  by  the  evaporation  of 
the  liquid,  after  which  it  is  converted  into  vanadic  acid  by  calcina- 
tion in  the  air.  Vanadic  acid  is  an  orange-coloured  or  brown 
powder,  nearly  insoluble  in  water.  It  is  reduced  to  a  lower  degree 
of  oxidation  by  many  reducing  substances,  such  as  alcohol,  sugar, 
oxalic  and  sulphurous  acids.  It  dissolves  in  cold  chlorohydric  acid, 
while,  if  heat  be  applied,  chlorine  is  disengaged,  and  the  solution 
contains  chloride  of  vanadium  VCI3.  By  pouring  carbonate  of  po- 
tassa into  this  solution,  hydrated  binoxide  of  vanadium  is  precipi- 
tated as  a  gray  flaky  substance,  which  dissolves  readily  in  acids, 
and  produces  crystallizable  salts,  of  which  the  solutions  are  blue. 

*  Vanadium  was  discovered  in  1830,  by  M.  Sefstrom,  a  Swedish  chemist. 


236  COPPER. 

By  heating  vanadic  acid  in  a  current  of  hydrogen  gas,  a  black 
powder  of  protoxide  of  vanadium  VO  is  obtained,  no  saline  com- 
pounds of  which  are  known. 

If  a  mixture  of  vanadic  acid  and  charcoal  be  heated  in  a  current 
of  chlorine,  a  volatile  chloride  VCI3  is  formed,  which  condenses  as 
a  yellow  liquid.  It  boils  at  a  few  degrees  above  212°,  and  exhales 
copious  fumes  in  the  air. 


COPPER. 
Equivalent  =  31.7  (396.25  J  0  =  100).    ^ 

§  1039.  Copper  has  been  known  from  the  earliest  times.  Although 
it  sometimes  occurs  in  the  native  state,  it  exists  more  frequently  in 
combination  with  oxygen,  sulphur,  or  arsenic.  Some  salts  "of  the 
oxide  of  copper,  chiefly  carbonates,  are  also  found. 

Some  kinds  of  commercial  copper  are  nearly  pure ;  the  Russian 
containing  only  a  trace  of  iron.  Native  copper  is  often  crystal- 
lized in  the  form  of  small,  regular  octahedrons,  which  form  it  also 
assumes  when  precipitated  slowly  from  its  solutions  by  galvanic 
processes,  or  on  being  allowed  to  cool  slowly  after  fusion  in  a  small 
quantity  in  a  crucible,  the  liquid  portion  having  been  •  poured  oJ0f 
Chemically  pure  copper  is  obtained  by  reducing  pure  oxide  of  cop- 
per heated  in  a  tube  by  means  of  hydrogen,  the  reduction  taking 
place  at  a  temperature  below  a  red-heat,  and  leaving  the  metal  in 
the  form  of  a  red  powder,  which  assumes  a  brilliant  metallic  lustre 
under  the  burnisher. 

Copper  has  a  characteristic  red  colour,  and  becomes  transparent 
when  reduced  to  a  very  thin  pellicle ;  in  which  case  it  displays,  by 
transmitted  light,  a  beautiful  green  colour.  Coppery  pellicles  suit- 
able for  the  experiment  are  obtained  by,  reducing  by  hydrogen,  in  a 
heated  glass  tube,  a  small  quantity  of  oxide  or  chloride  of  co  '^^i  r : 
when  a  very  thin  layer  of  metallic  copper,  which  displays  a  red 
colour  by  reflected,  and  a  beautiful  green  by  transmitted  light,  is 
deposited  in  certain  parts  of  the  tube. 

Copper  possesses  a  sufficient  degree  of  malleability  to  allow  its 
being  hammered  into  thin  sheets  or  drawn  out  into  very  fine  wire ; 
and  at  the  same  time  is  considerably  tenacious,  as  it  requires  a 
weight  of  140  kilog.  to  break  a  wire  of  2  mm.  in  diameter.  The 
density  of  copper  varies  from  8.78  to  8.96,  according  to  the  greater 
or  less  degree  of  aggregation  it  has  received  during  its  manufacture. 
By  rubbing,  copper  acquires  a  disagreeable  smell  and  a  peculiar 
taste.  It  fuses  at  a  strong  red-heat,  and  at  a  white-heat  gives  ofi' 
vapours  which  burn  with  a  green  flame  in  the  air. 


COMPOUNDS   OF   COPPER  WITH  OXYGEN.  237 

At  the  ordinary  temperature  copper  does  not  oxidize  in  dry  air, 
but  soon  changes  in  a  moist  atmosphere,  especially  if  acid  vapours 
be  present,  becoming  covered  with  a  green  substance  commonly 
called  verdigris.  A  blade  of  copper,  moistened  by  an  acid,  and 
exposed  to  the  air,  combines  with  the  oxygen  of  the  air,  and  first 
produces  a  neutral  salt,  which  after  some  time  is  converted  into  a 
basic  salt.  A  blade  of  copper  also  oxidizes  in  the  air  when  moist-, 
ened  with  an  ammoniacal  solution ;  and  dilute  solutions  of  sea-salt 
attack  copper  very  powerfully,  while  concentrated  solutions  exert 
less  influence  on  it.  Copper  decomposes  aqueous  vapour  at  a  strong 
white-heat,  while  hydrogen  gas  is  disengaged.  A  concentrated  solu- 
tion of  chlorohydric  acid  attacks  finely  divided  copper  with  disen- 
gagement of  hydrogen,  while  it  scarcely  affects  the  metal  in  a  solid 
form.  Copper  does  not  decompose  water  in  the  presence  of  pow- 
erful acids :  concentrated  sulphuric  acid  dissolves  it  with  disengage- 
ment of  sulphurous  acid ;  and  it  dissolves  readily  in  cold  nitric  acid 
of  any  degree  of  concentration,  with  disengagement  of  deutoxide  of 
nitrogen. 

COMPOUNDS  OF  COPPER  WITH  OXYGEN. 

§  1040.  Copper  forms  four  compounds  with  oxygen : 

1.  The  suboxide    Cu^O,*  or  red  oxide. 

2.  The  protoxide  CuO,  or  black  oxide. 

3.  Thcbinoxide    CuO^. 

4.  Cupric  acid,  the  composition  of  which  is  not  yet  known. 

The  first  two  compounds  are  basic,  and  form  well-defined  and 
crystallizable  salts,  while  the  third  is  an  indifferent  oxide;  and 
lastly,  the  fourth  is  an  acid. 

Suboxide  of  Qofper  Cu^O. 

§1041.  Suboxide  of  copper 'is  found  in  nature  in  masses  of  a 
beautiful  red  colour,  possessing  occasionally  a  vitreous  lustre,  and 
sometimes  consisting  of  beautiful  red  crystals.  It  may  be  obtained 
artificially  by  several  processes : — 1st,  by  heating  in  an  earthen 
crucible  equivalent  parts  of  black  oxide  of  copper  CuO  and  finely 
powdered  metallic  copper ;  which  mixture  aggregates  when  fused  at 
a  high  temperature ;  2d,  by  heating  in  a  crucible  a  mixture  of  chlo- 
ride of  copper  CugCl  with  carbonate  of  soda,  and  then  treating  the 
substance  with  water,  which  dissolves  the  chloride  of  sodium  and  ex- 
cess of  carbonate  of  soda,  leaving  the  suboxide  of  copper  in  the 
form  of  a  deep  red  crystalline  powder ;  3d,  by  adding  to  a  solution 
of  a  salt  of  copper,  for  example,  the  sulphate  CuO,S03,  sugar  and 
potassa,  until  the  oxide  of  copper,  which  is  at  first  precipitated,  is 


*  The  name  of  protoxide  of  copper  is  often  given  to  the  suboxide  CuaO,  and  that 
of  binoxide  of  copper  to  the  oxide  CuO.  We  shall  not  adopt  this  nomenclature 
because  it  does  not  agree  with  that  which  we  have  thus  far  adopted. 


238  -  COPPER. 

redissolved,  and  bj  then  boiling  the  liquid ;  when  suboxide  of  copper 
is  deposited  in  the  form  of  small  bright-red  crystals. 

Hydrated  suboxide  of  copper  is  obtained  by  adding  potassa  to  a 
solution  of  protochloride  of  copper,  in  the  form  of  a  yellow  powder, 
which  soon  absorbs  oxygen  from  the  air,  and  which,  when  dried  in 
vacuo,  presents  the  formula  4Cua04-H0.  Hydrated  suboxide  of 
copper  dissolves  in  ammonia  without  colouring  the  liquid,  but  by  its 
rapid  absorption  of  oxygen  from  the  air  soon  changes  the  colour  of 
the  solution  to  a  beautiful  blue. 

Suboxide  of  copper  imparts  a  beautiful  red  colour  to  fluxes  (§  702). 
When  heated  with  concentrated  acids  it  is  generally  decomposed 
into  protoxide  of  copper  CuO  which  dissolves,  and  metallic  copper 
which  is  separated. 

Protoxide  of  Qopper  CuO. 

§  1042.  On  heating  metallic  copper  in  the  air,  its  surface  first 
becomes  covered  with  suboxide  Cu^O,  which  subsequently  changes 
into  the  black  oxide  CuO.  Although  protoxide  of  copper  is  often 
prepared  by  roasting  copper  turnings,  or  better  still,  the  very  finely 
divided  copper  which  remains  after  the  calcination  of  the  acetate 
with  access  of  air,  it  is  obtained  more  readily  by  decomposing  the 
nitrate  by  heat,  when  the  oxide  remains  in  the  form  of  a  black  pow- 
der, which  rapidly  condenses  the  moisture  of  the  atmosphere. 

When  caustic  potassa  is  poured  into  the  solution  of  a  protosalt 
of  copper,  a  grayish-blue  precipitate  of  hydrated  protoxide  is  formed, 
the  water  of  which  is  readily  -driven  ofi"  by  heat :  it  suffices  to  boil 
the  solution  in  which  it  has  been  precipitated  to  convert  it  into  a 
black  powder  of  anhydrous  oxide.  Hydrated  protoxide  of  copper 
dissolves  in  ammonia,  producing  a  solution  of  a  slightly  purple-blue 
colour,  called  celestial  water, 

Deutoxide  of  Copper. 

§  1043.  This  oxide  is  prepared  by  treating  the  hydrated  prot- 
oxide of  copper  with  oxygenated  water,  when  the  blue  matter  is 
changed  into  a  brownish-yellow  substance,  from  which  a  slight  ele- 
vation of  temperature  easily  abstracts  one-half  of  its  oxygen. 

Cuprie  Acid. 

§  1044.  An  intimate  mixture  of  very  finely  divided  copper,  po- 
tassa, and  nitre,  heated  to  redness  and  then  treated  with  water, 
yields  a  blue  solution  which  appears  to  contain  a  combination  of  an 
oxide  of  copper  containing  more  oxygen  than  the  preceding  with 
potassa.  This  compound,  however,  is  so  evanescent  that,  if  the 
liquid  be  heated,  oxygen  is  disengaged,  and  the  copper  is  precipi- 
tated in  the  state  of  black  oxide  CuO. 


SALTS.  239 

SALTS  FORMED  BY  THE  SUBOXIDE  OF  COPPER  Cu,0. 

§  1045.  The  salts  of  the  suboxide  of  copper  are  obtained  by  dis- 
solving hydrated  suboxide  in  dilute  acids,  which,  when  they  are  con- 
centrated, decompose  the  suboxide  into  metallic  copper  which  sepa- 
rates, and  protoxide  which  combines  with  the  acids. 

A  suhsulphite  of  copper  CugOjSOg,  is  prepared  by  decomposing  a 
solution  of  protosulphate  of  copper  CuO,S03  by  a  solution  of  sul- 
phite of  soda,  when  an  orange  precipitate  is  formed  which  is  con- 
verted, by  boiling,  into  a  red  crystalline  powder. 

When  acetate  of  copper  is  distilled,  a  small  quantity  of  a  white 
sublimate,  consisting  of  sub-acetate  of  copper,  is  found  in  the  upper 
part  of  the  retort. 

The  soluble  subsalts  of  copper  produce  colourless  solutions,  from 
which  alkalies  throw  down  an  orange-yellow  precipitate.  Ammo- 
nia gives  the  same  reaction,  but  an  excess  of  the  reagent  redissolves 
the  precipitate,  producing  a  colourless  liquid  which  soon  turns  blue 
in  the  air.  Sulf  hydric  acid  throws  down  a  black  precipitate  of  these 
salts,  for  the  study  of  whose  reactions  the  subchloride  CuCl  is  ex- 
actly suitable. 

SALTS  FORMED  BY  THE  PROTOXIDE  OF  COPPER  CuO. 

§  1046.  These  salts,  which  are  obtained  by  dissolving  protoxide 
of  copper,  or  better  still,  its  hydrate  or  its  carbonate,  in  acids,  are 
blue  or  green,  when  they  contain  water  of  crystallization,  while  in 
the  anhydrous  state  they  are  of  a  dirty  white,  when  the  acid  is 
colourless,  and  their  solutions  are  blue  or  green.  They  exhibit  the 
following  characteristic  reactions : 

Caustic  potassa  and  soda  yield  a  grayish-blue  precipitate  of  hy- 
drated protoxide,  which  is  converted  into  a  brown  precipitate  by 
boiling.  The  blue  precipitate,  which  is  insoluble  in  weak  alkaline 
liquids,  dissolves  with  a  blue  colour  in  the  latter  when  they  are  con- 
centrated. 

Ammonia  throws  down  the  same  precipitate,  while  an  excess  of 
the  reagent  dissolves  the  precipitate  and  produces  a  beautiful  blue 
solution,  which  then  contains  a  double  salt  of  copper  and  ammonia, 
from  which  caustic  potassa  precipitates  oxide  of  copper. 

Sulf  hydric  acid  and  the  sulf  hydrates  throw  down  black  precipi- 
tates, which  are  insoluble  in  an  excess  of  sulf  hydrate. 

Prussiate  of  potash  forms,  with  protosalts  of  copper,  a  chestnut- 
brown  precipitate,  which  assumes  a  purplish  shade  when  the  precipi- 
tate is  very  weak.  The  test  is  a  very  delicate  one,  and  will  detect 
the  presence  of  the  smallest  quantities  of  copper  in  a  solution. 

Iron  and  zinc  precipitate  metallic  copper  in  the  form  of  a  brown 
powder,  which,  when  burnished,  assumes  the  metallic  lustre  and 
ordinary  appearance  of  copper.   , 

Protoxide  of  copper  turns  borax,  and  in  general  all  vitreous 


240  COPPER. 

fluxes,  green.  If  the  glass  be  heated  in  the  reducing  portion  of 
the  flame,  it  acquires  a  beautiful  red  colour,  produced  by  the  reduc- 
tion of  the  protoxide  of  copper  CuO  into  the  suboxide  Cu^O. 

Sulphate  of  Copper, 

§  1047.  Sulphate  of  copper  is  found  in  commerce,  where  it  is 
known  by  the  name  of  blue  vitriol,  in  which  state  it  generally  con- 
tains variable  quantities  of  sulphate  of  iron.  It  may  be  obtained  in 
a  state  of  purity  by  treating  copper  of  the  first  quality  with  sul- 
phuric acid  diluted  with  one-half  its  weight  of  water ;  when  sulphur- 
ous acid  is  disengaged,  and  sulphate  of  copper  is  formed  which 
contains  only  a  trace  of  sulphate  of  iron.  It  is  evaporated  to  dry- 
ness, and,  toward  the  close  of  the  evaporation,  a  few  drops  of  nitric 
acid  are  added,  which  convert  the  iron  into  sesquioxide.  By  dis- 
solving it  in  water  the  greater  portion  of  the  iron  remains  in  the 
state  of  an  anhydrous  basic  sesquisulphate ;  when,  after  boiling  the 
liquid  with  a  small  quantity  of  the  hydrate  or  carbonate  of  the 
protoxide  of  copper,  which  precipitates  the  least  traces  of  iron,  the 
liquor  is  crystallized. 

Sulphate  of  copper  is  soluble  in  4  parts  of  cold  and  2  parts  of  boil- 
ing water,  and  crystallizes  at  the  ordinary  temperature  in  beautiful 
blue  crystals,  which  belong  to  the  sixth  system,  and  of  which  the 
formula  is  CuO,S03+5HO.  They  are  isomorphous  with  those  pro- 
duced by  protosulphate  of  iron  when  crystallized  at  a  temperature 
of  about  40°,  and  which  likewise  contain  5  equiv.  of  water.  When 
these  two  sulphates  are  mixed  together,  and  the  compound  solution 
is  crystallized,  crystals  are  deposited  containing  the  two  sulphates 
in  difierent  proportions,  according  to  the  respective  quantities  of  the 
salts  in  the  solution.  A  crystal  of  sulphate  of  copper  may  even  be 
made  to  grow  at  pleasure,  in  a  solution  of  sulphate  of  iron.  The 
crystal  then  increases  by  the  superaddition  of  layers  of  sulphate 
of  iron,  which  are  easily  distinguished  by  their  colour.  The  same 
crystal,  suspended  in  a  solution  of  sulphate  of  copper,  becomes 
covered  with  layers  of  this  latter  sulphate,  without  any  remarkable 
change  in  its  external  appearance. 

Sulphate  of  copper  readily  parts  by  heat  with  4  equiv.  of  water, 
but  retains  the  fifth  with  more  tenacity.  It  is  entirely  decomposed 
at  a  high  temperature,  into  oxide  of  copper  which  remains,  and  a 
mixture  of  sulphurous  acid  and  oxygen  which  is  disengaged. 

Sulphate  of  copper  is  manufactured  in  various  ways ;  and  a  cer- 
tain quantity  of  this  salt  is  obtained  in  copper  furnaces.  ^  When 
sulphuretted  copper  ores  or  cupreous  matts,  are  roasted,  and  the 
roasted  matter  is  sprinkled  with  water,  a  certain  quantity  of  the 
sulphates  of  iron  and  copper  is  dissolved,  and  separates  by  crystal- 
lization. The  sulphate  of  copper  thus  obtained,  always  contains  a 
large  proportion  of  sulphate  of  iron. 

Large  quantities  of  sulphate  of  copper  are  manufactured  from  the 


SALTS.  241 

copper  sheathing  of  ships  which  has  been  rendered  useless  by  the 
corrosive  action  of  salt  water.  The  copper  is  heated  to  a  dull  red- 
heat  in  a  reverberatory  furnace,  and  sulphur  thrown  in,  the  doors 
of  the  furnace  being  previously  closed,  when  the  sulphur  attacks 
the  surface  of  the  copper,  covering  it  with  sulphide  of  copper  CugS, 
after  which  it  is  roasted,  and  air  allowed  to  enter  the  furnace  freely. 
A  portion  of  the  sulphur  is  then  disengaged  in  the  state  of  sulphur- 
ous acid,  while  another  portion  changes  into  sulphuric  acid,  and 
forms  a  basic  protosulphate  of  copper.  The  sulphatized  sheets  are 
then  placed  in  large  boilers  filled  with  water,  to  which  a  certain 
quantity  of  sulphuric  acid  has  been  added,  when  neutral  protosul- 
phate of  copper  dissolves,  and  is  crystallized  by  evaporation  as  soon 
as  the  liquid  contains  a  sufiicient  quantity  of  it.  This  process  is 
repeated  until  the  sheets  of  copper  have  disappeared. 

Large  quantities  of  sulphate  of  copper  have  been  obtained  in  the 
refining  of  old  silver  coin,  as  we  shall  mention  hereafter. 

If  sulphate  of  copper  be  dissolved  in  a  hot  solution  of  ammonia, 
a  beautiful  blue  solution  is  obtained,  which  deposits  on  cooling  deep 
blue  crystals,  the  composition  of  which  is  represented  by  the  formula 
CuO,S034-2NH3+HO. 

By  digesting  hydrated  oxide  of  copper  with  a  solution  of  proto- 
sulphate of  copper^  a  green  powder,  consisting  of  a  hydrated  basic 
sulphate  of  copper  CuO,S03+2CuO+3HO  is  obtained.  Analo- 
gous basic  sulphates  are  precipitated  when  solutions  of  sulphate  of 
copper  are  incompletely  precipitated  by  the  alkalies. 

Sulphate  of  copper  forms  with  the  alkaline  sulphates  double  salts 
which  are  readily  crystallizable,  and  also  produces  double  sulphates, 
of  various  proportions,  with  the  sulphate  of  magnesia,  and  with 
those  of  the  protoxides  of  iron,  zinc,  nickel,  etc.,  which  are  all  iso- 
morphous.  These  double  sulphates,  crystallized  at  the  ordinary 
temperature,  contain  5  equiv.  of  water  when  the  sulphate  of  copper 
predominates,  and  7  equiv.  of  water,  on  the  contrary,  when  the 
other  metallic  sulphate  is  prevailing.  In  both  cases,  the  sulphates 
are  isomorphous  whenever  they  contain  the  same  quantity  of  water. 

Nitrate  of  Copper, 

§  1048.  This  salt  is  prepared  by  dissolving  copper  in  dilute  nitric 
acid,  when  the  liquid  yields  on  evaporation  beautiful  blue  crystals, 
which  contain  3  or  6  equiv.  of  water,  according  to  the  temperature 
at  which  the  crystallization  has  been  effected.    It  is  used  in  dyeing. 

The  influence  of  heat  changes  nitrate  of  copper  into  the  green 
basic  nitrate  4CuO,N05,  and  subsequently  decomposes  it  at  a  more 
elevated  temperature,  leaving  protoxide  of  copper.  The  same  basic 
nitrate  is  obtained  by  precipitating  the  neutral  nitrate  of  ammonia. 

Carbonates  of  Copper. 
§  1049.  By  adding  a  solution  of  an  alkaline  carbonate  to  a  solu- 

VoL.  IL— 16 


242  '    COPPER. 

tion  of  sulphate  of  copper,  a  bright  blue  gelatinous  precipitate  is 
obtained,  which,  after  some  time,  chaiiges  into  a  green  powder,  the 
composition  of  which  is  represented  by  the  formula  2CUO5CO3+HO ; 
the  blue  gelatinous  precipitate  appearing  to  differ  from  it  only  in 
containing  more  water.  By  boiling  the  liquid  with  the  precipitate, 
the  latter  is  converted  into  a  brown  powder  of  anhydrous  protoxide 
of  copper.  The  green  carbonate  of  copper  is  used  in  oil-painting, 
under  the  name  of  mineral  green. 

A  hydrocarbonate  of  copper,  of  the  formula  Cu0,C03-f-Cu0,H0, 
called  malachite,  is  found  in  nature  in  the  form  of  green  concrete 
masses,  which  are  often  very  compact  and  of  considerable  size,  and  are 
fashioned  into  ornamental  objects,  such  as  vases,  shafts  of  columns, 
and  table  and  chimney  tops,  which  are  of  great  value.  When 
polished  they  display  veins  of  different  shades  of  colours,  which  are 
produced  by  the  mammillary  structure  of  the  material,  and  impart 
a  very  beautiful  appearance  to  the  polished  surfaces.  Malachite  is 
sufficiently  abundant  in  Siberia  to  be  worked  as  an  ore  of  copper. 

Another  hydrocarbonate  of  copper,  of  which  the  formula  is 
2CuO,C03-f  CuO,HO,  and  which  yields  fine  blue  crystals,  also 
occurs  in  nature,  which  substance  existed  in  great  abundance  in 
the  mines  of  Chessy,  near  Lyons,  where  it  was  long  smelted  as  an 
ore  of  copper.  When  finely  powdered  it  is  of  a  beautiful  blue 
colour,  in  which  state  it  is  used  in  the  manufacture  of  coloured 
wall-paper,  and  is  called  mountain  blue,  or  native  blue  ashes,  (bleu 
de  montagne,  or  cendres  bleues  naturelles.)  Artificial  blue  ashes^ 
of  a  more  brilliant  shade  than  the  native  product,  are  made  in  En- 
gland, by  a  process  which  is  kept  secret. 

Arsenite  of  Copper. 

§  1050.  Arsenite  of  copper,  which  is  used  in  oil-painting,  under 
the  name  of  ScheeWs  green,  is  prepared  by  dissolving  3  kilog.  of 
carbonate  of  potassa,  and  1  kilog.  of  arsenious  acid  in  14  litres  of 
water,  and  pouring  the  solution,  by  small  quantities  at  a  time,  into 
a  boiling  solution  of  3  kilog.  of  sulphate  of  copper  in  40  litres  of 
water,  the  solutions  being  stirred  constantly  during  the  precipita- 
tion. The  shade  of  colour  is  modified  by  varying  the  proportions 
of  arsenious  acid. 

Silicates  of  Copper, 

§  1051.  By  means  of  fusion  the  oxide  of  copper  combines  in  all 
proportions  with  silicic  acid,  forming  green  vitreous  substances.  A 
crystallized  silicate  of  copper,  called  dioptase  by  mineralogists,  is 
found  in  nature,  and  presents  the  formula  3CuO,2Si03+3HO. 

Acetates  of  Copper. 

§  1052.  By  dissolving  protoxide  of  copper  in  acetic  acid,  a  green 
liquid  is  obtained,  which,  when  evaporated  at  a  proper  temperature, 


SULPHIDE.  243 

deposits  beautiful  green  crystals  of  the  formula  CuOjC^HgOg+HO, 
and  which  are  soluble  in  5  parts  of  boiling  water.  It  is  known  in 
commerce  by  the  name  of  verdigris,  and  is  manufactured  by  dis- 
solving the  basic  acetate  of  copper  in  vinegar.  When  the  salt 
crystallizes  at  a  low  temperature,  the  crystals  are  blue,  and  present 
the  formula  CuO,C,H303+5HO. 

A  basic  acetate  of  copper  is  prepared  in  the  South  of  France  by 
allowing  sheets  of  copper,  moistened  with  vinegar  or  brought  into 
contact  with  the  grape  mash  which  is  undergoing  the  acid  fermenta- 
tion, to  oxidize  in  the  air.  The  copper  sheets  become  covered 
with  a  greenish-blue  coat,  which  is  scraped  off  from  time  to  time, 
and  of  which  the  formula  is  CuO,C,H303+CuO,HO-f-5HO.  If  it 
be  treated  with  water,  insoluble  crystalline  spangles  of  the  formula 
3CuO,CJl303  separate,  while  a  mixture  of  neutral  acetate  CuO, 
C^HgOa  and  basic  acetate  3CuO,2C4H303  dissolves. 

A  basic  acetate  of  copper  is  made  at  Grenoble,  by  exposing 
sheets  of  copper  moistened  with  vinegar  in  hot  stoves.  This  sub- 
stance appears  to  be  a  mixture  of  the  two  sub-acetates  3CuO,2C4H303 
and  3CuO,C,H303. 

A  colour  which  is  a  compound  of  acetate  and  arsenite  of  copper 
CuO,C4H303+3(2CuO,As03)  is  likewise  used  in  oil-painting,  under 
the  name  of  ScJiweinfurt  green,  and  is  prepared  by  mixing  boiling 
solutions  of  equal  parts  of  arsenious  acid  and  acetate  of  copper,  and 
boiling  the  mixture  for  some  time. 

COMPOUNDS  OF  COPPER  WITH  SULPHUR. 

§  1053.  Copper  burns  actively  in  the  vapour  of  sulphur  (§  306), 
while  a  sulphide  of  copper  CugS  corresponding  to  the  suboxide  Cu^O 
is  formed.  This  sulphide  fuses  more  easily  than  metallic  copper, 
and  becomes  crystalline  on  cooling :  it  is  sometimes  found  in  copper 
furnaces,  crystallized  in  regular  octahedrons.  It  is  prepared  in  the 
laboratory  by  heating  a  mixture  of  3  parts  of  sulphur  and  8  of  cop- 
per turnings,  grinding  the  substance  obtained  again  to  powder,  and 
reheating  with  sulphur.  This  sulphide  of  copper  exists  in  nature, 
and  sometimes  forms  beautiful  crystals,  which  are  sufficiently  soft 
to  be  cut  with  a  knife. 

The  sulphide  of  copper  CuS  corresponding  to  the  protoxide  CuO 
cannot  be  prepared  by  the  humid  way,  by  decomposing  the  solution 
of  a  protosalt  of  copper  by  sulf  hydric  acid  or  a  sulf  hydrate,  as  the 
black  powder  thus  obtained  soon  changes  in  the  air.  In  analyses, 
it  is  necessary  to  wash  it  with  water  containing  a  small  quantity  of 
sulf  hydric  acid.  The  sulphide  of  copper  CuS,  when  heated,  parts 
readily  with  one-half  of  its  sulphur,  and  is  converted  into  the  sulphide 
Cu^S. 

Compounds  of  sulphide  of  copper  CugS  and  sulphide  of  iron  FcgSa 
in  very  various  proportions  are  found  in  nature,  constituting  mine- 
rals which  are  called  copper  pyrites,  pyritous  copper,  and  variegated 


244  COPPER, 

copper^  according  to  their  external  mineralogical  characters,  which 
frequently  agree  with  their  chemical  composition.  These  minerals 
are  very  important,  as  they  are  the  most  common  ores  of  copper, 
and  furnish  the  largest  proportion  of  this  metal. 

COMPOUND  OF  COPPER  WITH  ARSENIC. 

§  1054.  Copper,  heated  in  a  vapour  of  arsenic,  combines  readily 
with  a  small  quantity  of  this  substance,  becoming  white  and  very 
brittle ;  but  hitherto  no  definite  compound  of  these  substances  has 
been  obtained. 

COMPOUND  OF  COPPER  WITH  PHOSPHORUS. 

§  1055.  A  gray  and  very  brittle  phosphuret  of  copper,  contain- 
ing about  20  per  cent,  of  phosphorus,  is  formed  when  very  finely 
divided  copper  is  heated  in  the  vapour  of  phosphorus.  A  definite 
compound  of  copper  and  phosphorus  CugPh  is  obtained  by  decom- 
posing neutral  phosphate  of  copper  by  hydrogen  at  a  low  tempera- 
ture. Phosphurets  of  copper  are  also  obtained  by  the  humid  way, 
by  passing  a  current  of  phosphuretted  hydrogen  gas  through  a  solu- 
tion of  sulphate  of  copper. 

COMPOUND  OF  COPPER  WITH  NITROGEN. 

§  1056.  A  nitride  of  copper  of  the  formula  Gu^N  is  obtained  by 
heating,  at  a  temperature  of  509°,  oxide  of  copper  CuO  in  a  cur- 
rent of  dry  ammoniacal  gas,  when  the  substance  is  treated  with  a 
solution  of  ammonia,  which  dissolves  the  oxide  of  copper  in  excess. 
Nitride  of  copper  is  a  deep  green  powder,  which  is  easily  decom- 
posed by  heat,  with  a  slight  explosion. 

COMPOUND  OF  COPPER  WITH  HYDROGEN. 

§  1057.  A  compound  of  copper  with  hydrogen  is  obtained  by 
heating,  at  a  temperature  of  158°,  a  solution  of  sulphate  of  copper 
with  hypophosphorous  acid.  The  hydride  of  copper  thus  prepared 
is  hydrated,  and  forms  a  bright  brown  powder,  which  suddenly  de- 
composes at  about  140°  into  metallic  copper  and  hydrogen  gas, 
which  is  disengaged.  Chlorohydric  acid  decomposes  it,  forming 
protochloride  of  copper,  while  the  hydrogen  is  set  free. 

COMPOUNDS  OF  COPPER  WITH  CHLORINE. 

§  1058.  Two  compounds  of  copper  with  chlorine  are  known  :  the 
first  CugCl  corresponds  to  the  suboxide,  while  the  second  CuCl  cor- 
responds to  the  protoxide. 

Subchloride  of  copper  CUgCl  is  obtained  by  boiling  a  solution  of 
protochloride  of  copper  CuCl  with  very  finely  divided  metallic  cop- 
per, when  the  colour  of  the  liquid  changes  from  green  to  brown, 
while  white  crystalline  chloride  of  copper  Cuj,Cl  is  soon  deposited. 


ANALYTIC  DETERMINATION.  245 

The  chloride  is  also  obtained  by  decomposing  the  protochloride 
CuCl  bj  heat,  the  latter  parting  with  one-half  of  its  chlorine.  The 
protochloride  CuCl  may  be  reduced  to  the  state  of  subchloride 
CugCl  by  pouring  protochloride  of  tin  into  a  solution  of  protochlo- 
ride of  copper,  the  decomposition  taking  place  in  the  cold,  while 
chlorohydric  acid,  which  prevents  the  precipitation  of  the  oxide  of  *- 
tin,  is  added  to  the  liquid.  The  chloride  Cu^^Cl  may  be  obtained 
crystallized  in  small  tetrahedrons  by  dissolving  it,  assisted  by  heat, 
in  chlorohydric  acid,  when  the  chloride  is  deposited  during  the  cool- 
ing of  the  liquid. 

Chloride  of  copper  Cu^Cl  fuses  at  a  temperature  of  about  752°, 
and  volatilizes  at  a  red-heat.  It  is  very  slightly  soluble  in  water, 
but  dissolves  more  freely  in  chlorohydric  acid,  and  particularly  in 
ammonia.  It  soon  alters  in  the  air,  and  is  converted  into  a  green 
powder  consisting  of  a  compound  of  hydrated  oxide  of  copper  CuO 
and  protochloride  CuCl.  In  consequence  of  the  affinity  of  this  sub- 
stance for  oxygen,  it  is  frequently  used  in  eudiometric  analyses,  and 
generally  in  the  form  of  solution  in  ammonia. 

Subchloride  of  copper  CuCl  is  obtained  by  dissolving  the  prot- 
oxide CuO  in  chlorohydric  acid,  or  by  dissolving  metallic  copper  in 
aqua  regia.  The  chloride  is  very  soluble  in  water,  and  crystallizes 
on  cooling  from  a  concentrated  solution  in  the  form  of  long  bluish- 
green  needles,  of  which  the  formula  is  CuCl+2H0. 

This  chloride  is  prepared  in  the  anhydrous  state  by  slightly  heat- 
ing copper  in  an  excess  of  chlorine,  when  a  yellowish-brown  com- 
pound is  obtained,  which  evolves  chlorine  when  heated  to  a  dark 
red-heat,  and  is  converted  into  the  chloride  CugCl.  The  chloride 
dissolves  readily  in  alcohol,  and  imparts  to  it  the  quality  of  burning 
with  a  beautiful  green  flame. 


DETERMINATION  OF  COPPER,  AND  ITS  SEPARATION  FROM  THE  METALS 
PREVIOUSLY  DESCRIBED. 

§  1059.  Copper  is  determined  either  as  anhydrous  protoxide  CuO 
or  in  the  metallic  state.  When  copper  exists  alone  in  a  liquid,  it 
is  precipitated  by  caustic  potassa,  after  which  the  liquid  should  be 
boiled,  because  the  hydrated  protoxide  is  then  changed  into  an  an- 
hydrous oxide,  which  is  more  easily  washed :  the  oxide  is  weighed 
after  being  calcined  in  the  air.  Copper  is  frequently  precipitated  by 
a  blade  of  iron  or  zinc,  and,  if  it  is  to  be  weighed  in  this,  state,  must 
be  rapidly  washed  with  boiling  water  and  dried  excluded  from  the  air, 
from  which  it  promptly  absorbs  oxygen.  When  copper  is  precipi- 
tated from  its  solutions  by  sulf  hydric  acid  gas,  the  precipitate  must 
be  washed  with  water  charged  with  sulf  hydric  acid,  while  the  filter 
on  which  the  substance  has  been  collected  must  be  calcined,  and  the 
whole  dissolved  in  aqua  regia,  from  which  solution  the  copper  is  then 
precipitated  by  caustic  potassa. 


246  COPPER. 

Copper  is  very  accurately  determined  by  the  following  process, 
used  in  the  analysis  of  many  cupreous  substances : 

The  substance  being  dissolved  in  an  acid,  an  excess  of  ammonia 
is  added  to  it,  which  redissolves  the  oxide  of  copper,  forming  a  blue 
solution,  remarkable  for  its  great  colouring  power.  A  standard  so- 
lution of  sulphide  of  sodium  is  poured  into  the  liquid  from  an  alkali- 
meter  ;  when  the  copper  is  precipitated  in  the  state  of  an  oxysul- 
phide  of  the  formula  CuO,5CuS.  By  careful  manipulation,  the 
moment  at  which  the  copper  is  entirely  precipitated  may  be  exactly 
ascertained,  as  the  reaction  is  finished  when  the  liquid  has  lost  its 
colour.  It  is  then  easy  to  calculate  the  quantity  of  copper  precipi- 
tated, from  the  volume  of  the  standard  solution  of  sulphide  of 
sodium,  supposing  always  that  no  other  substances  which  are  pre- 
cipitable  by  the  alkaline  sulphide  exist  in  the  liquid. 

In  order  to  prepare  the  standard  solution  of  sulphide  of  sodium, 
1  gm.  of  pure  copper  is  dissolved  in  5  or  6  gm.  of  nitric  acid ;  and 
about  50  gm.  of  a  concentrated  solution  of  ammonia  being  added, 
gentle  heat  is  applied  to  dissolve  completely  the  precipitate.  The 
solution  of  sulphide  of  sodium,  the  initial  volume  of  which  has 
been  measured  on  the  division  of  th^  alkalimeter  containing  it,  is 
then  poured  into  the  deep-blue  liquid ;  and  when  the  latter  is  only 
of  a  light  blue,  the  flask  is  shaken  several  times,  and  then  allowed 
to  rest  for  a  few  moments.  The  sulphide  of  sodium  is  then  added, 
drop  by  drop,  in  order  to  observe  exactly  the  moment  at  which  the 
liquid  loses  its  colour,  at  which  point  the  volume  of  solution  added 
is  marked  on  the  division  of  the  alkalimeter.  Supposing  this  vo- 
lume to  be  represented  by  137.5  div.,  it  will  be  thence  inferred  that 
137.5  div.  of  the  solution  of  sulphide  of  sodium  correspond  to 
1.000  gm.  of  metallic  copper ;  and  consequently,  if,  in  order  to 
remove  the  colour  of  an  ammoniacal  cupreous  liquid,  97.5  div.  of 
the  solution  of  sulphide  of  sodium  are  required,  the  conclusion  fol- 
lows that  the  tested  solution  contained  ^  .  1.000  gm.,  or  0.709  gm. 
of  metallic  copper. 

The  described  process  may  be  applied  to  solutions  containing 
other  .metals  than  copper,  as  experiment  has  shown  that  it  gave 
exact  results  even  when  the  liquid  contained  iron,  zinc,  cadmium, 
tin,  and  lead  or  antimony,  because  the  alkaline  sulphide  only  com- 
mences to  act  on  the  metals  named  after  the  copper  has  been  com- 
pletely precipitated  in  the  state  of  oxysulphide.  It  is  nevertheless 
indispensable  that  the  iron  should  be  in  the  state  of  sesquioxide, 
since  the  presence  of  protoxide  would  derange  the  result.  It  is  not 
necessary  to  separate  by  filtering  the  deposit  thrown  down  by  seve- 
ral of  these  metals  at  the  moment  of  adding  the  excess  of  ammonia ; 
although  it  may  be  of  advantage  when  the  deposit  is  very  copious, 
because  the  latter  would  prevent  the  colour  of  the  liquid  from  being 
distinguished. 

The  process  of  determination  just  described  becomes  inaccurate 


METALLURGY    OF    COPPER.  247 

when  the  liquor  contains  cobalt,  nickel,  mercury,  or  silver.  The 
presence  of  silver  may  be  easily  avoided,  as  it  is  sufl&cient  to  add  a 
few  drops  of  sulf  hydric  acid  to  the  nitric  solution,  when  the  silver 
is  entirely  precipitated  as  insoluble  chloride. 

§  1060.  Copper  is  easily  separated  from  the  alkaline,  alkalino- 
earthy,  and  earthy  metals,  from  manganese,  iron,  chrome,  cobalt, 
nickel,  zinc,  titanium,  and  uranium,  by  means  of  sulf  hydric  acid, 
passed  through  the  liquid  acidulated  by  chlorohydric  acid,  when  the 
copper  alone  is  precipitated  in  the  state  of  sulphide. 

It  is  separated  from  cadmium,  bismuth,  and  lead,  when  these 
metals  are  dissolved  in  nitric  acid,  by  means  of  an  excess  of  carbo- 
nate of  ammonia,  which  does  not  dissolve  the  copper ;  which  same 
process  may  be  employed  to  separate  copper  from  alumina  and  the 
sesquioxides  of  iron  and  chrome ;  but  the  results  are  less  exact  than 
those  of  precipitation  by  sulf  hydric  acid.  The  best  method  of  se- 
parating copper  from  lead  is  to  add  sulphuric  acid  to  the  nitric 
solution  of  the  two  metals,  and  evaporate  to  dryness  to  drive  off  the 
excess  of  acid,  when  the  residue,  after  being  moistened  with  a  small 
quantity  of  nitric  acid  and  treated  with  water,  consists  only  of  sul- 
phide of  lead. 

Copper  is  separated  from  tin  by  treating  the  two  metals  with 
nitric  acid,  evaporating  to  dryness,  moistening  the  residue  with  a 
small  quantity  of  nitric  acid,  and  dissolving  it  in  water,  when  the 
tin  remains  in  the  state  of  stannic  acid.  By  the  same  process, 
copper  may  be  separated  from  antimony ;  but  the  results  are  less 
exact,  because  a  small  proportion  of  antimony  is  always  dissolved. 
It  is  therefore  better,  after  having  dissolved  the  metals  in  aqua 
regia,  to  saturate  the  solution  by  ammonia,  and  add  an  excess  of 
sulf  hydrate  of  ammonia,  in  which  sulphide  of  antimony  is  soluble. 
The  same  process  will  serve  to  separate  copper  from  tin  and  arsenic. 

METALLURGY  OF  COPPER. 

§  1061.  Copper  is  found  in  nature  chiefly  in  the  state  of  sulphide, 
which  is  rarely  isolated,  being  generally  combined  with  sulphide  of 
iron,  constituting  copper  pyrites  CugS+FcgSg,  and  frequently  mixed, 
in  greater  or  less  proportions,  with  iron  pyrites  FeSg.  The  most 
common  ores  of  copper  are  therefore  mixtures  of  sulphide  of  iron 
and  copper.  Besides  copper  pyrites,  the  following  ores  occur: 
variegated  copper  2Cu3S+FeS  ',  fahlerz^  or  gray  copper^  which  is  a 
double  sulphide  of  antimony  and  copper ;  and  bournonite,  which  is  a 
multiple  sulphide  of  antimony,  copper,  and  lead ;  all  of  which  are 
very  important  minerals,  being  generally  very  rich  in  silver. .  All  the 
ores  just  named  are  found  in  veins  traversing  the  old  rocks ;  while 
near  these  primitive  veins  deposits  of  copper  ores  are  often  seen,  evi- 
dently arising  from  the  alteration  of  the  ore  by  the  action  of  water. 
When  slow  streams  of  water,  which,  in  their  course,  pass  over  beds 
of  copper  ore,  and  thus  generally  contain  sulphate  of  copper,  drop 


248  COPPER. 

into  calcareous  earths,  or  remain  in  the  cavities  of  calcareous  rocks, 
sulphate  of  lime  is  formed  and  carried  off  by  the  water,  while  car- 
bonate of  copper  is  deposited ;  and  if  the  reaction  takes  place  at  a 
high  temperature,  oxide  of  copper  is  deposited  instead  of  the  car- 
bonate. Lastly,  if  organic  substances  be  present,  the  sulphate  of 
copper  may  be  reduced  either  to  the  metallic  state  or  to  that  of 
sulphide  of  copper.  The  occurrence  of  masses  of  carbonate  and 
oxide  of  copper,  which  are  frequently  found  near  veins  of  copper 
pyrites,  is  thus  explained,  as  is  also  the  origin  of  small  crystals  of 
sulphide  of  copper  scattered  through  certain  schistose  rocks  which 
are  impregnated  with  bitumen  and  contain  many  organic  remains. 
In  this  way,  geologists  explain  the  formation  of  the  cupreous  pyrites 
found  scattered  in  small  crystals  through  bituminous  schist,  and 
exhibiting  impressions  of  fishes,  which  form  the  bottom  of  a  very 
extensive  basin  of  secondary  rocks  in  Mansfeld,  in  the  north  of 
Germany. 

More  or  less  considerable  masses  of  suboxide  of  copper  Cu^O  are 
sometimes  found,  which  yield  a  very  rich  copper  ore,  very  valuable 
mines  of  which  are  in  Peru  and  Chili.  The  principal  localities  of 
copper  ore  in  Europe  are  in  the  county  of  Cornwall  in  England, 
Mansfeld  and  Rammelsberg  in  the  north  of  Germany,  in  Sweden, 
Norway,  and  the  Ural  and  Altai  mountains  in  Russia.  There  for- 
merly existed  at  Chessy  and  Saint-Bel,  near  Lyons,  a  very  pro- 
ductive mine  of  oxide  and  carbonate  of  copper,  which  is  now 
exhausted.* 

§  1062.  The  ores  of  the  oxide  and  carbonate  of  copper  are  very 
easily  worked.  It  is  sufficient  to  smelt  them  in  contact  with  char- 
coal, in  cupola  furnaces,  with  scoriae  more  or  less  silicious,  when  an 
impure  copper,  called  hlack  copper^  is  obtained,  which,  after  refining, 
yields  marketable  copper. 

§  1063.  The  treatment  of  the  sulphuretted  ores  is  much  more 
complicated.  They  are  first  subjected  to  several  preliminary  roast- 
ings,  in  order  to  convert  a  certain  portion  of  the  sulphides  into  ox- 
ides, after  which  the  roasted  ores  are  smelted  in  blast  or  in  rever- 
beratory  furnaces,  with  the  addition  of  scoriae  or  other  fluxes,  if  the 
ore  does  not  itself  contain  a  sufficient  proportion  of  silicates.  Cop- 
per has  a  greater  affinity  for  sulphur  than  iron,  while  the  latter 
metal,  on  the  contrary,  has  a  greater  affinity  for  oxygen,  especially 
in  the  presence  of  silicic  acid ;  the  oxide  of  copper,  which  forms 
during  the  roasting,  therefore  passes  entirely  into  the  state  of  sul- 
phide, by  abstracting  the  sulphur  from  the  sulphide  of  iron  which 
remained  in  the  roasted  material,  the  products  of  the  operation 
being  a  slag,  which  contains  the  greater  part  of  the  iron  of  the 

*  The  principal  locality  of  copper  ores  in  the  United  States  is  that  at  Kewenaw 
Point,  Lake  Superior,  where  large  masses  of  native  copper  are  found.  Other 
great  localities,  omitted  in  the  text,  are  those  in  Cuba,  Siberia,  and  Burra  Burra 
ia  Australia,  all  of  which  yield  principally  oxidized  ores. —  W.  L.  F. 


METALLURGY   OP   COPPER.  249 

copper  pyrites,  and  a  sulphide  of  iron  and  copper,  and  the  cupreous 
matt,  containing  nearly  all  the  sulphide  of  copper  of  the  pyrites, 
and  a  much  smaller  proportion  of  sulphide  of  iron.  The  matt  is, 
consequently,  a  sulphuretted  ore  of  copper,  much  richer  in  copper 
than  the  original  pyrites.  It  is  again  roasted,  and  melted  with 
silicious  scoriae,  and  frequently  with  ores  of  oxide  of  copper,  when 
they  are  at  hand,  which  process  produces  a  new  slag,  containing  a 
great  portion  of  the  iron  of  the  first  matt,  and  a  second  cupreous 
matt,  still  richer  in  copper  than  the  first.  These  successive  opera- 
tions are  repeated  until  an  impure  copper,  black  copper,  a  last 
cupreous  matt,  and  scoriae,  are  obtained,  the  matt  being  then  sub- 
jected to  similar  processes,  or  added  to  the  preceding  matt,  so  that 
the  ultimate  product  is  black  copper,  which  is  refined.  We  shall 
give  examples  of  this  metallurgic  process  as  adopted  in  some  of  the 
most  important  European  works. 

§  1064.  At  Fahlun,  in  Sweden,  the  principal  ore  is  copper  pyrites, 
mixed  intimately  with  iron  pyrites  and  accompanied  by  a  quartzose 
gangue.  The  pyritous  ores  are  roasted,  mixed  with  silicious  ores, 
in  the  proportion  of  2  parts  of  pyritous  and  1  of  silicious  ore,  and 
10  to  30  per  cent,  of  scoriae,  arising  from  a  previous  smelting, 
added.  This  mixture  is  smelted  in  a  blast-furnace  of  about  3  metres 
in  height,  and  a  matt  composed  of  sulphide  of  iron  FcgS  and  sul- 
phide of  copper  CugS,  with  a  slag  which  should  present  nearly  the 
composition  of  bisilicate  of  iron  FeO,2Si03,  are  removed  from  it. 
The  matt,  which  contains  8  to  10  per  cent,  of  copper,  is  subjected 
to  four  successive  roastings,  which  remove  nearly  all  the  sulphur 
and  leave  the  metals  in  the  state  of  oxide.  The  roasted  matts  are 
smelted  in  blast-furnaces,  resembling  those  used  for  the  smelting  of 
the  roasted  ores,  quartz  and  oxidized  or  sulphuretted  silicious  ores 
which  have  been  previously  roasted  being  added.  This  smelting 
yields  black  copper,  a  small  quantity  of  cupreous  matt,  and  scoriae, 
which  are  chiefly  simple  silicates  of  iron  FeO,SiOg.  The  cupreous 
matt  is  then  treated  like  the  first  matt  arising  from  the  smelting  of 
the  ores,  while  the  black  copper  is  refined  by  a  process  soon  to  be 
described. 

§  1065.  The  copper  ores  of  Mansfeld  are  argillaceous  schists, 
containing  pyrites  scattered  through  in  small  crystals,  their  rich- 
ness in  copper  being  very  variable,  while  they  are  strongly  impreg- 
nated with  bitumen.  They  are  roasted  by  being  heaped  on  a  pile 
of  wood,  which  is  easily  done,  the  consumption  of  fuel  being  small, 
as  the  fire  is  kept  up  by  the  bitumen.  Five  to  eight  per  cent,  of 
fluor-spar,  scoriae  poor  in  copper,  arising  from  subsequent  opera- 
tions, and  frequently  small  quantities  of  cupreous  schists  containing 
carbonate  of  lime,  are  added,  and  the  mixture  is  smelted  in  blast- 
furnaces 5  or  6  metres  high,  heated  by  coke.  Fig.  558  represents 
a  vertical  section  of  the  furnace  passing  through  one  of  the  twyers, 
while  fig.  557  represents  a  front  view.  (The  breast  of  the  furnace  has 


250 


COPPER. 


been  removed  to  show  the  interior.)    The  lower  part  of  the  furnace 
is  built  of  quartzose  sandstone,  and  the  upper  part  of  bricks.     The 


Fig.  557. 


Fig.  558. 


furnace  has  two  twyers,  either  on  the  same  side,  as  in  fig.  559,  or  on 
opposite  sides.  At  the  base  of  the  breast  of  the  furnace  are  two 
openings  o,  o',  which  are  opened  alternately  for  the  escape  of  the 
liquid  products,  and  which  communicate  by  means  of  canals  with 

two  large  crucibles  C,  C  outside.  The 
smelter  allows  a  nose  of  0.2  m.  in  length 
to  form  in  front  of  the  twyers,  and  the 
fuel  and  ore  are  charged  alternately  in 
layers.  The  furnaces  are  surmounted 
by  chimneys  of  12  or  15  metres  in  height, 
to  carry  oj0f  the  products  of  combustion. 
The  matts  and  scorise  escape  constantly 
from  the  furnace,  and  flow  into  one  of  the 
receiving  basins  C,  the  opening  o'  corre- 
sponding to  the  basin  C  being  closed.  When  the  crucible  C  is 
filled,  the  hole  o'  is  opened  and  the  material  allowed  to  run  into  C, 
after  which  the  products  in  the  basin  C  are  immediately  removed. 
The  slags  are  generally  moulded  into  large  bricks,  which  are  \ised 
in  building ;  while  the  matts,  in  the  shape  of  disks,  are  removed  as 
fast  as  their  surface  solidifies.  The  crucible  C  being  emptied,  when 
C  is  filled,  the  substances  flowing  from  the  furnace  are  again  col- 
lected. 

The  matt,  which  forms  only  about  ^  of  the  weight  of  the  melted 
ores,  is  composed  of  sulphide  of  iron  FeS  and  sulphide  of  copper 
CugS ;  its  proportion  of  copper  varying  from  20  to  60  per  cent., 
according  to  the  nature  of  the  ore.  When  the  matt  contains  only 
20  or  30  per  cent,  of  copper,  it  is  subjected  to  three  successive 


METALLURGY   OF   COPPER.  2^ 

roastings  on  heaps  of  wood,  and  is  again  passed  through  the  fur- 
nace, with  the  addition  of  a  certain  quantity  of  slag  arising  from 
the  first  smelting  of  the  ores ;  for  which  purpose  the  slag  which 
immediately  covered  the  matt  in  the  receiving  basins,  and  which 
is  richer  than  the  superficial  scoriae,  is  selected.  A  new  matt  is 
thus  obtained,  presenting  the  same  percentage  of  copper  as  that 
arising  from  the  smelting  of  rich  ores. 

§  1066.  The  rich  matts  are  subjected  to  six  successive  roastings 
on  heaps  of  wood,  the  operation  being  performed  in  small  stalls 

(fig.  560),  formed  by  three  stone 
walls,  and  having  openings  at  o, 
to  facilitate  the  draught.  The 
matt  which  has  been  roasted  in 
the  first  stall  is  passed  to  that 
of  No.  2,  and  so  on  until  it 
reaches  No.  6.  A  considerable 
„.     ^gQ  quantity  of  sulphate  of  copper, 

which  is  formed  during  the 
roasting,  is  subsequently  removed  by  washing,  as  it  can  be  sold  to 
a  good  profit.  Beginning  with  the  third  roasting,  the  matts  are 
lixiviated,  after  each  roasting,  in  large  wooden  boxes,  superimposed 
upon  each  other,  a  methodical  process  of  washing  (§  447)  being 
adopted,  so  that  the  water  which  flows  from  the  last  box  is  nearly 
saturated,  and  soon  deposit  crystals  when  evaporated  by  heat  in 
leaden  boilers. 

The  roasted  matt  is  smelted  in  a  blast-furnace  resembling  that 
in  which  the  ores  are  smelted,  but  smaller ;  the  scoriae  intended  to 
combine  with  the  oxide  of  iron  of  the  matt  being  added.  This 
smelting  yields  black  copper,  scoriae,  and  a  matt  which,  being  very 
rich  in  copper,  is  added  to  the  second  matts  resulting  from  the 
preceding  operation.  The  black  copper  is  removed  in  disks,  for 
which  purpose  a  small  quantity  of  water  is  poured  on  the  melted 
mass,  to  render  the  superficial  stratum  solid.  Black  copper  con- 
tains about  95  per  cent,  of  copper,  3  or  4  of  iron,  and  small  quanti- 
ties of  silver  and  antimony. 

§  1067.  Cupreous  ores  often  contain  enough  silver  to  render  the 
extraction  of  this  metal  advantageous ;  which  operation  is  eff'ected 
either  on  the  black  copper  or  on  the  last  roasted  matts.  The  black 
copper  is  worked  by  eliquation,  and  the  matts  by  amalgamation. 
The  following  is  the  principle  of  eliquation : — By  fusing  copper  and 
lead  in  an  elbow-furnace,  the  two  metals  are  alloyed ;  and  if  the 
fused  alloy  be  suddenly  cooled  at  the  moment  of  its  escape  from 
the  furnace,  the  metals  remain  intimately  mixed.  But,  if  the  solid 
alloy  be  gradually  reheated,  or  if  the  melted  alloy  be  slowly  cooled, 
the  metals  separate,  and  the  lead  retains  all  the  silver  which  origin- 
ally existed  in  the  copper,  while  the  latter  metal  is  merely  com- 


252  COPPER. 

bined  with  a  certain  quantity  of  lead.     Bj  cupellation  the  lead 
gives  up  its  silver,  and  the  impure  copper  is  refined. 

Three  parts  of  black  copper,  and  10  or  12  parts  of  lead,  as 
argentiferous  as  possible,  are  fused  in  a  small  elbow-furnace, 
litharge  rich  in  silver  being  often  substituted  for  the  lead.  The 
fused  alloy  is  run  into  cast-iron  moulds,  where  it  suddenly  cools, 

and  takes  the  shape 
of  disks,  which  are 
hesited  on  the  eliquat- 
ing  furnace.  This 
apparatus  consists  of 
two  cast-iron  plates 
(figs.  561  and  562), 
slightly  inclined  to- 
ward each  other,  and 
leaving  a  small  space 
llgTsGl.  above      an      empty 

space  M  in  the  ma- 
son-work which  supports  the  plates.  The 
disks  D  are  placed  perpendicularly  on 
the  plates,  and  kept  separate  by  wooden 
wedges,  the  open  part  of  the  floor  being 
closed  by  sheet-iron  plates  F,  F.  Char- 
coal is  heaped  between  the  disks,  and  the 
wedees  are  removed,  after  which  wood  is 
^'  placed  in  the  space  M  and  kindled,  the 

draught  being  increased  by  small  chimneys  o  made  in  the  mason- 
work.  As  the  temperature  rises,  the  lead  fuses  and  runs  through 
a  canal  a  in  the  floor  of  the  space  M,  into  a  crucible  <?,  whence  it 
is  run  into  moulds  of  a  lenticular  shape.  The  copper,  still  alloyed 
with  a  certain  quantity  of  lead,  remains  on  the  floor  in  the  form 
of  a  half-melted,  spongy  mass,  while  the  lead  which  separates  by 
eliquation  contains  nearly  all  the  silver,  which  is  afterward  sepa- 
rated by  cupellation. 

As  the  cupreous  masses  may  still  yield  a  certain  quantity  of 
argentiferous  lead,  if  the  temperature  be  raised,  they  are  heated 
in  a  peculiar  furnace,  called  a  sweating -furnace^  of  which  fig.  564 
represents  a  vertical  section  through  the  line  CD  of  the  plane 
(fig.  565),  while  fig.  565  shows  a  horizontal  section  at  the  height 
of  the  line  AB  (fig.  564) ;  and  lastly,  fig.  563  exhibits  a  front 
view  of  the  same.  The  cupreous  masses  are  placed  on  the  floor 
of  the  furnace  above  the  strainers  F,  F,  which  are  filled  with  wood ; 
when  the  door  of  the  furnace  is  closed  and  the  fuel  kindled, 
the  draught  being  assisted  by  small  holes  o,  o,  which  open  into 
a  chimney  H.  An  additional  quantity  of  lead  separates  by  eli- 
quation ;  but  as  the  air  in  the  furnace  is  very  oxidizing,  the 
greater  portion  of  this  lead  is  converted  into  litharge,  which  falls 


METALLURGY  OE   COPPER. 


253 


to  the  bot-  Fig.  563. 

torn  of  the 
strainers 
F.  A  small 
quantity 
of  oxide 
of  copper 
also  oxid- 
izes, but 
remains 
dissolved 
in  the 
litharge. 

There  will  be,  therefore,  on  the 
floor,  black  copper  which  has  lost 
the  greater  proportion  of  the  lead 
and  silver  it  retained,  and  argen- 
tiferous litharge  rich  in  copper, 
which  are  thrown  as  plumbeous 
material  into  the  elbow-furnace  in 
which  the  black  copper  is  smelted 
with  lead,  for  the  preparation  of 
disks  for  eliquation. 

§  1068.  The  black  cop- 
per produced  by  eliquation 
is  refined  in  a  reverberatory 
resembling  a  cupelling  fur- 
nace, of  which  fig.  566  re- 
presents a  vertical  section 
through  the  line  YX  of  the 
plane  (fig.  567),  while  fig. 
567  gives  a  horizontal  sec-  v 
tion  through  the  line  VU  of 
fig.  566,  Wood  is  burned 
on  the  grate  F,  and  the 
flame  passes  through  the 
furnace  A  into  the  chim- 
ney C. 

The  copper  to  be  refined 
is  placed  on  the  hearth-sole 
of   the    furnace,    made   of 

moistened  charcoal  solidly  y 

pounded ;  the  charging  be- 
ing done  through  an  open- 
ing D,  which  is  afterward 
closed  by  a  door.  When  the 
metal  is  fused,  the  wind  of 


Fig.  564. 


Fig.  565. 
Fig.  566. 


Fig.  567. 


254  COPPER. 

two  twyers  t  is  allowed  to  blow  over  the  surface  of  the  bath,  by  the 
oxidizing  action  of  which  the  sulphur,  lead,  and  iron  first  oxidize, 
Avhile  scoriae  and  skimmings  are  formed,  which  are  removed  through 
the  door  A.  After  a  certain  time,  the  copper  has  lost  its  foreign 
metals,  and  red  scoriae,  very  rich  in  suboxide  of  copper  CugO,  are 
formed.  The  workman  judges  of  the  progress  of  the  operation 
by  plunging  an  iron  rod  from  time  to  time  into  the  bath  of  metal, 
thus  taking  out  a  thimble  of  copper,  which  he  hammers  to  ascertain 
its  physical  qualities.  When  the  refining  is  finished,  he  runs  the 
metal  into  the  basins  B,  B',  pours  into  them  a  small  quantity  of 
water  to  solidify  the  superficial  stratum,  which  he  immediately  re- 
moves, and  so  on,  until  he  has  removed  all  the  copper.  The  me- 
tallic disks  are  called  rosettes.  In  this  state  the  copper  is  not 
malleable,  as  a  small  quantity  of  suboxide  of  copper  Cu^O,  which 
it  always  contains,  destroys  this  property. 

Black  copper  is  frequently  refined,  in  this  way,  before  being 
subjected  to  eliquation ;  but  it  is  not  carried  so  far,  and  the  par- 
tially refined  black  copper  is  run  into  cold  water,  which  reduces  it 
to  the  state  of  grains  or  drops.  The  granulated  metal  is  then 
fused  with  the  plumbeous  material  in  the  elbow-furnace,  by  which 
more  homogeneous  alloys  of  copper  and  lead  are  obtained,  than 
when  disks  of  black  copper  are  fused  with  lead.  After  eliquation 
and  sweating,  the  cupreous  material  is  refined  by  a  process  pre- 
sently to  be  described. 

The  process  by  amalgamation  will  be  described  in  treating  of 
the  metallurgy  of  silver.* 

§  1069.  When  black  copper  contains  no  silver,  it  is  not  subjected 
to  eliquation,  but  is  generally  refined  in  a  refining-furnace^  a  verti- 
cal section  of  which  is  seen  in  fig.  668,  and  a  perspective  view  in 
fig.  569.     It  is  composed  of  a  hemispherical  crucible  C,  of  a  radius 


*  A  recently  introduced  process  of  extracting  the  silver  from  cupreous  matts 
is  now  employed  to  great  advantage  in  Swansea,  South  Wales,  and  at  several 
places  in  Germany.  The  manipulations  are  as  yet  kept  secret,  while  the  succes- 
sive operations  are  as  follows : — The  second  or  third  cupreous  matt,  after  having 
been  granulated,  or  stamped,  and  reduced  to  an  impalpable  powder,  is  roasted  in 
a  reverberatory  until  all  the  sulphate  of  copper  formed  is  decomposed,  and  the 
sulphuric  acid  is  completely  expelled.  The  roasted  substance  is  again  powdered, 
and  roasted  with  a  certain  quantity  of  common  salt,  the  chlorine  of  which  com- 
bines with  the  silver  to  form  chloride  of  silver.  The  product  resulting  from  this 
operation  is  sieved ;  and  while  the  coarser  particles,  which  consist  of  imperfectly 
roasted  matt  which  has  sintered  together,  are  again  roasted  with  common  salt, 
the  powder  which  has  passed  through  the  sieve  is  treated  with  a  boiling  saturated 
solution  of  common  salt,  which  dissolves  the  chloride  of  silver.  The  silver  is 
precipitated  from  its  solution  in  the  metallic  state  by  pieces  of  metallic  copper, 
while  the  copper  in  solution  is  in  its  turn  precipitated  by  iron.  The  more  per- 
fectly the  first  roasting  was  effected,  i.  e.  the  less  sulphuric  acid  was  allowed  to 
remain,  the  less  chloride  of  copper  will  form  by  the  subsequent  roasting  with 
common  salt ;  and  the  less  copper  the  solution  of  silver  contains,  the  more  per- 
fectly will  the  silver  be  precipitated,  and  consequently,  the  more  economical  will 
the  operation  be.     The  whole  process  requires  great  care. —  W.  L.  F. 


METALLURGY   OF   COPPER. 


255 


of  about  0.2  m.  lined  with  brasque  made  of  2  parts  of  charcoal  and  1 
of  clay.  It  is  surrounded  by  an  edge  having  an  opening  A,  closed  by 
a  door,  the  object  of  which  is  to  more  readily  support  the  charcoal. 
When  first  made,  or  repaired,  it  is  dried  for  several  hours,  by 
filling  it  with  burning  charcoal ;  and,  fresh  charcoal  being  added, 
the  pieces  of  black  copper  are  placed  on  the  side  opposite  to  the 
twyer  T,  and  the  blast  is  admitted.  When  the  charge  of  black 
copper  is  melted,  fresh  is  added,  taking  care  to  always  keep  the 
furnace  filled  with  charcoal.  A  tap-hole  zV,  allows  the  escape  of 
the  scoriae  which  form  during  the  refining.  Sulphurous  acid,  and 
white  vapours  of  oxide  of  antimony,  when  this  metal  exists  in  the 
black  copper,  are  disengaged,  while  the  first  scoriae  contain  a 


Fig.  568. 


considerable  amount  of  oxide  of  iron,  which  gives  them  a  greenish 
hue,  while  the  succeeding  slag  is  of  a  deep  red  colour,,  and  very  rich 
in  oxide  of  copper.  When  the  workman  has  melted  the  quantity 
of  black  copper  intended  for  a  single  operation,  he  takes,  from 
time  to  time,  a  thimble  of  copper  on  the  end  of  an  iron  rod,  and 
judges,  by  the  appearance  of  the  metal,  of  the  progress  of  the 
operation.  When  he  thinks  the  refining  is  terminated,  he  stops' 
the  blast,  throws  a  bucket-full  of  water  on  the  hearth,  removes  the 
charcoal,  uncovers  the  surface  of  the  metallic  bath,  and  skims  off 
the  supernatant  scoriae ;  and  when  its  surface  is  clean,  throws  on 
it  a  small  quantity  of  water  to  consolidate  its  superficial  stratum, 
and  immediately  removes  it  in  the  form  of  a  rosette.  Water  is 
again  poured  on,  a  second  rosette  removed,  and  so  on,  until  the 
operation  is  terminated.  The  process  generally  lasts  two  hours,  and 
produces  a  loss  of  about  25  per  cent,  on  black  copper,  furnishing 
75  per  cent,  of  rosette  copper. 

§  1070.  Rosette  copper  does  not  possess  the  malleability  of  the 
copper  of  commerce,  and,  in  order  to  give  it  the  desired  properties, 
must  be  subjected  to  a  very  delicate  operation,  requiring  a  skilful 
workman.  The  rosettes  are  remelted  in  a  small  furnace,  resem- 
bling that  of  figs.  568  and  569,  for  refining  black  copper,  and, 
when  the  fused  metal  has  run  into  the  crucible,  it  is  covered  with 
fine  charcoal,  when,  after  some  time,  all  the  suboxide  of  copper  is 
reduced,  and  the  metal  has  attained  its  greatest  degree  of  mallea- 


256  COPPER. 

bility.  But  if  the  workman  does  not  seize  exactly  the  proper 
moment,  the  metal  again  loses  its  malleability  by  combining  with 
a  small  quantity  of  carbon.  When  this  happens,  (which  the  refiner 
soon  discovers  by  occasional  experiment,)  he  uncovers  the  metal, 
and  allows  the  air  of  the  twyer  to  play  for  a  few  moments  over 
the  surface  of  the  bath,  which  operation  he  repeats  until  he  attains 
the  favourable  period.  The  purified  metal  is  then  vun  into  moulds 
of  various  shapes  and  sizes. 

§  1071.  England  alone  manufactures  more  than  half  of  the 
copper  used  in  the  world.  The  most  important  copper-mines  are 
in  Devonshire  and  Cornwall,  while  the  principal  smelting-works 
are  in  Wales,  and  smelt,  besides  the  British  ores,  many  foreign 
ores  coming  from  Chili,  Peru,  Cuba,  New  Zealand,  Algiers,  Nor- 
way, &c. 

The  ores  smelted  in  the  Welsh  copper-works  may  be  divided 
into  several  classes,  according  to  their  richness  in  copper  and  their 
chemical  composition: 

1.  Copper  pyrites,  mixed  with  a  large  proportion  of  iron  pyrites, 
and  containing  but  a  small  quantity  of  oxidized  cupreous  sub- 
stances, and  accompanied  by  a  quartzose  and  earthy  gangue  of 
little  value.     They  contain  from  3  to  15  per  cent,  of  copper. 

2.  Copper  pyrites,  presenting  the  same  composition  as  the  fore- 
going, but  containing  from  15  to  25  per  cent,  of  copper. 

3.  Copper  pyrites,  containing  very  little  iron  pyrites  and 
matter  injurious  to  the  quality  of  the  copper,  but  in  larger  pro- 
portion of  oxidized  cupreous  substances,  and  the  gangue  of  which 
is  essentially  quartzose,  while  they  yield  from  12  to  20  per  cent, 
of  copper. 

4.  Ores  composed  principally  of  oxidized  copper-ores,  mixed 
with  pyritous  and  variegated  copper.  Their  gangue  is  quartzose, 
and  they  contain  from  25  to  45  per  cent,  of  copper. 

5.  Very  rich  oxidized  ores,  free  from  sulphides  and  injurious 
substances,  accompanied  by  a  quartzose  gangue,  and  containing 
from  60  to  80  per  cent,  of  copper,  in  the  metallic  state,  and  in 
that  of  suboxide  or  carbonate.  This  valuable  ore  is  imported 
chiefly  from  Chili. 

§  1072.  The  metallurgic  treatment  begins  with  ores  of  the  first 
class,  which  are  roasted  in  large  reverberatory  furnaces,  a  hori- 
zontal section  of  one  of  which  is  represented  in  fig.  571,  while 
fig.  570  shows  a  vertical  section  through  the  line  XY  in  fig.  571. 
The  hearth-sole  of  this  furnace  is  21  feet  in  length  by  21  in  width, 
and  made  of  refractory  bricks.  The  vaulted  roof  descends  rapidly 
from  the  grate  F  to  the  flue  R,  which  conveys  the  gases  into  a 
tall  chimney.  Four  doors  p  on  the  sides  of  the  furnace  serve  as 
working-holes,  while  an  opening  o  near  the  fire-bridge  or  altar, 
serves  for  the  introduction  of  a  certain  quantity  of  fresh  air, 
which  can  be  regulated  by  a  register.     The  hearth-sole  has  four 


METALLURGY   OF   COPPER. 


257 


Fig.  570. 


Fig.  571. 

rectangular  apertures  r  immediately  against  the  working-doors, 
serving  for  the  extraction  of  the  roasted  material,  and  which  are 
kept  closed  during  the  roasting,  by  cast-iron  plates.  In  the 
vaulted  roof  are  two  large  sheet-iron  hoppers,  through  which  the 
ore  to  be  roasted  is  introduced,  and  which  are  provided  with  re- 
gisters which  on  being  opened  allow  the  material  to  fall  on  the 
hearth-sole. 

The  combustible  employed  for  the  roasting  and  smelting  is  the 
Welsh  anthracite,  which,  as  it  burns  with  difficulty,  and  is  reduced 
to  dust  by  the  influence  of  heat,  cannot  furnish,  under  ordinary 
circumstances,  the  necessary  flame  to  heat  a  reverberatory  of 
21  feet  in  length  throughout  the  whole  of  its  extent ;  and  which, 
moreover,  cannot  be  burned  on  a  common  grate,  as  it  would  either 
fall  through  between  the  bars,  or  completely  fill  up  the  interstices. 
These  inconveniences  have  been  remedied  in  a  very  ingenious 
way,  by  which  the  manner  of  combustion  is  rendered  different 
from  that  generally  taking  place  in  reverberatories.  The  anthra- 
cite leaves,  on  being  burned  at  a  high  temperature,  an  ash  which  by 

Vol.  IL— 17 


258  COPPER. 

fusion  is  rendered  pasty,  and  constitutes  a  vitreous  slag,  a  pro- 
perty which  the  workmen  make  use  of  to  obtain  a  kind  of  earthy 
grate,  which  is  supported  only  by  a  few  bars  of  iron,  placed  wide 
apart.  Different-sized  fragments  of  this  slag  are  heaped  on  the 
bars,  until  the  layer  has  attained  the  thickness  of  about  1  or  IJ 
feet,  after  which  the  ash  of  the  fuel  burned  on  this  support  forms  a 
kind  of  slag,  which  encloses  numerous  pieces  of  coal ;  and  when 
the  slag,  owing  to  the  accumulation  of  a  fresh  quantity  above, 
becomes  further  removed  from  the  sonrce  of  heat,  it  cools,  and 
thus  forms  new  interstices,  large  enough  to  allow  the  current  of 
air  necessary  for  the  combustion  to  pass,  but  too  narrow  to  permit 
the  escape  of  powdered  fuel.  The  workman  contrives  to  keep  the 
thickness  of  the  layer  of  slag  uniform,  by  breaking  away  pieces 
from  below  from  time  to  time,  and  allowiug  them  to  fall  into  the 
ash-pit. 

About  J  of  its  weight  of  bituminous  coal,  in  small  pieces,  is 
added  to  the  anthracite,  in  order  that  the  former,  by  adhering  to 
the  anthracite,  and  swelling  by  the  heat,  may  mnintain  the  desired 
porosity  throughout  the  mass.  The  thickness  of  the  layer  of 
anthracite  is  about  1  foot  above  the  support  of  slags.  The  air 
traverses  the  layer  at  innumerable  points,  and  its  oxygen  is  en- 
tirely converted  into  carbonic  oxide,  which,  with  the  nitrogen, 
enters  the  furnace,  where  it  is  consumed  at  the  expense  of  the 
cold  air  introduced  through  the  aperture  o  and  through  the  small 
holes  in  the  working-doors.  The  whole  of  the  inside  of  the  furnace 
is  thus  filled  with  a  long  flame  of  carbonic  oxide,  which  burns  by 
contact  with  jets  of  air  containing  an  excess  of  oxygen,  and  which 
spread  out  like  a  sheet  on  the  floor  of  the  furnace,  because  they 
enter  through  holes  pierced  as  low  as  possible. 

The  ore  spread  out  on  the  floor  of  the  furnace  is  thus  constantly 
exposed  to  a  layer  of  oxidizing  air,  near  a  mass  of  combustible  gas 
which  is  consumed  slowly  on  its  under  surface,  thus  furnishing  the 
heat  necessary  to  the  roasting.  The  roasting  of  a  charge  of  ore 
is  commenced  immediately  after  the  former  charge  has  been  ex- 
tracted, without  allowing  the  furnace  to  rest.  Each  charge  consists 
of  3J  tons,  which  are  introduced  by  opening  the  valves  of  the 
hoppers  in  which  the  ore  has  been  previously  heaped ;  and  the 
workmen  immediately  spread  the  whole  charge  uniformly  over  the 
floor,  by  means  of  iron  rakes,  introduced  through  the  four  working- 
holes,  which  are  afterward  closed.  Every  2  hours  a  fresh  surface 
is  exposed  by  stirring  with  long  iron  poles  ;  and  the  whole  roasting 
lasts  12  hours.  In  order  to  extract  the  roasted  ore,  the  workmen 
open  the  working-doors,  and  lift  up  the  cast-iron  plates  which 
cover  the  openings  r,  into  which  they  rake  the  ore,  thus  causing  it 
to  pass  into  a  reservoir  U  under  the  furnace,  whence  other  work- 
men take  it,  after  it  has  cooled,  to  the  smelting-furnace. 

§  1073.    The  smelting-furnace  is   a  reverberatory,   fed   by  a 


METALLURGY   OF   COPPER. 


259 


mixture  of  f  of  anthracite  and  J  of  fine  pit-coal,  which  are  hurned 
on  a  bed  of  scoriae,  the  flame  being  produced  by  the  combustion 
of  the  carbonic  oxide  gas  which  forms  in  the  stratum  of  fuel.  By 
forcing  the  draught  a  higher  temperature  can  be  attained  than  in 
the  roasting-furnace.  Fig.  573  represents  a  horizontal,  and  fig. 
572  a  vertical  section  of  the  furnace.  The  hearth-sole  is  made 
of  scoriae,  having  a  depression  at  B,  constituting  a  kind  of  inner 
basin.     The  roasted  ores  are  smelted  by  adding  to  them  the  rich 


Fig.  572. 


Fig.  573. 

scoriae  arising  from  the  preceding  operations  and  unroasted  crude 
ores  belonging  to  the  third  class ;  a  certain  quantity  of  fluor-spar 
being  added,  to  give  fluidity  to  the  scoriae.  Influenced  by  the 
high  temperature,  the  oxides  and  sulphides  react  upon  each  other, 


260  COPPER. 

and  while  the  copper  combines  chiefly  with  the  sulphur,  the  iron 
selects  the  oxygen  and  passes  into  the  scoriae.  There  is,  more- 
over, a  reaction  between  the  oxygen  of  the  oxides  and  the  sulphur 
of  the  sulphides,  and,  consequently,  disengagement  of  sulphurous 
ficid.  The  operation  is  terminated  in  4  hours,  and  the  products 
of  smelting  are — a  matt  which  contains  the  greater  portion  of 
the  copper  combined  with  the  sulphur  and  a  certain  quantity  of 
sulphide  of  iron  ;  and  a  slag  highly  charged  with  oxide  of  iron, 
and  containing  many  fragments  of  quartz,  giving  it  a  muddy  con- 
sistence. The  workman  draws  out  the  slag,  by  means  of  his  rake, 
which  he  introduces  through  the  working-hole  p  near  the  flue,  and 
causes  the  slag  to  fall  into  rectangular  cavities  U,  made  in  the 
same,  the  shape  of  which  it  assumes.  At  the  same  time,  the 
smelter  opens  a  tap-hole  which  penetrates  to  the  bottom  of  the 
inner  reservoir  B,  when  the  matt  flows  in  a  small  stream,  and  is 
conducted  by  a  canal  ah  into  a  reservoir  R  filled  with  water,  when 
it  is  divided  into  very  small  grains. 

The, matt  arising  from  this  smelting  is  called  coarse  metal,  and 
contains  about  33  per  cent,  of  copper.  The  scoriae  are  broken  up, 
and  the  pieces  sorted ;  the  richest  being  kept  to  be  added  to  an- 
other smelting  of  roasted  ore,  while  the  remainder  is  rejected.* 

§  1074.  The  coarse  metal  is  then  roasted,  and  again  smelted. 
As  the  substance  has  lost  the  greater  part  of  its  sulphur  during 
the  roasting,  it  is  not  to  be  prevented  that  a  certain  portion  of 
copper  should  pass  into  the  slag,  in  the  state  of  oxide,  which  is, 
however,  of  no  importance,  as  the  scoriae  must  pass  through  other 
operations.  The  furnaces  for  roasting  the  coarse  metal  resemble 
those  for  roasting  the  ore,  and  the  process  is  similarly  conducted, 
with  the  exception  that  toward  the  close  of  the  operation  the  tem- 
perature is  raised  higher.  The  charge  is  4J  tons,  and  the  roasting 
lasts  36  hours,  during  which  time  the  material  must  be  frequently 
turned  with  a  rake.  The  roasted  substance  falls  through  the 
working-holes  r. 

The  roasted  coarse  metal  is  smelted  with  the  copper  ore  of  the 
fourth  class,  scoriae  very  rich  in  copper  arising  from  the  refining  of 
the  crude  copper,  as  will  be  hereafter  described,  and  the  scales 
from  the  rollers  being  added.  The  smelting-furnace  resembles 
that  for  smelting  roasted  ores,  but  the  hearth  has  no  inner  reser- 

*  The  rich  slag  is  separated  from  the  poorer  portions  in  an  ingenious  manner ; 
— The  slag  being  run  out  from  the  furnace  into  rectangular  cavities,  and  thus 
obtained  in  blocks  of  about  2^  feet  by  1^,  by  1  in  depth,  is  removed  before  it  has 
solidified,  but  not  before  an  outer  crust  of  a  certain  thickness  has  formed,  and 
set  up  in  a  slanting  position,  the  side  which  lay  undermost  in  the  pit,  and  which 
consequently  contains  all  the  grains  of  matt,  which,  by  their  greater  specific 
gravity,  occupy  the  lowest  position,  now  forming  the  upper  surface.  The  cake 
is  then  tapped  at  both  ends,  when  the  liquid  interior,  which  is  poor  in  copper, 
flowing  out,  leaves  a  hollow  box  of  slag,  the  upper  side  of  which  is  broken  out 
and  used,  while  the  other  parts  are  rejected. —  W.  L.  F. 


METALLURGY   OF   COPPER.  261 

voir.  The  fire  is  managed  in  the  same  way,  but  a  higher  tempe- 
rature is  produced,  and  the  operation  lasts  2  hours  longer.  It  is 
endeavoured  to  mix  the  materials  in  such  proportions  that  the 
sulphide  of  iron  in  the  smelting-bed  may  be  oxidized  bj  the  oxygen 
of  the  metallic  oxides,  and  pass  nearly  wholly  into  the  slag,  while 
the  copper  combines  with  the  superfluous  sulphur  to  form  the  matt. 
The  materials  react  upon  each  other  principally  after  fusion,  the 
reaction  being  almost  entirely  limited  to  a  double  decomposition 
between  the  sulphide  of  iron  and  the  oxide  of  copper,  while  very 
little  sulphurous  acid  is  disengaged.  Toward  the  close  of  the 
operation,  the  workman  stirs  the  mass  with  his  rod,  and  then  blows 
up  the  fire  in  order  to  properly  separate  them ;  after  which  he 
opens  the  tap-hole,  when  the  matt  runs  out  first,  and  is  received 
in  small  canals,  while  it  is  followed  by  the  fluid  slag.  The  latter 
is  separated  into  2  parts,  and  while  the  richest  are  reserved  for 
special  treatment,  which  yields  copper  of  the  first  quality,  the 
poorest  are  added  to  a  new  smelting  of  roasted  coarse  metal. 

The  matt  is  of  a  grayish-white  colour,  sometimes  slightly  bluish, 
and  is  caWed  fine  metal.  It  contains  about  73  per  cent,  of  copper, 
and  resembles  in  composition  the  sulphide  of  copper  Cu^S,  although 
it  is  rarely  entirely  free  from  sulphide  of  iron. 

The  rich  scoriae  arising  from  this  smelting  are  subjected,  as  we 
have  before  said,  to  a  special  treatment,  being  smelted  in  a  rever- 
beratory  furnace  with  a  certain  quantity  of  crude  ores  of  class 
No.  3,  which  contain  but  few  injurious  substances,  and  sulphur 
sufficient  to  transform  the  copper  of  the  smelting-bed  into  sulphide, 
which  passes  into  a  matt,  which  is  then  treated  like  the  ordinary 
matts. 

§  1075.  The  fine  metal  is  subjected  to  an  operation  of  which 
the  object  is  to  ultimately  expel,  in  the  form  of  sulphurous  acid, 
the  sulphur  which,  until  then,  had  been  preserved  as  an  agent  of 
concentration  for  the  copper,  and  to  drive  off",  at  the  same  time, 
either  by  gasification  by  the  assistance  of  oxygen  alone,  or  by 
scorification  by  the  united  aid  of  oxygen  and  silex,  the  foreign 
matters,  such  as  arsenic,  iron,  nickel,  cobalt,  tin,  &c.  This  is 
eff'ected  by  means  of  two  successive  reactions  which  take  place  in 
the  same  furnace :  first,  by  the  direct  action  of  the  air  on  the  mate- 
rial kept  at  a  temperature  near  its  fusing  point,  and  liquefying 
drop  by  drop,  which  operation  is  the  roasting  of  the  matt ;  and 
secondly,  by  the  reaction  of  the  oxide  of  copper,  which  is  formed  iu 
great  excess,  on  the  sulphides  which  are  not  decomposed  by  roasting. 
The  two  products  of  the  operation  are  coarse  or  blistered  copper^ 
which  is  purer  than  the  black  copper  of  the  continental  manufac- 
tories, and  a  very  rich  scoriae,  which  is  passed  through  the  smelting 
of  the  roasted  coarse  metal. 

This  process  is  carried  on  in  a  reverberatory  furnace  resembling 
other  smelting-furnaces,  but  having  a  side-door  through  which  the 


•262  COPPER. 

matt  is  charged.  The  matt  is  in  pretty  large  cakes,  which  are 
heaped  upon  the  hearth-sole,  while  the  rich  oxidized  ores  of  the 
fifth  class  are  added ;  the  charge  being  about  3  tons.  In  half  an 
hour  the  matt  begins  to  fuse,  and  the  first  liquid  drops  fall  upon 
the  sole,  which  process  lasts  about  4  hours ;  after  which  all  the 
materials  are  collected  on  the  sole  in  a  semi-doughy  state,  when  a 
strong V  bubbling  is  observed,  owing  to  the  disengagement  of  sul- 
phurous acid  produced  by  the  reaction  of  the  oxides  on  the 
sulphides.  The  temperature  is  allowed  to  fall,  so  as  to  prolong 
this  reaction  until  the  twelfth  hour,  at  which  period  the  disengage- 
ment of  sulphurous  acid  ceases,  because  the  temperature  has 
greatly  fallen.  The  fire  is  then  blown  up,  the  materials  become 
more  fluid,  and  the  reaction  is  completed.  In  18  hours,  reckon- 
ing from  the  commencement  of  the  operation,  the  material  contains 
but  little  sulphur,  and  the  smelter  then  raises  the  temperature  as 
high  as  possible,  in  order  to  assist  the  separation  of  the  substances. 
In  24  hours  he  skims  the  bath  with  his  rake,  and  runs  off  the 
coarse  copper  into  thin  cakes,  the  surface  of  which  is  covered 
with  blisters.     The  scoriae  contain  about  20  per  cent,  of  copper.* 

§  1076.  Blistered  copper  is  refined  without  the  admixture  of 
any  other  substance,  the  reagents  being  atmospheric  oxygen,  the 
siliceous  material  of  the  sole  and  sides  of  the  furnace,  and  that 
furnished  by  the  sand,  adhering  to  the  cakes  of  copper.  The 
refining-furnace  differs  but  slightly  from  other  smelting-furnaces, 
the  grate  being  merely  deeper,  in  order  to  accommodate  more 
fuel,  and  its  capacity  being  more  ample.  As  much  as  10  tons  of 
blistered  copper  are  charged  on  the  sole,  arranged  in  a  heap  rising 
as  high  as  the  vault  of  the  furnace.  The  process  lasts  24  hours, 
comprising  the  time  necessary  for  charging ;  but,  during  the  first 
18  hours,  the  workman  attends  only  to  the  fire.  The  copper 
melts  gradually  under  the  oxidizing  influence  of  the  air,  and  the 
oxide  of  copper  thus  formed  reacts,  either  immediately,  or  by 
combination  with  the  silex,  on  substances  more  oxidizable  than 
copper,  while  a  slag  is  formed,  into  which,  in  addition  to  suboxide 
of  copper  Cu^O  in  great  excess,  the  oxides  of  all  the  other  foreign 
metals  enter. 

In  22  hours,  the  copper  is  completely  freed  from  the  sulphur 
and  foreign  metals,  and  the  workman  then  skims  the  bath  and 
removes  all  the  scoriae  from  its  surface. 

The  copper  is  then  in  the  same  state  as  the  rosette  copper  of 
the  continental  foundries,  and  contains  a  certain  quantity  of 
oxide  of  copper,  which  destroys  its  malleability  ;  but  it  is  obtained 


*  In  most  of  the  Welsh  copper-works  the  fine  metal  is  subjected  to  a  third 
successive  roasting  and  smelting,  from  which  there  results  a  matt  which  in  this 
case  is  called  coarse  copper,  while  the  product  arising  from  the  operations  described 
in  this  section  is  called  blistered  copper. 


ALLOYS.  263 

directly  in  a  malleable  state  in  the  English  works  by  the  following 
process : — Four  or  five  shovelfuls  of  charcoal  are  thrown  on  the  bath, 
which  spread  immediately  over  its  whole  surface,  and  then  a  long 
stick  of  green  wood  is  plunged  into  the  bath.  In  consequence  of 
the  elevated  temperature  to  which  it  is  suddenly  subjected,  the  wood 
disengages  reducing  gases,  which  cause  the  metallic  bath  to  bubble 
strongly,  and  considerably  hasten  the  effect  which  would  be  ulti- 
mately produced  by  the  charcoal  on  the  surface.  After  twenty 
minutes  of  this  bubbling,  the  refiner  tests  the  copper  by  means  of  a 
small  mould  fastened  to  an  iron  rod :  he  dips  out  a  small  sample  of 
copper,  places  it  on  an  anvil,  and  tests  its  malleability  by  striking 
it  with  a  hammer.  When  he  is  satisfied  with  its  quality,  he  makes 
a  last  skimming  and  removes  the  balance  of  the  charcoal  and  the 
small  quantity  of  scoriae  which  has  formed,  and  then  runs  the  cop- 
per into  moulds.  v 

COPPER  OF  CEMENTATION. 

§  1077.  The  water  of  copper-mines,  or  that  flowing  from  the 
washing  of  roasted  copper-ores,  often  contains  a  large  quantity  of 
sulphate  of  copper,  which  is  separated  by  precipitating  it  by  metallic 
iron.  The  water  is  conveyed  into  large  basins,  in  which  iron  bars, 
plates  of  sheet-iron,  or  scrap-iron,  are  placed,  on  which  the  copper 
precipitates  in  the  form  of  a  crystalline  powder,  while  an  equiva- 
lent quantity  of  iron  dissolves.  The  copper  thus  obtained  is  called 
copper  of  cementation^  (cuivre  de  cement,)  and  is  refined  as  above 
described.* 

ALLOYS. 

Alloys  of  Copper  and  Zinc, 

§  1078.  Pure  copper  is  moulded  with  difficulty,  because  it  is  often 
filled  with  flaws  and  air-bubbles,  which  spoil  the  casting ;  but  by  al- 
loying it  with  a  certain  quantity  of  zinc,  a  metal  is  obtained  free 
from  this  objection,  harder,  and  more  easily  worked  in  the  lathe. 
Zinc  renders  the  colour  of  copper  more  pale ;  and  when  it  exists  in 
certain  proportions  in  the  alloy,  it  communicates  to  it  a  yellow  hue, 
resembling  that  of  gold  ;  but  when  present  in  larger  quantity,  the 
colour  is  a  bright  yellow ;  and  lastly,  when  the  zinc  predominates, 
the  alloy  becomes  of  a  grayish  white.  Various  names  are  given  to 
these  different  alloys.     The  one  most  used  in  the  arts  is  brass,  or 

*  A  similar  method  is  employed  at  Stadtberg,  in  Westphalia,  and  on  Anglesea, 
England,  to  extract  copper  from  carbonated  ores ;  the  latter  being  heaped  in  large 
pits,  and  covered  with  water,  while  sulphuric  acid,  generated  on  the  spot  by  burn- 
ing sulphur  and  a  small  quantity  of  nitre  in  a  small  furnace  with  a  closed  top,  is 
led  into  the  pits,  and  gradually  converts  the  copper  entirely  into  sulphate.  When 
the  mother  liquid  has  become  neutral,  it  is  pumped  off,  and  the  copper  is  precipi- 
tated from  it  by  scraps  of  iron. 

The  same  method  would  probably  apply  to  the  working  of  the  large  blocks  of 
copper  found  at  Lake  Superior. —  W.  L.  F. 


264 


COPPER. 


yellow  copper,  composed  of  about  f  of  copper  and  J  of  zinc.  Other 
alloys  are  also  known  in  commerce,  by  the  names  of  tombac,  similor 
or  Mannheim  gold ^  pinchbeck  or  prince's  metal,  (chrysocale,)  etc.: 
they  contain  in  addition  greater  or  less  quantities  of  tin. 

Tombac,  used  for  ornamental  objects  which  are  intended  to  be 
gilded,  contains  10  to  14  per  cent,  of  zinc ;  the  composition  of  Dutch 
gold,  whicji  can  be  hammered  into  very  thin  sheets,  being  nearly  the 
same.  Similor,  or  Mannheim  gold,  contains  10  to  12  per  cent,  of 
zinc,  and  6  to  8  of  tin ;  and  pinchbeck  contains  6  to  8  per  cent,  of 
zinc,  and  6  of  tin.  The  statues  in  the  park  of  Versailles  are  made 
of  the  following  alloy : 


Copper 
Zinc... 

Tin 

Lead ... 


91 
6 
2 
1 


The  alloys  of  copper  and  zinc  are  altered  by  a  high  temperature  and 
a  portion  of  the  zinc  is  volatilized.  If  brass  be  heated  in  a  brasqued 
crucible  in  a  forge-fire,  the  zinc  is  nearly  wholly  driven  off. 

Brass  is  made  by  melting  directly  copper  and  zinc ;  rosette  cop- 
per being  used,  fused  in  a  crucible,  and  run  into  water  to  granulate 
it.    The  zinc  is  broken  into  small  pieces.     The  fusion  is  effected  in 

earthen  crucibles  which  can  contain  from 
30  to  40  pounds  of  alloy,  the  metals  being 
introduced  in  the  proportion  of  f  of  cop- 
per and  J  of  zinc,  to  which  scraps  of  brass 
are  added.  A  certain  number  of  crucibles 
are  placed  in  an  egg-shaped  furnace  A, 
(fig.  574,)  lined  with  refractory  bricks, 
and  supported  by  a  brick  dome,  having 
apertures  through  which  the  flame  of  the 
fuel  passes,  the  grate  F  being  immediately 
beneath  the  dome.  The  crucibles  are  in- 
troduced through  the  upper  opening  of 
the  furnace,  which  is  covered,  during  the 
smelting,  by  a  lid  having  a  hole  0  for  the 
escape  of  the  gases.  A  register  beneath 
the  grate  regulates  the  draught,  and 
^^'       •  serves  for  the  extraction  of  the  crucibles. 

When  the  alloy  is  fused,  the  crucibles  are  removed  with  tongs,  and 
the  brass  run  into  clay  moulds ;  and,  sometimes  it  is  run  between 
two  very  smooth  slabs  of  granite,  kept  at  a  proper  distance  from 
each  other  by  iron  rods. 

Small  quantities  of  lead  and  tin  are  frequently  added  to  brass  to 
make  the  alloy  harder  and  more  easily  worked :  brass  which  con- 
tains no  lead  soon  chokes  a  file,  which  defect  is  remedied  by  the 
addition  of  1  or  2  hundredths  of  lead. 


ALLOYS.  265 

ALLOYS  OF  COPPER  AND  TIN. 

§  1079.  Copper  and  tin  mix  in  various  proportions,  and  form 
alloys  which  differ  vastly  in  appearance  and  physical  properties,  as 
tin  imparts  a  great  degree  of  hardness  to  copper.  Before  the  an- 
cients became  acquainted  with  iron  and  steel,  they  made  their  arms 
and  cutting  instruments  of  bronze,  composed  of  copper  and  tin. 

Copper  and  tin,  however,  combine  with  difficulty,  and  their  union 
is  never  very  perfect.  By  heating  their  alloys  gradually  and  slowly 
to  the  fusing  point,  a  large  portion  of  the  tin  will  separate  by  eli- 
quation,  which  effect  also  occurs  when  the  melted  alloys  solidify 
slowly,  causing  circumstances  of  serious  embarrassment  in  casting 
large  pieces. 

Different  names  are  given  to  the  alloys  of  copper  and  tin,  accord- 
ing to  their  composition  and  uses :  they  are  called  bronze  or  brass, 
cannon  metal,  bell  metal,  telescope-speculum  metal,  etc.  All  these 
alloys  have  one  remarkable  property :  they  become  hard  and,  fre- 
quently, brittle,  when  slowly  cooled ;  while  they  are,  on  the  contrary, 
malleable,  when  they  are  plunged  into  cold  water,  after  having  been 
heated  to  redness.  Tempering  produces,  therefore,  in  these  alloys 
an  effect  precisely  opposite  to  that  produced  qj|J  steel. 

When  alloys  of  copper  and  tin  are  melted  in  the  air,  the  tin  ox- 
idizes more  rapidly  than  the  copper,  and  pure  copper  may  be  sepa- 
rated by  continuing  the  roasting  for  a  sufficient  length  of  time. 

The  following  are  the  principal  alloys  of  copper  and  tin : 

Cannon  metal,  which  in  France  is  thus  composed : 

Copper 100  90.09 

Tin _11  0.91 

111  100.00 

Bell  metal,  which  contains 

Copper 78 

Tin _22 

100 
Cymbal  and  tam-tam  metal,  composed  of 

Copper 80 

Tin ^ 

100 
Telescope-speculum  metal,  made  of 

Copper 67 

Tin , J3 

100 
Bronze  for  medals  varies  slightly  in  its  composition,  and  generally 
consists  of 

Copper 95 

Tin 5 

Zinc some  thousandths. 


266  COPPER. 

Bronze  used  for  the  manufacture  of  ornamental  objects  generally 
contains  larger  quantities  of  zinc.  A  portion  of  the  small  French 
coin  is  made  of  alloys  of  copper  and  tin;  and  although  the  red 
*'sous"  consist  of  nearly  pure  copper,  the  yellow  "sous,"  coined 
under  the  Republic,  from  a  metal  obtained  by  melting  the  bells, 
contain  on  an  average  86  of  copper  and  14  of  tin.  Other  "sous" 
made  during  the  Republic,  with  refined  bell-metal,  are  composed  of 
96  of  copper  and  4  of  tin. 

Cannon-casting, 

§  1080.  Gun-metal  must  fulfil  several  important  conditions.  It 
should  be  very  tenacious,  that  the  pieces  may  not  burst  under  the 
enormous  pressure  caused  by  the  explosion  of  the  powder,  while  it 
should  be  sufiiciently  hard  not  to  be  injured  by  the  ball,  which 
strikes  the  sides  several  times  before  leaving  the  muzzle ;  and, 
lastly,  it  should  be  fusible,  because  large  guns  can  only  be  made 
by  casting. 

Copper  and  iron  are  the  only  metals  which  possess  sufficient 
tenacity ;  but  as  pure  iron  will  not  fuse  very  readily,  it  is  necessary 
to  substitute  for  it  cast-iron,  the  tenacity  of  which  is  much  inferior. 
Copper  possesses  great  tenacity,  but  is  too  soft;  and,  in  rapid  ser- 
vice, would  soon  be  so  battered  as  to  be  useless.  Recourse  must  then 
be  had  to  alloys  of  copper  with  other  metals ;  and  long  experience 
has  shown  that  alloys  of  copper  and  tin  are  the  most  suitable ;  but 
as,  while  tin  greatly  increases  the  hardness  of  copper,  it  diminishes 
its  tenacity,  it  becomes  necessary  to  stop  at  certain  proportions  of 
the  two  metals,  at  which  the  alloy  possesses  both  the  requisite  de- 
gree of  hardness  and  tenacity.  These  proportions,  which  have  been 
determined  by  numerous  experiments,  made  at  various  times  and  in 
different  countries,  have  been  fixed  at  11  of  tin  for  100  of  copper. 
It  has,  however,  been  ascertained,  that  for  pieces  of  a  calibre  below 
8,  an  alloy  of  8  or  9  per  cent,  of  tin  is  preferable.  Many  experi- 
ments have  also  been  made  to  ascertain  if  the  alloy  could  not  be 
improved  by  the  addition  of  other  metals,  as  zinc,  iron,  or  lead ;  but 
these  complicated  alloys  have  all  been  rejected,  on  account  of  the 
great  variation  of  their  results ;  and  pieces  were  frequently  ren- 
dered useless  in  consequence  of  the  difficulty  of  obtaining  such 
alloys  homogeneous  and  of  uniform  composition. 

The  use  of  cast-iron  for  the  manufacture  of  cannon  is  long  subse- 
quent to  that  of  brass.  As  it  is  cheaper,  it  might  be  very  advan- 
tageously substituted  for  bronze,  but  it  is  very  brittle,  and  pieces  of 
the  same  calibre  must  be  much  thicker  than  of  the  latter  metal, 
thus  becoming  too  ponderous  for  field-service.  They  are  well  adapted 
to  stationary  batteries,  fortifications,  coast  defence,  and  ships  of  war. 
Cast-iron  guns  ring  much  less  than  those  of  bronze,  and,  for  this 
reason,  are  preferable  on  board  of  ships,  where  brass  pieces,  on  the 
lower-deck  batteries,  would  make  a  noise  insupportable  by  the  gun- 


ALLOYS  OF  COPPER. 


26T 


ners.  Very  soft  cast-iron,  made  with  charcoal,  should  alone  be  used 
for  artillery ;  and  some  of  the  Swedish  iron  is  highly  valued  for  this 
purpose. 

The  furnaces  in  which  bronze  is  melted  should  contain  no  oxidiz- 
ing gases,  and  the  atmospheric  air  traversing  them  should  be  de- 
prived by  combustion,  as  far  as  possible,  of  its  oxygen,  because  the 
tin,  which  is  more  oxidizable  than  copper,  would  constantly  separate 
from  the  alloy  in  the  form  of  oxide,  and  the  composition  of  the 
bronze,  at  the  time  of  casting,  would  not  be  known  with  certainty. 

Figs.  575  and  576  represent  a  melting-furnace,  used  in  the 
cannon-foundry  at  Toulouse.  It  is  a  circular  reverberatory  furnace 
,A,  with  a  surbased  dome,  heated  by  the  grate  F,  on  which  small 
billets  of  wood  are  burned.     The  wood  being  charged  through  the 

Fig.  575. 


opening  o,  a  thick  layer  of  fuel  is  heaped  on  the  grate,  in  order  that 
the  atmospheric  air,  which  does  not  enter  the  furnace  until  it  has 
passed  through  the  fuel,  shall  be  completely  deprived  of  its  oxygen. 
The  draught  is  regulated  by  4  elongated  working-holes  A,  A,  arising 


268  COPPER. 

from  the  hearth-sole  and  terminating  at  the  vent-holes  eg^  eg^  which 
open  into  the  chimney  C,  by  means  of  which  arrangement  the  flame 
is  obliged  to  spread  over  the  metallic  bath  which  covers  the  hearth- 
sole.  Near  the  furnace  are  cavities  M,  M',  lined  with  cement  to 
preserve  them  from  dampness,  and  in  which  the  moulds  are  placed, 
and  kept  firm  by  heaping  earth  around  them.  The  moulds,  which 
are  made  of  cky,  cow's-hair,  and  horse-dung,  intimately  mixed,  are 
fashioned  on  a  model  in  relief,  partly  of  earth  and  partly  of  plaster, 
which  is  destroyed  when  the  mould  is  finished,  and  strengthened  by 
iron  bands  or  loops.  Above  the  mouth  of  the  gun  is  a  prolongation, 
called  the  masselotte,  or  lump,  the  use  of  which  will  soon  be  ex- 
plained. The  moulds,  after  being  baked  at  a  high  temperature,  so 
as  to  dry  them  as  much  as  possible,  are  fixed  in  their  places,  the 
breech  being  downward.  Between  the  tap-hole  i  and  the  moulds, 
canals  are  made  which  convey  the  liquid  bronze  into  each  mould ; 
and  above  is  a  railway  ab,  with  a  car  R,  containing  a  capstan,  by 
means  of  which  the  moulds,  when  filled,  can  be  lifted  out  and  carried 
away. 

Moulding-sand,  so  well  adapted  to  the  moulding  of  cast-iron  and 
other  metals,  has  been  substituted  for  the  earth  with  which  the 
moulds  are  made,  but  never  with  success,  as  the  walls  of  the  sand- 
mould  are  too  compact  and  too  impervious  to  gases.  Now,  imme- 
diately after  the  casting  of  bronze,  the  metal  disengages  num*erous 
gaseous  bubbles,  which  pass  through  the  porous  walls  of  the  mould, 
and  present  less  resistance  than  the  high  column  of  melted  metal ; 
while  in  the  sand-moulds,  the  gases  not  being  able  to  escape  through 
the  sides,  produce  a  constant  bubbling  in  the  mass,  giving  rise  to 
numerous  flaws,  and  assisting  the  separation,  by  eliquation,  of  the 
tin,  or  alloys  rich  in  tin. 

The  charge  of  a  furnace  is  composed  of  old  brass,  chiefly  con- 
demned cannons,  and  masselottes  taken  from  pieces  previously  cast, 
with  brass  turnings  taken  from  the  lathe  or  the  boring-machine, 
and  a  certain  quantity  of  new  metals,  copper  and  tin,  besides  white 
metals,  or  alloys  very  rich  in  tin,  which  separate  by  eliquation  in 
the  moulds.  The  proportions  of  copper  and  tin  in  the  several  com- 
ponents being  determined  by  analysis,  they  are  mixed  in  the  pro- 
portion of  100  copper  to  13  or  14  tin,  which  is  reduced  by  oxidation 
of  tin  in  the  furnace  to  the  normal  proportion  of  100  :  11. 

The  condemned  cannons  and  mas'selottes  are  laid  on  the  hearth- 
sole,  near  the  bridge,  where  the  temperature  is  highest ;  while  the 
copper,  which  should  be  very  pure,  in  bars,  and  the  turnings,  are 
placed  thereon,  the  white  metals  and  tin  being  added  at  a  later 
period.  In  6  or  7  hours  the  mass  is  almost  entirely  fused,  and  the 
flame  escapes  by  every  avenue.  The  smelter  first  stirs  the  material 
with  sticks  of  very  dry  wood,  and  draws  the  portions  which  a¥e  not 
melted  toward  the  bridge ;  after  which  he  completes  the  charge  by 
adding  the  white  metals  and  tin,  which  he  runs  in  the  form  of  pigs 


TINNING   OF   COPPER   AND    BRASS.  269 

into  different  parts  of  the  bath.  He  stirs  it  a  second  time,  in  order 
to  render  it  homogeneous,  and,  after  skimming  off  the  superabun- 
dant scoriae,  closes  the  doors  of  the  furnace  and  blows  up  the  fire,  to 
bring  the  alloy  to  a  proper  state  of  liquidity ;  stirs  and  skims  it  a 
third  time,  and  then  opens  the  tap-hole.  Other  workmen  direct  the 
melted  metal  into  each  mould. 

A  remarkable  phenomenon  ensues  in  a  few  moments  after  the 
casting.  A  bubbling  takes  place  in  the  upper  part  of  the  mould, 
proportioned  to  the  size  of  the  piece  and  the  elevation  of  tem- 
perature, and  a  portion  of  the  bronze  rises  in  the  form  of  a  mush- 
room, being  an  alloy  much  richer  in  tin  than  the  cast  metal.  *  A 
partial  eliquation  therefore  takes  place  during  the  cooling,  which 
causes  the  separation  of  an  alloy  more  fusible  and  containing  more 
tin.  The  composition  of  the  piece  itself  is  not  uniform,  as  the  pro- 
portion of  tin  diminishes  from  the  breech  to  the  upper  part  of  the 
masselotte.  The  intention  of  the  masselottes  is,  not  only  to  exert 
considerable  hydrostatic  pressure  on  the  lower  strata  of  the  piece, 
but  also  to  furnish  metal  necessary  to  compensate  for  the  contrac- 
ti<m  of  the  metal  by  cooling  and  its  loss  of  substance  by  eliquation. 

Twelve  hours  after  the  casting,  the  earth  is  cleared  away  in  order 
to  hasten  the  cooling  of  the  moulds  ;  and  the  latter  are  removed  after 
48  hours,  broken,  and  the  cast  guns  carried  to  the  boring  and  turn- 
ing sbops. 

When  the  surface  of  the  piece  is  turned,  and  it  has  been  bored  to 
a  certain  point,  it  is  examined  to  ascertain  if  it  be  free  from  such 
defects  as  would  render  it  unserviceable.  Such  defects  are  various, 
and  called  by  different  names ;  but  they  are  nearly  all  produced  by 
eliquation  of  the  tin  or  very  fusible  alloys. 

Flaws,  or  bubbles,  are  cavities  with  smooth  surfaces,  produced  by 
bubbles  of  gas  which  have  been  unable  to  escape  ;  while  Jioneyeombs 
are  cavities  with  rough  surfaces,  arising  from  irregular  distribution 
of  the  materials  or  badly  proportioned  alloy ;  and  worm-holes  are 
similar  but  smaller  cavities.  Cendrures  are  owing  to  impurities  in 
the  alloy,  remaining  in  the  metal,  or  detached  from  the  sides  of  the 
mould ;  and  tin-spots  are  produced  by  small,  very  hard  masses  of  an 
alloy  containing  20  or  25  per  cent,  of  tin,  which  became  separated 
by  eliquation,  and  were  unable  to  ascend  as  far  as  the  masselotte. 
Blasts,  or  cracks,  (sifilets,)  which  are  longitudinal  or  traverse  grooves, 
sometimes  extending  through  the  whole  thickness  of  the  piece,  are 
likewise  owing  to  a  separation  of  the  tin. 

If  the  piece  is  found  to  be  perfect,  the  boring  and  turning  are 
completed,  and  it  is  subsequently  examined  and  proved  according 
to  the  regulations  of  the  service. 

TINNING  OF  COPPER  AND  BRASS. 

§  1081.  The  use  of  copper  and  brass  for  culinary  purposes  is 
dangerous,  on  account  of  the  ease  with  which  copper,  on  oxidizing 


270  COPPER. 

by  contact  -with  the  air  and  acid  substances,  forms  very  poisonous 
salts,  unless  the  vessels  are  lin^d  with  a  coat  of  tin,  which  prevents 
the  liquids  from  coming  in  contact  with  the  copper.  The  tinning 
of  copper  is  effected  by  cleansing  the  pieces  with  chlorohydrate  of 
ammonia,  and  spreading,  with  a  piece  of  cloth  or  tow,  melted  tin 
over  their  surface  when  properly  heated.  The  tin  thus  adheres  to 
the  copper  and  covers  it  completely. 

Pins  are  made  of  brass  wire,  and  whitened  by  being  covered  with 
a  thin  coat  of  tin  by  the  humid  way.  The  pins  are  first  cleansed 
by  heating  them  in  a  solution  of  cream  of  tartar,  and  then  placed 
in  k  copper  basin  with  a  solution  of  cream  of  tartar  and  tin.  The 
liquid  is  boiled  for  about  one  hour,  when  the  tin  dissolves  in  the 
cream  of  tartar  with  disengagement  of  hydrogen  gas,  and  is  pre- 
cipitated on  the  brass  of  the  pins,  covering  them  with  a  very  thin 
pellicle  of  metal. 

ANALYSIS  OF  BRASS  AND  BRONZE. 

§  1082.  We  have  said  {§  1078)  that  brass  is  composed  of  copper 
and  zinc,  but  that  a  small  quantity  of  lead  and  tin  is  usually  added, 
to  make  the  alloy  more  easy  to  work.  Cannon-metal  is  composed 
of  copper  and  tin  alone,  but  the  metal  used  for  ornamental  objects 
and  medals  contains  in  addition  zinc  and  frequently  lead.  We 
shall  therefore  consider  the  more  general  case,  and  suppose  that  the 
alloy  to  be  analyzed  contains  copper,  zinc,  tin,  and  lead. 

The  alloy  is  dissolved  in  pure  nitric  acid,  which  converts  the  tin 
into  insoluble  metastannic  acid  ;  while  the  copper,  zinc,  and  lead  are 
transformed  into  soluble  nitrates.  After  treatment  with  water,  the 
metastannic  acid  is  collected  on  a  filter ;  and  the  weight  of  tin  in 
the  alloy  is  inferred  from  that  of  the  metastannic  acid. 

The  filtered  liquid  is  evaporated  to  dryness,  and  sulphuric  acid 
added,  which  converts  the  nitrates  into  sulphates;  and  then,  after 
having  driven  off  the  nitric  acid  by  heat,  the  residue  is  dissolved  in 
water,  when  the  sulphate  of  lead,  being  insoluble,  is  separated  on  a 
filter  and  weighed  after  calcination,  the  quantity  of  lead  in  the  alloy 
being  deduced  from  its  weight. 

The  liquor  is  then  supersaturated  with  sulf  hydric  acid  gas,  which 
precipitates  the  copper  entirely  in  the  state  of  sulphide,  while  the 
zinc  remains  in  solution,  because  it  is  not  precipitated  by  sulf  hydric 
acid  in  a  liquid  containing  an  excess  of  acid.  The  sulphide  of  cop- 
per is  treated  as  described,  (§  1059,)  and  the  copper  is  determined 
in  the  state  of  oxide,  by  means  of  the  standard  solution  of  sulphide 
of  sodium. 

The  liquid  is  boiled  in  order  to  drive  off  the  sulf  hydric  acid,  and 
"arbonate  of  soda  is  added,  which  precipitates  the  zinc  in  the  state 
of  hydrocarbonate,  which  is  collected  on  a  filter  and  weighed  after 
calcination,  the  zinc  being  thus  determined  in  the  state  of  oxide. 
In  very  accurate  analyses,  it  is  proper  to  ascertain  if  the  filtered 


MERCURY.  271 

liquid  does  not  still  contain  a  small  quantity  of  zinc,  which  often 
happens,  because,  when  acting  on  the  alloy  by  nitric  acid,  ammo- 
niacal  salts  are  frequently  formed,  which  prevent  the  complete  pre- 
cipitation of  the  zinc  by  the  alkaline  carbonates.  In  order  to  be 
sure  of  this,  the  liquid  is  evaporated  to  dryness  and  the  residue  cal- 
cined to  drive  off  the  ammonia,  when,  by  treatment  with  water,  the 
zinc  remains  in  the  state  of  carbonate. 

It  frequently  happens  that  brass  or  bronze  contains  a  small 
quanty  of  iron,  introduced  by  the  fact  of  impure  metals  being  used 
in  making  the  alloy.  In  this  case,  after  having  boiled  the  liquid, 
the  copper  of  which  is  precipitated  by  sulfhydric  acid,  a  few  pinches 
of  chlorate  of  potassa  must  be  thrown  into  the  boiling  liquid,  or  a 
current  of  chlorine  passed  through  the  solution,  in  order  to  convert 
the  iron  into  the  sesquioxide.  The  liquid  is  saturated  by  ammonia, 
and  the  succinate  of  ammonia,  which  precipitates  the  iron  from  it,  is 
added.  The  filtered  liquid  which  contains  the  zinc,  contains  too  large 
a  proportion  of  ammoniacal  salts  to  allow  this  metal  to  be  imme- 
diately precipitated  by  carbonate  of  soda,  for  which  reason  the  liquid 
must  be  evaporated,  the  carbonate  of  soda  added,  and  the  substance 
be  perfectly  dried.  By  treating  it  with  water  the  hydrocarbonate  is 
wholly  precipitated. 


MERCURY. 

Equivalent  =  109  (1250.0 ;  0  =  100). 

§  1083.  Mercury  is  the  only  metal  which  is  liquid  at  the  ordinary 
temperature.  It  congeals  at  temperatures  below  40° ;  and  then 
forms  a  white,  very  brilliant  metal,  resembling  silver.  Solid  mer- 
cury is  malleable,  and  flattens  under  the  hammer,  so  that  medals 
may  be  struck  of  it.  In  the  polar  regions,  mercury  frequently  con- 
geals from  the  intense  degree  of  cold  ;  and  it  may  be  solidified  in  a 
refrigerating  mixture  of  solid  carbonic  acid  and  ether,  (§  254,)  or  in 
a  mixture  of  ice  and  chloride  of  calcium,  (§  374).  It  is  sufficient  to 
use  finely  pounded  ice,  cooled  below  32°,  and  small  crystalline 
grains  of  chloride  of  calcium,  such  as  are  obtained  by  crystallizing 
a  concentrated  hot  solution,  and  disturbing  the  crystallization.  By 
operating  on  a  moderate  quantity  of  mercury^  placed  in  a  large 
crucible,  which  is  gradually  cooled  in  the  refrigerating  mixture,  the 
metal  may  be  obtained  crystallized,  if,  as  soon  as  a  thin  crust  of 
solid  mercury  forms  on  the  sides  of  the  crucible,  the  liquid  portion 
is  poured  off;  when  brilliant  regular  octohedrons,  often  clearly  ter- 
minated, are  found  on  the  inside. 

The  density  of  solid  mercury  has  been  found  to  be  14.4,  at  a  tem- 
perature a  little  below  that  of  its  congelation ;  while  the  specific 


272  MERCURY. 

gravity  of  the  metal  in  the  liquid  state  is  13.596,  at  a  temperature 
of  32°.  Mercury  expands,  while  passing  from  32°  to  212°,  by  a 
fraction  0.018153  of  its  volume  at  32°,  or  by  ~  for  every  degree, 
which  is  equal  to  ~  for  each  centigrade  degree.  It  boils  at  662° 
of  the  air  thermometer,  and  the  density  of  its  vapour  is  6976.  The 
tension  of  the  vapour  of  mercury  is  appreciable  at  the  ordinary  tem- 
perature, although  it  is  too  feeble  to  be  accurately  measured ;  but 
the  volatility  of  mercury  is  placed  beyond  doubt  by  the  action  which 
the  metal  exerts,  at  the  ordinary  temperature  and  distance,  on  da- 
guerreotype plates  which  have  been  exposed  to  iodine  and  affected 
by  light.  The  globules  of  mercury  which  condense  in  the  upper 
part  of  the  vacuum  of  barometers,  also  attest  its  volatility.  At 
the  temperature  of  212°  fhe  tension  of  mercurial  vapour  is  about  J 
millimetre.  .  By  boiling  the  metal  with  water,  in  a  glass  retort,  a 
considerable  quantity  of  mercury  is  distilled.  Below  32°  the  vola- 
tilization of  mercury  is  nearly  inappreciable,  and  its  vapour  appears 
to  no  longer  possess  the  expansive  force  characterizing  elastic  fluids. 
In  fact,  on  suspending  a  leaf  of  gold  in  a  bottle  containing  a  small 
quantity  of  mercury,  and  allowing  the  bottle  to  rest  for  several 
days  in  a  low  temperature,  the  leaf  is  whitened  by  the  mercurial 
vapour  only  to  the  height  of  a  few  centimetres  above  the  surface  of 
the  bath,  the  upper  portion  always  retaining  its  characteristic  yel- 
low colour. 

§  1084.  The  mercury  of  commerce  is  nearly  pure  when  it  comes 
directly  from  the  furnace,  while  that  used  in  the  laboratory  almost 
always  contains  small  quantities  of  foreign  metals  and  oxide  of  mer- 
cury in  solution.  After  some  time,  especially  in  summer,  mercury 
absorbs  oxygen  from  the  air ;  and  when  the  metal  is  agitated,  the 
oxide  is  scattered  through  the  whole  mass,  but,  when  at  rest,  rises 
to  the  surface  and  forms  a  gray  pellicle.  When  mercury  is  pure,  it 
adheres  neither  to  glass  nor  to  porcelain,  but  flows  freely  over  its 
surface ;  but  when  it  contains  foreign  matters,  or  even  oxide  of 
mercury,  it  adheres  remarkably,  and  on  rolling  it  slowly  over  a 
glass  plate,  does  not  form  spherical  globules,  but  drops  elongated 
in  the 'shape  of  tears,  which  are  wrinkled  on  their  surface,  and  leave 
a  gray  pellicle  adhering  to  the  glass :  the  mercury  is  then  said  to 
leave  a  tail,  (faire  une  queue.)  The  mercury  of  the  laboratory 
cistern  may  be  greatly  purified  by  passing  over  the  surface  of  the 
bath,  a  very  dry,  large  glass  tube,  to  which  the  superficial  pellicle 
of  gray  oxide  adheres,  and  may  thus  be  removed. 

Mercury  is  purified,  in  the  first  place,  by  distillation,  which  opera- 
tion is  easily  effected  in  the  cast-iron  bottles  in  which  it  is  usually 
transported.  One  of  these  bottles  being  half-filled  with  mercury, 
and  a  curved  gun-barrel  abo  introduced  into  its  mouth,  the  bottle  is 
arranged  in  a  furnace,  as  represented  in  fig.  577,  and  a  tube  cd, 
formed  of  several  layers  of  linen  and  dipping  into  a  pan  of  water, 
is  attached  to  the  gun-barrel.     The  end  of  the  latter  and  the  linen 


MERCURY. 


273 


are  kept  wet  by  a  stream  of  water  flowing  constantly ;  and,  lastly, 
the  bottle  is  heated  to  the  boiling  point  of  mercury,  when  ebullition' 
takes  place  with  violent  bubbling,  and  the  mercury  distils  over, 

leaving  the  greater  pro- 
portion of  the  foreign 
metals  in  the  bottle.  A 
considerable  quantity, 
however,  is  carried  over 
by  distillation,  and  it 
cannot  be  expected  to 
obtain  pure  mercury 
from  a  single  operation. 
The  distilled  mercury  is 
placed  in  a  cast-iron  re- 
ceiver, ordinary  nitric 
acid  diluted  with  twice 
its  weight  of  water  is 
poured  upon  it,  and  it  is  heated  to  50°  or  60° ;  when  protonitrate  of 
mercury  is  formed,  which,  together  with  the  free  acid,  react  on  the 
foreign  metals,  while  the  latter  dissolve  in  the  acid  liquid,  the  oxide 
of  mercury  which  may  have  formed  by  contact  with  the  air,  during 
distillation,  also  entering  into  solution.  The  acid  is  allowed  to  act 
for  at  least  24  hours,  stirring  the  mass  from  time  to  time;  and 
lastly,  it  is  gently  heated  to  drive  off  the  water,  when  the  nitrate 
of  mercury  remains  in  the  form  of  a  crystalline  crust,  which  is  re- 
moved, and  from  which  the  metallic  mercury  can  be  extracted. 
The  mercury  is  washed  rapidly  in  water,  and  dried,  first  with  tissue 
paper,  and  then  under  a  bell-glass  with  quicklime. 

The  distillation  of  mercury  frees  it  so  imperfectly  from  foreign 
substances  that  it  is  rarely  useful,  and  it  is  in  all  cases  preferable 
to  treat  the  impure  mercury  directly  with  nitric  acid  and  repeat  the 
operation  as  often  as  may  be  necessary. 

When  mercury  merely  contains  oxide,  it  is  sufficient  to  place  it  in 
a  bottle  with  a  small  quantity  of  concentrated  sulphuric  acid,  and 
to  shake  it  from  time  to  time,  in  order  to  bring  all  its  parts  into  con- 
tact with  the  acid.  In  2  or  3  days  the  acid  is  poured  off  and  the 
mercury  washed. 

After  a  time,  mercury  exerts  a  deleterious  action  on  the  animal 
economy.  Workmen  in  this  metal,  or  those  who  are  frequently 
exposed  to  its  vapours,  are  liable  to  paralysis  and  copious  salivation. 
We  have  mentioned  that  mercury  absorbs,  after  some  time,  a 
small  quantity  of  oxygen  from  the  air,  even  at  the  ordinary  tem- 
perature ;  but  the  oxide,  mixed  with  or  dissolved  in  a  large  quantity 
of  free  metal,  forms  a  gray  pellicle,  which  adheres  to  glass,  or  the 
surface  of  the  bath.  In  order  to  ascertain  that  the  pellicle  contains 
oxide  of  mercury,  it  suffices  to  distil  a  certain  quantity  of  it  in  a 
current  of  nitrogen  gas,  when  it  deposits  a  small  crystalline  residue 
Vol.  II.— 18 


274  MERCURY. 

of  red  oxide  of  mercury.  Oxidation  advances  more  rapidly  at  the 
boiling  point  of  mercury ;  and  by  boiling  the  metal  slowly  in  a  long- 
necked  balloon,  into  which  the  air  enters  freely,  a  considerable 
quantity  of  oxide  of  mercury  can  be  produced  in  the  form  of  small, 
red  prismatic  crystals.  This  oxide  was  originally  prepared  in  this 
way,  and  called  by  the  old  chemists  precipitate  per  se  ;  and  it  has 
already  been  shown  (note  to  §  95,  vol.  i.)  that  by  keeping  mercury 
for  a  very  long  time  at  a  temperature  approaching  its  boiling  point, 
it  is  possible  to  determine  by  approximation  the  composition  of  at- 
mospheric air. 

Concentrated  chlorohydric  acid  does  not  sensibly  act  on  mercury 
even  when  hot,  and  dilute  sulphuric  acid  does  not  attack  it ;  while 
concentrated  hot  sulphuric  acid  soon  transforms  it*  into  sulphate  of 
mercury,  with  disengagement  of  sulphurous  acid. 

Nitric  acid,  even  when  cold,  attacks  mercury  when  the  acid  is 
dilute,  while  deutoxide  of  nitrogen  is  disengaged. 

COMPOUNDS  OF  MERCURY  WITH  OXYGEN. 

§  1085.  Two  compounds  of  mercury  with  oxygen  are  known :  the 
less  oxygenated,  to  which  we  shall  give  the  name  of  black-oxide,  or 
suboxide  of  mercury ^^  corresponding  to  the  formula  Hg^O  ;  while 
the  formula  of  the  more  oxygenated,  which  we  shall  call  red^  or 
protoxide  of  mercury,  is  HgO. 

Suboxide  of  mercury  HggO  is  not  a  very  fixed  compound,  but 
forms  with  the  acids  well-defined  salts,  which  crystallize  readily.  It 
is  obtained  by  precipitating  one  of  its  salts,  the  nitrate,  for  example, 
by  caustic  potassa,  when  a  black  precipitate  is  formed,  which  de- 
composes spontaneously  into  the  red  oxide  and  metallic  mercury. 
By  grinding  the  powder  in  a  mortar  for  some  time,  small  globules 
of  metallic  mercury  will  be  found,  which  decomposition  takes  place 
much  more  rapidly  at  the  temperature  of  212°,  or  even  at  the  or- 
dinary temperature,  when  assisted  by  solar  light. 

The  protoxide  or  red  oxide  of  mercury  HgO  is  formed  when  mer- 
cury is  exposed  to  the  air  at  a  high  temperature,  which  process, 
however,  yields  only  a  small  quantity ;  and  it  is  more  easily  ob- 
tained by  decomposing  nitrate  of  mercury  by  moderate  heat.  The 
same  oxide  is  obtained  by  calcining  the  subnitrate  Hg20,N05  or 
the  protonitrate  HgO,N05 ;  but  the  product  diff'ers  slightly  in  ap- 
pearance, according  to  the  nature  of  the  nitrate  from  which  it  was 
formed.  Thus,  the  nitrate  HgOjNO^  in  small  crystals,  produces 
crystalline  oxide  of  mercury  of  a  brickdust  colour,  while  the  nitrate 
HgjjOjNOg  yields  an  orange-yellow  oxide. 

By  adding  potassa  to  a  solution  of  protonitrate  of  mercury 

*  The  name  of  protoxide  is  sometimes  given  to  the  suboxide  of  mercury  Hg^O, 
and  that  of  binoxide  to  the  protoxide  HgO :  we  shall  not  adopt  this  nomenclature, 
for  the  reasons  given,  (§  1040,)  because  it  does  not  agree  with  our  chemical 
formulae. 


SALTS  OF  BLACK  OXIDE.  275 

HgOjNOg,  a  yellow  precipitate  of  anhydrous  oxide  of  mercury  is 
obtained. 

The  red  and  the  yellow  oxide  of  mercury  constitute  two  isomeric 
states,  which  afe  evinced  in  some  chemical  reactions.  The  non- 
calcined  yellow  oxide,  that  is,  the  oxide  obtained  by  the  humid  way, 
is  more  easily  attacked  by  chlorine  than  the  red  oxide,  and,  when 
cold,  combines  with  oxalic  acid,  which  under  the  same  circumstances 
exerts  no  action  on  the  red  oxide. 

SALTS  FORMED  BY  THE  SUBOXIDE  OF  MERCURY,  Hg,0. 

§  1086.  The  suboxide  of  mercury  Hg^O  forms  with  the  majority 
of  the  acids  well-defined  salts,  which  are  often  called  salts  of  mer- 
cury at  the  minimum.  The  subnitrate  is  obtained  by  dissolving 
cold  mercury  in  dilute  nitric  acid,  taking  care  to  keep  the  mercury 
in  excess;  and  the  subsulphate  is  prepared  by  heating  mercury 
in  excess  with  concentrated  sulphuric  acid.  Many  salts  of  mercury 
at  the  minimum  are  prepared  by  double  decomposition. 

Suboxide  of  mercury  forms  several  salts  with  the  same  acid ;  and 
the  neutral  salts  are  colourless  when  the  acid  is  free  from  colour, 
while  the  basic  salts  are  yellow.  The  latter  are  insoluble  in  water, 
while  the  majority  of  the  neutral  salts  produce  colourless  solutions. 
Some  neutral  salts  of  the  suboxide  are  decomposed  by  water  into 
basic  salts  which  are  precipitated,  and  salts  with  excess  of  acid 
which  dissolve.     These  salts  are  known  by  the  following  characters : 

The  caustic  alkalies  and  ammonia  throw  down  a  black  precipitate, 
insoluble  in  an  excess  of  reagent,  and  which,  when  slightly  heated, 
yields  globules  of  metallic  mercury.  If  it  be  rubbed  with  a  blade 
of  very  bright  copper,  the  latter  becomes  white  by  being  alloyed 
with  the  mercury.  The  alkaline  carbonates  yield  dirty-yellow  pre- 
cipitates which  soon  turn  black. 

Prussiate  of  potash  throws  down  a  white  precipitate. 

Sulf  hydric  acid  gives  a  black  precipitate,  and  the  alkaline  sulf- 
hydrates  yield  the  same  precipitate,  which  does  not  dissolve  in  an 
excess  of  the  reagent. 

Chlorohydric  acid  and  the  chlorides  throw  down  a  white  precipi- 
tate of  chloride  of  mercury  Hg^Cl,  perfectly  insoluble  in  water  and 
dilute  acids. 

Iodide  of  potassium  gives  a  greenish-yellow  precipitate,  which  dis- 
solves in  an  excess  of  reagent. 

Iron,  zinc,  and  copper  precipitate  mercury  from  its  solutions,  in 
the  state  of  an  amalgam. 

Suhnitrates  of  Mercury, 

§  1087.  Suboxide  of  mercury  forms  several  compounds  with  nitric 
acid.  The  neutral  nitrate  is  obtained  by  pouring  an  excess  of  dilute 
nitric  acid  on  metallic  mercury,  and  allowing  the  action  to  ensue  in 
the  cold ;  when  the  mercury  oxidizes  at  the  expense  of  the  oxygen 


276  MERCURY. 

of  a  portion  of  the  nitric  acid,  and,  after  some  time,  large,  colour- 
less crystals  of  subnitrate  separate,  the  formula  of  which  is  HggOjNOg 
4-2HO,  and  which  dissolve  in  a  small  quantity  of  cold  water,  but 
are  decomposed  by  a  large  quantity  of  this  fluid,  a  basic  nitrate 
being  precipitated,  which  may  be  redissolved  by  the  addition  of 
nitric  acid. 

If,  on  the  contrary,  dilute  nitric  acid  be  added  to  a  large  excess 
of  metallic  mercury,  and  allowed  to  react,  when  cold,  for  a  sufficient 
length  of  time,  the  metal  becomes  covered  with  large,  colourless  crys- 
tals, generally  well  defined,  belonging  to  a  basic  nitrate,  of  which 
the  formula  is  3Hg30,2N05+3HO.  If  this  salt  or  the  neutral  ni- 
trate be  treated  with  tepid  water,  a  bibasic  nitrate  of  the  formula 
2Hg30,N05  is  obtained.  By  boiling  the  latter  compound  with 
water,  it  is  converted  into  a  green  powder,  which  appears  to  be  a 
still  more  basic  nitrate. 

The  neutral  nitrate  is  easily  distinguished  from  the  basic  nitrates 
by  rubbing  them  up  with  a  concentrated  solution  of  sea-salt,  in 
which  case  the  neutral  nitrate  remains  colourless,  because  the  mer- 
cury passes  entirely  into  the  state  of  chloride  Hg^Cl,  while  the  basic 
nitrates  turn  blackish  gray,  because  suboxide  of  mercury  HgaO  is 
separated  simultaneously  with  the  chloride  HgaCl. 

When  a  dilute  solution  of  ammonia  is  added  to  an  equally  dilute 
solution  of  subnitrate  of  mercury,  a  gray  precipitate  of  the  formula 
(NH3+3Hg30)N05  is  obtained,  and  which  is  used  in  pharmacy 
under  the  name  of  soluble  mercury  of  Hahnemann.  The  composi- 
tion of  this  precipitate  varies  according  to  the  concentration  and 
temperature  of  the  solutions. 

Suhsulphate  of  Mercury. 

§  1088.  By  adding  sulphuric  acid  to  a  solution  of  subnitrate  of 
mercury,  the  suhsulphate  is  precipitated  as  a  white  crystalline  pow- 
der, which  is  very  slightly  soluble  in  water,  one  part  of  the  salt 
requiring  500  parts  of  cold  and  800  of  boiling  water.  It  is  also 
obtained  by  heating  concentrated  sulphuric  acid  with  a  large  excess 
of  mercury,  but  it  is  difficult  to  prevent  the  formation  of  the  proto- 
sulphate  HgO,S03. 

Subcarhonate  of  Mercury. 

§  1089.  By  pouring  a  solution  of  carbonate  of  soda  into  a  solu- 
tion of  subnitrate  of  mercury,  a  white  granular  precipitate  of  the 
formula  Hg30,C03  is  obtained. 

SALTS  OF  THE  PROTOXIDE  OF  MERCURY,  HgO. 

§  1090.  The  neutral  salts  of  the  protoxide  of  mercury  HgO  are 
colourless,  while  the  basic  salts  are  yellow ;  and  their  solutions  ex- 
hibit the  following  reactions : 

Caustic  potassa  and  soda,  in  excess,  yield  a  yellow  precipitate  of 


SALTS   OF    RED    OXIDE.  277 

the  protoxide,  while  ammonia  in  general  produces  white  precipitates, 
containing  ammonia  or  its  elements. 

Carbonate  of  potassa  throws  down  a  red  precipitate,  which  does 
not  dissolve  in  an  excess  of  reagent,  and  carbonate  of  ammonia 
gives  a  white  precipitate. 

The  alkaline  phosphates  and  arseniates  form  white  precipitates, 
easily  soluble  in  an  excess  of  acid. 

Sulf  hydric  acid,  in  small  quantity,  throws  down  a  white  precipi- 
tate, which  contains,  at  the  same  time,  sulf  hydric  acid  and  the 
elements  of  the  mercurial  salt ;  while  the  same  acid,  in  larger 
quantity,  produces  an  orange  precipitate.  But  if  the  solution  of 
the  mercurial  salt  be  digested  with  an  excess  of  sulf  hydric  acid,  the 
precipitate  turns  black,  owing  to  the  forming  of  sulphide  of  mer- 
cury HgS.  The  alkaline  sulf  hydrates  also  yield  white  or  orange 
precipitates  when  used  in  small  quantity,  and  in  excess  they  turn 
the  precipitate  black. 

Ferrocyanide  of  potassium  throws  down  with  protosalts  of  mer- 
cury in  solution  a  white  precipitate,  which  turns  blue  after  long  ex- 
posure to  the  air,  the  ferrocyanide  of  mercury  being  then  decom- 
posed ;  and  while  soluble  simple  cyanide  of  mercury  is  formed,  prus- 
sian-blue  is  separated. 

Iodide  of  potassium  gives  a  beautiful  red  precipitate,  which  may 
dissolve  both  in  an  excess  of  alkaline  iodide  and  in  an  excess  of  the 
mercurial  salt,  soluble  double  iodides  being  formed  in  both  cases. 

Chlorohydric  acid  and  the  solutions  of  the  soluble  chlorides  do  not 
precipitate  protosalts  of  mercury,  unless  their  solution  be  very  con- 
centrated ;  which  characteristic  distinguishes  them  from  the  subsalts 
of  mercury,  which  yield,  in  this  case,  a  white  precipitate  HggCl, 
whatever  may  be  the  degree  of  their  dilution.  In  order  to  ascer- 
tain if  a  mercurial  solution  contains,  at  the  same  time,  subsalts  and 
protosalts  of  mercury,  chlorohydric  acid  is  poured  into  it,  when  all 
the  mercury  which  existed  in  the  state  of  suboxide  is  precipitated 
in  the  form  of  chloride  Hg^Cl,  while  that  which  was  in  the  state  of 
protoxide  is  dissolved.  It  is,  therefore,  sufficient  to  ascertain  if  the 
filtered  solution  produces  a  yellow  precipitate  of  protoxide  of  mer- 
cury with  potassa,  or  a  red  precipitate  with  iodide  of  potassium. 

Protonitrate  of  Mercury. 

§  1091.  Protonitrate  of  mercury  is  obtained  by  dissolving  mer- 
cury, when  hot,  in  an  excess  of  nitric  acid,  and  boiling  the  salt  with 
nitric  acid  until  no  more  reddish  vapours  are  disengaged.  It  may 
be  admitted  that  the  neutral  salt  exists  in  the  acid  solution,  but,  if 
the  latter  be  evaporated,  it  deposits,  on  cooling,  crystals  of  the 
basic  nitrate  2HgO,N05+2HO.  The  neutral  nitrate  cannot  be 
separated  by  pouring  alcohol  into  the  solution,  as  the  bibasic  nitrate 
is  again  precipitated.  Nevertheless,  the  solution  with  an  excess  of 
acid,  evaporated  to  the  consistence  of  syrup,  deposits  crystals  of 


278  MERCURY. 

neutral  nitrate,  when  kept  for  some  time  in  a  refrigerating  mixture. 
If  the  preceding  nitrates  be  dissolved  in  a  large  quantity  of  water, 
they  are  decomposed,  and  throw  down  a  white  precipitate,  of  which 
the  formula  is  BHgOjNO^+HO,  and  which  is  remarkable  for  its 
great  fixedness,  for  it  dissolves  with  difficulty  in  nitric  and  sulphuric 
acid.  Boiled  with  water,  it  again  gives  ofi"  acid,  and,  if  the  ebulli- 
tion were  sufficiently  prolonged,  it  would  probably  be  converted  into 
an  oxide.  If  a  solution  of  protonitrate  of  mercury  be  boiled  with 
metallic  mercury,  the  subnitrate  Hg30,N05  is  obtained. 

ProtosulpJiate  of  Mercury, 

§  1092.  Protosulphate  of  mercury  is  obtained  by  heating  metallic 
mercury  with  concentrated  sulphuric  acid  in  excess,  a  white  crys- 
talline powder  being  formed.  But  the  evaporation  with  sulphuric 
acid  must  be  prolonged  until  copious  vapours  of  the  acid  are  given 
off,  as,  otherwise,  the  protosulphate  of  mercury  would  be  mixed  with 
subsulphate.  This  compound  is  often  prepared  in  manufactories 
of  chemicals,  because  it  is  used  in  the  manufacture  of  the  chloride 
of  mercury  HgCl,  or  corrosive  sublimate.  One  part  of  mercury 
and  slightly  more  than  1  part  of  concentrated  sulphuric  acid  are 
then  heated  in  a  glass  retort,  and  when  the  metallic  mercury  has 
disappeared,  the  heat  is  still  continued  in  a  sand-bath  until  the  pro- 
duct is  perfectly  dried,  when  anhydrous  sulphate  is  obtained.  It  is 
decomposed,  when  treated  by  a  large  quantity  of  water,  into  a  yel- 
low basic,  salt  3HgO,S03,  used  in  medicine  under  the  name  of 
turpeth  mineral^  and  into  a  salt  with  a  great  excess  of  acid,  which 
crystallizes  on  the  evaporation  of  the  liquid.  Turpeth  mineral  is 
itself  decomposed  by  being  boiled  with  water,  and  oxide  of  mercury 
is  left  only  at  last. 

Protochromates  of  Mercury, 

§  1093.  Two  protochromates  of  mercury  are  known,  the  formulae 
of  which  are  3HgO,Cr03  and  4HgO,Cr03.  The  first  is  obtained 
by  pouring  protonitrate  of  mercury  into  a  solution  of  bichromate 
of  potassa,  or  by  boiling  the  yellow  oxide  of  mercury  with  the  bi- 
chromate ;  it  is  a  brick-red  precipitate.  The  chromate  4HgO,CrOg 
is  obtained  by  boiling  for  a  long  time  the  red  protoxide  of  mercury 
with  a  solution  of  bichromate  of  potassa. 

Protocarlonates  of  Mercury. 

§  1094.  By  adding  a  solution  of  protonitrate  of  mercury  to  a 
solution  of  neutral  carbonate  of  potassa  in  great  excess,  an  ochrous 
brown  precipitate  of  carbonate  of  protoxide  of  mercury  is  formed, 
having  the  formula  4HgO,C03;  ^^^  if  ^^^  same  experiment  be 
made  by  substituting  the  bicarbonate  for  the  neutral  alkaline  car- 
bonate, a  brown  precipitate  of  the  formula  3HgO,C03  is  obtained. 
The  precipitates  which  are  formed  when  alkaline  carbonates  are 


SALTS   OF   RED   OXIDE.  279 

poured  into  a  solution  of  nitrate  of  mercury  are  very  complicated, 
because  subnitrates  of  mercury  are  first  deposited. 

Fulminate  of  Mercury, 

§  1095.  This  is  a  highly  explosive  compound,  consisting  of  prot- 
oxide 'of  mercury  united  with  an  acid,  fulminic  acid,  formed  of 
cyanogen  and  oxygen,  and  of  which  the  formula  is  CyO  or  C^NO, 
and  used  for  the  manufacture  of  percussion  caps.  Fulminate  of 
mercury  is  prepared  by  causing  alcohol  to  react  on  the  acid  proto- 
nitrate.  A  quantity  of  mercury  is  dissolved  in  12  parts  of  nitric 
acid  of  35°  or  40°  of  Baumd,  and  11  parts  of  alcohol  at  .86  are 
gradually  added  to  the  solution;  and,  while  the  temperature  is 
slowly  elevated,  a  lively  reaction  accompanied  by  a  copious  evolu- 
tion of  reddish  vapours  soon  ensues,  when  the  liquid,  on  cooling, 
deposits  small  crystals  of  a  yellowish- white  colour. 

Fulminate  of  mercury  is  one  of  the  most  explosive  compounds 
known,  and  should  be  handled  with  great  care,  especially  when  it  is 
dry,  as  it  detonates  when  rubbed  against  a  hard  body.  It  dissolves 
readily  in  boiling  water,  but  the  greater  portion  of  it  is  again  de- 
posited in  crystals  during  cooling.  ' 

The  fulminating  material  of  percussion  caps  is  made  of  fulminate 
of  mercury,  prepared  as  just  stated,  after  having  been  washed  in 
cold  water.  The  substance  is  allowed  to  drain  until  it  contains 
only  about  20  per  cent,  of  water,  and  is  then  mixed  with  f  of  its 
weight  of  nitre,  which  mixture  is  ground  on  a  marble  table  with  a 
muller  of  guaiacum-wood.  A  small  quantity  of  the  paste  is  then 
placed  in  each  copper  cap  and  allowed  to  dry,  the  fulminating  pow- 
der in  the  cap  being  often  covered  with  a  thin  coat  of  varnish  to 
preserve  it  from  moisture. 

OXIDE  OF  MERCURY  AND  AMMONIA. 

§  1096.  By  treating  protoxide  of  mercury  HgO  with  a  large  ex- 
cess .  of  perfectly  caustic  liquid  ammonia,  a  yellow  powder  is  ob- 
tained, which  must  be  rapidly  washed  and  dried  under  a  bell-glass 
with  quicklime,  and  the  composition  of  which  is  expressed  by 
4HgO,NH3  +  2HO,  although  a  more  rational  formula  would  be 
3HgO,HgNH3+3HO.  It  is  called  oxide  of  mercury  and  ammonia. 
The  preparation  of  this  substance  must  be  effected  without  access 
of  air,  as,  otherwise,  the  compound  would  soon  absorb  carbonic  acid, 
and  a  mixture  of  oxide  of  mercury  and  ammonia  with  carbonate  of 
the  same  compound  oxide  would  be  obtained ;  for  which  purpose, 
the  oxide  of  mercury  is  placed  in  a  bottle  completely  filled  with  a 
concentrated  solution  of  perfectly  caustic  ammonia,  and  then  corked. 
Either  the  red  or  yellow  variety  of  protoxide  of  mercury  may  be 
used,  but  the  red  oxide  requires  a  greater  length  of  time.  The 
hydrated  oxide  of  mercury  and  ammonia,  when  left  for  a  long  time 


280  MERCURY. 

in  a  dry  vacuum,  loses  its  water ;  and  if  it  be  left  until  it  no  longer 
loses  in  weight,  a  brown  powder  remains,  which  consists  of  anhy- 
drous oxide  of  mercury  and  ammonia  SHgOjHgNHg.  The  dishy- 
dration  takes  place  very  rapidly  at  a  temperature  of  266°,  without 
any  decomposition  of  the  substance. 

The  hydrated  oxide  of  mercury  and  ammonia  is  insoluble  in  water 
and  in  alcohol.  A  cold  solution  of  caustic  potassa  exerts  scarcely 
any  action  on  it ;  while  at  the  boiling  point  ammonia  is  disengaged, 
but  the  ebullition  must  be  long  continued  to  effect  complete  decom- 
position. 

Anhydrous  oxide  of  mercury  and  ammonia  is  much  more  fixed, 
as  potassa  decomposes  it  only  when  heated  to  the  fusing  point  of 
the  alkali.  The  combination  exhibits  all  the  characters  of  a  power- 
ful base :  it  combines  with  the  acids  and  forms  well-defined  salts. 
It  absorbs  carbonic  acid  nearly  as  readily  as  lime  and  baryta,  and 
its  carbonate  does  not  decompose  at  212°  ;  it  also  expels  ammonia 
from  its  salts  as  rapidly  as  lime  and  baryta.  The  proportion  of  oxide 
of  mercury  and  ammonia  represented  by  the  formula  SHgOjHgNHjj, 
corresponds  to  1  equivalent  of  a  base  RO,  and  saturates  1  equiva- 
lent of  acid. 

The  following  compounds  have,  thus  far,  been  obtained : 

Hydrated  base 3HgO,HgNH,4-3HO. 

Intermediate  hydrate 8HgO,HgNH3-fHO. 

Anhydrous  base 3IIgO,HgNH3. 

Sulphate (3HgO,HgNH,),S03. 

Hydrated  carbonate (8HgO,HgNHJ,C034-HO. 

Carbonate  dried  at  275° (3HgO,HgNH,),CO,. 

Oxalate (3HgO,HgNHJ,CA- 

Nitrate (3HgO,HgNH,),NO,+HO. 

Bromate (8HgO,HgNHJ,BrO,. 

Several  chlorides  and  iodides  are  also  known  which  are  derived 
from  the  oxide  of  mercury  and  ammonia  by  reactions  resembling 
those  by  which  the  ordinary  metallic  oxides  are  converted  into 
chlorides  and  iodides.     The  formulae  of  these  compounds  are : 

Chloride (2HgO,HgCl),HgNH,. 

Another  chloride 3HgCl,HgNH,. 

Iodide (2HgO,HgIo),HgNH3. 

Sulphate  of  Mercury  and  Ammonia, 
§  1097.  If  protosulphate  of  mercury  HgOjSOg  be  added,  by  small 
quantities  at  a  time,  to  caustic  ammonia,  the  salt  is  dissolved  in  very 
large  quantity;  but  if  the  liquid  be  diluted  with  a  great  deal  of 
water,  a  copious  white  precipitate  forms,  which  was  long  known  as 
ammoniacal  turpeth,  and  which  may  be  regarded  as  the  sulphate  of 


CINNABAR.  281 

mercury  and  ammonia  (3Hg05HgNH3)S03.      The  composition  of 
this  product  does  not,  however,  appear  to  be  constant. 

Carbonate  of  Mercury  and  Ammonia, 

§  1098.  This  salt  is  readily  prepared  by  the  direct  combination 
of  carbonic  acid  with  oxide  of  mercury  and  ammonia  suspended  in 
water ;  when  an  insoluble  yellow  compound,  consisting  of  the  hy- 
drated  carbonate,  is  obtained.  It  parts  with  its  water  at  about  284° 
and  passes  into  the  state  of  anhydrous  carbonate. 

Oxalate  of  Mercury  and  Ammonia, 

§  1099.  The  oxalate  of  mercury  and  ammonia  is  obtained  by 
digesting  the  protoxalate  of  mercury,  made  by  double  decomposi- 
tion, with  caustic  ammonia  in  excess,  when  a  white  granular  pow- 
der is  obtained,  which  explodes  when  heated. 

COMPOUNDS  OF  MERCURY  WITH  SULPHUR. 

§  1100.  If  a  current  of  sulf  hydric  acid  be  passed  through  a  solu- 
tion of  a  subsalt  of  mercury  a  black  precipitate  is  obtained,  which 
is  the  sulphide  of  mercury  Hg^S,  corresponding  to  the  suboxide 
HggO ;  but  if  the  temperature  be  raised  the  precipitate  is  rapidly 
converted,  even  in  the  water,  into  the  protosulphide  HgS,  and  into 
metallic  mercury. 

If  a  current  of  sulf  hydric  acid  be  passed  through  a  solution  of  a 
protosalt  of  mercury,  there  results  first  a  white  precipitate,  which  is 
a  compound  of  protosulphide  of  mercury  with  the  mercurial  salt 
subjected  to  the  reaction.  Thus,  the  protosulphate  HgO,S03  is  con- 
verted into  a  compound  of  which  the  formula  is  HgO,S03-f-2HgS, 
while  the  protonitrate  HgOjNO^  gives  the  compound  HgO,N05+ 
2HgS,  and  the  protochloride  HgCl  yields  the  product  HgCl+2HgS. 
But  if  the  liquid  be  completely  saturated  by  the  gas,  the  precipitate 
turns  black,  and  consists  entirely  of  sulphide  of  mercury  HgS,  which, 
when  heated  in  a  retort,  sublimes  completely  without  change,  and 
yields  a  red  product  of  a  crystalline  fibrous  texture,  having  the 
same  composition  as  the  black  precipitate,  and  known  by  the  name 
of  cinnabar.  The  same  compound  is  obtained  by  a  continued 
trituration  of  mercury  with  sulphur,  when  a  black  substance  is 
formed,  which  is  sometimes  used  in  medicine  under  the  name  of 
sethiops  mineral.  In  order  to  obtain  the  sulphide  of  mercury  HgS, 
it  is  better  to  rub  together  6  parts  of  mercury  and  1  of  sulphur,  the 
black  substance  which  results  yielding  cinnabar  by  sublimation. 
Sulphide  of  mercury  HgS  is  found  in  nature,  most  frequently  in 
deep  red,  compact  masses,  but  also  forming,  sometimes,  beautiful 
red  transparent  crystals  derived  from  the  rhombohedron  of  71°. 
It  is  the  principal  ore  of  mercury. 

Under  the  ordinary  pressure  of  the  atmosphere,  cinnabar  vola- 
tilizes before  fusing,  and  produces  a  brownish-yellow  vapour,  the 


282  MERCURY. 

density  of  which  is  5.4,  while  the  specific  gravity  of  solid  cinnabar 
is  8.1. 

The  sulphide  of  mercury  HgS  sometimes  exhibits  a  red  colour 
more  beautiful  than  that  of  sublimed  cinnabar,  and  is  used  in  oil 
and  aquarelle  painting  under  the  name  of  vermilion.  The  most 
beautiful  vermilion  is  prepared  by  the  reaction,  assisted  by  water, 
of  the  alkaline  polysulphides  on  sulphide  of  mercury:  300  parts 
of  mercury  and  114  of  sulphur  being  triturated  for  2  or  3  hours  in 
a  mortar,  and  75  parts  of  potassa  and  400  of  water  added,  the  whole 
is  maintained  at  a  temperature  of  about  113°,  and  shaken  from  time 
to  time,  when  the  black  precipitate  soon  turns  red ;  and  when  it  has 
attained  the  proper  shade,  it  is  rapidly  washed  with  hot  water.  If 
the  action  of  the  alkaline  sulphide  were  prolonged  too  much,  the 
substance  would  again  become  brown.  Very  fine  vermilion  is  also 
obtained  by  heating,  for  a  considerable  length  of  time,  at  an  average 
temperature  of  122°,  ordinary  cinnabar,  reduced  to  an  impalpable 
powder,  with  a  solution  of  alkaline  sulphide.  The  phenomenon 
of  the  change  of  colour  of  the  sulphide  of  mercury,  by  contact  with 
the  alkaline  sulphides,  has  not  yet  been  properly  explained. 

Cinnabar  is  manufactured  on  a  large  scale  in  the  furnaces  for 
working  ores  of  mercury.  At  Idria,  in  Carinthia,  100  parts  of  mer- 
cury and  18  parts  of  powdered  sulphur  are  placed  in  small  wooden 
tubs,  which  are  turned  for  3  or  4  hours  around  their  horizontal  axis, 
when  a  black  sulphide  of  mercury  is  formed,  which  is  then  sublimed 
in  cast-iron  vessels,  covered  with  capitals  of  baked  clay,  on  which 
the  cinnabar  condenses. 

Cinnabar  is  readily  roasted  in  the  air,  sulphurous  acid  being  dis- 
engaged, while  metallic  mercury  distils  over.  It  is  easily  decom- 
posed by  hydrogen,  carbon,  and  many  of  the  metals.  The  non- 
oxidizing  acids  act  on  it  with  difficulty,  while  it  is  readily  attacked 
by  concentrated  nitric  acid,  and  especially  by  aqua  regia. 

COMPOUNDS  OF  MERCURY  WITH  CHLORINE. 

§  1101.  Two  compounds  of  mercury  with  chlorine  are  known : 

The  subchloride  HggCl,  called  calomel;  and 

The  protochloride  HgCl,  commonly  called  corrosive  sublimate. 

The  majority  of  chemists,  even  at  this  day,  give  the  name  oi  pro 
tochloride  of  mercury  to  calomel  Hg^Cl,  and  that  of  bichloride  to 
corrosive  sublimate  HgCl ;  but  we  have  not  retained  these  names, 
because  they  clash  with  the  rules  of  nomenclature  and  chemical 
formulae  which  it  has  been  agreed  to  assign  to  these  substances. 
We  deem  it  necessary  to  insist  particularly  on  this  point,  in  order 
to  avoid  mistakes,  which  might  prove  very  serious,  because  these 
substances  are  used  in  medicine. 

The  subchloride  Hg^Cl  may  be  prepared  by  pouring  a  solution 
of  subnitrate  of  mercury  into  a  "dilute  solution  of  sea  salt,  the  sub- 
chloride of  mercury  HggCl  being  precipitated  in  the  form  of  a  white 


CALOMEL.  283 

powder.  It  may  be  also  obtained  by  the  reaction  of  metallic  mer- 
cury on  protochloride  of  mercury  HgCl,  or  corrosive  sublimate,  for 
which  purpose  4  parts  of  corrosive  sublimate  and  3  parts  of  mercury 
are  mixed  and  rubbed  together  for  some  time,  moistening  the  whole 
with  a  small  quantity  of  alcohol,  to  prevent  injury  from  the  poisonous 
dust  of  the  sublimate.  It  is  then  heated  in  a  large  phial,  in  a  sand- 
bath,  when  the  calomel  sublimes  and  condenses  in  the  upper  part 
of  the  phial.  As  this  product  may  be  mixed  with  corrosive  sub- 
limate, it  is  necessary  to  reduce  it  to  a  fine  powder,  and  wash  it 
with  boiling  water  until  the  water  afibrds  no  precipitate  with  po- 
tassa  or  sulf  hydric  acid.  Calomel  is  prepared  in  manufactories  of 
chemical  products  by  heating  a  mixture  of  subsulphate  of  mercury 
Hg^OjSOg  and  sea  salt ;  but  as  the  preparation  of  the  subsulphate  is 
somewhat  difficult,  a  mixture  of  protosulphate  of  mercury  HgOjSOg 
and  metallic  mercury  is  substituted.  Sixteen  parts  of  mercury, 
being  divided  into  two  equal  portions,  the  first  is  converted  into 
protosulphate  (§  1092)  and  mixed  intimately  with  the  second  por- 
tion, after  which  the,  mixture  is  rubbed  up  with  3  parts  of  sea  salt 
and  the  whole  distilled. 

Calomel  used  in  pharmacy  should  be  very  finely  powdered,  be- 
cause it  is  then  more  easily  separated  from  the  corrosive  sublimate, 
which  acts  as  a  poison  on  the  animal  economy.  It  is  obtained  im- 
mediately in  an  impalpable  powder  by  efiecting  the  distillation  in  a 
vessel,  the  wide  and  short  neck  of  which  enters  a  large  receiver, 
where  the  calomel  vapour  condenses  before  touching  its  sides.  The 
calomel  thus  obtained  should  be  washed  with  boiling  water  until  no 
precipitate  is  formed  by  potassa  or  sulf  hydric  acid. 

By  subliming  large  quantities  of  calomel,  beautiful  transparent 
crystals  are  frequently  obtained,  which  are  square  prisms,  having 
an  octohedral  termination.  They  are  remarkable  for  their  great 
refracting  and  dispersive  power,  and  belong  to  the  second  system  of 
crystallization.  Light  slowly  decomposes  subchloride  of  mercury, 
and  causes  it  to  assume  a  grayish  hue,  owing  to  the  disengagement 
of  chlorine,  while  a  portion  of  the  mercury  is  set  free.  The  density 
of  this  substance  is  6.5;  and  it  fuses  and  volatilizes  at  nearly  the 
same  temperature  under  the  ordinary  pressure  of  the  atmosphere. 
The  density  of  its  vapour  is  8.2,  the  gaseous  chloride  being  there- 
fore composed  of 

1  vol.  vapour  of  mercury 6.976 

J    "    chlorine 1.220 

1  vol.  gaseous  subchloride  HgaCl 8.196 

Calomel  is  very  slightly  soluble  in  water,  and  a  solution  of  1  part 
of  chlorohydric  acid  in  250,000  parts  of  water  is  very  sensibly 
aifected  by  subnitrate  of  mercury.  In  time,  chlorohydric  acid  acts 
on  it  at  the  boiling  point,  when  metallic  mercury  separates,  while 
the  protochloride  HgCl  is  dissolved.     Concentrated  nitric  acid  soon 


284  MERCURY. 

converts  it  into  corrosive  sublimate  and  protonitrate  of  mercury. 
Aqua  regia  and  a  solution  of  chlorine  dissolve  it  in  the  state  of 
protochloride  HgCl.  Calomel  combines  readily  with  dry  ammo- 
niacal  gas,  producing  a  black  compound,  of  which  the  formula  is 
HggCH-NHg,  and  which,  when  treated  with  liquid  ammonia,  yields 
a  gray  powder  of  the  formula  Hg2Cl,HgNH3. 

Calomel  is  used  in  medicine  as  a  vermifuge  and  purgative,  and  is 
also  applied  to  the  treatment  of  venereal  diseases. 

Protochloride  of  Mercury  HgCl,  or  Corrosive  Sublimate. 

§  1102.  Corrosive  sublimate  can  be  prepared  by  dissolving  mer- 
cury in  aqua  regia  containing  an  excess  of  chlorohydric  acid,  when, 
by  treatment  with  boiling  water,  the  greater  part  of  the  proto- 
chloride is  deposited  in  acicular  crystals  during  the  cooling  of  the 
liquid.  This  compound  is  generally  prepared  on  a  large  scale,  by 
heating  on  a  sand-bath  a  mixture  of  protosulphate  of  mercury 
HgO,S03  and  sea  salt,  when  the  protochloride  sublimes  on  th< 
upper  parts  of  the  distilling  apparatus.  The  protosulphate  of  mer 
cury  often  contains  a  small  quantity  of  subsulphate,  which  yields 
calomel  by  its  reaction  on  sea  salt ;  to  avoid  which,  a  small  quantity 
of  peroxide  of  manganese  is  generally  added  to  the  mixture.  As 
corrosive  sublimate  fuses  at  a  pressure  much  below  that  at  which  it 
distils  at  the  ordinary  pressure  of  the  atmosphere,  advantage  is 
taken  of  this  property  to  give  more  consistency  to  the  sublimed  pro- 
duct ;  to  effect  which,  the  fire  is  increased  toward  the  close  of  the 
operation,  when  the  sublimate,  by  beginning  to  fuse,  is  more  com- 
pactly aggregated.  When  the  distilling  vessels  are  cool  they  are 
broken,  and  the  cakes  of  corrosive  sublimate  removed. 

Protochloride  of  mercury  is  colourless,  and  its  density  is  Q.^.  It 
fuses  at  about  509°,  and  boils  at  about  563°  under  the  ordinary 
pressure  of  the  atmosphere,  yielding  a  colourless  vapour,  the  density 
of  which  is  9.42.     Gaseous  protochloride  therefore  contains 

1  vol.  vapour  of  mercury 6.976 

1    "    chlorine 2.440 

1  vol.  gaseous  chloride  HgCl 9.416 

Corrosive  sublimate  dissolves  in  16  parts  of  cold  and  3  parts  of 
boiling  water,  and  its  curve  of  solubility  is  represented  on  the  plate 
at  page  407,  vol.  i.  It  is  more  easily  soluble  in  alcohol  than  in 
water,  as  2J^  of  absolute  and  1 J  of  boiling  alcohol  dissolve  1  part  of 
the  binary  compound.     It  is  also  soluble  in  3  parts  of  cold  ether. 

It  dissolves  readily  in  a  solution  of  chlorohydric  acid,  especially 
when  the  latter  is  hot,  and  the  liquid  sets  in  a  crystalline  mass  on 
cooling. 

Corrosive  sublimate  is  often  used  in  the  laboratory  as  an  agent 
of  chlorination ;  and  it  has  already  been  shown  (§  943).  that  bi- 
chloride of  tin  is  obtained  by  distilling  a  mixture  of  1  part  of  tin 


CORROSIVE   SUBLIMATE.  285 

filings  and  5  parts  of  sublimate.  Many  substances  also  abstract 
from  it,  by  the  humid  way,  a  portion  of  its  chlorine,  and  cause  it  to 
pass  into  the  state  of  subchloride,  which  decompositions  are  more 
easily  effected  when  assisted  by  solar  light. 

Corrosive  sublimate  is  sometimes  employed  in  medicine,  chiefly 
in  che  treatment  of  venereal  diseases ;  but,  being  a  dangerous  medi- 
cine, it  should  only  be  administered  with  the  greatest  care.  It  is 
used  advantageously  to  protect  wood  from  insects,  and  wooden  bed- 
steads may  be  kept  free  from  vermin  by  impregnating  the  wood  with 
a  weak  solution  of  sublimate.  Zoological  specimens  and  anatomical 
preparations  are  frequently  preserved  by  being  soaked  in  a  dilute 
solution  of  it.* 

Protochloride  of  mercury  forms,  with  the  metallic  chlorides,  a 
great  number  of  crystallizable  double  chlorides.  Three  of  these 
compounds  with  chloride  of  potassium  have  been  obtained,  the 
formula  of  which  are  KCl+HgCH-HO,KCH-2HgCl+2HO  and 
KCl+4HgCl+4H0.  But  one  compound  has  been  obtained  with 
chlorohydrate  of  ammonia,  with  the  formula  NHgjHCl+IIgCl+HO, 
and  isomorphous  with  the  corresponding  compound  with  chloride 
of  potassium. 

When  caustic  alkalies  or  alkaline  carbonates  are  poured  into  a 
solution  of  corrosive  sublimate,  very  variable  compounds  are  ob- 
tained, according  to  the  proportions  of  the  reacting  substances  and 
the  temperature  and  degree  of  concentration  of  the  liquids.  When 
the  alkali  is  in  excess  the  yellow  or  red  oxide  is  produced ;  but 
by  using  the  reagent  in  weaker  and  more  varying  proportions,  gray, 
red,  or  violaceous  precipitates  are  obtained,  which  are  oxychlorides ; 
the  formulae  are  2HgO,HgCl,  3HgO,HgCl,  4HgO,HgCl.  Analo- 
gous oxychlorides  are  obtained  by  boiling  oxide  of  mercury  with  a 
solution  of  corrosive  sublimate. 

Ammonia,  poured  into  a  solution  of  corrosive  sublimate,  throws 
down  white  precipitates,  making  the  liquid  emulsive  and  varying  in 
composition.  They  have  all,  for  a  long  time,  been  indiscriminately 
called  white  precipitate,  but  are  now  divided  into  several  well- 
defined  compounds.  If  a  solution  of  corrosive  sublimate  be  poured 
into  a  solution  of  caustic  ammonia,  and  the  precipitate  be  washed 
with  cold  water,  a  white  substance  is  obtained,  of  which  the  formula 
is  HgaClNHg,  and  which  is  called  chloramide  of  mercury,  because 
it  is  admitted  to  contain  the  compound  NHg,  which  is  called  amide, 
(§  514.)  The  reaction  from  which  this  product,  arises  is  represented 
by  the  following  equation : 

2HgCl4-2IS[H3  =  NH3,HCl+Hg,ClNH,. 

*  Meat  may  be  kept  fresh  for  a  great  length  of  time,  by  being  allowed  to  re- 
main for  several  hours  in  a  bucket  filled  with  water  into  which  the  merest  trace 
of  corrosive  sublimate  has  been  thrown ;  and  several  other  metallic  salts,  espe- 
cially nitrate  of  silver,  have  the  same  property.  This  method  of  preserving  meat 
would,  however,  be  too  dangerous  for  family  use. —  W.  L.  F. 


286  MERCURY. 

The  formula  HgCl^HgNHa  is  sometimes  assigned  to  this  sub- 
stance. It  is  decomposed  by  boiling  water,  and,  when  heated,  gives 
off  ammonia,  ammoniacal  chloride  of  mercury  2Hg2Cl,NH3,  and 
leaves  in  the  retort  a  red  compound,  which  is  destroyed  only  at  a 
temperature  of  662°,  and  of  which  the  composition  is  represented 
by  the  formula  2HgCl4-NHg3. 

By  boiling  chloramide  of  mercury  with  water  until  the  sub- 
stance no  longer  undergoes  any  change,  a  white  compound  of  which 
the  formula  is  (2HgO,HCl)HgNH3  is  obtained,  which  may  be  re- 
garded as  the  chloride  of  the  compound  oxide  of  mercury  and  am- 
monia 3HgO,HgNH3 ;  and,  in  fact,  when  treated  with  potassa,  it  is 
converted  into  oxide  of  mercury  and  ammonia. 

If  caustic  ammonia  be  dropped  into  a  solution  of  corrosive  subli- 
mate, taking  care  to  keep  the  latter  substance  always  in  excess,  a 
white  precipitate  is  obtained,  of  which  the  formula  may  be  written 
3HgCl,HgNH3,  and  which  is  then  regarded  as  oxide  of  mercury 
and  ammonia,  in  which  all  the  oxygen  is  replaced  by  an  equivalent 
quantity  of  chlorine.  This  compound  is  soon  changed  even  by  wash- 
ing in  cold  water. 

COMPOUNDS  OF  MERCURY  WITH  BROMINE. 

§  1103.  Mercury  forms  with  bromine  two  compounds  which  cor- 
respond to  the  two  chlorides.  The  bromide  Hg^Br  is  obtained  by 
pouring  a  solution  of  bromide  of  potassium  into  that  of  subnitrate 
of  mercury,  when  the  precipitate  which  forms  is  nearly  insoluble  in 
water,  and  volatilizes  without  change.  The  bromide  of  mercury 
HgBr  is  obtained  by  pouring  bromine  in  excess  on  mercury  covered 
by  a  stratum  of  water,  when  the  mercury  soon  dissolves  in  the  state 
of  protobromide,  which  may  be  crystallized  by  evaporation.  The 
protobromide  may  then  be  sublimed  without  alteration,  and  it  forms 
crystallizable  compounds  with  the  alkaline  bromides. 

COMPOUNDS  OF  MERCURY  WITH  IODINE. 

§  1104.  By  adding  iodide  of  potassium  to  a  solution  of  corrosive 
sublimate,  a  red  precipitate  of  protiodide  of  mercury  Hgl  is  ob- 
tained, which  may  also  be  prepared  by  triturating  together  equal 
quantities  of  mercury  and  iodine,  with  a  small  quantity  of  alcohol 
to  assist  their  reaction.  The  protiodide  of  mercury  dissolves  largely 
in  a  hot  solution  of  iodide  of  potassium,  and  the  liquid,  on  cooling, 
deposits  a  portion  of  the  protiodide  in  the  form  of  beautiful  red 
crystals.  If  the  red  iodide  of  mercury  be  heated,  it  suddenly 
changes  colour  and  becomes  of  a  clear  yellow,  while,  if  the  tem- 
perature be  raised  still  higher,  it  fuses  into  a  yellow  liquid,  and  sub- 
limes in  the  form  of  yellow  crystals.  The  fused  yellow  iodide  and 
the  large  yellow  crystals  frequently  retain  their  colour,  even  after 
cooling ;  but  the  substance,  on  being  broken,  turns  red,  first  at  the 


CYANIDE.  287 

point  of  the  rupture,  and  then  gradually  through  the  whole  mass, 
which  change  of  colour  is  very  rapid  when  the  substance  is  pow- 
dered. The  protiodide  of  mercury  presents,  therefore,  two  modifi- 
cations, distinguishable  by  their  colour,  and  which  also  affect  two 
different  crystalline  forms,  the  primitive  form  of  the  red  crystals 
being  an  octahedron  with  a  square  base  belonging  to  the  second 
system,  while  the  yellow  crystals  belong  to  the  fourth. 

Protiodide  of  mercury  volatilizes  without  change,  and  the  density 
of  its  vapour  has  been  found  to  be  15. 68,. being  the  greatest  of  all 
gaseous  bodies.  It  is  very  slightly  soluble  in  water,  only  in  the 
proportion  of  1  to  150. 

An  iodide  of  mercury  Hg^I  is  obtained  by  pouring  iodide  of  po- 
tassium- into  a  solution  of  subnitrate  of  mercury,  as  a  dirty-green 
precipitate,  which  volatilizes  unchanged  when  rapidly  heated,  and 
which,  on  the  contrary,  is  decomposed  into  protiodide  of  mercury 
Hgl  and  metallic  mercury  when  heated  slowly. 

COMPOUND  OF  MERCURY  WITH  CYANOGEN. 

§  1105.  Only  one  compound  of  mercury  with  cyanogen  is  known, 
corresponding  to  the  protoxide  HgO.  The  combination  is  made  by 
dissolving  protoxide  of  mercury  in  cyanohydric  acid,  for  which  pur- 
pose the  dilute  cyanohydric  acid  obtained  by  the  solution  of  the 
ferrocyanide  of  potassium  in  dilute  sulphuric  acid  is  used.  Cyanide 
of  mercury  is  generally  prepared  in  the  laboratory  by  boiling  to- 
gether 8  parts  of  Prussian  blue,  1  of  protoxide  of  mercury,  and  8 
of  water,  when  the  boiling  solution,  after  being  filtered,  deposits  on 
cooling  white  prismatic  crystals  of  anhydrous  cyanide  of  mercury 
HgCy  or  HgC^N.  When,  as  often  happens,  the  liquid  contains  a 
small  quantity  of  iron  in  solution,  it  is  boiled  with  protoxide  of  mer- 
cury, which  precipitates  the  oxide  of  iron.  Cyanide  of  mercury 
may  also  be  prepared  by  boiling  2  parts  of  ferrocyanide  of  potassium 
with  3  of  protosulphate  of  mercury  dissolved  in  15  or  20  parts 
of  water ;  when  the  liquid  deposits,  on  cooling,  crystals  of  cyanide 
of  mercury. 

The  affinity  of  mercury  for  cyanogen  is  considerable,  as  oxide 
of  mercury  decomposes  cyanide  of  potassium,  potassa  and  cyanide 
of  mercury  being  formed.  When  boiled  for  a  long  time  the  prot- 
oxide of  mercury  dissolves  in  the  cyanide  of  mercury,  and  the  liquid 
deposits  crystals  of  oxycyanide  of  mercury.  Cyanide  of  mercury 
combines  with  a  great  number  of  metallic  cyanides,  and  yields 
crystallizable  double  cyanides.  The  double  cyanide  of  mercury 
and  potassium  crystallizes  in  regular  octahedrons  of  the  formula 
KCy+HgCy.  Cyanide  of  mercury  also  combines  with  the  chlo- 
rides, alkaline  bromides,  and  iodides,  forming  several  crystallizable 
compounds. 


288  MERCURY. 

COMPOUND  OF  MERCURY  WITH  NITROGEN. 

§  1106.  If  dry  ammoniacal  gas  be  passed  over  protoxide  of  mer- 
cury, prepared  by  the  humid  way,  until  the  latter  can  absorb  no 
more,  and  the  product  be  then  slowly  heated  in  an  oil-bath  to  302°, 
still  maintaining  the  current  of  ammonia,  a  brown  powder  is  ob- 
tained, which  is  a  compound  of  mercury  with  nitrogen,  having  the 
formula  Hg^N.  The  substance  is  generally  mixed  with  a  small 
quantity  of  suboxide  of  mercury,  which  can  be  removed  by  weak 
nitric  acid.  Nitride  of  mercury  detonates  by  heat,  and  by  percus- 
sion, or  by  contact  with  concentrated  sulphuric  acid  properly  pre- 
pared. Acids  dissolve  it,  producing  mixtures  of  mercurial  and  am- 
moniacal salts. 

DETERMINATION  OF  MERCURY,  AND  ITS  SEPARATION  FROM  THE 
METALS  PREVIOUSLY  DESCRIBED. 

§  1107.  Mercury  is  generally  determined  in  the  metallic  state, 
and  sometimes  also  in  the  state  of  subchloride  HggCl.  In  order  to 
separate  mercury  from  its  compounds,  uiider  conditions  in  which 
the  metal  can  be  very  exactly  weighed,  a  tube  ah  of  hard  glass  is 
^  employed,  resembling  those  used 

fl^-  ■;.-^....^fr^-.^,T:;,^^..v:>>^  a  )  ^^  *^®  analysis  of  organic  sub- 
\;^^/  stances,  and  drawn  out  in  one  of 
Fig.  678.  its  ends,  as  represented  in  fig.  578, 

having  a  globe  A  at  the  narrow 
portion,  in  which  the  mercury  condenses.  A  small  quantity  of  as- 
bestus  being  placed  at  a  in  the  tube,  upon  it  is  poured  a  volume  of 
quicklime,  and  the  mercurial  substance,  exactly  weighed,  is  intro- 
duced at  c,  and  lastly,  the  tube  is  filled  with  lime.  This  being  done, 
the  tube  is  arranged  over  a  sheet-iron  furnace,  and  a  current  of  dry 
hydrogen  gas  passed  through  the  extremity  h  ;  the  anterior  portion 
ca  of  the  tube  containing  the  lime  being  first  heated,  while  the  coals 
are  gradually  carried  toward  the  end  h.  The  mercurial  product  is 
decomposed,  the  mercury  is  carried  over  in  the  state  of  vapour  by 
the  hydrogen  gas  and  condenses  in  the  globe  A,  while  the  small  quan- 
tity of  water  which  sometimes  also  collects  there  is  soon  carried  off 
by  the  dry  hydrogen.  At  the  c«lose  of  the  operation,  the  globe  A  is 
detached  and  weighed  with  the  mercury  it  contains ;  after  which  the 
metal  is  poured  out,  and,  for  greater  exactness,  the  interior  of  the 
globe  is  washed  with  nitric  acid  and  then  with  distilled  water.  The 
globe,  being  empty  and  perfectly  dry,  is  weighed,  and  the  weight  of 
the  condensed  mercury  thus  ascertained.  In  order  to  obtain  exact 
results,  care  must  be  had  that  the  temperature  of  the  globe  does  not 
rise,  in  consequence  of  the  condensation  of  a  large  quantity  of  water, 
as  in  that  case  a  small  quantity  of  vapour  of  mercury  would  be  lost. 

When  the  mercurial  product  contains  nitric  acid  metallic  copper 
must  be  substituted  for  the  lime,  in  order  to  decompose  the  nitrous 
vapours,  which  would  attack  the  mercury  in  the  globe  A. 


AMALGAMS.  289 

§  1108.  Advantage  is  generally  taken  of  the  volatility  of  mer- 
cury to  separate  it  from  the  other  metals  with  which  it  is  mixed. 
When  it  is  dissolved  in  acids  it  is  always  precipitated  by  sulf  hydric 
acid,  and  the  precipitate  is  then  restored  to  the  metallic  state  by 
heating  the  product,  mixed  with  a  small  quantity  of  quicklime,  in  a 
current  of  hydrogen  gas.  When  the  sulphide  of  mercury  is  mixed 
with  other  metallic  sulphides  the  latter  are  separated,  as  the  mer- 
cury alone  distils  over. 

When  the  mercury  is  precipitated  from  its  solutions  in  the  me- 
tallic state  by  a  blade  of  iron,  or  by  protochloride  of  tin,  it  is  still 
necessary,  in  order  to  obtain  it  perfectly  pure,  to  distil  it  in  the 
apparatus  first  described. 

ALLOYS  OF  MERCURY,  OR  AMALGAMS. 

§  1109.  Mercury  combines  with  a  large  number  of  metals,  form- 
ing alloys,  called  amalgams^  which  are  fluid  when  the  mercui-y 
largely  predominates,  and  solid  in  the  contrary  case.  The  presence 
of  a  very  small  quantity  of  foreign  metal  suffices  to  destroy  the 
fluidity  of  mercury  and  its  other  physical  characters. 

Mercury  combines  with  potassium  and  sodium  and  evolves  heat, 
while  doughy  amalgams  are  formed  which  decompose  water.  With 
lead  and  tin  it  forms  amalgams  the  consistency  of  which  varies  with 
the  proportion  of  metal  combined.  If  these  amalgams  be  heated  so 
as  to  make  them  perfectly  liquid,  and  then  allowed  to  cool  slowly, 
crystals  of  solid  amalgam  separate,  exhibiting  compounds  of  definite 
proportions.  An  amalgam  of  silver,  crystallized  in  regular  dode- 
cahedrons, and  the  usual  composition  of  which  is  expressed  by  the 
formula  HggAg,  is  found  in  nature.  Amalgams  are  readily  decom- 
posed by  heat,  and  give  ofi"  the  whole  of  their  mercury,  which  distils 
over. 

PLATING  OP  MIRRORS. 

§  1110.  Mirrors  are  made  by  covering  one  side  of  the  glass  with 
an  amalgam  of  mercury  and  tin  in  the  following  manner : — A  sheet 
of  tin-foil,  of  the  same  size  as  the  glass,  is  laid  upon  a  very  smooth 
marble  table,  set  in  a  wooden  frame  and  surrounded  by  little  canals. 
The  table,  which  is  movable  and  may  be  inclined  in  various  ways, 
is  first  made  perfectly  horizontal,  and  the  sheet  of  tin,  being  smoothed 
with  a  hare's  foot,  is  then  completely  saturated  with  mercury  ap- 
plied by  the  same  instrument.  It  is  then  covered  with  a  coat  of 
mercury  4  or  5  millimetres  in  thickness,  after  which  the  glass  plate 
is  brought  to  the  end  of  the  table,  and  pushed  over  the  sheet  of  tin, 
so  as  to  drive  before  it  the  mercury  in  excess,  which  runs  into  the 
canal  around  the  table.  The  glass  is  then  loaded  with  lumps  of 
plaster,  distributed  uniformly  over  its  surface,  and  the  table  is  in- 
clined to  facilitate  the  escape  of  the  mercury  expelled  by  pressure. 
It  is  then  left  in  this  position  for  15  or  20  days,  after  which  the 

Vol.  XL— 19 


290 


MERCURY. 


coating  adhering  to  the  glass  is  composed  of  about  4  parts  of  tin 
and  1  of  mercury. 

METALLURGY  OF  MERCURY. 

§  1111.  The  principal  ore  of  mercury  is  the  sulphide  or  cinnabar, 
which  mineral  is  found  in  two  different  geological  positions.  It 
sometimes  forms  veins  in  the  oldest  transition  rocks,  and  sometimes 
is  scattered  through  the  strata  of  sandstone,  schist,  or  compact  lime- 
stone, which  appear  to  belong  to  the  Jurassic  epoch.  The  famous 
mines  of  Almaden,  in  the  province  of  La  Mancha  in  Spain,  consist 
of  veins  traversing  micaceous  transition  schists,  while  the  mines  of 
Idria,  in  Illyria,  are  an  example  of  the  second  formation.  Mercury 
is  also  found  in  the  native  state,  in  small  globules  scattered  through 
bituminous  strata,  but  always  in  the  vicinity  of  bearings  of  cinnabar, 
and  probably  arising  from  certain  chemical  reactions  which  have 
taken  place  in  the  bosom  of  the  earth. 

Mercury  is  procured  from  cinnabar,  at  Idria  and  Almaden,  by 
roasting  the  ore  in  a  distilling  apparatus,  when  the  sulphur  burns  in 
the  state  of  sulphurous  gas,  while  the  mercury,  being  set  free,  distils 
over  and  condenses  in  the  chambers. 

§  1112.  Figures  579,  580,  and  581  represent  the  apparatus  used 
at  Idria.  A  is  a  large  roasting  furnace  (figs.  579  and  581)  furnished 
on  each  side  with  a  series  of  condensing  chambers  C,  C,...D.  The 
'ore  in  large  pieces  is  heated  on  an  arch  nn'  having  a  great  num- 


Fig.  579. 


ber  of  holes,  until  the  space  V  is  entirely  filled  with  it,  while  on  the 
second  arch  ff'  smaller  pieces  of  ore  are  placed ;  and  lastly,  on  a 
third  rr',  the  dust  and  mercurial  residues  of  preceeding  operations 
are  changed.    The  pulverulent  ore  is  placed  in  earthen  vessels  with 


METALLURGY  OF   MERCURY. 


291 


which  the  space  U  is  entirely  filled;  and  when  the  furnace  is 
charged,  fire  is  kindled  on  the  grate  F,  and  the  temperature  is 
gradually  raised.  The  sulphide  of  mercury  roasts  in  a  very  oxidiz- 
ing current  of  air,  which  enters  the  furnace  by  small  canals  opening 

into  the  spaces  G,  H, 
and  the  mercurial  va- 
pours are  carried  into 
the  condensing  cham- 
bers C,  C,  C,  C,  in  the 
first  three  of  which  the 
greater  portion  of  the 
metal  condenses, whence 
it  flows  into  the  conduits 
ahcd,  a'6'c'c?',  which  con- 
convey  it  into  a  reser- 
■p.     gg|  voir.     A  great  deal  of 

water  and  but  little  mer- 
cury condenses  in  the  last  chamber ;  and  as  the  latter  is  mixed  with 
dust,  it  is  collected  in  separate  conduits,  and  then  purified  by  filter- 
ing, while  the  residue  is  again  introduced  into  the  furnace.  In 
order  to  condense  the  last  mercurial  vapours  in  the  last  chambers 
E,  D,  water  is  poured  .over  the  inclined  planes  which  extend  from 
one  side  to  the  other,  and  between  which  the  gas  and  vapours  are 
obliged  to  circulate  before  passing  out  into  the  atmosphere. 

The  mercury  is  filtered  through  ticking-cloth,  and  then  placed  in 
cast-iron  bottles,  each  containing  about  60  pounds. 

The  ore  at  Idria  consists  of  several  kinds,  according  to  the  nature 
of  the  substances  with  which  the  cinnabar  is  intimately  mixed.  The 
richest  ores,  which  are  found  in  limestone,  and  yield  50  to  60  per 
cent,  of  mercury,  are  called  stahlerz  ;  and  the  lebererz,  or  cinnabar 
scattered  through  very  bituminous  schist  yields  40  to  50  per  cent, 
of  mercury.  The  ziegelerz  only  contain  from  10  to  20  per  cent., 
as  in  them  the  sulphide  is  disseminated  in  schists  and  quartzose 
sandstone.  * 

§  1113.  Certain  parts  of  the  veins  at  Almaden  contain  pure  cin- 
nabar, while  the  greater  portion  is  composed  of  cinnabar  scattered 
through  quartzose  and  argillaceous  gangues,  yielding  only  about  10 
per  cent,  of  mercury.  The  Spanish  mines  furnish  annually  more 
than  2000  tons  of  mercury. 

At  Almaden,  as  at  Idria,  the  treatment  consists  in  roasting  the 
ore  in  furnaces,  one  of  which  is  represented  in  figs.  582  and  583, 
and  which,  in  Spain,  are  called  huytrones.  The  furnace  consists  of 
a  prismatic  space  AB,  separated  into  two  compartments  by  a  brick 
arch  pierced  with  holes.  The  ore  is  heaped  in  the  space  B  above 
the  arch,  the  larger  pieces  being  at  the  bottom,  and  the  whole  is , 
covered  with  bricks  made  of  a  mixture  of  clay,  powdered  ore,  and 
mercurial  dust  arising  from  the  operation.     At  the  upper  part  of 


292 


MERCURY. 


Fig.  583.  •  ^ 

the  furnace  B,  apertures  p  communicate  with  earthen  receivers, 
arranged  on  each  other  in  rows.  Fig.  584  represents  some  of  these 
^^^!«»?^^^^^^^^*^^  receivers  or  aludells.  The  condensed 
^^^i^^^^**^^^"****  mercury  oozes  through  the  joints  of  the 
^^^'  ^^^'  aludells  on  the  lower  row,   and  flows 

into  a  canal  hh,  which  conveys  it  into  a  receiving  basin  w,  n^  n, 
while  the  gases,  mixed  with  the  mercurial  vapours  which  have  not 
been  condensed,  are  conveyed  into  a  chamber  E,  where  mercurial 
dust,  which  is  to  be  removed  from  time  to  time,  is  deposited.  The 
dust  yields,  by  filtering,  a  certain  quantity  of  fluid  mercury,  and  the 

residue  is  mixed  with  clay  of  which 
clay  bricks  are  made,  to  be  again 
heated  in  the  furnace  as  above 
stated.  The  firing  lasts  for  12  or 
13  hours,  after  which  the  furnace 
is  allowed  to  cool  for  3  or  4  days, 
when  the  materials  are  withdrawn 
and  a  second  operation  commenced. 
§  1114.  Mercurial  ores,  consisting 
of  mixtures  of  cinnabar  and  lime- 
stone, are  also  found  in  the  duchy 
of  Deux-Ponts,  (France,)  and  are 
worked  by  being  heated  in  earthen 
Fig.  585. .  retorts  A  (fig.  585)  furnished  with 


SILVER.  293 

earthen  receivers  B,  and  disposed  in  a  galley-furnace  M.  A  cer- 
tain quantity  of  water  is  placed  in  the  receivers,  where  the  sulphide 
of  mercury  in  this  case  is  decomposed  by  the  lime,  while  sulphide 
of  calcium  and  sulphate  of  lime  are  found.  The  mercury  set  free 
condenses  in  the  receivers. 


SILVER. 
Equivalent  =  108  (1350.0;  0  =  100). 

§  1115.  The  silver  used  for  coin  and  plate  is  never  pure,  but 
contains  a  certain  proportion  of  copper.  In  order  to  obtain  pure 
silver  the  alloyed  metal  is  dissolved  in  nitric  acid  and  sea-salt  added 
to  the  solution,  when  the  silver  is  precipitated  in  the  state  of  insoluble 
chloride,  while  the  other  metals  remain  in  solution.  100  parts  of 
the  dried  chloride  of  silver  being  mixed  up  with  70  of  chalk  and  4 
or  5  of  charcoal,  are  introduced  into  a  clay  crucible  and  heated  to  a 
strong,  white-heat,  when  carbonic  oxide  is  disengaged,  while  chloride 
of  calcium  and  metallic  silver  are  formed.  After  cooling,  the  silver 
is  found  in  a  button,  at  the  bottom  of  the  crucible,  covered  by  a  slag 
of  chloride  of  calcium. 

Silver  is  distinguished  from  all  other  metals  by  its  brilliant  white 
colour,  and  a  lustre  which  does  not  tarnish  in  the  air,  unless  the 
latter  contain  sulphuretted  vapours.  When  highly  polished,  silver 
reflects  light  and  heat  better  than  any  other  metal,  and  its  radiating 
power  is,  consequently,  very  feeble,  for  which  reason  a  close  silver 
vessel  will  retain  the  heat  of  a  liquid  which  it  may  contain  longer 
than  a  vessel  of  any  other  metal.  Silver,  the  density  of  which  of 
10.5,  is  harder  than  gold,  but  softer  than  copper,  while  the  addition 
of  a  small  quantity  of  copper  increases  its  hardness.  It  is  the  most 
malleable  of  the  metals,  after  gold,  and  can  be  beaten  into  very  thin 
leaves,  /ind  drawn  out  into  extremely  fine  wire.  It  possesses  also 
great  tenacity,  for  a  wire  of  2  millimetres  in  diameter  breaks  only 
under  a  weight  of  85  kilogrammes. 

The  fusing  point  of  silver,  which  is  at  a  white-heat,  is  supposed 
to  be  about  1000°  of  the  air  thermometer.  It  gives  off  very  appre- 
ciable vapours  at  the  temperature  of  a  forge-fire,  and  soon  vola- 
tilizes when  exposed  to  the  elevated  temperature  obtained  between 
two  coals  terminating  the  conductors  of  a  powerful  battery. 

Silver  may  be  crystallized  in  cubes  by  fusion  by  the  method 
stated,  (§  991),  and  native  silver,  which  is  often  found  in  beautiful 
crystals,  also  affects  the  cubic  form,  modified  by  the  faces  of  the 
octahedron  or  other  simple  forms  of  the  regular  system.    The  small 


294  SILVER. 

crystals  obtained  by  precipitating  silver  by  means  of  feeble  galvanic 
action  are  likewise  cubes. 

Although  silver  neither  absorbs  oxygen  at  the  ordinary  tempera- 
ture, nor  combines  permanently  with  that  substance  at  a  high  tem- 
perature, it  will,  when  kept  in  a  very  pure  state  for  a  long  time 
fused  in  the  air,  absorb  a  considerable  proportion  of  oxygen,  with 
which  it  parts,  on  cooling,  before  solidifying.  A  portion  of  the 
metal  is  frequently  thrown  out  of  the  crucible  by  the  evolution  of 
the  gas.  The  absorbing  power  of  silver  is  shown  by  the  following 
experiment : — 3  or  4  kilogrammes  of  very  pure  silver  are  fused  in 
an  earthen  crucible,  and  when  the  metal  has  attained  a  very  high 
temperature  the  crucible  is  uncovered,  and  a  small  quantity  of  salt- 
petre is  added,  which,  by  decomposing,  maintains  an  atmosphere  of 
oxygen  in  the  crucible.  After  the  addition  of  the  last  portion  of 
the  saltpetre  the  crucible  is  kept  covered  for  half  an  hour,  the  high 
temperature  still  being  maintained,  and  is  then  plunged  into  a 
w^ater-cistern,  beneath  a  bell-glass  filled  with  water,  when  the  oxy- 
gen absorbed  is  immediately  disengaged,  and  collected  in  the  glass. 

It  has  been  ascertained  that  silver  can  absorb  22  times  its  volume 
of  oxygen,  which  property  is  destroyed  by  the  presence  of  a  very 
small  quantity  of  foreign  metals. 

Silver  is  not  oxidized,  at  a  red-heat,  by  contact  with  the  caustic 
alkalies  and  alkaline  nitrates,  for  which  reason  silver  crucibles  are 
used  when,  in  chemical  analysis,  substances  are  to  be  treated  with 
caustic  potassa  or  saltpetre,  which  would  attack  platinum  crucibles. 
But  silver  is  affected  by  fused  alkaline  silicates,  oxide  of  silver, 
which  dissolves  in  the  silicate  and  colours  it  yellow,  being  formed. 

Silver  decomposes,  only  in  a  very  feeble  manner,  chlorohydric 
acid  in  solution,  and  reaction  takes  place  only  when  the  metal  is 
very  finely  divided  and  the  acid  is  kept  at  the  boiling  point.  Dilute 
sulphuric  acid  does  not  attack  silver,  while  the  acid  when  hot  and 
concentrated  soon  decomposes  it,  sulphurous  acid  being  disengaged 
while  sulphate,  of  silver  is  formed.  Nitric  acid  acts  on  silver,  even 
at  the  ordinary  temperature,  disengaging  deutoxide  of  nitrogen  and 
converting  the  silver  into  a  nitrate.  Sulf  hydric  acid  is  decomposed 
by  silver  at  the  ordinary  temperature ;  and  a  polished  blade  of  silver 
soon  blackens  in  a  solution  of  a  sulf  hydric  acid,  and  becomes  covered 
with  a  black  pellicle  of  sulphide  of  silver.  Chlorine,  bromine,  and 
iodine  act  on  silver  even  when  cold. 

COMPOUNDS  OF  SILVER  WITH  OXYGEN. 
§  1116.  Three  compounds  of  silver  with  oxygen  are  known : 

The  suboxide,    AggO. 

The  protoxide,  AgO. 

The  binoxide,    AgOj,. 
The  protoxide  is  the  only  oxide  of  silver  possessing  any  interest. 


FULMINATING   SILVER.  295 

By  heating  to  212°  in  a  current  of  hydrogen  gas,  certain  salts 
formed  by  the  protoxide  of  silver  with  organic  acids,  for  example 
the  nitrate,  the  protoxide  loses  one-half  of  its  oxygen,  and  a  subsalt 
of  silver  is  formed,  which  dissolves  in  water  and  produces  a  brown 
solution,  from  which  caustic  potassa  precipitates  the  suboxide  AggO 
as  a  black  powder.  The  subsalts  of  silver  appear  to  be  formed  under 
several  other  circumstances,  when  protosalts  of  the  metal  are  sub- 
jected to  deoxidizing  agencies. 

Protoxide  of  silver  AgO  is  obtained  by  pouring  potassa  in  excess  into 
a  solution  of  nitrate  of  silver,  when  a  brown  precipitate  of  hydrated 
protoxide  is  formed,  which  readily  parts  with  its  water  in  a  dry  vacuum 
or  at  a  moderate  heat,  becoming  converted  into  an  olive-coloured 
powder  of  anhydrous  protoxide.  Heat  soon  drives  off  the  oxygen 
from  the  protoxide  of  silver,  and  it  is  also  decomposed  by  the  solar 
rays.  The  hydrated  protoxide  dissolves  slightly  in  water  and  causes 
the  latter  subsequently  to  exert  an  alkaline  reaction  on  coloured 
tinctures  ;  but  it  does  hot  combine  with  the  caustic  alkalies.  Prot- 
oxide of  silver  is  a  powerful  base  which  combines  with  even  the  most 
feeble,  and  completely  neutralizes  the  most  powerful  acids ;  thus  ni- 
trate of  silver  behaves  perfectly  neutral  with  coloured  litmus  paper. 

When  the  two  platinum  conductors  of  a  battery  are  dipped  into  a 
dilute  solution  of  nitrate  of  silver,  contained  in  a  W  shaped  tube, 
the  positive  conductor  becomes  coated  with  brilliant,  black  prismatic 
crystals  of  binoxide  of  silver  AgG^,  which  is  more  fixed  than  the 
protoxide,  as  it  resists  a  temperature  of  212°  and  is  decomposed 
only  at  about  302°,  when  it  is  converted  immediately  into  metallic 
silver.  It  disengages  oxygen  when  in  contact  with  acids,  yielding 
protosalts  of  silver.  With  chlorohydric  acid  it  evolves  chlorine.  It 
decomposes  ammonia  with  effervesence,  the  oxygen  given  off  by  the 
binoxide  while  the  latter  is  reduced  to  protoxide,  uniting  to  form  water 
with  the  hydrogen  of  the  ammonia,  while  nitrogen  is  disengaged. 

Ammoniuret  of  Oxide  of  Silver, 

§  1117.  By  digesting  oxide  of  silver  with  a  concentrated  solution 
of  caustic  ammonia,  a  black,  highly  explosive  powder  is  formed, 
which  is  also  obtained  by  pouring  caustic  potassa  into  the  solution 
of  a  salt  of  silver  in  an  excess  of  caustic  ammonia..  This  compound, 
Called  fulminating  silver^  detonates  very  easily,  and  should  be 
handled  with  the  greatest  care,  as  it  even  explodes  under  water 
when  the  latter  is  heated  to  212°.  Chemists  are  not  agreed  as 
to  the  composition  of  fulminating  silver ;  while  some  regard  it  as 
formed  by  the  direct  combination  of  ammonia  with  oxide  of  silver, 
and  assign  it  the  formula  AgO,NH3,  others  consider  it  as  an  amidide 
of  silver  AgNH^  produced  by  the  reaction  AgO-fNHg  =  AgNHgH- 
HO  ;  and  lastly,  a  large  number  suppose  it  to  be  a  simple  nitrate  of 
silver  arising  from  the  reaction  expressed  by  the  equation  3AgO  + 
NH3  =  Ag3N+3H0. 


296  SILVER. 

SA^TS  FORMED  BY  PROTOXIDE  OF  SILVER. 

§  1118.  As  has  already  been  said,  (§  1116,)  protoxide  of  silver  is 
a  powerful  base,  which  combines  with  even  the  weakest  acids,  and 
perfectly  neutralizes  powerful  acids  as  regards  their  action  on 
coloured  reagents.  Under  some  circumstances  potoxide  of  silver 
even  behaves  like  a  base  stronger  than  the  alkalies,  for  it  decom- 
poses some  alkaline  salts  by  abstracting  a  portion  of  their  acid ; 
which  reaction,  however,  only  takes  place  when  a  double  salt  can 
be  formed.  The  salts  of  silver  are  colourless  w^hen  the  acid  itself  is 
colourless.  The  soluble  salts  of  silver  are  obtained  by  dissolving 
the  carbonate  of  silver  in  acids,  while  those  that  are  insoluble  are 
prepared  by  double  decomposition  by  means  of  the  nitrate  of  silver 
obtained  by  dissolving  the  metal  in  nitric  acid.  The  soluble  salts 
of  silver  have  a  disagreeable  metallic  taste,  and  are  very  poisonous. 
All  the  salts  of  silver  are  blackened  by  solar  light :  they  are  decom- 
posed, and  metallic  silver  separates.  The  soluble  salts  present  the 
following  characteristic  reactions : 

Potassa  and  soda  throw  down  a  brown  precipitate  of  hydrated 
protoxide,  which  does  not  dissolve  in  an  excess  of  reagent,  while 
ammonia  produces  the  same  precipitate  in  neutral  solutions,  but  re- 
dissolves  it  entirely  when  present  in  excess ;  and  if  the  solution 
contains  a  great  excess  of  acid,  it  is  not  clouded  by  ammonia,  be- 
cause a  double  salt  of  silver  and  ammonia,  indecomposable  by  an 
excess  of  ammonia  is  formed.  Carbonates  of  potassa  and  soda  yield 
a  dirty-white  precipitate  of  carbonate  of  silver,  which  does  not  dis- 
solve in  an  excess  of  reagent,  and  carbonate  of  ammonia  produces 
the  same  precipitate,  which  dissolves  in  an  excess  of  carbonate  of 
ammonia  and  in  caustic  ammonia.  The  precipitated  oxide  and  car- 
bonate of  silver  are  easily  decomposed  by  heat,  and  yield  a  spongy 
mass  of  metallic  silver,  which  becomes  compact  by  percussion  and 
presents  all  the  physical  characters  of  malleable  silver. 

Sulf  hydric  acid  produces  a  black  precipitate  of  sulphide  of  silver, 
and  the  alkaline  sulf  hydrates  yield  the  same  black  precipitate,  which 
does  not  dissolve  in  an  excess  of  sulf  hydrate. 

Ferrocyanide  of  potassium  yields  a  white,  and  the  cyanoferride 
or  red  prussiate,  a  brownish-red  precipitate. 

Chlorohydric  acid  and  the  soluble  chlorides  form  in  solutions  of 
silver  a  white  precipitate,  which  readily  collects,  on  shaking,  into  a 
consolidated  mass  if  the  liquid  contains  an  excess  of  nitric  acid. 
This  precipitate  is  insoluble  in  an  excess  of  nitric  acid,  but  dissolves 
readily  in  ammonia ;  and  if  the  latter  be  saturated  by  an  acid  the 
chloride  of  silver  is  again  precipitated.  The  precipitate  soon  turns 
black  in  the  light,  first  assuming  a  violaceous  hue,  which  distinguishes 
it  from  freshly  precipitated  subchloride  of  mercury  Hg^Cl,  which  is 
formed  when  a  soluble  chloride  is  poured  into  a  solution  of  a  subsalt 
of  mercui-y,  and  which  remains  white  for  a  long  time.     A  blade  of 


NITRATE   OF   SILVER.  297 

zinc  or  iron  brought  into  contact  with  the  moist  chloride  decom- 
poses it  and  separates  the  metallic  silver. 

The  soluble  iodides  form,  in  solutions  of  silver,  a  yellowish-white 
precipitate  of  iodide  of  silver,  which  dissolves  with  difficulty  in  a 
great  excess  of  acid  or  ammonia. 

Silver  is  precipitated  from  its  solutions  in  the  metallic  state  by  a 
great  number  of  metals,  particularly  by  iron,  zinc,  and  copper. 
Mercury  effects  the  same  decomposition,  but  the  silver  precipitated 
combines  gradually  with  the  mercury  until  a  solid  amalgam  is 
formed,  the  silver  subsequently  deposited  forming  long  brilliant 
needles  of  an  amalgam  of  silver,  filling  sometimes  the  whole  solu- 
tion.    This  crystallization  is  called  the  arhor  Dianse. 

Nitrate  of  Silver, 

§  1119.  Silver  dissolves  readily  in  nitric  acid,  and  on  evaporating 
the  liquid  the  nitrate  of  silver  formed  crystallizes,  in  the  anhydrous 
state,  in  the  form  of  large  colourless  plates.  Nitrate  of  silver  is 
generally  made,  in  the  laboratory,  from  coin  which  contains  y^  of  its 
weight  of  copper,  by  dissolving  it  in  nitric  acid,  and  evaporating  to 
dryness  the  blue  solution  obtained,  which  contains  both  nitrate  of 
silver  and  nitrate  of  copper.  The  residue  is  fused  in  a  porcelain 
capsule,  at  a  temperature  below  a  dull-red  heat,  when  the  nitrate 
of  copper  is  converted  into  protoxide  of  copper  CuO,  which  colours 
the  fused  nitrate  of  silver  black.  The  temperature  is  maintained 
until  the  nitrate  of  copper  is  entirely  decomposed,  which  is  ascer- 
tained by  extracting  a  certain  portion  by  means  of  a  glass  rod,  dis- 
solving it  in  a  small  quantity  of  water,  and  pouring  an  excess  of 
ammonia  into  the  filtered  solution  ;  if  the  liquid  does  not  turn  blue 
the  nitrate  of  copper  is  entirely  decomposed.  The  substance  is 
then  dissolved  in  water,  and  the  oxide  of  copper  separated  by  fil- 
tration. 

The  oxide  of  copper  remaining  in  the  liquid  may  also  be  precipi- 
tated by  oxide  of  silver.  After  having  evaporated  to  dryness  the 
solution  of  the  nitrates  to  drive  off  the  excess  of  acid,  and  dissolved 
the  residue  in  water,  about  \  of  the  liquid  is  separated,  and  is  com- 
pletely precipitated  by  caustic  potassa  in  excess,  when  the  oxides 
of  silver  and  copper  are  deposited.  They  are  washed  with  cold 
water  and  then  boiled  with  the  remaining  *  of  the  liquid,  when  the 
oxide  of  silver  completely  precipitates  the  oxide  of  copper,  while 
nitrate  of  silver  alone  remains  in  solution,  the  deposit  consisting  of 
a  large  quantity  of  oxide  of  copper  and  very  little  oxide  of  silver. 

Nitrate  of  silver  is  also  frequently  prepared  from  the  chloride, 
which  is  always  obtained  in  large  quantities  in  laboratories  where 
minerals  are  analyzed.  The  chloride  of  silver  may  be  decomposed 
by  hme,  in  a  crucible  heated  to  a  white-heat,  as  stated,  (§  1115), 
and  pure  metallic  silver  may  be  thus  obtained  and  afterwards  dis- 
solved in  nitric  acid ;  but  generally,  an  iron  rod,  previously  moist- 


208  SILVER. 

ened  with  water  acidulated  by  clilorohydric  acid,  is  dipped  into  the 
chloride  of  silver,  which  is  thus  gradually  decomposed  and,  after 
some  time,  leaves  only  metallic  silver,  which  is  washed  with  acidu- 
lated water  and  dissolved  in  nitric  acid. 

Nitrate  of  silver  is  soluble  in  its  weight  of  cold,  and  one-half  of 
its  weight  of  boiling  water,  and  also  dissolves  in  4  parts  of  boiling 
alcohol.  It  has  been  mentioned  that  nitrate  of  silver  fuses  without 
change  at  a  temperature  below  a  dull-red:  it  solidifies  on  cooling 
into  a  crystalline  mass,  and,  if  further  heated,  it  decomposes.  At 
the  commencement  of  the  decomposition  oxygen  alone  is  disen- 
gaged, and  the  salt  is  transformed  in  the  nitrite  AgO,N03,  while 
subsequently,  both  oxygen  and  nitrogen  are  disengaged,  and  finally 
metallic  silver  alone  remains. 

Fused  nitrate  of  silver  is  used  in  surgery  as  a  cautery,  under  the 
name  of  lapis  infernalis,  which  is  usually  employed  in  the  shape  of 
small  sticks  fixed  in  the  end  of  a  pencil-holder.  The  sticks  are 
made  by  pouring  fused  nitrate  of  silver  into  an  iron  mould  similar 
to  that  represented  in  fig.  323,  (page  445,  vol.  i. ;)  and  because  the 
sides  of  the  mould  decompose  a  small  quantity  of  the  nitrate,  the 
sticks  generally  appear  black  at  the  surfaces. 

Nitrate  of  silver  is  also  used  internally  in  certain  forms  of  epi- 
lepsy, but  it  is  a  dangerous  remedy  and  should  be  administered 
with  great  prudence.  Persons  who  have  taken  this  medicine  should 
avoid  exposure  to  the  light  of  day  until  the  salt  of  silver,  which  is 
distributed  throughout  the  whole  organism,  has  been  carried  ofi", 
without  which  precaution  all  the  parts  of  the  body  exposed  to  light 
turn  blue,  in  consequence  of  the  decomposition  of  the  salt  of  silver 
in  the  subcutaneous  tissue. 

Nitrate  of  silver  is  decomposed  feebly  by  solar  light,  and  more 
rapidly  in  the  presence  of  organic  substances.  A  drop  of  a  solution 
of  nitrate  produces  a  brownish-black  mark  on  the  skin,  which  can  be 
removed  only  by  a  solution  of  cyanide  of  potassium.  When  a  piece 
of  linen  soaked  in  nitrate  of  silver  is  exposed  to  a  current  of  hy- 
drogen gas,  it  remains  covered  with  metallic  silver  presenting  a 
certain  degree  of  lustre ;  which  property  has  been  applied  to  the 
silvering  of  designs  on  muslins,  but  without  much  success. 

Nitrate  of  silver  absorbs  dry  ammoniacal  gas,  and  forms  a  com- 
pound of  the  formula  AgOjNOs+SNHg,  from  which  heat  com- 
pletely expels  the  ammonia.  If  nitrate  of  silver  be  poured  into  an 
excess  of  ammonia  and  the  liquid  be  evaporated,  it  deposits  crystals 
of  which  the  formula  is  AgO,N05+2NA3. 

When  a  solution  of  nitrate  of  silver  is  boiled  with  very  finely 
divided  metallic  sliver,  obtained  by  chemical  preparation,  a  consi- 
derable quantity  of  silver  will  be  found  to  dissolve ;  and  compounds, 
analogous  to  those  formed  when  a  solution  of  nitrate  of  lead  is  boiled 
with  metallic  lead,  (§  967,)  are  probably  produced. 


ACETATE   OF   SILVER.  299 

Sulphate  of  Silver. 

§  1120.  Sulphate  of  silver  is  obtained  by  heating  metallic  silver 
with  concentrated  sulphuric  acid,  when  sulphurous  acid  is  disen- 
gaged while  a  white  crystalline  powder  of  sulphate  of  silver  is 
formed.  It  is  also  obtained  by  pouring  sulphuric  acid  or  sulphate 
of  soda  into  a  boiling  solution  of  nitrate  of  silver,  in  which  case  the 
sulphate  of  silver  is  precipitated  in  the  form  of  small  prismatic  crys- 
tals. During  the  cooling  of  the  liquid,  new  crystals  are  deposited 
which  are  sufficiently  developed  to  allow  their  shape,  which  is  the 
same  as  that  of  anhydrous  sulphate  of  soda,  to  be  distinguished. 
Sulphate  of  silver  is  very  slightly  soluble  in  water,  as  hot  water 
scarcely  dissolves  ~  part  of  it ;  but  it  readily  dissolves  in  ammonia, 
and  the  liquid,  when  evaporated,  yields  crystals  of  a  compound 
sulphate  of  silver  and  ammonia  of  the  formula  AgO,S03  4-2NHg. 

Hy2:)osulpMte  of  Silver. 

§  1121.  Protoxide  of  silver  has  so  great  an  affinity  for  hyposul- 
phurous  acid  that  it  abstracts  it  from  potassa  and  soda.  If  oxide 
of  silver  be  digested  with  a  solution  of  hyposulphite  of  soda,  a  con- 
siderable proportion  of  oxide  of  silver  dissolves,  and  the  liquid,  when 
evaporated,  yields  crystals  of  the  double  hyposulphite  of  soda  and 
silver.  The  chloride,  bromide,  and  iodide  of  silver  also  dissolve 
readily  in  a  solution  of  hyposulphite  of  soda,  and  after  evaporation 
the  liquid  affords  the  same  crystals  of  double  hyposulphite.  The 
solubility  of  the  chloride,  bromide,  and  iodide  of  silver  is  applied  in 
photography,  to  the  fixing  of  the  image :  that  is,  to  the  removal  of 
the  compounds  of  silver  from  the  parts  which  have  not  been  acted 
on  by  light.  Solutions  of  the  double  hyposulphites  when  boiled 
give  off  sulphide  of  silver,  and  sulphate  of  soda  is  formed.  The  hy- 
posulphite of  silver  can  be  obtained  isolated,  in  the  form  of  a  white 
powder,  by  pouring  a  solution  of  hyposulphite  of  soda  into  a  solu- 
tion of  nitrate  of  silver ;  but  the  precipitate  soon  blackens  in  the 
light,  sulphide  of  silver  being  formed. 

Carbonate  of  Silver. 

§  1122.  Carbonate  of  silver,  which  is  obtained  in  the  form  of  a 
white  precipitate,  by  pouring  carbonate  of  soda  into  a  solution  of 
nitrate  of  silver,  soon  turns  brown  when  exposed  to  solar  light,  and 
is  readily  decomposed  by  heat. 

Acetate  of  Silver. 

§  1123.  Acetate  of  silver  is  prepared  by  dissolving  the  carbonate 
in  acetic  acid,  or  by  pouring  acetate  of  soda  into  a  concentrated 
hot  solution  of  nitrate  of  silver ;  in  which  case  the  acetate  of  silver 
crystallizes  in  small  prisms  during  the  cooling  of  the  liquid. 


300  SILVER. 


COMPOUNDS  OF  SILVER  WITH  SULPHUR. 

§  1124.  Silver  and  sulphur  combine  directly  when  a  mixture  of 
the  two  substances  is  heated.  The  excess  of  sulphur  distils  over, 
and  if  it  be  heated  to  redness,  the  sulphide  of  silver  fuses  and  so- 
lidifies into  a  crystalline  mass  on  cooling.  Sulphide  of  silver  cor- 
responds to  the  protoxide :  its  formula  is,  consequently,  AgS.  It 
is  found  crystallized  in  nature  in  regular  octohedrons,  commonly 
modified  by  secondary  facets,  forming  a  blackish-gray  mineral  of  a 
metalloid  lustre,  the  density  of  which  is  7.2.  Sulphide  of  silver 
possesses  a  certain  degree  of  malleability,  and  will  receive  impres- 
sions under  the  coining-press;  but  it  is  so  soft  that  it  can  be 
scratched  with  the  nail.  Sulphide  of  silver  is  converted  by  roast- 
ing into  sulphurous  acid  and  metallic  silver.  Concentrated  boiling 
chlorohydric  acid  decomposes  it  by  disengaging  sulf  hydric  acid  and 
forming  the  chloride.  Concentrated  hot  sulphuric  acid  also  acts  on 
it  and  converts  it  into  a  sulphate,  the  action  of  nitric  acid  yielding 
the  same  product.  Sea-salt,  protochloride  of  copper,  and  some 
other  metallic  chlorides  convert  the  sulphide  of  silver  into  a  chlo- 
ride when  assisted  by  heat. 

The  same  sulphide  of  silver  is  produced,  by  the  humid  way,  when 
a  salt  of  silver  is  precipitated  by  sulf  hydric  acid,  or  by  an  alkaline 
sulf  hydrate.  Silver  decomposes  sulf  hydric  acid  even  when  cold, 
especially  in  the  presence  of  water,  and  its  surface  becomes  covered 
with  a  black  pellicle  of  sulphide.  On  account  of  which  property, 
silver  soon  blackens  in  the  vicinity  of  sulphuretted  emanations ;  as 
for  example,  silver  plate  soon  becomes  tarnished  when  eggs  or  fish, 
or  any  kind  of  food  which  can  evolve  sulf  hydric  acid,  is  heated  in 
it ;  especially  when  the  articles  are  not  very  fresh. 

Sulphide  of  silver  combines  with  a  great  number  of  metallic  sul- 
phides, and  principally  with  the  electro  negative  sulphides,  such 
as  those  of  arsenic  and  antimony,  forming  double  sulphides,  many 
of  which  occur  crystallized  in  nature. 

Native  sulphide  of  silver  is  isomorphous  with  native  subsulphide 
of  copper  CugS,  and  the  two  sulphides  appear  to  possess  the  pro- 
perty of  replacing  each  other  in  every  proportion,  as  occurs  for  ex- 
ample, in  the  gray  copper-ore  or  fahlerz.  We  have  said  that  such 
isomorphism  exists  only  between  substances  presenting  the  same 
chemical  formulae,  and  have  frequently  insisted  on  this  law  to  esta- 
blish the  equivalents  of  simple  bodies.  But  sulphide  of  silver  would 
present  an  exception  to  the  law  if  its  formula  was  written  HgS,  that 
is,  if  the  number  108  were  adopted  for  the  equivalent  of  the  metal ; 
which  consideration  has  induced  several  chemists  to  assign  to  sul- 
phide of  silver  the  formula  AgjjS,  that  of  Ag^O  to  our  protoxide  of 
silver,  and  to  take  the  number  54  for  the  equivalent  of  silver.  This 
opinion  is  also  confirmed  by  several  other  circumstances,  on  which 
"we  shall  briefly  dwell.    It  has  been  demonstrated  by  a  great  number 


COMPOUND   OF   SILVER  WITH   CHLORINE.  301 

of  experiments,  that  a  very  simple  ratio  exists  between  the  specific 
heats  of  simple  bodies  and  their  chemical  equivalents,  and  a  law  has 
been  observed  according  to  which  the  specific  heats  of  simple  bodies 
are  to  each  other  nearly  in  the  inverse  ratio  of  their  equivalents. 
Now,  silver  only  satisfies  this  law  by  admitting  the  number  54  for 
its  equivalent.  Moreover,  an  analogous  law  has  been  found  for 
compound  bodies,  by  which  the  specific  heats  of  compound  bodies^ 
of  the  same  formula^  are  to  each  other  very  nearly  in  the  inverse  ratio 
of  the  numbers  which  represent  their  chemical  equivalents.  Now,  the 
sulphides  of  silver  and  copper  Cu^S  satisfy  this  law,  if  the  formula 
AggS  be  admitted  for  the  sulphide  of  silver. 

But,  if  the  formula  of  sulphide  of  silver  be  written  AggS,  and, 
consequently,  that  of  our  protoxide  of  silver  AggO,  the  formula  of 
soda  should  be  written  NagO  and  not  NaO,  as  we  have  hitherto 
done ;  for  we  have  seen  (§  1120)  that  sulphate  of  silver  is  isomor- 
phous  with  anhydrous  sulphate  of  soda.  The  salts  of  potg-ssa  and 
lithia  being  isomorphous  with  the  corresponding  salts  of  soda,  when 
they  contain  the  same  quantity  of  water  of  crystallization,  the  formula 
of  potassa  should  be  written  K^O  and  that  of  lithia  Li^O ;  which  new 
formulae  are  justified  by  the  laws  of  specific  heat,  and  by  several 
important  considerations.  In  fact,  it  has  been  found  that  the  spe- 
cific heats  of  the  chlorides  of  potassium,  sodium,  silver,  and  the  sub- 
chlorides  of  mercury  Hg^Cl  and  copper  CugCl,  are  to  each  other  in 
the  inverse  ratio  of  the  equivalents  of  these  substances.  Now,  there 
is  no  doubt  that  CugCl  is  the  formula  of  subchloride  of  copper,  on 
account  of  the  indisputable  isomorphism  of  the  salts  of  the  protoxide 
of  copper  CuO  with  the  corresponding  salts  of  the  protoxide  of  iron, 
manganese,  zinc,  and  nickel.  The  chlorides  of  potassium,  sodium, 
and  silver  should,  therefore,  have  formulae  similar  to  that  of  sub- 
chloride  of  copper  CuaCl,  and  these  should  be  written  K^Cl,  NagCl, 
AggCl.  On  the  other  hand,  potassa,  soda,  and  lithia  have  hitherto 
presented  no  case  of  isomorphism  with  the  oxides,  the  formulae  of 
which  are  written  RO  ;  they  never  replace  baryta,  lime,  magnesia, 
the  protoxides  of  iron,  manganese,  zinc,  etc.,  which  circumstance 
becomes  very  natural  if  the  formula  R3O  is  assigned  to  the  alkaline 
oxides,  but  is  not  explained  if  the  formula  RO  be  retained. 

Considering  these  circumstances,  it  appears  that  the  equivalents 
of  the  alkaline  metals  ought  to  be  reduced  to  their  half :  we  have, 
however,  been  unwilling  to  make  this  change  in  the  present  work 
before  it  has  been  adopted  by  a  majority  of  chemists. 

COMPOUND  OF  SILVER  WITH  CHLORINE. 

§  1125.  Only  one  combination  of  silver  with  chlorine  is  known, 
corresponding  to  the  protoxide.  Chloride  of  silver  AgCl  is  ob- 
tained by  adding  chlorohydric  acid  or  a  solution  of  sea-salt  to  the 
solution  of  any  soluble  salt  of  silver,  when  a  white  precipitate  is 
formed,  which  soon  collects,  by  shaking,  in  cheesy  lumps,  especially 


302  SILVER. 

if  the  liquid  contains  an  excess  of  nitric  acid.  Chloride  of  silver  is 
nearly  insoluble  in  water  and  in  weak  solutions  of  nitric  acid,  but 
dissolves  sensibly  in  solutions  of  chlorohydric  acid  or  the  alkaline 
chlorides.  Concentrated  boiling  chlorohydric  acid  dissolves  a  con^ 
siderable  quantity  of  cliloride  of  silver,  and  the  saturated  solution 
deposits,  on  cooling,  small  octohedral  crystals  of  the  chloride.  Am- 
monia is  a  very  powerful  solvent  of  chloride  of  silver,  and  the  liquid, 
on  being  exposed  to  the  air,  gradually  loses  its  ammonia  and  de- 
posits octohedral  crystals  of  chloride  of  silver,  which  frequently 
attain  quite  a  considerable  size.  By  saturating  the  ammoniacal 
liquid  with  nitric  acid,  the  chloride  of  silver  is  again  deposited. 
Solutions  of  the  alkaline  hyposulphites  dissolve  a  large  quantity  of 
the  chloride,  (§  1121.) 

Chloride  of  silver  fuses  at  about  500°,  forming  a  yellow  liquid, 
which,  on  solidifying,  yields  a  translucent  substance  resembling 
horn,  easily  cut  with  a  knife.  At  a  red-heat,  chloride  of  silver 
gives  off  appreciable  vapours,  although  it  is  not  sufficiently  volatile 
to  allow  of  distillation.  It  soon  blackens  in  solar  light.  If  the 
chloride  be  suspended  in  water,  oxygen  is  given  off,  and,  after  some 
time,  the  liquid  contains  chlorohydric  acid,  while,  if  the  chloride  be 
dry,  chlorine  is  disengaged :  in  both  cases,  by  treating  the  altered 
substance  with  ammonia,  chloride  of  silver  is  dissolved  without  colour, 
while  metallic  silver  remains  in  the  form  of  a  black  powder. 

Chloride  of  silver  absorbs,  when  cold,  a  large  quantity  of  dry 
ammoniacal  gas,  giving  rise  to  a  compound,  the  composition  of 
which  is  expressed  by  the  formula  AgCl  +  SNHg,  and  which  readily 
parts  with  its  ammonia  by  the  application  of  heat.  It  has  been 
shown  (§  123)  that  liquid  ammonia  can  be  obtained  from  this  sub- 
stance. 

Chloride  of  silver  is  sometimes  found  crystallized  in  nature,  form- 
ing cubic  or  octohedral  crystals,  of  a  pearl-gray  colour  when  found 
in  the  interior  of  the  rock,  and  of  a  more  or  less  violaceous  hue 
when  occurring  very  near  to  or  on  the  surface. 

COMPOUND  OF  SILVER  WITH  BROMINE. 

§  1126.  A  bromide  of  silver  AgBr,  resembling  the  chloride,  is 
obtained  by  pouring  an  alkaline  bromide  into  a  solution  of  nitrate 
of  silver,  in  the  shape  of  a  white,  slightly  yellowish  precipitate, 
which  is  insoluble  in  water  and  nitric  acid,  but  readily  dissolves  in 
ammonia  and  the  alkaline  hyposulphites.  Chlorine  easily  decom- 
poses bromide  of  silver,  and  transforms  it  into  chloride.  Bromide 
of  silver  has  been  found  native  in  certain  silver-ores  from  Mexico. 

COMPOUND  OF  SILVER  WITH  IODINE. 

§  1127.  By  adding  iodide  of  potassium  to  a  solution  of  nitrate  of 
silver,  a  yellowish-white  precipitate  of  iodide  of  silver  Agl  is  ob- 
tained, which  is  insoluble  in  water,  slightly  soluble  in  nitric  acid,. 


DETERMINATOIN   OF   SILVER.  303 

and  soluble  but  to  a  small  degree  in  ammonia,  which  properties 
serve  easily  to  distinguish  it  from  the  chloride  and  bromide  of  silver. 
Chlorine  decomposes  it  and  sets  the  iodine  free,  and  chlorohydric 
acid  converts  it  into  a  chloride.  It  fuses  below  a  red-heat.  Al- 
though the  effect  of  light  on  the  iodide  is  less  rapid  than  on  the 
chloride,  the  former  soon  turns  black,  first  assuming  a  brown  tinge. 
Iodide  of  silver  dissolves  easily  in  a  solution  of  iodide  of  potassium, 
and  the  liquid  deposits,  on  evaporation,  crystals  of  a  double  iodide 
Agl+KI.  Native  iodide  of  silver  has  been  found  in  several  silver- 
ores,  in  crystals  belonging  to  the  regular  system. 
* 

COMPOUND  OF  SILVER  WITH  FLUORINE. 

§  1128.  Fluoride  of  silver  is  obtained  by  dissolving  the  oxide  or 
carbonate  in  fluohydric  acid,  forming  a  compound  which  is  very 
soluble  in  water  and  partly  decomposes  by  evaporation. 

COMPOUND  OF  SILVER  WITH  CYANOGEN. 

§  1129.  By  adding  a  solution  of  cyanohydric  acid  to  a  solution 
of  nitrate  of  silver,  a  white  precipitate  of  cyanide  of  silver  AgCy 
or  AgCgN  is  obtained,  which  is  insoluhle  in  water  and  dilute  nitric 
acid,  while  chlorohydric  acid  decomposes  it  and  converts  it  into  a 
chloride.  Ammonia  dissolves  it  readily,  and  it  is  also  easily  soluble 
in  the  alkaline  cyanides,  with  which  it  forms  crystallizable  double 
cyanides. 

COMPOUNDS  OF  SILVER  WITH  CARBON. 

§  1130.  Definite  compounds  of  silver  with  carbon  are  obtained  by 
decomposing  by  heat  certain  salts  formed  by  the  oxide  of  silver 
with  organic  acids.  Two  definite  carburets  have  hitherto  been  ob- 
served, corresponding  to  the  formulae  AgC  and  AgCg.  When 
heated  in  the  air  they  become  incandescent,  and,  after  burning  like 
tinder,  leave  metallic  silver. 

DETERMINATION   OF   SILVER,  AND    ITS   SEPARATION   FROM   THE 
METALS  PREVIOUSLY  DESCRIBED. 

§  1131.  Silver  is  determined  either  in  the  metallic  state,  or  in 
that  of  the  chloride,  the  first-named  method  being  employed  in  the 
case  of  cupellation,  a  process  presently  to  be  described.  When  silver 
is  in  solution,  it  is  generally  precipitated  by  a  slight  excess  of  chlo- 
rohydric acid ;  and,  in  order  to  collect  the  precipitate  more  easily,  it 
is  better  to  employ  a  boiling  solution  to  which  an  excess  of  nitric 
acid  has  been  added.  The  clear  supernatant  liquid  may  be  de- 
canted off,  and,  if  proper  care  be  taken,  none  of  the  precipitate  need 
be  lost.  In  order  to  wash  chloride  of  silver,  it  is  poured  into  a  thin 
porcelain  capsule,  filled  with  water  slightly  acidulated  with  nitric 
acid,  and  the  liquid  is  heated  to  ebullition  by  means  of  an  alco- 
hol-lamp, the  precipitate  being  kept  suspended  in  the  liquid  by 


304  SILVER. 

stirring  with  a  glass  rod.  After  it  has  been  allowed  to  rest,  and 
the  chloride  has  settled  at  the  bottom  of  the  capsule,  the  clear 
liquid  is  removed  with  a  pipette  and  introduced  into  a  cylinder, 
which  process  is  repeated  until  the  washing  is  completed.  Lastly, 
any  particles  of  chloride  that  may  have  found  their  way  into  the 
cylinder,  are  removed  thence  and  added  to  that  in  the  capsule, 
where  the  whole  is  dried ;  for  which  purpose,  the  capsule  is  placed 
upon  another  capsule  heated  by  an  alcohol-lamp,  by  which  means 
a  hot-air  bath  is  obtained  which  completely  dries  the  chloride. 
Finally,  the  capsule  is  weighed  when  cooled,  and,  the  chloride  bein» 
removed,  the  equilibrium  is  restored  by  weights.  The  dried  chloritle 
is  sometimes  fused  in  the  capsule,  in  which  case  the  separation, 
which  is  attended  with  some  difficulty,  is  effected  by  boiling  a  small 
quantity  of  concentrated  chlorohydric  acid  in  the  capsule  contain- 
ing the  chloride,  when  the  latter  generally  separates  in  a  single 
mass.  If  it  still  adheres,  water  must  be  added,  and  a  piece  of  zinc 
must  be  placed  on  the  chloride,  which,  by  being  restored  to  the 
metallic  state  by  the  zinc,  immediately  separates. 

The  chloride  of  silver  may  also  be  collected  in  a  very  finely 
pointed  glass  tube,  the  aper-ture  of  which  soon  becomes  closed,  by 
small  lumps  of  chloride,  sufficiently  to  prevent  the  escape  of  any  of 
the  precipitate,  without  interfering  with  the  filtration  of  the  clear 
liquid.  The  chloride  is  washed  in  the  tube,  which  is  then  dried  in 
a  stove.  In  all  cases,  chloride  of  silver  should  be  washed  in  a  room 
lighted  by  a  lamp,  so  that  it  may  not  be  affected  by  solar  light. 

§  1132.  The  solubility  of  silver  in  nitric  acid,  and  the  complete 
insolubility  of  chloride  of  silver,  renders  the  separation  of  this  metal 
from  all  the  metals  previously  described  an  easy  matter.  Silver 
cannot  be  immediately  precipitated  by  chlorohydric  acid,  only  in 
the  case  when  it  exists  in  solution  with  a  subsalt  of  mercury,  because 
a  mixture  of  chloride  of  silver  and  chloride  of  mercury  HggCl  is  de- 
posited. But  it  is  sufficient  to  treat  the  precipitate  with  boiling 
nitric  acid,  to  which  a  few  drops  of  chlorohydric  acid  have  been 
added,  to  dissolve  the  mercury  in  the  state  of  protochloride  HgCl. 
The  two  metals  may  also  be  precipitated  by  sulf  hydric  acid,  and 
the  mixture  of  the  sulphides  roasted  in  the  air,  when  the  mercury 
volatilizes,  while  the  silver  remains  entirely  in  the  metallic  state. 

METALLURGY  OF  SILVER. 

§  1133.  The  most  common  ores  of  silver  are : — 

1.  Sulphide  of  silver,  either  pure,  or  mixed  with  greater  or  less 
quantities  of  sulphide  of  copper  Cu^S,  which  do  not  change  its  crys- 
talline form. 

2.  Sulphide  of  silver,  combined  with  the  sulphide  of  arsenic  and 
antimony,  forming  a  great  number  of  minerals,  to  which  mineralogists 
give  different  names ;  e.  g.^  sulfantimoniate  of  silver,  of  which  the 
formula  is  3AgS  +  Sbj,Sa,  and  sulfarseniate  of  silver  SAgS+AsaSg. 


METALLURGY   OF   SILVER.  305 

These  two  minerals  aiFect  the  same  form  of  crystallization,  clearly 
proving  the  isomorphism  of  the  sulphides  of  arsenic  AsgSg  and  of 
antimony  SbgSg,  which,  however,  is  still  better  established  in  certain 
minerals  containing  at  the  same  time  sulphide  of  arsenic  and  sul- 
phide of  antimony  in  varying  proportions  6AgS  +  (Sbj„AS3)S3.  Sulf- 
arseniates  and  sulfantimoniates  of  silver  are  also  found  in  which  a 
portion  of  the  silver  is  replaced  by  copper  9(Cua,Ag)S  +  (Sb2,As2)S3. 

3.  The  arseniuret  of  silver  AggAs,  and  the  antimoniuret  Ag^Sb. 

4.  The  chloride,  bromide,  and  iodide  of  silver,  which  are  some- 
times found  in  sufficient  quantity  to  be  worked  as  ores  of  silver. 

5.  Many  galenas,  and  cupreous  ores  containing  silver,  are  the 
most  common  ores  of  silver  on  the  European  continent. 

6.  Native  silver,  frequently  scattered  through  the  le veilings  of 
lead  and  argentiferous  copper  veins,  and  probably  owing  its  pre- 
sence to  chemical  reactions  to  which  the  ore  has  been  subjected  in 
the  bosom  of  the  earth,  and  which  have  removed  the  other  metals 
in  the  state  of  soluble  compounds,  and  left  the  metallic  silver. 
Large  masses  of  native  silver  are  sometimes  found,  and  at  Konigs- 
berg,  in  Norway,  have  been  seen  to  weigh  280  kilogs. 

§  1134.  Argentiferous  lead-ores  are  first  worked  for  their  lead, 
from  which,  as  it  retains  all  the  silver,  the  latter  is  separated  by 
cupellation,  (§  98T.)  Argentiferous  copper-ores  are  also  worked  for 
their  copper,  and  the  black  copper  resulting,  is  passed  through  a 
furnace  with  lead,  furnishing  an  alloy,  from  which  the  argentiferous 
lead  is  separated  by  eliquation,  (§  1067,)  and  is  subsequently  sub- 
jected to  cupellation.  Again,  the  last  coppery  matts  are  subjected 
to  an  amalgamation,  which  shall  soon  be  described. 

Ores  of  silver  which  are  too  poor  in  lead  or  copper  to  be  worked 
for  the  advantageous  extraction  of  these  metals,  are  immediately 
subjected  to  amalgamation,  after  having  undergone  a  preliminary 
preparation.  Two  different  methods  of  amalgamation  are  used — 
that  of  Freiberg,  in  Saxony,  generally  adopted  in  Europe,  and  the 
American  method,  which  differs  essentially  from  the  European  plan 
in  requiring  no  fuel,  and  in  being  the  only  applicable  method  where 
fuel  is  scarce,  as  it  is  in  Mexico  and  South  America. 

Freiberg  Process. 

§  1135.  The  argentiferous  ores  of  Saxony  are  composed  of  sul- 
phide of  silver  combined  or  mixed  with  sulphides  of  arsenic,  anti- 
mony, iron,  zinc,  etc.  It  is  important  that  they  should  not  contain 
more  than  5  per  cent,  of  lead,  and,  at  most,  1  per  cent,  of  copper, 
as  these  metals  greatly  interfere  with  the  amalgamation :  they  amal- 
gamate with  mercury  as  readily  as  silver,  and  render  the  amalgam 
very  tough.  The  various  ores  are  sorted  so  that  the  charge  shall 
contain  2  or  3  thousandths  of  silver  and  a  proper  quantity  of  py- 
rites, which  latter  are  necessary,  because,  during  the  preliminary 
roasting,  they  furnish  a  certain  proportion  of  oxide  and  sulphate  of 

Vol.  II.— 20 


806 


SILVER. 


iron,  indispensable  in  the  chemical  reactions  of  amalgamation.  They 
are  to  be  added,  if  they  do  not  exist  in  sufficient  proportion ;  and 
sometimes  a  certain  quantity  of  sulphate  of  iron  is  also  added. 
Lastly,  10  or  12  parts  of  sea-salt  are  added  to  100  parts  of  ore. 

The  mixture  is  roasted  in  a  reverberatory  furnace,  heated  at  first 
very  gently,  in  order  to  dry  the  material,  which  is  then  spread  over 
the  sole  of  the  furnace,  and  the  temperature  being  gradually  raised, 
a  red-heat  is  maintained  for  about  4  hours,  when  a  large  quantity 
of  sulphurous  acid  is  disengaged  while  the  metals  oxidize.  The 
temperature  being  now  raised  still  higher,  sulphurous  acid  is  dis- 
engaged anew,  accompanied  by  vapours  of  sesquichloride  of  iron 
and  chlorohydric  acid,  arising  from  the  action  of  the  steam  and 
oxygen  on  the  chloride  of  iion.  After  roasting  for  f  of  an  hour, 
the  roasted  ore  is  withdraw^n  and  thrown  on  a  screen,  where  the 
consolidated  fragments  are  retained,  which  are  again  ground,  mixed 
with  2  per  cent,  of  sea-salt,  and  subjected  to  a  new  roasting.  The 
ore  which  has  passed  through  the  screen  is  again  sifted,  ground  to 
an  impalpable  powder,  bolted,  and  then  sent  to  the  amalgamating 
barrels. 

During  the  roasting,  the  sulphides  of  iron  and  copper  disengage 
sulphurous  acid,  oxides  and  sulphates  being  formed,  while  the  sulphide 
of  silver,  being  heated  with  the  sulphates  of  iron  or  copper,  is  entirely 
converted  into  sulphate  at  the  expense  of  the  sulphates  of  iron  and 
copper,  which,  while  being  transformed  into  oxides,  cause  the  dis- 
engagement of  sulphurous  acid.  The  sulphates  of  iron  and  copper 
fuse  together  with  the  sea-salt  before  attaining  a  red-heat ;  and  if 
the  mixture  contain  sulphide  of  silver,  sulphurous  acid  is  disengaged 
by  the  reaction  of  the  sulphur  of  the  sulphides  on  the  sulphuric  acid 
of  the  sulphates,  and  the  final  products  resulting  from  the  roasting 
are  thus,  sulphate  of  soda,  chloride  of  silver,  and  the  chlorides  of 
copper  and  iron.  If  the  reaction  takes  place  in  the  air,  the  iron 
passes  partly  into  the  state  of  sesquichloride  and  partly  into  that  of 
sesquioxide ;  and  the  sulphides  of  arsenic  and  antimony  are  also 
oxidized.  As  all  these  reactions  take  place 
during  the  roasting  in  the  reverberatory  fur- 
nace, the  roasted  ore  may  be  admitted  to 
consist,  in  addition  to  the  quartzose  gangues, 
of  sulphate  of  soda,  chloride  of  sodium, 
chlorides  of  manganese  and  lead,  sesqui- 
chloride of  iron  FcgCl,  subchloride  of  copper 
CugCl,  chloride  of  silver,  and  several  me- 
tallic oxides. 

The  amalgamating  barrels  are  made  of 

wood,  (fig.  586,)  strengthened  by  iron  hoops 

and  bars,  and  the  ends  have  iron  plates, 

furnished  with  gudgeons  exactly  in  the  axis 

A  cog-wheel  rr''  is  attached  to  one  end,  working  in 


Fig 

of  the  barrel. 


METALLURGY   OF    SILVER. 


307 


another  cog-wheel  rr'  (figs.  587  and  588)  on  a  shaft  AB  turned  by 
a  water-wheel.  Each  barrel  has  a  hole  a  closed  by  a  bung  kept  in 
place  by  an  iron  stirrup.     One  of  the  pedestals  on  which  the  gud- 


Fig.  587. 


geons  revolve  is  fixed,  while 
the  other  is  rendered  mov- 
able by  the  screw  v,  so  that 
the  wheel  rr"  may  be  thrown 
into  or  out  of  gear  without 
arresting  the  other  barrels 
C,  C  placed  near  the  hori- 
zontal staff  A  B,  and  work- 
ing in  the  same  cog-wheel 
rr' .  Above  each  barrel  is  a 
box  E  containing  the  bolted 
ore,  which  is  introduced  into 
the  former  by  means  of  a 
leather  hose  /,  entering  the 
opening  a,  while  reservoirs 
D  placed  above  each  barrel 
contain  the  quantity  of  water 
necessary  for  a  charge.  Be- 
neath the  barrels  are  re- 
ceivers mnm\  intended  to 
hold  the  material  after  the  opera- 
tion. 

After  150  litres  of  water  have 
been  introduced  into  each  barrel, 
the  charge  of  ore,  amounting  to 
500  kilogs.,  is  inserted,  being  taken 
from  the  box  E,  while  50  kilogs.  of 
scrap  sheet-iron  are  added.  The 
opening  in  the  barrel  is  then  closed 
with  the  bung,  and  when  all  the 
barrels  are  charged  in  the  same 
manner,  they  are  made  to  revolve  gently  for  2  hours,  after  which 
each  barrel  is  successively  thrown  out  of  gear,  in  order  to  allow  of 
an  examination  of  the  consistence  of  the  muddy  substance  it  con- 
tains. If  it  is  too  tough,  water  is  added ;  and  if  too  liquid,  more 
roasted  ore  is  thrown  in ;  and  when  the  proper  consistency  is  at- 
tained, 250  kilogs.  of  mercury  are  thrown  into  each  barrel,  and  the 
whole  is  again  set  in  motion,  the  temperature  in  the  barrels  rising 
considerably  after  some  time,  in  consequence  of  the  chemical  re- 
actions which  take  place  in  the  mixture.  After  the  barrels  have 
revolved  for  20  hours,  at  the  rate  of  20  revolutions  a  minute,  they 
are  stopped,  completely  filled  with  water,  and  made  to  revolve  for 
2  hours  more,  making  8  revolutions  per  minute,  when  the  amalgam 
separates  from  the  muddy  substances,  which  have  now  become  very 


808  SILVER. 

fluid.  Each  barrel  being  then  successively  thrown  out  of  gear,  and 
the  bung  turned  downward,  the  small  cork  of  the  bung  is  removed, 
and  as  soon  as  all  the  amalgamated  mercury  has  escaped  and  fallen 
into  the  receiver  mnm\  which  is  the  case  as  soon  as  the  mud  ap- 
pears, the  workman  replaces  the  cork.  The  mercury  runs  through 
the  tube  ii'  into  a  canal  A,  which  leads  it  into  a  particular  reservoir. 
When  all  the  mercury  has  escaped,  the  bung  of  the  barrel  is  re- 
moved, the  opening  a  turned  downward,  and  the  mud  allowed  to 
run  into  the  box  mnm'^  whence  it  flows  into  large  reservoirs  be- 
neath, the  scrap-iron  being  retained  by  a  grate. 

We  have  said  that,  before  adding  the  mercury ,-the  loaded  barrels 
are  turned  for  2  hours :  the  intention  of  this  is  to  decompose,  during 
this  period  of  the  process,  the  sesquichloride  of  iron  by  the  metallic 
iron,  and  restore  it  to  the  state  of  protochloride,  because,  if  the 
mercury  were  introduced  immediately,  it  would  act  on  the  sesqui- 
chloride of  iron  which  it  would  reduce  to  protochloride,  while  a 
certain  quantity  of  subchloride  of  mercury  HggCl  would  be  formed, 
which  would  decompose  no  longer,  arid  occasion  a  considerable 
waste  of  mercury ;  all  of  which  is  avoided  by  first  bringing  the  ses- 
quichloride of  iron  to  the  state  of  protochloride.  The  chloride  of 
silver,  which  dissolves  in  the  solution  of  sea-salt,  is  decomposed  by 
metallic  iron,  while  the  silver  set  free  combines  with  the  mercury ; 
and  the  chlorides  of  copper  and  lead  being  decomposed  in  the  same 
way  by  contact  with  the  iron,  these  metals  also  amalgamate  with 
the  mercury.  About  1  kilog.  of  iron  is  dissolved  in  each  operation. 
The  mud  escaping  from  the  barrels  is  placed  in  tubs,  where  it  is 
stirred  by  paddles  attached  to  a  vertical  axis,  after  being  diluted 
with  a  large  quantity  of  water,  the  tubs  being  provided  with  open- 
ings at  different  levels,  through  which  the  muddy  water  escapes. 
A  certain  quantity  of  amalgam,  which  separates  and  falls  to  the 
bottom  of  the  tubs,  is  then  removed  and  added  to  that  taken  from 
the  amalgamating  barrels. 

The  mercury  is  filtered,  with  the  assistance  of  slight  pressure, 

through  leather  bags,  through  the  pores  of  which,  a  small  portion 

J         c  ^  ^^  liquid  mercury,  containing  only  a 

^ fH— — slight   admixture  of  foreign    metals, 

escapes ;  while  a  doughy  amalgam,  con- 
taining nearly  5  parts  of  mercury  and 
1  part  of  silver,  mixed  with  foreign 
metals,  remains  in  the  bags.  The 
mercury  is  separated  from  the  amal- 
gam by  distillation,  which  is  eff'ected  by 
various  kinds  of  apparatus,  of  which  it 
will  suffice  to  describe  the  most  simple 
one.  To  the  opening  of  the  cast-iron 
tube  ah^  (fig.  589,)  which  is  closed  at 
Fig.  589.  one  end  a,  and  has  been  charged  with 


METALLURGY  OF   SILVER. 


309 


about  150  kilogs.  of  amalgam,  is  fitted  a  bent  tubing  cde,  the  tubu- 
lure  e  of  which  enters  a  sheet-iron  tube  fg^  which  dips  slightly  into 
the  water  contained  in  the  receiver  V.  The  tube  ah  being  gradually 
heated  to  redness,  the  mercury  distils  and  condenses  in  the  receiver 
V,  while  the  silver,  mixed  with  a  greater  or  less  quantity  of  copper 
and  lead,  remains  in  the  tube  ab. 

Amalgamation  of  the  Cupreous  Matts  hy  the  Mansfeld  Process, 

§  1136.  Amalgamation  is  applied  to  the  last  cupreous  matts 
arising  from  the  process  described,  (§  1066).  The  matt  is  stamped 
and  sifted,  and  then  ground  to  an  impalpable  powder,  which  is 
moistened  with  a  small  quantity  of  water  and  roasted  in  a  reverbe- 
ratory  furnace.  The  furnace,  a  vertical  section  of  which  is  seen  in 
fig.  590,  has  generally  2  stories,  surmounted  by  condensing  chambers 

where  the  vapours  and  dust  carried 
over  are  retained.  The  matt  is  first 
roasted  in  the  upper  space  B,  while  in 
the  lower  space  A  a  charge  is  being 
roasted,  consisting  of  about  200  kilogs. 
of  matt,  spread  in  a  thin  layer  over  the 
sole.  A  very  high  temperature  is  not 
applied,  because  it  is  indispensable  to 
prevent  the  softening  of  the  substance, 
which  would  interfere  with  the  roast- 
ing. The  workman  stirs  the  material 
with  an  iron  rake,  in  order  to  renew 
the  surfaces  exposed  to' the  oxidizing 
action  of  the  air,  and  the  roasting  lasts 
about  3  hours,  after  which  the  mate- 
rial is  removed  with  an  iron  scoop  and 
dropped  into  a  box.  After  the  first  roasting,  the  material  is  mixed 
with  9  or  10  per  cent,  of  sea-salt  and  10  per  cent,  of  very  finely 
powdered  limestone ;  water  is  added,  and  the  whole  is  worked  into 
a  homogeneous  paste,  which  is  dried  in  stoves.  The  mass  is  again 
ground  to  powder  and  roasted  in  a  lower  furnace  A,  where  a  higher 
temperature  prevails. 

The  limestone  is  added  to  decompose  a  portion  of  the  sulphates 
of  iron  and  copper ;  which,  if  present  in  too  great  quantity  for  amal- 
gamation, would  occasion  a  waste  of  mercury.  When  the  workman 
supposes  that  the  material  is  sufficiently  prepared,  he  proceeds  to 
test  it  by  mixing  a  small  quantity  of  the  roasted  powder  with  water 
and  mercury,  and,  after  diluting  it  with  a  larger  quantity  of  water, 
separating  a  mercurial  amalgam,  the  nature  of  which  he  estimates 
by  its  physical  properties.  According  to  the  appearance  of  the 
amalgam,  he  adds  a  small  quantity  of  salt,  lime,  or  even  of  roasted 
matt. 

The  second  roasting  lasts  only  about  IJ  or  2  hours. 


Fig.  590. 


810  .     SILVER. 

The  material  thus  prepared  is  poured  into  the  amalgamating 
barrels,  which  resemble  those  of  Freiberg,  500  kilogs.  of  roasted  ma- 
terial, 150  litres  of  hot  water,  and  40  kilogs.  of  scrap-iron  being 
introduced  into  each  barrel.  After  having  caused  the  barrels  to 
revolve  for  some  time,  150  kilogs.  of  mercury  are  added,  and  then 
the  barrels  are  made  to  turn  at  the  rate  of  15  revolutions  per 
minute  for  14  hours.  100  litres  of  water  are  then  added  to  each 
barrel,  which  is  turned  gently  for  some  time  to  facilitate  the  sepa- 
ration of  the  amalgam. 

The  deposit  of  cupreous  matt  which  remains  after  the  complete 
separation  of  the  amalgam,  after  being  mixed  and  pounded  with  15 
per  cent,  of  clay,  is  made  into  lenticular  cakes,  which  are  smelted, 
after  drying,  in  a  furnace,  with  the  addition  of  quartz,  furnishing 
black  copper,  which  is  subsequently  refined,  (|  1068.) 

The  amalgam  of  silver  is  treated  in  the  same  way  as  at  Freiberg. 

American  Process. 

§  1137.  The  principal  mines  in  America  are  those  in  Mexico 
and  Chili,  which  furnish  ores  consisting  of  metallic  silver,  sulphide  of 
silver  isolated  or  combined  with  sulphides  of  arsenic  and  antimony, 
chloride  of  silver,  etc.,  these  minerals  being  generally  disseminated 
in  such  fine  particles  as  not  to  be  perceived  in  the  gangue. 

The  ores  are  first  stamped,  then  ground  to  a  fine  powder,  and 
made  into  heaps,  called  tarts,  (tourtes,)  containing  500  to  600  quin- 
tals, on  platforms  built  of  stone.  The  material,  after  being  moist- 
ened with  water,  to  which  2  to  5  per  cent,  of  sea-salt  are  added,  is 
rendered  homogeneous  by  being  stamped  by  horses  or  mules.  In  a 
few  days,  about  J  or  1  per  cent,  of  magistral  is  added  to  it,  con- 
sisting of  a  roasted  copper  pyrite,  containing  8  to  10  per  cent,  of 
sulphate  of  copper.  It  is  again  stamped,  and  the  first  portion  of 
mercury  added ;  and  when  this  has  been  well  disseminated  through 
the  mass,  a  small  portion  of  the  material  is  washed  in  a  wooden 
bowl  to  separate  the  amalgamated  mercury.  By  its  appearance 
the  workman  judges  if  it  be  necessary  to  add  lime  or  magistral.  If 
the  surface  of  the  amalgam  is  grayish  and  the  metal  agglomerates 
easily,  the  amalgamation  is  going  on  correctly ;  but  if  the  mercury 
is  much  divided,  and  its  surface  exhibits  a  dark  colour  with  brown 
spots,  the  magistral  is  in  excess,  and  the  tart  is  then  said  to  be  too 
hot.  As  a  continuation  of  the  process  under  these  conditions  would 
occasion  a  great  loss  of  mercury,  lime  is  added,  which  decomposes  a 
portion  of  the  sulphate  and  chloride  of  copper  produced  by  the  re- 
action. If,  on  the  contrary,  the  mercury  retains  its  fluidity,  the 
chemical  reactions  do  not  advance,  and  the  tart,  being  too  cold, 
must  be  heated  by  the  addition  of  magistral. 

After  about  15  days,  when  the  first  portion  of  mercury  has  com- 
bined with  a  sufiicient  quantity  of  silver  to  be  converted  into  a 
doughy  amalgam,  a  second  portion  of  mercury  is  added ;  and  when 


KEFINING    OF   SILVER.  311 

this  is  well  incorporated  with  the  mass,  a  third  and  last  addition  is 
made;  the  test  just  described  being  frequently  repeated,  in  order  to 
judge  of  the  progress  of  the  operation.  The  whole  process  lasts  2 
or  3  months,  according  to  the  nature  of  the  ore  and  the  tempera- 
ture. When  it  is  finished,  the  material  is  washed  in  water  to  sepa- 
rate the  amalgam  from  it,  which  is  filtered  through  cloth,  and  the 
solid  part  which  remains  is  distilled.  By  the  American  process,  1  to 
3  parts  of  mercury  are  lost  for  1  part  of  silver  obtained. 

The  following  is  the  theory  of  the  operation : — The  sea-salt  and 
sulphate  of  copper  of  the  magistral  usually  decompose  each  other, 
protochloride  of  copper  CuCl  and  sulphate  of  soda  being  formed, 
while  the  metallic  silver  decomposes  the  protochloride  of  copper, 
and,  by  restoring  it  to  the.  state  of  subchloride  CugCl,  is  itself  con- 
verted into  chloride  of  silver.  The  subchloride  of  copper  dissolves 
in  the  solution  of  sea-salt,  and  reacts  on  the  sulphide  of  silver,  form- 
ing sulphide  of  copper  and  chloride  of  silver.  The  mercury,  in  its 
turn,  acts  on  the  chloride  of  silver,  which  dissolves  in  a  solution  of 
sea-salt,  forming  subchloride  of  mercm-y  Hgj,Cl,  while  the  metallic 
silver  combines  with  the  rest  of  the  mercury.  It  is  necessary,  in 
this  operation,  as  in  the  Freiberg  process,  that  no  free  protochloride 
of  copper  should  remain,  because  this  would  increase  the  waste  of 
mercury,  by  parting  with  one-half  of  its  chlorine  to  the  latter  metal 
in  order  to  transform  it  into  subchloride  HggCl.  The  intentioi» 
of  the  addition  of  lime  is  to  decompose  the  chloride  of  copper  in 
excess,  and  destroy  the  bad  effects  of  an  excess  of  magistral.  The 
subchloride  of  copper  Cu^Cl  exerts  no  injurious  influence. 

REFINING  OF  SILVER  ARISING  FROM  CUPELLATION  OR 
AMALGAMATION. 

§  1138.  The  impure  silver  is  melted,  exposed  to  a  current  of  air 
which  oxidizes  the  foreign  metals,  in  a  furnace  consisting  of  a  hemi- 
spherical cast-iron  cavity,  lined  with  a  thick  coat  of  marl  or  wood- 
ashes,  which  forms  a  sort  of  porous  cupel,  serving  to  absorb  the 
liquid  oxides  produced  by  the  oxidation  of  the  foreign  metals.  The 
cavity  is  filled  with  charcoal,  on  which  the  silver  to  be  refined  is 
placed,  and  the  combustion  is  assisted  by  a  bellows,  which,  at  the 
same  time,  furnishes  the  air  necessary  for  oxidation.  When  the 
silver  has^become  liquid  in  the  cupel,  the  air  is  projected  over  the 
surface  of  the  bath  until  no  spots  form  on  its  surface,  and  the  metal, 
being  then  refined,  contains  at  most  1  per  cent,  of  foreign  matter. 

Alloys  of  Silver, 

§  1139.  Silver  is  rarely  used  in  a  state  of  purity,  as  it  is  too  soft, 
and  articles  made  of  it  would  soon  be  worn  and  lose  the  sharpness 
of  their  edges  and  angles.  It  is  generally  alloyed  with  a  certain 
quantity  of  copper,  which  increases  its  hardness  ;  and  the  alloy  does 
not  assume  a  decided  yellow  tinge  unless  a  considerable  quantity 


312  SILVER. 

of  copper  is  present,  more  than  J  being  necessary  to  destroy  the 
white  colour,  to  which,  as  it  is  less  fresh  than  that  of  pure  silver, 
the  brilliancy  of  the  latter  is  artificially  given,  by  a  process  called 
washing.  The  intention  of  this  operation  is  to  remove  the  copper 
which  is  immediately  on  the  surface  of  the  alloy ;  for  which  purpose 
the  article  is  heated  to  a  dull  red-heat,  when  the  superficial  layer  of 
copper  oxidizes,  and  by  plunging  it  immediately  into  water,  acidu- 
lated by  nitric  or  sulphuric  acid,  the  oxide  of  copper  dissolves. 
After  the  washing,  the  surface  of  the  article  is  necessarily  dead, 
because  the  particles  of  silver  are,  as  it  were,  separated  from  each 
other  ;  but  it  is  readily  polished  by  burnishing. 

Alloys  of  silver  for  coin,  jewelry,  and  plate  are  subjected  to  a 
legal  standard,  regulated  by  law,  and  secured  by  a  stamp  for  jewelry 
and  plate. 

The  standard  of  French  coin  is  ^,  that  is,  it  must  contain  900 
of  silver  and  100  of  copper;  but  as  the  exact  proportions  cannot 
always  be  obtained,  a  variation  of  ^  is  allowed.  Thus  an  alloy 
of  897  of  silver  and  103  of  copper  is  received,  while  an  alloy  of  896 
of  silver  and  104  of  copper  is  illegal.  Alloys  containing  more  than 
903  of  silver  are  not  admitted,  as  it  is  more  advantageous  to  melt 
them  again  with  a  small  quantity  of  copper,  to  reduce  them  to  the 
legal  standard. 

The  standard  of  silver  medals  is  ^,  with  a  variation  of  ^  as  for 
coin.  ^ 

The  ordinary  standard  of  jewelry  and  plate  is  ^,  but  the  varia- 
tion is  greater  than  in  coin,  being  allowed  to  reach  :^^  below.  No 
superior  limit  is  fixed,  because  it  is  not  the  interest  of  the  silver- 
smith to  exceed  the  legal  standard. 

The  solder  used  for  silver  plate  consists  of  667  parts  of  silver, 
233  of  copper,  and  100  of  zinc. 

§  1140.  Many  articles  are  made  of  sheet-copper  covered  with  a 
lamina  of  silver,  and  are  then  called  plated-ware,  the  ordinary 
standard  of  which  is  ^,  that  is,  the  sheet  should  be  composed  of  ~ 
of  copper  and  l^  of  silver ;  while  sometimes,  however,  an  inferior 
standard  is  adopted.  Plated-ware  is  made  in  the  following  manner : — 
A  plate  of  copper,  and  one  of  silver  having  the  same  surface  and 
weighing  ^  of  the  copper,  being  selected,  the  surface  of  the  copper 
is  carefully  scraped,  and  it  is  then  dipped  into  a  strong  solution  of 
nitrate  of  silver,  where  it  is  covered  with  a  thin  coat  of  metallic 
silver.  This  being  done,  the  silver  plate  is  applied  to  the  copper, 
and,  the  whole  being  heated  to  a  brownish-red  colour  in  an  oven,  is 
then  passed  through  a  roller  until  the  sheet  has  attained  the  re- 
quired thickness.  The  two  metals  adhere  so  strongly  as  to  defy 
mechanical  separation. 


ASSAY   OF   ALLOYS   OF    SILVER.  313 

ASSAY  OF  ALLOYS  OF  SILVER. 

§  1141.  It  is  important  to  be  able  to  ascertain  quickly  and  ex- 
actly the  standard  of  alloys  of  silver,  in  order  that  the  manufacture 
of  coin  and  silver  plate  shall  remain  under  protection  of  the  govern- 
ment. The  assay  is  made  in  two  ways  :  the  first,  and  older,  by  cu- 
pellation ;  and  the  second,  by  analysis  by  the  humid  way^  which 
latter  process,  being  much  more  exact,  has  taken  the  place  of  cupel- 
lation  in  the  government  assay-office. 

Assay  by  Qupellation, 

§  1142.  The  analysis  of  alloys  of  silver  and  copper  by  cupellation 
is  founded  on  the  property  of  silver  not  to  oxidize  when  kept  in  a 
fused  state  in  the  air,  and  to  yield  nearly  insensible  ^vapours ;  while 
copper,  on  the  contrary,  oxidizes  under  these  circumstances,  and  is 
converted  into  the  suboxide  Cu^O ;  but,  in  order  to  separate  this 
substance  from  the  alloy,  it  has  been  found  necessary  to  introduce 
into  the  latter  a  certain  quantity  of  lead,  which,  by  oxidizing,  pro- 
duces liquid  litharge  in  which  the  suboxide  of  copper  dissolves. 
Fig.  591.  ^^®  roasting  is  effected  in  a  cupel,  (fig.  591,)  that  is, 

^=1^^^^  in  a  thick  porous  capsule  made  by  compressing  bone- 
^^r^^^^  ashes,  slightly  m(>istened  with  water,  in  moulds, 
:^^K^^^^^P  where  it  takes  the  shape  of  which  a  vertical  sec- 
""^^^^^^^^^^  tion  is  seen  in  fig.  592.  The  fused  oxide  of  lead, 
which  holds  the  other  oxides  in  solution,  soaks  into  the 
cupel,  and  nothing  remains  at  last  in  the  latter  but  the 
globule  of  refined  silver.  A  cupel  of  bone-ash  can  absorb 
about  its  own  weight  of  litharge. 
The  quantity  of  lead  necessary  to  add  to  an  alloy  of  silver  and 
copper,  to  effect  its  easy  cupellation,  should  be  in  proportion  to  the 
quantity  of  copper  contained ;  because  the  litharge,  after  having 
dissolved  the  suboxide  of  copper,  which  is  simultaneously  formed, 
must  preserve  sufficient  fluidity  to  soak  readily  into  the  cupel.  If 
the  infiltration  does  not  ensue,  the  metal  becomes  covered  with 
litharge  and  oxidation  ceases,  in  which  case  the  assay  is  said  to  be 
drowned,  {noj6.) 

Assay  by  cupellation  is  generally  performed  upon  1  gramme  of 
alloy ;  and  experience  has  shown  that  the  following  quantity  of  lead 
must  be  added  according  to  the  standard  of  the  alloy. 

Lead  necessary  for  refining 
Standard  of  the  Alloy.  1  gramme  of  silver. 

Silver  at  1000 0.5  gm. 

"  950 3 

"  900 7 

«  800 10 

"  700 12 

«  600 14 


814 


SILVER. 


16  to  17  gm. 


Lead  necessary  for  refining 
Standard  of  the  Alloy.  1  gramme  of  silver. 

Silver  at        500 

"  400 

"  300 

"  200 

"  100 

Pure  copper 

The  standard  of  the  alloy,  of  which  the  exact  composition  is  to 
be  ascertained,  being  in  general  approximately  known,  an  inspection 
of  the  table,  therefore,  gives  immediately  the  quantity  of  lead  to  be 
added.  Supposing,  for  example,  that  the  standard  of  a  piece  of 
coin  is  to  be  exactly  determined ;  knowing  that  its  standard  must 
be  nearly  ^,  sn).  addition  of  abou^  7  gm.  of  lead  must  be  made  to  1 
gm.  of  alloy  very  exactly  weighed. 

Fig.  593  repre- 
sents a  cupelling- 
furnace,  of  which 
a  vertical  section 
is  seen  in  fig.  594. 
The  muffle  A, 
which  is  the  most 
important  part  of 
the  furnace,  is 
a  semi-cylindri- 
cal earthen  cradle 
(fig.  595)  closed 
at  one  end,  and 
arranged  in  the 
furnace  so  that  it 
can  be  entirely 
surrounded  with 
fuel,  and  its  open- 
ing corresponds 
exactly  to  the 
aperture  D  of  the 

furnace.  The  sides  of  the  muflle  are  furnished  with  longitudi- 
nal slits,  through  which  the  external  air  which  enters  at  the  mouth 
of  the  mufile  escapes  into  the  current  of  air  in  the  furnace;  by 
which  arrangement  the  muflSe  is  constantly  traversed  by  a  very 
oxidizing  current  of  air.  The  reverberatory  furnace  has  generally 
a  sheet-iron  pipe  M  to  increase  its  draught. 

The  furnace  being  filled  with  charcoal  through  the  hole  F,  the 
cupels  are  introduced  into  the  muffle,  after  having 
been  previously  dried  on  the  platform  N,  if  newly 
made.    When  the  cupels  are  in  the  muffle,  the  open- 
Fig.  595.      ,ing  D  is  closed  with  the  door  E,  in  order  to  raise  the 


Fig.  593. 


Fig.  594. 


ASSAYING   OF   SILVER.  315 

temperature  in  the  muffle,  and  when  this  is  done  the  aperture  T>  is 
opened,  through  which  the  portion  of  lead  to  be  added  to  each  assay 
is  dropped  into  each  cupel.  As  soon  as  the  lead  is  in  fusion,  the 
assai/  (prise  d'essai)  is  introduced,  when  the  metals  soon  melt,  while 
the  alloy  of  silver  dissolves  entirely  in  the  lead ;  and  in  a  few  mo- 
ments the  alloy  forms  in  each  cupel  a  round  liquid  globule.  White 
vapours,  arising  from  the  oxidation  of  the  metallic  lead  in  the  air, 
are  soon  disengaged,  and  the  surface  of  the  metallic  globule  is 
covered  with  a  pellicle  and  fine  drops  of  fused  oxide,  which  move 
rapidly  over  its  surface.  The  oxides  gradually  soak  into  the  cu- 
pel, and  when  the  lead  and  copper  are  completely  converted  into 
oxides  and  absorbed  by  the  bone-ash,  the  silver  is  refined,  and  the 
motion  on  its  surface  ceases ;  the  phenomenon  of  lightning,  as  de- 
scribed §  997,  being  produced  on  a  small  scale.  The  cupel  must 
then  be  brought  slowly  to  the  opening  of  the  muffle,  in  order  that 
the  globule  of  silver  may  not  be  too  rapidly  cooled.  It  has  been 
mentioned  (§  1115)  that  pure  silver  absorbs  a  certain  quantity  of 
oxygen  from  the  air,  and  that  the  absorbed  gas  is  suddenly  disen- 
gaged at  the  moment  of  solidification,  while  the  metal  is  cooling 
rapidly,  causing  a  sudden  evolution  of  gas  by  which  a  small  quantity 
of  the  metal  is  generally  projected  from  the  vessel,  in  which  case 
the  silver  is  said  to  sputter,  (roche.)  It  is  easy  to  tell  by  the 
appearance  of  the  button,  when  cooled,  whether  a  sputtering  has 
taken  place,  as  in  that  case  a  kind  of  vegetation,  like  a  little  mush- 
room, may  always  be  seen  at  the  places  where  the  gas  has  escaped ; 
and  all  assays  presenting  this  character  should  be  rejected,  as  they 
necessarily  imply  too  small  a  quantity  of  silver. 

In  order  that  the  assay  may  be  admitted,  the  globule  should  be 
slightly  adherent  to  the  cupel,  its  lower  surface  should  appear  very 
smooth  and  of  a  dead  colour,  and  the  upper  surface  polished  and 
free  from  roughness.  When  the  upper  surface,  is  dull  and  furrowed, 
it  proves  either  that  the  silver  has  sputtered^  that  the  refining  has 
been  imperfect  because  the  temperature  has  been  too  great,  or  that 
there  was  too  little  lead. 

§  1143.  As  the  temperature  of  the  furnace  exerts  great  influence 
over  the  cupellation,  the  assay  always  presents  some  degree  of  un- 
certainty, and  the  assayer  is,  in  fact,  between  two  difficulties  :  if 
the  temperature  rises  too  high,  the  silver  is  perfectly  refined,  but 
there  is  considerable  loss  from  volatilizing,  and  a  small  quantity 
of  silver  is  carried  into  the  cupel  by  the  litharge,  which,  in  that 
case,  is  very  fluid ;  while,  if  not  heated  sufficiently  high,  the  loss 
of  silver  is  le^s,  but  the  reflning  is  imperfect,  and  the  globule  retains 
a  small  quantity  of  lead.  These  two  causes  of  error  exist  simulta- 
neously in  all  assays,  and  neutralize  each  other  more  or  less  com- 
pletely ;  and,  accordingly,  as  one  or  the  other  predominates,  the 
standard  will  be  found  too  low  or  too  high. 

The  assayer  should  always  endeavour  to  heat  his  furnace  in  the 


316  SILVER. 

same  manner,  and  he  can  then  construct  a  table  by  which  he  knows, 
for  each  alloy,  the  correction  which  should  be  made  in  each  assay 
in  order  to  obtain  the  exact  standard.  A  table  of  this  kind,  which 
is  made  by  cupelling  alloys  of  known  proportions,  obtained  by  melt- 
ing, with  a  proper  quantity  of  lead,  determinate  proportions  of  silver 
and  copper,  can  be  of  use  only  to  the  assayer  who  has  made  it,  and 
who  always  operates  with  the  same  furnace.  As  a  measure  of 
greater  certainty,  the  assayer,  from  time  to  time,  performs  a  cupel- 
lation  on  a  trial-piece^  (t^moin,)  that  is,  on  an  alloy  the  composition 
of  which  he  knows  a  priori,  in  order  to  ascertain  whether  the  assay 
yields  a  loss  equal  to  that  indicated  by  his  table.  If  otherwise,  he 
modifies  the  results  of  all  the  assays  simultaneously  made,  in  the 
manner  suggested  by  the  assay  of  the  trial-piece.  We  subjoin  the 
table  adopted  in  the  Mint  at  Paris,  according  to  the  standard  of  the 
alloys : 

B+     A    Acfr^T.  A  Waste,  or  quantities  necessary  to  add 

Real  standards.  ^tanaa^as  louna  ^  ^^    standard  obtained,  in  order 

by  cupellation.  ^  ^^^^^  ^^^  ^^^  standard. 

1000 998.97 1.03 

950 947.50 2.50 

900 896.00 4.00 

850 845.85 4.15 

800 795.70 4.30 

750 745.48 4.52 

700 695.25 4.75 

650 645.29 4.71 

600 595.32 4.68 

550 545.32 4.68 

500 495.32 4.68 

400 396.05 3.95 

300 297.40 2.60 

200 197.47 2.53 

100 99.12 0.88 

When  the  cupellation  has  been  carefully  performed,  the  true  com- 
position may  be  ascertained  within  2  or  3  thousandths. 

The  lead  used  in  cupellation,  which  should  be  as  free  as  possible 
from  silver,  is  called  in  commerce  assay-lead.  In  all  cases,  the 
assayer  should  ascertain  previously  the  purity  of  his  lead  by  a  pre- 
liminary assay. 

Assays  hy  the  Humid  Way. 

§  1144.  Assays  by  the  humid  way  are  made  by  precipitating  sil- 
ver in  the  state  of  insoluble  chloride  by  a  standard  solution  of  com- 
mon salt.  As  chloride  of  silver  readily  aggregates  by  agitation,  in 
a  liquid  acidulated  with  nitric  acid,  the  exact  moment  when  precipi- 
tation of  silver  no  longer  takes  place  may  be  easily  ascertained. 
The  solution  of  salt  used  being  such  that  1  cubic  diameter  of  the 


HUMID    AySAY   OF    SILVER.  317 

liquid  exactly  precipitates  1  gm.  of  pure  silver,  the  standard  of  an 
alloy  is  determined  by  dissolving  1  gm.  of  it  in  5  or  6  gm.  of  nitric 
acid,  and  carefully  pouring  the  solution  of  salt  into  the  liquid  until 
precipitation  ceases  after  the  addition  of  one  drop.  After  each 
addition  of  the  saline  solution,  when  the  moment  of  complete  pre- 
cipitation  approaches,  the  bottle  containing  the  solution  of  silver 
must  be  shaken  in  order  to  aggregate  the  precipitate  and  clear  the 
liquid.  The  number  of  cubic  centimetres  necessary  to  completely 
precipitate  the  silver  gives  the  standard  of  the  alloy. 

The  process  may  be  simplified  and  brought  to  great  exactness 
when  it  is  applied  to  the  exact  determination  of  the  standard  of  an 
alloy  of  which  the  approximate  value  is  known ;  for  example,  of  a 
piece  of  silver  coin  or  plate.  Two  solutions  of  sea-salt  are  then 
used :  one,  which  is  called  the  normal  solution^  and  which  is  such 
that  1  decilitre  precipitates  exactly  1  gm.  of  pure  silver ;  and 
another,  called  the  decimal  liquid^  which  is  10  times  more  dilute, 
and  of  which  1  litre  is  required  to  precipitate  1  gm.  of  silver. 
Lastly,  a  third  standard  solution  is  sometimes  used,  called  the  deci- 
mal solution  of  silver,  which  contains  1  gm.  of  silver  in  1  litre. 

Supposing  that  the  standard  of  a  piece  of  coin  is  to  be  ascer- 
tained, consisting  of  an  alloy  which  must  contain,  at  least,  ^^  of 
silver,  but  which  we  will  assume  to  contain  only  ^ ;  then,  accord- 
ing to  the  latter  composition,  1.116  gm.  of  alloy  contains  1  gm.  of 
silver.  After  having  dissolved  1.116  gm.  of  alloy,  very  exactly 
weighed,  in  a  ground-stoppered  bottle,  by  means  of  5  or  6  gm.  of 
pure  nitric  acid,  1  decilitre  of  the  normal  solution  of  sea-salt  is 
poured  into  the  bottle.  It  is  evident  that,  if  the  standard  of  the 
alloy  be  really  2,  the  silver  will  be  completely  precipitated,  and 
the  liquid  will  not  contain  an  excess  of  salt,  while,  if  the  standard 
be  higher,  silver  still  remains  in  solution,  and  if  lower,  the  silver 
has  been  completely  precipitated,  but  there  is  an  excess  of  salt  in 
the  liquid.  In  order  to  ascertain  this,  the  bottle  is  corked  and 
shaken  quickly,  in  order  to  clear  the  liquid,  after  which  one  cubic 
centimetre  of  decimal  saline  solution  is  added,  which  can  precipitate 
1  thousandth  of  silver.  If  silver  is  still  contained  in  the  liquid, 
a  very  perceptible  white  cloud  is  formed,  and  the  bottle  being  then 
again  shaken,  a  second  cubic  centimetre  of  decimal  solution  is  added. 
If  a  precipitate  be  produced,  the  same  process  is  repeated  until  the 
liquid  remains  clear.  Supposing  that  5  cubic  centimetres  of  the 
decimal  solution,  gradually  added,  have  produced  precipitates,  but 
that  the  6th  cubic  centimetre  has  not  affected  the  transparency  of 
the  liquid,  it  will  be  hence  inferred,  that  after  the  precipitation  of 
1  gm.  of  pure  silver  by  the  cubic  decimetre  of  the  normal  solution 
of  salt,  the  liquid  contained,  at  least,  4  thousandths  of  silver.  The 
fifth  cubic  centimetre  of  decimal  solution  having  produced  cloudi- 
ness, while  the  6th  did  not,  it  is  evident  that  the  liquid  did  not 


318 


SILVER. 


contain  more  than  5  thousandths  of  silver,  and,  by  assuming  4| 
thousandths,  we  are  sure  of  having  found  the  amount  of  silver  con- 
tained in  the  alloy  within  nearly  |  thousandth.  The  real  standard 
of  the  alloy  is,  therefore,  896H-4J,  or  900J  thousandths. 

If  the  first  cubic  centimetre  of  a  decimal  saline  solution  does 
not  yield  a  fresh  precipitate  in  the  solution  of  silver  which  has 
already  received  the  cubic  decimetre  of  normal  saline  solution,  it  is 
evident  that  the  standard  of  the  alloy  is  not  above  2,  and  that^ 
consequently,  it  should  be  rejected. 

The  exact  composition  of  the  alloy  may  be  determined  by  means 
of  the  decimal  solution  of  silver,  always  beginning  by  adding  one 
cubic  centimetre  of  the  latter,  which  precipitates  the  cubic  centimetre 
of  decimal  saline  solution  which  had  been  added,  and  which  must 
be  neutralized.  The  liquid  being  cleared  by  agitation,  one  more 
cubic  centimetre  of  decimal  solution  of  silver  is  added,  and  if  cloudi- 
ness be  produced,  the  bottle  is  again  shaken  before  a  second  cubic 
centimetre  of  the  same  liquid  is  added,  which  process  is  continued 
until  the  addition  of  another  cubic  centimetre  of  the  decimal  solu- 
tion of  silver  no  longer  clouds  the  liquid.  Supposing  that  the  first 
three  cubic  centimetres  have  yielded  precipitates,  but  that  the  liquid 
remains  clear  on  the  addition  of  the  fourth,  it  is  very  probable  that 
the  third  cubic  centimetre  has  not  been  entirely  decomposed,  and 

it  may  be  admitted  that  one-half  of  it  has 
been  useless,  and  that  2  J  cubic  centimetres 
of  the  decimal  solutionof  silver  have  sufiiced 
to  decompose  the  salt  which  remained  free 
after  the  addition  of  the  cubic  decimetre 
of  the  normal  saline  solution ;  for  which 
reason  2J  thousandths  must  be  subtracted 
from  the  standard  2,  thus  leaving  for 
the  exact  standard  of  the  coin  exa- 
mined '^. 

We  shall  now  briefly  describe  the  assay- 
ing apparatus  used  in  the  Mint  at  Paris, 
where  these  assays  are  daily  made. 

The  normal  solution  of  salt  is  contained 
in  a  copper  vessel  V,  (fig.  596,)  tinned  on 
the  inside,  and  completely  closed  to  pre- 
vent evaporation,  which  would  alter  the 
standard  of  the  liquid,  only  a  Mariotte's 
tnheuv  allowing  the  extrance  of  air.  The 
vessel,  which  is  fixed  in  the  upper  part 
of  the  laboratory,  has  a  curved  tube  ede, 
with  a  stopcock  r,  and  to  the  lower  part 
of  which  the  pipette  A,  which  measures 
Fig.  696.     "  exactly  1  decilitre  of  normal  solution,  is 


'1- 

r 

A'^ 

m 

1           li 
A          1 

11 

XJ 

b  a 

li 

r 

w 

n.r 

A 

^ 

HUMID   ASSAY   OF   SILVER. 


319 


Fig.  598. 


connected  by  means  of  a  tube  he  which  contains  a  thermometer. 

The  metallic  piece  which  connects  the  glass  tube  be  with  the  pipette 

(fig.  597)  has  two  stopcocks  r',  r",  the  one  of  which  shall  presently 

Fig.  597.    be  explained.     The  assayer  having  closed  the  end  a  of 

the  pipette  with  his  finger,  opens  the  stopcocks  r',  r", 

thus  allowing  the  saline  solution  to  flow  in  a  thin  stream 

into  the  pipette,  without  stopping  the  upper  tube  of  the 

latter,  so  that  the  air  contained  in  the  pipette  can  escape 

freely  through  the  stopcock  r'  and  the  small  tubulure 

which  terminates  it.     When  the  pipette  is  filled  a  little 

above  the  mark  a,  the  assayer  closes  the  stopcocks  r' 

and  r". 

The  bottle  which  contains  the  alloy  dissolved  in  nitric 
acid  is  placed  in  the  compartment  C  of  a  support  I, 
(fig.  596,)  which  slides  between  the  grooves 
MN,  M'N',  anji  which  is  provided  with  an 
appendix  D,  furnished  at  its  upper  part 
with  a  small  sponge  k,  placed  at  the  height 
of  the  lower  orifice  a  of  the  pipette.  The 
assayer  having  so  placed  the  support  as  to 
bring  the  sponge  in  contact  with  the  pi- 
pette, opens  the  stopcock  r',  and  allows 
the  liquid  to  descend  slowly  to  the  level  a, 
where  the  sponge  absorbs  the  last  drop  of 
liquid,  which  would  adhere  to  the  end  of 
the  pipette.  The  assayer  then  brings  the 
opening  of  the  bottle  under  the  pipette, 
and  empties  it  entirely  by  opening  the 
stopcock  r'. 

»As  a  large  number  of  assays  is  gene- 
rally made  at  once,  there  are  a  series  of 
bottles  numbered,  in  each  of  which  are  dis- 
solved 1.116  gm.  of  alloy  of  coin.  In  order 
to  hasten  the  solution,  all  the  bottles  are 
placed  on  a  stand,  (fig.  598,)  and  after  hav- 
ing introduced  into  each  the  alloy  and  the 
nitric  acid  which  is  to  dissolve  it,  the  stand 
is  plunged  into  hot  water.  When  the  metals 
are  dissolved  the  nitrous  vapours  are  driven 
ofi"  by  blowing  into  the  bottles,  and  the 
decilitre  of  normal  solution  is  introduced, 
after  which  they  are  placed  on  a  second 
stand,  (fig.  599,)  suspended  on  a  steel 
spring,  and  held  below  by  a  spiral  spring 
ah.  The  bottles  having  been  closed  by  their  ground  stoppers,  the 
assayer  grasps  the  handle  ef  of  the  stand  and  shakes  it  for  a  few 
moments,  in  order  to  collect  the  precipitate  and  render  the  liquids 


320  SILVER. 

clear.  He  then  carries  the  bottles  to  a  black  table  having  niimbere(! 
compartments,  each  one  being  placed  in  the  compartment  corre- 
sponding to  its  number.  The  decimal  solution  is  contained  in  a 
bottle  (fig.  600)  provided  with  a  tube,  drawn  out  at  its  lower 
extremity  and  having  a  mark  corresponding  to  a  capacity 
of  1  cubic  centimetre,  which  dips  into  the  liquid.  The  as- 
sayer,  applying  his  finger  to  the  upper  aperture  of  the  tube, 
withdraws  the  latter,  and  allows  the  liquid  to  flow  slowly 
until  it  reaches  the  level  of  the  mark,  and  then  carries  the 
Fig-  600.  q^}^[q  centimetre  thus  measured  off  into  the  first  bottle,  re- 
peating the  process  with  the  other  bottles.  He  then  examines  the 
bottles  successively,  and  makes  with  chalk  a  mark  on  the  black  table 
near  each  bottle  in  which  a  precipitate  is  formed,  and  then  replaces 
the  bottles  on  the  stand  of  fig.  599,  clears  the  liquids  by  agitation, 
deposits  the  bottles  onthe  table,  and  adds  another  cubic  centimetre 
of  the  decimal  solution  to  all  the  bottles  in  which  there  was  pre- 
viously a  precipitate  formed,  gradually  excluding  the  bottles  in  which 
the  liquid  was  not  clouded.  By  counting  the  number  of  chalk-marks 
near  each  bottle,  a  number  which  represents  that  of  the  cubic  centi- 
metres of  decimal  solution  which  have  been  efficient,  and  deducting 
J  for  the  last  cubic  centimetre,  which,  probably,  has  not  been  wholly 
used,  the  assayer  finds  the  number  of  thousandths  which  must  be 
added  for  each  alloy  to  the  supposed  standard  of  ^. 

As  the  standard  solution  of  sea-salt  has  been  prepared  for  the 
temperature  of  59°  degrees,  and  as  it  expands  by  heat,  it  is  evident 
thalt  its  standard  must  be  altered  in  volume  by  the  changes  of  tem- 
perature. It  is  therefore  indispensable,  when  the  temperature  of 
the  solution  is  not  59°,  to  correct  all  the  results  by  means  of  tables 
made  for  the  purpose,  the  temperature  of  the  saline  solution  being 
read  off  on  the  thermometer  contained  in  the  tube  ch,  (fig.  596.) 
But  the  corrections  are  always  uncertain,  and  may  be  avoided  by 
the  following  de\dce,  by  means  of  wliich,  at  the  same  time,  any 
wrong  preparation  of  the  normal  solution  is  ascertained.  An  assay 
upon  1  gm.  of  pure  silver,  made  daily,  simultaneously  with  the  tests 
on  the  coin,  gives  for  each  day  the  exact  value  of  the  standard  of 
the  normal  saline  solution,  and  all  assays  made  simultaneously  may 
be  corrected  by  the  difference  of  the  standard  thus  found  with  the 
normal  standard. 

A  large  quantity  of  normal  solution  of  salt  is  generally  made  at 
once,  by  dissolving  500  gm.  of  common  impure  salt  of  commerce  in 
4  litres  of  water,  filtering  the  liquid,  and  adding  the  quantity  of 
water  necessary  to  obtain  the  necessary  degree  of  dilution  of  the 
normal  solution,  supposing  the  salt  to  be  pure ;  by  which  means  a 
solution  is  obtained  of  a  degree  of  concentration  only  approximative 
to  that  desired.  In  order  to  ascertain  its  exact  concentration,  1 
cubic  decimetre  of  the  liquid  is  poured  into  a  solution  of  1  gm.  of 
pure  silver  in  nitric  acid.     The  liquid  being  cleared  by  agitation,  it 


ASSAYING   OF   SILVER    ORES.  821 

is  easy,  by  means  of  a  decimal  saline  solution  or  a  decimal  solution 
of  silver,  to  determine  exactly  the  number  of  thousandths  of  silver, 
or  of  salt,  which  remain  free.  The  additional  quantity  of  water  or 
salt  necessary  to  obtain  the  proper  dilution  of  the  saline  solution  is 
thus  found,  and,  after  it  has  been  added,  a  new  test  is  made,  and  so 
on,  until  the  normal  degree  of  concentration  is  attained. 

In  order  to  prepare  the  decimal  solution,  a  decilitre  of  the  normal 
solution  is  introduced  into  a  bottle  wMch  measures  1  litre  to  a  mark 
traced  on  its  neck,  up  to  which  the  bottle  is  then  filled  with  distilled 
water. 

The  decimal  solution  of  silver  is  prepared  by  dissolving  1  gm.  of 
pure  silver  in  5  or  6  gm.  of  nitric  acid,  and  diluting  with  water 
until  the  liquid  exactly  assumes  the  volume  of  1  litre. 

When  silver  contains  mercury,  the  results  of  the  assay  by  the 
humid  way  are  inaccurate,  because  the  mercury,  being  precipitated 
in  the  state  of  chloride,  decomposes  a  portion  of  the  chloride  of 
sodium.  The  presence  of  any  considerable  quantity  of  mercury  in 
an  alloy  is  easily  perceived,  because  the  liquid,  in  that  case,  is  not 
cleared  by  shaking,  and  the  first  deposite  of  chloride  of  silver  does 
not  blacken  in  the  light.  The  exact  standard  of  the  alloy  may, 
however,  be  obtained  by  the  humid  way,  by  recommencing  the  test 
on  another  portion  of  the  substance  after  having  added  a  certain 
quantity  of  acetate  of  soda  to  the  nitric  solution,  by  which  means 
the  precipitation  of  the  mercury  is  prevejited. 

ASSAYING  OF  SILVER  ORES. 

§  1145.  The  argentiferous  galenas  are  assayed  by  cupelling  the 
lead,  after  having  isolated  it  by  the  process  described  §  980.  The 
galena  is  sometimes  also  fused  with  3  or  4  tenths  of  its  weight  of 
nitre,  when  the  sulphur  of  the  galena  is  converted  into  sulphuric 
acid  which  combines  with  the  potassa,  while  the  greater  portion  of 
the  lead  separates  in  the  metallic  state,  retaining  the  whole  of  the 
silver. 

The  argentiferous  copper-ores  are  first  assayed  for  their  copper, 
after  which  the  lump  of  copper  is  introduced  into  the  cupel,  with 
the  addition  of  16  times  its  weight  of  lead. 

The  assay  for  copper  is  made  as  follows : — If  the  ore  be  sulphu- 
retted, it  is  first  roasted  in  a  small  earthen  capsule,  (called  tile  in 
England,)  the  heat  being  properly  regulated  in  order  to  prevent 
the  substance  from  running  together,  and  the  temperatui-e  being 
kept  elevated  until  sulphurous  acid  is  no  longer  disengaged.  The 
tile  being  then  covered  with  its  lid,  the  temperature  is  raised  to  a 
white-heat,  in  order  to  decompose  the  sulphates ;  after  which  the 
roasted  material  is  fused  in  an  earthen  crucible  with  3  or  4  times  its 
weight  of  black  flux,  the  fusion  being  effected  in  a  forge-fire  or  an 
ordinary  calcining  furnace,  having  a  strong  draught.  After  cool- 
ing, the  crucible  is  broken,  and  a  lump  of  malleable  copper  and  an 

Vol.  IL— 21 


322  GOLD. 

alkaline  slag  containing  merely  a  trace  of  copper  are  found.  Oxi- 
dized copper-ores  need  not  be  previously  roasted,  but  can  be  imme- 
diately subjected  to  the  fusion  with  black  flux. 

Oxidized  silver-ores  are  mixed  with  8  or  10  times  their  weight 
of  litharge  and  double  their  weight  of  black  flux,  and  the  mixture  is 
fused  in  an  earthen  crucible,  when  a  portion  of  the  litharge  is  con- 
verted, by  the  carbon  of  the  black  flux,  into  metallic  lead,  which 
carries  with  it  all  the  silver;  the  quartzose  and  earthy  gangues 
•being  transformed  into  slag  with  the  litharge  and  potassa  of  the 
tblack  flux.  Ores  of  silver  which  contain  sulphides  and  arseniurets 
are  also  fused  with  litharge,  but  it  is  in  this  case  frequently  unne- 
cessary to  add  black  flux,  because  the  reaction  of  the  sulphides  and 
;arse£tiurets  on  the  litharge  furnishes  a  sufficient  quantity  of  metallic 
lead -t©tentirely  remove  the  silver. 


GOLD. 

Equivalent  =  98.5  (1231.25;  0  =  100). 

§  1146.  The  gold  in  gold  coin  and  jewelry  is  never  pure,  being 
alloyed  with  a  certain  quantity  of  copper  and  frequently  of  silver,  to 
give  it  a  greater  degree  of  hardness.  In  order  to  obtain  pure  gold, 
gold  coin  is  dissolved  in  aqua  regia,  and  the  solution  being  evapo- 
rated to  dryness,  by  gentle  heat,  to  drive  off  the  excess  of  acid,  the 
residue  is  treated  with  water,  by  which  means  the  silver  is  separated 
as  insoluble  chloride.  An  excess  of  protosulphate  of  iron,  which  pre- 
cipitates the  gold  in  the  metallic  state,  in  the  form  of  brown  powder, 
is  then  poured  into  the  liquid,  the  reaction  ensuing  according  to  the 
following  equation : 

Au,Cl3+6(FeO,S03)  =  2Au+2(Fe,03,3S03)+Fe,Cl3. 

The  precipitate  is  digested  with  weak  chlorohydric  acid,  and, 
after  being  well  washed,  is  fused  in  an  earthen  crucible  with  a  small 
quantity  of  borax  and  saltpetre.  The  protosulphate  of  iron  may  be 
replaced  by  sesquichloride  of  antimony  Sb3Cl3  dissolved  in  an  excess 
of  chlorohydric  acid;  the  sesquichloride  of  antimony  being  con- 
verted into  the  perchloride  Sb^Cl^,  while  the  gold  is  precipitated  in 
the  metallic  state. 

Gold  has  a  characteristic  yellow  colour,  and  its  density  is  19.5^ 
It  fuses  at  a  strong  white-heat,  or  at  about  2200°  of  the  air  ther- 
mometer, giving  off  sensible  vapours  at  a  very  high  temperature. 
A  gold  wire  is  converted  into  vapour  when  traversed  by  the  current 
of  a  powerful  electric  battery;  and  if  this  take  place  over  a  sheet 


PROPERTIES   OF   GOLD.  323 

of  paper  placed  at  a  small  distance,  the  paper  becomes  coloured  of 
a  purplish  brown,  by  the  very  finely  divided  gold  which  is  precipi- 
tated on  it.  A  blade  of  silver  substituted  for  the  paper  soon  becomes 
gilded.  A  globule  of  gold  gives  off  vapour  very  copiously  when  held 
between  two  pieces  of  charcoal  terminating  the  conductors  of  a  pow- 
erful galvanic  battery. 

Gold  is  the  most  malleable  of  all  the  metals,  (§  295,)  and  when 
beaten  into  v^ery  thin  leaves  is  transparent^  the  transmitted  light 
appearing  of  a  beautiful  green  colour.  Gold  may  be  crystallized  by 
fusion,  when  it  assumes  the  shape  of  cubes  modified  by  other  facets 
of  the  regular  system.  Native  gold  is  sometimes  found  in  well- 
defined  crystals  presenting  the  same  form. 

When  precipitated  in  a  metallic  state  from  its  solutions,  gold 
forms  a  brown  powder,  which  by  burnishing  soon  recovers  the  me- 
tallic lustre  and  characteristic  colour  of  malleable  gold,  and  which 
aggregates  by  percussion.  If  the  mass  be  heated  to  redness  before 
being  hammered,  a  perfectly  aggregated  metal  can  be  obtained 
without  having  heated  it  to  fusion. 

Gold  does  not  combine  directly  with  oxygen  at  any  temperature. 
Chlorohydric,  nitric,  and  sulphuric  acids  do  not  affect  it,  while  aqua 
regia,  on  the  contrary,  readily  dissolves  it  in  the  state  of  sesqui- 
chloride,  AugClg.  Gold  is  also  dissolved  by  chlorohydric  acid  when 
a  substance  capable  of  disengaging  chlorine  is  added,  such  as  per- 
oxide of  manganese,  chromic  acid,  etc.  Chlorine  and  bromine  also 
attack  gold,  even  when  cold,  while  iodine  acts  on  it  but  feebly. 

Sulphur  does  not  attack  gold  at  any  temperature,  nor  does  the 
metal  decompose  sulf  hydric  acid ;  but  by  fusing  it  with  the  alkaline 
polysulphides  it  is  powerfully  acted  on,  a  double  sulphide  being 
formed,  in  which  the  sulphide  of  gold  AugSg  acts  the  part  of  a  sulph- 
acid.  Arsenic  when  assisted  by  heat  combines  with  gold,  and  forms 
a  very  brittle  alloy. 

Gold  is  attacked  neither  by  the  alkalies  nor  the  alkaline  carbo- 
nates or  nitrates. 

COMPOUNDS  OF  GOLD  WITH  OXYGEN. 

§  1147.  Two  combinations  of  gold  with  oxygen  are  known : 

1.  A  suboxide  Au^O, 

2.  A  sesqui oxide  Au^Og, 

neither  of  which  forms  salts  with  the  oxides. 

The  suboxide  AugO  is  obtained  by  decomposing  the  chloride 
AugCl  by  a  dilute  solution  of  potassa,  in  the  shape  of  a  deep  violet- 
coloured  powder,  which  decomposes  at  about  77°,  disengaging  oxy- 
gen. The  oxacids  exert  no  action  on  this  substance,  while  chloro- 
hydric acid  decomposes  it,  forming  sesquichloride  of  gold  AuaClg, 
while  metallic  gold  is  separated. 

Sesquioxide  of  gold  (often  called  auric  acid  on  account  of  its 
property  of  combining  with  bases)  is  prepared  by  digesting  a  hot 


324  GOLD. 

solution  of  sesquichloride  of  gold  with  magnesia,  when  aurate  of 
magnesia  is  formed,  which  remains  mixed  with  the  free  magnesia. 
The  deposit  is  boiled  with  nitric  acid,  which  dissolves  the  magnesia 
and  leaves  hydrated  sesquio:?^ide  of  gold.  Auric  acid  may  also  be 
obtained  by  exactly  saturating  a  solution  of  sesquichloride  of  gold 
by  carbonate  of  soda,  and  then  boiling  the  liquid,  when  a  large 
proportion  of  the  gold  is  precipitated  in  the  state  of  sesquioxide, 
while  the  other  portion  remains  in  solution,  but  may  be  precipitated 
by  successively  adding  to  the  liquid  an  excess  of  caustic  potassa 
and  acetic  acid. 

Hydrated  auric  acid  is  a  yellow  or  brown  powder,  which  loses  its 
water  at  a  low  temperature  and  becomes  anhydrous,  while  at  about 
482°  it  decomposes  into  gold  and  oxygen,  which  reaction  is  also 
effected  by  the  solar  light.  Deoxidizing  substances,  such  as  the 
organic  acids,  or .  boiling  alcohol,  reduce  it  to  the  metallic  state ; 
while  chlorohydric  acid  dissolves  it  and  produces  the  sesquichloride 
AugClg.  The  most  energetic  oxacids  do  not  form  definite  com- 
pounds with  sesquioxide  of  gold,  while  the  latter  dissolves,  on  the 
contrary,  readily  in  cold  alkaline  solutions,  producing  alkaline 
aurates  which  crystallize  by  evaporation. 

By  adding  a  small  quantity  of  ammonia  to  a  solution  of  sesqui- 
chloride of  gold,  a  fulminating  substance  is  produced,  which  con- 
tains, at  the  same  time,  oxide  of  gold,  ammonia,  and  chloride,  and 
which,  by  digesting  with  an  excess  of  ammonia,  furnishes  a  bright 
brown  powder  of  still  higher  detonating  properties  than  the  first, 
and  which  is  a  simple  combination  of  sesquioxide  of  gold  with  am- 
monia Au303+2NH3-f  HO. 

COMPOUNDS  OF  GOLD  WITH  SULPHUR. 

§  1148.  Although  sulphur  does  not  combine  directly  with  gold, 
two  sulphides  corresponding  to  the  two  oxides  are  obtained  by  de- 
composing the  sesquioxide  of  gold  by  sulf  hydric  acid,  which,  on 
being  passed  through  a  cold  solution  of  sesquichloride  of  gold,  yields 
a  brownish-yellow  precipitate,  which  is  the  sulphide  AugSg,  readily 
soluble  in  the  alkaline  sulphides.  If  the  solution  of  the  chloride  is 
boiling,  a  sulphide  AugS,  of  a  deep  brown  colour,  is  precipitated, 
while  sulphuric  and  chlorohydric  acids  are  formed : 

2Au,Cl3+3HS+3HO  =  2Au,S+6HCl+S03. 

COMPOUNDS  OF  GOLD  WITH  CHLORINE. 

§  1149.  By  dissolving  gold  in  aqua  regia  a  yellow  solution  of 
sesquichloride  of  gold  AugClg  is  obtained,  which,  when  allowed  to 
evaporate  slowly  in  dry  air,  deposits  yellow  crystals  of  a  compound 
of  sesquichloride  of  gold  and  chlorohydric  acid.  If  the  solution  be 
evaporated  to  drive  off  the  excess  of  acid,  the  substance  assumes  a 
brown  colour,  and  a  deliquescent  crystalline  mass  remains,  which 


HALOID  COMPOUNDS  OF  GOLD.  325 

dissolves  readily  in  alcohol  and  in  ether.  Sesquichloride  of  gold 
dissolves  even  more  rapidly  in  ether  than  in  water ;  for,  if  an  aque- 
ous solution  of  the  chloride  be  shaken  with  ether  and  water,  the 
supernatant  ether  contains  nearly  all  the  chloride  of  gold  in  solu- 
tion. The  solution  of  sesquichloride  of  gold  in  ether  was  formerly 
used  in  medicine  under  the  name  of  aurum  potahile. 

Sesquichloride  of  gold  forms  with  several  other  metallic  chlorides 
double  crystallizable  chlorides,  in  order  to  obtain  which  it  is  suffi- 
cient to  mix  and  evaporate  the  solutions  of  the  two  chlorides.  The 
formula  of  the  double  chloride  of  gold  and  potassium,  which  is  deli- 
quescent, is  KCl-f  AU3CI3+5HO,  while  the  formula  of  that  of  gold 
and  sodium  is  NaCl4-Au2Cl3+4H0,  and  that  of  the  double  chloride 
of  gold  and  ammonia  is  NH3HCI+AU3CI3+2HO.  Compounds  of 
chloride^of  gold  with  the  chlorides  of  barium,  calcium,  manganese, 
iron,  zinc,  etc.,  are  also  known. 

Subchloride  of  gold  Au^Cl  is  prepared  by  heating  the  sesquichlo- 
ride of  gold  AU3CI3  to  a  temperature  of  about  400°,  when  chlorine 
is  disengaged,  while  a  greenish  insoluble  powder  remains. 

COMPOUND  OF  GOLD  WITH  CYANOGEN. 

§  1150.  By  adding  a  solution  of  cyanide  of  potassium  to  a  con- 
centrated hot  solution  of  perchloride  of  gold,  until  the  liquid  loses 
its  colour,  a  solution  is  obtained,  which,  on  cooling,  deposits  pris- 
matic crystals  of  a  double  cyanide  of  gold  and  potassium  of  the 
formula  KCy+AugCyg.  The  crystals,  which  are  efflorescent  and 
very  soluble,  disengage  cyanogen  when  subjected  to  moderate  heat ; 
and,  when  treated  with  water,  a  solution  is  obtained,  which,  on  cool- 
ing, deposits  a  double  cyanide  of  the  formula  KCy-|-Auj,Cy. 

PURPLE  OF  CASSIUS. 

§  1151.  The  name  of  purple  of  Cassius  is  given  to  a  precipitate 
containing  gold,  tin,  and  oxygen,  which  is  used  by  painters  on  por- 
celain and  glass,  (§  730,)  and  which  is  prepared  in  various  ways. 
Its  composition  not  being  always  uniform,  chemists  are  not  yet 
agreed  upon  its  nature.  It  is  generally  obtained  by  pouring  into 
a  sufficiently  dilute  solution  of  sesquichloride  of  gold,  a  mixture  of 
protochloride  and  bichloride  of  tin,  the  precipitate  showing  a  beau- 
tiful purple  hue  when  it  is  of  small  bulk,  while  it  assumes  a  brown 
colour  when  more  copious. 

A  purple  of  Cassius  of  uniform  composition  is  prepared  by  dis- 
solving 20  gm.  of  gold  in  100  gm.  of  aqua  regia  made  of  20  parts 
of  nitric  and  80  of  chlorohydric  acid  ;  driving  off  the  excess  of  acid 
by  evaporation  in  a  water-bath  and  dissolving  the  residue  in  7  or  8 
decilitres  of  water.  Some  pieces  of  tin  being  then  placed  in  the  liquid, 
a  purple  precipitate  of  the  formula  Au20,Sn03-fSnO,SnOs4-4HO 
is  formed,  but  which  may  also  be  considered  as  2Au-f  3Sn03+4H0. 
The  substance,  on  being  subjected  to  heat,  evolves  water  alone  and 


326  GOLD. 

no  oxygen,  while  the  calcined  residue  presents  all  the  characters  of 
a  mixture  of  metallic  gold  and  stannic  acid.  But  as  before  calcina- 
tion the  substance  will  not  give  off  gold  to  mercury,  it  is  evident  that 
the  gold  did  not  exist  in  it  in  the  metallic  state. 

A  beautiful  purple  of  Cassius  is  obtained  by  heating  suboxide  of 
gold  AugO  with  a  solution  of  stannate  of  potassa. 

Lastly,  purple  of  Cassius  is  obtained  by  fusing  together  in  a  cru- 
cible 1  part  of  gold,  J  part  of  tin,  and  4  or  5  of  silver,  forming  a 
ternary  alloy,  from  which  nitric  acid  extracts  the  silver,  while  the 
gold  and  tin  are  precipitated  in  combination  with  oxygen,  and  a 
brilliant  purple  is  formed,  the  shades  of  which  can  be  changed  by 
altering  the  relative  proportions  of  gold  and  tin. 

A  solution  of  sesquichloride  of  gold  stains  linen  of  a  purple  colour, 
as  it  also  does  the  skin  and  the  organic  tissues  generally ;  which 
colouring  is  probably  owing  to  suboxide  of  gold,  as  friction  does 
not  restore  a  metallic  lustre  to  the  spots,  although  they  acquire  it 
in  a  short  time  when  exposed  to  solar  light  in  a  bottle  filled  with 
hydrogen  gas. 

DETERMINATION  OF  GOLD,  AND  ITS  SEPARATION  FROM  THE  METALS 
PREVIOUSLY  DESCRIBED. 

§  1152.  Gold  is  always  determined  in  the  metallic  state,  and  is 
precipitated  from  its  solutions  by  means  of  protosulphate  of  iron, 
after  having  added  chlorohydric  acid  to  the  liquid  in  order  to  main- 
tain the  sesquioxide  of  iron  which  forms  during  the  reaction  in  so- 
lution. But  it  is  important,  in  order  to  completely  precipitate  the 
gold,  that  the  liquid  should  contain  no  nitric  acid ;  in  which  case  it 
must  be  previously  evaporated  with  chlorohydric  acid.  The  gold, 
when  collected  on  a  filter,  is  calcined  to  redness  before  being 
weighed. 

§  1153.  In  order  to  separate  gold  from  the  metals  previously  de- 
scribed, the  insolubility  of  the  metal  in  nitric  acid  is  sometimes 
relied  on,  while  at  other  times  all  the  metals  are  dissolved  in  aqua 
regia,  and  the  gold  is  precipitated  by  protosulphate  of  iron,  or,  better 
still,  by  heating  the  solution  with  a  certain  quantity  of  oxalic  acid ; 
which  latter  method  has  the  advantage  of  not  introducing  a  new 
metal  into  the  liquid.  Gold  is  sometimes  also  separated  by  precipi- 
tating it  in  the  state  of  sulphide,  by  sulfhydric  acid  gas,  the  sul- 
phide leaving  metallic  gold  after  calcination. 

METALLURGY  OF  GOLD. 

§  1154.  Gold  is  almost  always  found  in  the  native  state,  being 
sometimes  pure,  but  more  generally  alloyed  with  certain  quantities 
of  silver.     It  occurs  in  three  kinds  of  bearings : 

1.  In  veins,  generally  quartziferous,  which  contain  other  metallic 
minerals,  as  ores  of  copper,  lead,  silver,  and  pyrites;  the  veins 
usually  traversing  the  primitive  rocks. 


METALLURGY   OF   GOLD.  327 

2.  In  small  veins  scattered  through  rocks  situated  at  the  separa- 
tion of  the  crystalline  and  stratified  rocks. 

3.  In  disaggregated  quartzose  sands,  often  extensively  seen  in 
alluvial  formations,  and  owing  their  presence  to  the  disintegration 
of  auriferous  crystalline  rocks  which  exist  in  the  vicinity.  The 
greater  specific  gravity  of  the  gold  prevents  its  particles  from  being 
carried  as  far  as  those  of  the  other  minerals  with  which  it  was 
mixed,  and  its  resistance  to  the  action  of  the  greater  part  of  chemi- 
cal agents  preserves  it  in  the  state  of  spangles.  Alluvious  soils 
containing  gold  chiefly  occur  in  open  valleys  between  primitive 
mountains,  where  gold  is  frequently  found  in  place.  The  principal 
localities  of  auriferous  sands  are  in  California,  Australia,  Brazil, 
Mexico,  Chili,  Africa,  the  Ural  and  Altai  Mountains  in  Siberia — the 
quantity  of  gold  annually  extracted  from  all  of  which  amounted,  in 
1851,  to  178  tons,  of  which  California  alone  produced  110.  Gold 
is  generally  found  in  the  sands  in  the  form  of  spangles,  or  shapeless 
and  rounded  grains,  which,  when  they  are  of  any  considerable  size, 
are  called  river  or  wash  gold^  (p^pites.)  Grains  are  sometimes 
found  of  the  size  of  a  hazel-nut,  and  pieces  weighing  several  kilogs. 
have  been  met  with :  one  lump  weighing  36  kilogs.  was  found  in 
the  Ural. 

Gold  exists  in  the  drift-sand  of  all  rivers  which  arise  from,  or 
flow  over  a  large  extent  of,  primitive  rocks ;  and  several  auriferous 
alluvige  are  known  in  France,  such  as  those  of  the  Ariege  in  the 
Pyrenees,  of  the  Gardon  in  Cevennes,  the  Garonne,  and  the  Rhine 
near  Strasburg.  It  is  found  in  too  small  quantity  to  be  worked  to 
advantage ;  but  the  inhabitants  look  for  it  when  they  would  other- 
wise be  idle,  and  are  then  called  gold-finders.  The  spangles  of  gold 
scattered  through  the  river-sand  are  generally  so  excessively  small 
that  more  than  20  are  often  required  to  make  a  milligramme. 

In  Siberia,  sands  containing  only  0.000001  of  gold  are  not  con- 
sidered worthy  of  being  worked ;  and  the  Rhenish  sands  contain, 
on  an  average,  about  \  of  this  quantity. 

Gold  exists  also,  combined  with  tellurium,  in  certain  mines  of 
Transylvania.  An  alloy  of  gold  with  silver  and  palladium,  in  the 
form  of  small  crystalline  grains,  occurs  in  Brazil,  and  is  called  auro- 
powder  or  auro-dust.  Lastly,  all  pyrites  in  primitive  rocks  contain 
a  small  quantity  of  gold,  and  are  often  rich  enough  to  be  worked  to 
advantage. 

§  1155.  When  gold  exists  in  veins  which  contain  other  metals, 
as  lead,  copper,  or  silver,  those  metals  in  which  the  gold  is  concen- 
trated are  first  extracted  from  the  ores,  and  the  gold  is  then  sepa- 
rated by  refining,  a  process  presently  to  be  described. 

The  ore  is  frequently  first  subjected  to  amalgamation,  as  in  the 
case  of  silver  ores,  when  the  gold  dissolves  in  the  mercury,  and, 
after  the  liquid  amalgam  has  been  filtered,  a  more  solid  amalgam  is 
obtained,  from  which  the  gold  is  separated  by  distillation.    The  ore 


828 


GOLD. 


is  then  smelted,  so  as  to  obtain  a  matt  from  which  a  certain  quantity 
of  gold  can  still  be  extracted. 

§  1156.  Auriferous  sands  are  washed  in  the  most  simple  manner, 
either  in  wooden  tubs,  or  on  inclined  planes  over  which  a  current 
of  water  flows,  and  they  are  then  treated  by  amalgamation. 

In  the  Ural,  the  auriferous  sand  is  poured  into  boxes,  the  sheet- 
iron  bottom  of  which  is  provided  with  openings  of  2  centimetres  in 
diameter,  and,  while  a  stream  of  water  flows  through  the  boxes,  the 
workman  stirs  the  sand  constantly  with  a  shovel,  when  the  finer 
portions  fall  through  the  holes  and  are  collected  on  large  sleeping 
tables  covered  with  muslin.  The  sand  is  frequently  swept  toward 
the  head  of  the  table,  where  the  gold  remains  with  the  heavier  mine- 
rals ;  and  the  sand,  being  enriched  by  this  washing,  is  again  more 
carefully  washed  on  smaller  tables.  The  titanic  iron  and  magnetic 
oxide  of  iron  being  separated  by  a  magnet,  the  material  is  fused  in 
large  graphite  crucibles,  at  the  bottom  of  which  the  gold  collects, 
while  the  upper  part  is  filled  by  a  slag  containing  a  quantity  of  un- 
melted  grains  of  gold.  The  slag  being  stamped  and  washed,  the 
rich  schlich  thus  obtained  is  smelted,  yielding  an  auriferous  lead, 
from  which  the  gold  is  separated  by  cupellation. 

§  1157.  In  Tyrol  a  certain  quantity  of  gold  is  extracted  from 
pyrites  by  amalgamating  them  in  mills  resembling  that  represented 
in  fig.  601,  several  mills  being  generally  placed  above  each  other. 
(The  figure  gives  an  external  view  of  the  upper  mill  and  a  section 
of  the  lower  one.) 

The  pyrites,  in  the 
state  of  an  impal- 
pable powder,  is 
suspended  in  water, 
and  conveyed  into 
the  upper  mill  by 
the  conduit  G, 
whence  it  flows  into 
the  second  mill  by 
the  sluice  G'.  The 
bed  of  each  mill  is 
made  of  a  cast-iron 
vessel  cdef,  securely 
fastened  on  a  strong  wooden  table ;  and  in  the  centre  of  the  vessel 
is  a  tubulure  traversed  by  an  axis  of  rotation  ah,  set  in  motion  by 
the  cog-wheel  rr'.  The  runner-stone  mm'  of  each  mill  is  of  wood, 
and  resembling  the  shape  of  the  bed ;  but,  being  about  2  centimetres 
smaller,  is  furnished  with  several  sheet-iron  teeth  projecting  about 
1  centimetre.  The  upper  surface  of  the  runner-stone  is  shaped  like 
a  funnel,  into  which  is  poured  the  liquid  mud,  which  passes  between 
the  stones  and  flows  out  by  the  conduit  G'. 

The  stones  make  about  15  or  20  revolutions  per  minute ;  and  25 


's^^tto 


SEPARATION   OF   GOLD   AND    SILVER.  329 

kilogs.  of  mercury  are  placed  at  the  bottom  of  each,  making  a  layer 
of  about  1  centimetre  in  thickness,  against  which  the  teeth  of  the 
wheel  constantly  strike,  while  at  the  same  time  they  stir  up  the  ore. 
The  gold  is  dissolved  by  the  mercury,  and,  after  continuing  this 
process  for  4  weeks,  it  is  withdrawn  and  filtered  through  a  chamois- 
skin,  which  retains  a  solid  amalgam  containing  nearly  one-third  of 
its  weight  of  gold,  which  is  then  separated  from  the  other  metals 
by  cupellation. 

ALLOYS  OF  GOLD. 

§  1158.  Gold  is  rarely  used  in  a  state  of  purity,  as  it  is  too  soft, 
and  its  hardness  must  be  increased  by  the  addition  of  a  small  quan- 
tity of  silver  or  copper,  forming  more  fusible  alloys  than  pure  gold. 

The  standard  of  French  gold  coin  is  ^^^^^  the  law  allowing  a  va- 
riation of  Yo2_  above  and  ysm  below;  while  medals  contain  0.916 
per  cent,  ©f  gold,  with  the  same  variation.  There  are  three  legal 
standards  for  jewelry,  the  most  common  of  which  is  y^^,  while  those 
of  ^^-^^  and  1^^  are  rarely  used ;  and  the  legal  variation  is  j^o  below 
the  standard,  no  superior  limit  being  fixed. 

Gold  is  soldered  with  an  alloy  called  red  gold,  of  5  parts  of  gold, 
and  1  of  copper ;  an  alloy  made  of  4  parts  of  gold,  1  of  copper, 
and  1  of  silver  also  being  used. 

The  clear  colour  of  gold  is  given  to  jewelry  by  dissolving  the  cop- 
per which  exists  in  the  superficial  layer ;  to  efiect  which  the  articles 
are  heated  to  a  dull  red-heat,  and  dipped,  after  cooling,  into  a  weak 
solution  of  nitric  acid,  which  dissolves  the  copper.  A  thicker  coat- 
ing of  pure  gold  is  obtained  by  allowing  them  to  remain  for  15 
minutes  in  a  paste  formed  of  saltpetre,  common  salt,  alum,  and 
water ;  the  chlorine  set  free  by  the  action  of  the  sulphuric  acid 
on  the  salt  and  saltpetre  dissolving  the  copper,  silver,  and  gold, 
while  the  latter  metal  is  again  deposited  on  the  article.  The  sur- 
faces are  then  burnished. 

SEPARATION  OF  GOLD  AND  SILVER. 

§  1159.  The  separation  of  gold  and  silver,  more  generally  called 
the  refining  of  the  precious  metals,  is  now  done  by  treating  the  alloy 
by  concentrated  hot  sulphuric  acid,  which  dissolves  the  silver  only. 
But,  in  order  that  the  alloy  may  be  completely  acted  on,  it  should 
neither  contain  more  than  20  per  cent,  of*  gold,  nor  than  10  per 
cent,  of  copper,  because  sulphate  of  copper  is  but  slightly  soluble 
in  concentrated  sulphuric  acid.  The  alloy&  are  fused  in  crucibles, 
and  when  they  are  too  rich  in  gold,  a  certain  quantity  of  silver  is 
added — silver  containing  a  small  quantity  of  gold  being  preferred. 
The  fused  alloy  is  granulated  by  being  poured  into  water,  and 
then  placed  in  a  large  kettle  with  2 J  times  its  weight  of  concentrated 
sulphuric  acid  marking  6Q°  on  the  areometer,  the  kettle  being  co- 
vered with  a  lid  furnished  with  a  disengaging  tube.     The  acid,  being 


830  GOLD. 

heated  to  boiling,  is  partly  decomposed,  and  sulphates  of  silver  and 
copper  are  formed,  while  sulphurous  acid  is  disengaged,  which  is 
sometimes  passed  into  the  leaden  chambers  where  sulphuric  acid  is 
manufactured,  (§  139.)  When  gold  coin  is  to  be  refined,  it  is  merely 
roasted. 

After  4  hours,  when  the  alloy  is  completely  destroyed,  there  is 
introduced  into  the  kettle  a  certain  quantity  of  sulphuric  acid 
marking  58°,  and  obtained  by  the  concentration  of  the  acid  mother 
liquid  of  the  sulphate  of  copper  obtained  in  refining,  as  will  pre- 
sently be  explained.  After  having  boiled  the  liquid  for  fifteen 
minutes,  the  kettle  is  taken  from  the  fire  and  allowed  to  rest,  when 
the  greater  part  of  the  gold  collects  at  the  bottom  of  the  vessel, 
from  which  the  nearly  boiling  liquid  is  decanted  ofi"  into  leaden 
boilers  containing  the  mother  liquid  arising  from  the  purification  of 
the  sulphate  of  copper  by  crystallization.  The  boilers  are  heated  by 
steam ;  and  after  the  sulphate  of  copper  at  first  deposited  is  re- 
dissolved,  the  liquid  is  allowed  to  rest  for  some  time,  when  the  whole 
of  the  gold  is  deposited.  The  clear  liquid  is  then  drawn  ofi*  by  a 
siphon,  and  passed  into  other  boilers  heated  by  steam,  and  contain- 
ing blades  of  copper,  which  precipitate  the  silver  in  the  form  of 
small  crystalline  griains ;  the  metal  being  in  a  short  time  so  per- 
fectly precipitated  that  the  liquid  is  not  clouded  by  common  salt. 
The  precipitated  silver  is  carefully  washed,  and  then  compressed  by 
an  hydraulic  press  into  compact  prisms,  which,  after  being  dried,  are 
melted  in  earthen  crucibles,  furnishing  a  metal  which  contains  only 
a  few  thousandths  of  copper. 

As  the  gold  arising  from  the  first  action  of  the  sulphuric  acid 
still  contains  a  certain  quantity  of  silver,  it  is  heated  anew,  in  a 
platinum  crucible,  with  concentrated  sulphuric  acid,  which  abstracts 
the  balance  of  the  silver ;  a  third  treatment  with  sulphuric  acid 
being  often  required.  The  gold  dust,  after  being  well  washed  and 
fused,  contains  995  thousandths  of  pure  gold. 

The  acid  solution  of  sulphate  of  copper  which  arises  from  the 
precipitation  of  the  silver  by  copper  is  evaporated  in  leaden  kettles 
until  it  marks  40°  on  the  areometer ;  a  large  proportion  of  the  sul- 
phate of  copper  being  deposited  in  small  crystals  during  the  cool- 
ing. After  another  evaporation,  the  mother  liquid  yields  an  addi- 
tional quantity  of  crystals ;  and  the  last  liquid,  which  refuses '  to 
crystallize,  is  used  as  absolution  of  sulphuric  acid,  and  poured  into 
the  cast-iron  boiler,  after  this  action  on  the  alloy.  The  sulphate  of 
copper  is  purified  by  recrystallization. 

When  the  quantity  of  gold  and  silver  contained  in  an  alloy  does 
not  exceed  0.200  or  0.300,  the  granular  material  is  first  heated  in 
a  reverberatory  furnace,  when  a  portion  of  the  copper  is  converted 
into  oxide,  which  is  dissolved  by  treating  the  roasted  substance  with 
weak  sulphuric  acid ;  and  the  alloy,  being  thus  brought  to  the  me- 


GILDING   AND    SILVERING.  831 

dium  standard  of  0.500  or  0.600,  may  be  refined  by  tbe  ordinary 
process.* 

GILDING  AND  SILVERING. 

§  1160.  Ornamental  objects  of  copper  or  bronze  were  formerly 
gilded  by  means  of  an  amalgam  of  gold,  which  method  has  now 
been  superseded  by  galvanic  processes.  The  amalgam  used  in 
mercurial  gilding  is  prepared  in  the  following  manner  : — Gold-leaf 
is  heated  to  a  dull  red-heat  in  a  crucible,  and  triturated  with  eight 
times  its  weight  of  mercury,  and,  when  the  gold  is  dissolved,  it  is 

*  The  process  of  refining  gold  pursued  at  the  United  States  Mint,  in  Philadel- 
phia, is  similar  to  the  method  formerly  called  quartation,  and  consists  in  melting 
gold  with  silver,  and  then  extracting  the  silver  with  pure  nitric  acid.  The  depo- 
site  of  grains  of  native  gold  is  first  melted  with  borax  and  saltpetre,  occasionally 
with  soda  to  remove  quartz,  and  being  cast  into  a  bar,  is  carefully  weighed,  accu- 
rately assayed  to  ^g'^j^  for  gold,  and  from  the  assay  and  weight  the  value  of  the 
deposite  calculated.  Although  a  million  of  dollars  may  be  deposited  in  a  day, 
upon. an  arrival  from  California,  yet  such  is  the  expedition  of  the  assay-depart- 
ment, that  in  a  few  days  the  deposites  are  all  paid  off.  As  soon  as  the  gold  is  as- 
sayed, each  pound  of  it  is  melted  with  2  pounds  of  pure  silver,  and  the  mixture, 
after  stirring,  poured  into  cold  water,  by  which  it  is  granulated,  divided  into  small 
irregular  fragments,  presenting  a  large  surface  to  the  subsequent  action  of  the 
acid.  The  granulations  are  then  put  into  large  porcelain  jars  of  50  gallons  each, 
of  which  there  are  about  70  in  use,  and  nitric  acid  poured  in  them.  The  jars 
being  placed  in  leaden-lined  wooden  troughs,  containing  water,  are  heated  by  a 
steam  coil  in  the  water,  causing  the  nitric  acid  to  dissolve  out  the  larger  propor- 
tion of  silver.  A  steam-heat  is  given  during  several  hours,  and  the  liquid  allowed 
to  repose  until  the  following  morning,  when  the  solution  of  nitrate  of  silver  is 
drawn  off  by  a  gold  siphon,  and  transferred  to  a  large  vat  of  1200  gallons,  con- 
taining a  saturated  solution  of  common  salt.  Fresh  acid  is  then  added  to  the 
gold  in  the  pots,  already  nearly  parted,  steam-heat  applied  again  for  several  hours, 
and  the  whole  left  again  to  repose.  On  the  following  morning  the  acid  liquid  of 
one  of  the  pots  being  drawn  off  and  the  fine  gold  removed  to  its  filter,  fresh  granu- 
lations of  gold  and  silver  are  introduced,  and  the  acid  liquid  of  the  adjoining 
pot,  containing  only  a  small  quantity  of  nitrate  of  silver  poured  over  it.  A  fresh 
charge  of  granulated  metal  is  thus  first  worked  by  the  yet  strong  acid,  which  acted 
on  the  nearly  fine  gold  of  the  previous  charge.  A  charge  of  $800,000  or  more  is 
easily  worked  off,  refined,  in  two  days,  by  A\  pounds  of  parting  acid  to  every  pound 
of  gold.  The  gold  is  washed  thoroughly  on  a  filter  by  hot  water,  pressed  in  a 
hydraulic  press,  further  dried,  melted  with  copper,  and  cast  into  bars,  about  2400 
ounces  Troy  constituting  a  melt.  After  being  assayed,  they  are  then  remelted 
with  the  calculated  quantities  of  copper  or  fine  gold  requisite  to  bring  them  to 
our  standard  of  900  thousandths  fine,  and  cast  into  ingots.  Upon  their  proving 
correct  in  the  assay,  usually  to  within  ^^\j^  of  the  standard,  they  are  delivered 
to  be  coined.  The  chloride  of  silver,  accurately  precipitated  with  a  slight  excess 
of  salt,  is  filtered  and  washed  thoroughly  on  large  filters,  of  3  by  5  feet  and  14 
inches  deep.  It  is  then  transferred  to  lead-lined  wooden  vats,  reduced  to  metallic 
silver  by  granulated  zinc,  and,  the  excess  of  zinc  being  removed  by  sulphuric  acid, 
washed,  pressed  in  the  hydraulic  press,  dried  by  heat,  and  remelted  with  a  new 
portion  of  gold. 

This  method  of  parting  formerly  required  3  parts  of  silver  to  1  part  of  gold, 
and  the  latter  constituting  a  fourth  part  of  the  alloy,  the  process  was  termed 
quartation.  We  have,  however,  found  that  2  parts  silver  to  1  part  gold  are  quite 
sufficient;  and  if  the  metal  be  well  granulated,  the  acid  will  not  leave  10  thou- 
sandths of  silver  in  the  gold,  which  is  sufficient  to  prevent  the  too  darkening  effect 
of  copper  in  the  coin. — J.  C.  B. 


832  GOLD. 

thrown  into  cold  water,  in  order  to  prevent  the  formation  of  crystals 
by  slow  cooling.  The  excess  of  mercury  being  removed  by  pres- 
sure, a  doughy  amalgam  remains,  consisting  of  2  parts  of  gold  and 
1  of  mercury. 

Bronze  objects  require  several  preliminary  preparations.  They 
are  heated  to  redness  and  then  dipped  into  dilute  sulphuric  acid  to 
dissolve  the  oxide  which  forms  on  the  surface,  which  operation  is 
called  the  cleaning,  (d^rochage,)  and  they  are  sometimes  dipped  for 
a  moment  into  concentrated  nitric  acid,  in  order  to  obtain  a  more 
perfect  cleansing,  called  ravivage.  The  surface  is  then  amalgamated 
by  means  of  the  scratch-brush,  made  of  fine  brass  wire,  which  is 
first  dipped  into  a  solution  of  nitrate  of  mercury,  and  then  pressed 
on  the  amalgam  of  gold,  part  of  which  adheres.  The  article,  being 
rubbed  with  the  brush,  is  placed  on  an  iron  grate  over  coals,  in  a 
chimney  which  must  draw  well,  in  order  to  carry  ofi"  the  mercurial 
vapours,  which  would  injure  the  health  of  the  workmen.  The  arti- 
cle is  then  cleaned  with  a  brush  dipped  in  vinegar,  and  the  parts 
which  are  to  be  bright  are  polished  with  blood-stone. 

By  substituting  an  amalgam  of  silver  for  one  of  gold,  and  ope- 
rating in  the  same  manner,  copper,  bronze,  and  brass  can  be  covered 
with  a  coating  of  silver.  The  brass  scales  of  barometers  and  other 
instruments  are  silvered  by  being  rubbed  with  a  cork  moistened  with 
mixture  of  1  part  of  chloride  of  silver,  2  of  carbonate  of  potassa,  1 
of  common  salt,  and  f  of  a  part  of  chalk. 

Grilding  hy  Immersion. 

§  1161.  This  process,  which  is  chiefly  used  for  gilding  copper 
jewelry,  consists  in  plunging  the  articles,  after  being  cleanly 
scraped,  into  a  boiling  solution  of  chloride  of  gold  in  an  alkaline 
carbonate,  which  is  prepared  by  dissolving,  on  the  one  hand,  100 
grammes  of  gold-leaf  in  250  grammes  of  nitric  acid  at  97°,  250  gm. 
of  concentrated  chlorohydric  acid,  and  250  of  water,  and  on  the 
other  hand,  3  kilogs.  of  carbonate  of  potassa  in  20  litres  of  water, 
heated  in  a  cast-iron  kettle.  When  the  gold  is  entirely  dissolved  in 
the  aqua  regia,  the  liquid  is  poured  into  a  porcelain  capsule,  and 
3  kilogs.  of  bicarbonate  of  potassa  are  gradually  added,  when  a 
lively  efiervescence  ensues,  after  the  termination  of  which  the 
contents  of  the  capsule  are  thrown  into  the  kettle.  The  liquid  is 
boiled  for  2  hours,  replacing  by  hot  water  that  which  evaporates ; 
after  which  the  gold-bath  is  ready  for  gilding. 

When  the  copper  articles  are  prepared  for  gilding,  they  are 
bound  together  with  a  brass  wire  and  suspended  to  a  glass  hook. 
At  the  right  of  the  bath  are  placed,  1st.  A  vessel  containing  a 
mixture  of  nitric,  sulphuric,  and  chlorohydric  acids ;  2d.  Two  ves- 
sels filled  with  water ;  3d.  A  vessel  containing  a  solution  of  nitrate 
of  mercury;  4tL  A  vessel  containing  water;  while  at  the  left  of 
the  bath  are  2  or  3  pots  holding  water.     The  workman  first  dips 


GALVANIC   GILDING. 


388 


the  articles  into  the  acid  liquid,  and  then,  successively,  into  the  two 
vessels  holding  water,  into  that  of  nitrate  of  mercury,  into  the  suc- 
ceeding one  of  water,  and  lastly,  into  the  gold-bath.  When  they 
have  remained  in  the  bath  for  about  30  seconds  they  have  taken  all 
the  gold  they  can  receive,  and  are  then  removed,  washed  in  the  pots 
on  the  left,  and  dried  in  heated  sawdust. 

Their  colour  is  then  given  by  means  of  a  mixture  of  6  parts  of 
nitre,  2  of  sulphate  of  iron,  and  1  of  sulphate  of  zinc,  dissolved  in 
a  small  quantity  of  boiling  water,  into  which  the  gilded  articles  are 
dipped ;  after  which  they  are  dried  before  a  bright  fire  until  the 
saline  coating  turns  brown.     They  are  then  washed  with  water. 

Gralvanic  Gilding, 

§  1162.  By  means  of  galvanism  a  perfectly  adherent  coating  of 
gold,  of  any  desired  thickness,  may  be  applied  to  copper,  brass, 
bronze,  silver,  platinum,  iron,  steel,  etc. ;  and  by  using  corre- 
sponding solutions,  silver,  platinum,  cobalt,  zinc,  etc.,  can  also  be 
deposited  on  copper  and  its  alloys.  The  solutions  used  for  galvanic 
processes  are  those  of  cyanide  of  potassium  in  w^hich  a  cyanide 
of  the  metal  to  be  deposited  has  been  dissolved;  and  the  same 
liquid  may  be  used  ad  infinitum  if  a  clean  blade  of  the  metal  to  be 
precipitated  be  kept  in  the  solution  and  placed  in  communication 
with  the  positive  pole  of  the  battery.  As  the  metal  in  solution 
is  deposited  on  the  articles  which  communicate  with  the  negative 
pole,  an  equivalent  quantity  of  the  metal  fixed  to  the  positive  pole 
dissolves,  while  the  composition  of  the  liquid  remains  uniform, 
if  the  surface  of  the  metallic  blade  is  nearly  equal  to  that  of  the  ob- 
jects to  be  covered.  The  best  solution  for  gilding  is  made  of  100 
parts  of  distilled  water,  10  parts  of  cyanide  of  potassium,  and  1 
part  of  cyanide  of  gold.     The  liquid  is  placed  in  a  large  wooden  vat 

CC  (fig.  602)  lined 
with  mastic,  and  tra- 
versed by  two  gilded 
I  metallic  rods  W^  vv'^ 
which  dip  into  the 
liquid,  the  rod  tt^ 
communicating  with 
the  negative  pole, 
and  the  rod  vv'  with 

„.     „^^  the  positive  pole  of 

Fjg.  602.  ,1        u  ^x  1-1 

°  the     battery,    while 

two  large  sheets  of  gold  or,  heavily  gilded  copper  oo^  dip  into  the 

bath  and  communicate  with  the  rod  vv^.     Resting  on  the  rods  tt' 

and  vv^  are  movable  rods  ab,  of  gilded  brass,  to  which  the  objects  to 

be  gilded  are  suspended. 

The  battery  is  formed  of  plates  of  zinc  and  cop]5er,  dipping  into 

a  weak  solution  of  sulphuric  acid ;  each  element  being  commonly 


334  GOLD. 

composed  of  a  wooden  vessel,  lined  with  mastic,  in  which  two  con- 
centric cylinders  of  copper  and  zinc,  kept  apart  by  wooden  pegs, 
are  arranged.  The  zinc  cylinder  has  been  first  amalgamated  with 
mercury,  in  order  to  protect  it  from  too  rapid  solution.  Water 
acidulated  with  sulphuric  acid,  marking  5°  degrees  on  Baum^'s 
areometer,  being  placed  in  the  vessels,  the  zinc  of  each  element  is 
made  to  communicate  with  the  copper  of  the  succeeding  one  by 
means  of  a  strong  brass  wire  attached  to  the  upper  part  of  the 
cylinders,  while  the  free  zinc  cylinder  of  one  of  the  two  extreme 
elements  is  placed  in  communication  with  the  rod  vv'  which  forms 
the  positive  pole,  and  the  copper  cylinder  of  the  other  extreme  ele- 
ment communicates  with  the  rod  tt'  which  constitutes  the  negative 
pole  of  the  battery. 

The  objects  to  be  gilded  should  be  prepared  as  for  gilding  by 
immersion,  but  the  ravivage  is  unnecessary.  The  time  of  immer- 
sion varies  with  the  thickness  of  the  coat  required ;  and  the  tem- 
perature of  the  bath  should  be  between  59°  and  68°.  In  order  to 
ascertain  the  quantity  of  gold  deposited,  it  is  sufficient  to  weigh  the 
object  before  and  after  immersion. 

Although  the  solution,  the  composition  of  which  was  just  ex- 
plained, is  ordinarily  used,  the  same  effect  can  be  obtained  with 
different  materials  y  and  either  the  cyanide  of  potassium  may  be 
replaced  by  the  double  cyanide  of  iron  and  potassium,  or  the  cyanide 
of  gold  by  its  sesquioxide,  or  by  the  double  chloride  of  gold  and  po- 
tassium, or,  lastly,  by  sulphide  of  gold.  The  same  process  is  adopted 
for  the  gilding  of  iron,  steel,  or  tin  ;  but  a  small  quantity  of  copper 
must  previously  be  deposited  on  the  object  by  dipping  it,  for  a  few 
moments,  in  a  bath  composed  of  1  part  of  cyanide  of  copper  and 
10  parts  of  cyanide  of  potassium  dissolved  in  100  parts  of  water. 

Galvanic  Silvering. 

§1163.  Galvanic  silvering  is  applied  chiefly  to  objects  made  of 
German  silver,  or  other  compositions  which  closely  resemble  silver- 
plate.  The  thickness  of  the  coating  of  silver  may  be  increased  at 
pleasure. 

The  solution  used  for  silvering  is  made  of  100  parts  of  distilled 
water,  10  of  cyanide  of  potassium,  and  1  of  cyanide  of  silver ;  the 
process  being  the  same  as  that  for  gilding,  with  the  exception  that 
the  sheets  of  gold  in  the  bath  (fig.  602)  are  necessarily  replaced  by 
sheets  of  silver.  The  silvered  pieces,  which,  on  leaving  the  bath 
are  of  a  dead-white  colour,  are  polished  by  the  burnisher,  and  then 
heated  to  a  dull  red-heat  in  a  muflEle,  after  being  dipped  into  a  solu- 
tion of  borax.  When  cooled,  they  are  plunged  into  a  weak  solution 
of  sulphuric  acid,  and  then  dried. 

By  an  analogous  process,  platinum  may  be  deposited  on  copper  or 
silver ;  but  it  adheres  with  difficulty,  and,  as  yet,  it  has  been  found 
impossible  to  protect  articles  covered  with  platinum  from  the  action 


GALVANOPLASTICS.  335 

of  nitric  acid.  Solutions  for  the  deposition  of  zinc  and  lead  are 
prepared  by  dissolving  oxide  of  zinc  or  oxide  of  lead  in  a  solution 
of  cyanide  of  potassium. 

GALVANOPLASTICS. 

§  1164.  By  means  of  a  feeble  electrical  current  a  uniform  and  firm 
coat  of  copper  can  be  deposited  on  any  given  object,  and  a  raised 
surface  thus  be  reproduced  in  relief  with  extreme  exactness.  The 
copper  plate  thus  produced  can  be  used  as  a  mould  to  form,  by 
means  of  a  galvanic  current,  a  second  deposit  -of  metallic  copper, 
I'eproducing  faithfully  the  original  object.  These  processes  are 
applied  to  the  reproduction  of  medals  and  copper  plates,  the  battery 
used  being  the  same  as  that  employed  for  gilding,  while  the  liquid 
for  coppering  consists  of  a  slightly  acidulated  saturated  solution  of 
sulphate  of  copper,  into  which  the  object  on  which  the  metallic 
copper  is  to  be  precipitated  is  dipped,  after  being  brought  into  com- 
munication with  the  negative  pole.  The  positive  pole  terminates 
in  a  plate  of  copper  of  about  the  same  size  as  the  object  to  be  cop- 
pered, and  parallel  to  it  at  a  short  distance.  In  order  to  reproduce 
a  medal,  the  first  step  is  to  make  its  mould  in  relief,  either  with 
plaster,  (§  560,)  or  with  fusible  alloy,  (§  316,)  or  with  stearic  acid, 
and  afterward  render  it  impervious,  by  immersing  it,  for  a  few  mo- 
ments, in  a  melted  mixture  of  stearic  acid  and  white  wax,  after 
which  it  is  lined  with  plumbago,  uniformly  spread  over  it  with  a 
brush.  The  object  of  this  coating  is  to  render  the  surface  of  the 
mould  a  conductor  of  electricity ;  which  being  done,  the  mould  is 
dipped  into  the  solution  of  sulphate  of  copper,  after  having  secured 
it  by  a  small  copper  band  around  its  circumference  and  fastened  it  to 
the  negative  wire  of  the  battery.  The  copper  which  is  deposited  on 
the  mould  can  be  made  of  any  thickness  by  keeping  it  for  a  sufficient 
length  of  time  in  the  bath,  and  it  separates  very  readily  from  the 
mould,  which  can  be  used  for  any  number  of  times.  The  copper 
thus  precipitated  by  the  galvanic  current  is  in  crystalline  grains, 
which  are  the  smaller  the  more  feeble  the  current  is. 

In  order  to  reproduce  the   medal, 

it  is  riot  necessary  to  use  a  separate 

battery,  as  the  experiment  may  be  so 

arranged  as  to  produce  the  galvanic 

current  in  the  bath  itself.     Fig.  603 

represents  a  small  apparatus  generally 

used  for  this  purpose.     A  is  a  glass 

vessel,  filled  with  a  saturated  solution 

of  sulphate  of  copper,  to  maintain  the 

saturation  of  which  crystals  of  sulphate 

Fig-  603.  of  copper  are  placed  on  the  stand  m, 

A  glass  cylinder  B,  open  at  both  ends,  is  held  up  by  the  support 

?,  Z',  I"  in  the  vessel  A ;  the  bottom  of  the  cylinder  being  made  of 


336  GOLD. 

some  porous  membranes — a  bladder,  for  instance.  A  weak  solution 
of  sulphuric  acid  is  poured  into  the  vessel  B ;  and  two  metallic 
rings  a,  5,  terminating  in  metallic  rods  united  at  their  upper  part, 
are  dipped,  the  one  b  into  the  solution  of  sulphate  of  copper,  the 
other  a  into  a  solution  of  sulphuric  acid,  and  are  kept  separated 
by  the  membrane.  A  plate  of  amalgamated  zinc  is  placed  on  the 
ring  a,  while  the  mould,  on  which  the  copper  is  to  be  precipitated 
is  set  on  the  ring  b ;  and  the  intensity  of  the  electrical  current  is 
gauged  by  passing  the  upper  leg,  n\  of  the  metallic  rods  which  sup- 
port the  rings  a  and  b,  below  a  movable  magnetic  ring,  the  devia- 
tions of  which  are  in  proportion  to  the  activity  of  the  current. 

ANALYSIS  AND  ASSAYING  OF  ALLOYS  OF  GOLD. 

§  1165.  Alloys  of  gold  and  copper  may  be  analyzed  by  cupelling 
them  with  lead,  and  following  exactly  the  same  process  as  described 
for  the  cupellation  of  alloys  of  silver  and  copper.  If  the  alloy  con- 
tains no  silver,  the  weight  of  the  lump  obtained  represents  pretty 
exactly  the  quantity  of  pure  gold  which  existed  in  the  alloy ;  but 
if,  as  more  frequently  happens,  the  alloy  contains  a  certain  propor- 
tion of  silver,  this  latter  metal  remains  alloyed  with  the  gold  after 
the  cupellation.  However,  the  process  of  direct  cupellation  is  at- 
tended with  surplusses  and  losses  which  sometimes  reach  3  thou- 
sandths: when  the  temperature  of  the  muffle  is  very  great,  there 
is  a  small  loss  arising  from  the  absorption  of  a  small  quantity  of 
gold  by  the  cupel ;  and  when  the  heat  is  too  low,  the  gold  retains 
a  small  quantity  of  copper  and  lead ;  although  gold  loses  less  by 
volatilizing  than  silver. 

In  order  to  determine  exactly  the  quantity  of  gold  existing  in  a 
ternary  alloy  of  gold,  silver,  and  copper,  it  is  cupelled  at  a  mode- 
rate heat  with  a  certain  quantity  of  silver  and  lead,  in  order  to  obtain 
an  alloy  of  silver  and  gold,  from  which  the  latter  can  be  perfectly 
separated  by  means  of  an  excess  of  nitric  acid,  which  dissolves  the 
silver  and  leaves  the  gold  pure.  In  order,  however,  to  insure  exact 
results,  there  must  be  a  certain  ratio  between  the  quantities  of  gold 
and  silver ;  because,  if  the  proportion  of  silver  be  too  ^  small,  the 
nitric  acid  does  not  dissolve  it  entirely ;  and  if,  on  the  contrary, 
the  quantity  of  silver  be  too  great,  the  silver  and  copper  are  com- 
pletely dissolved,  while  the  gold  separates  in  the  form  of  powder, 
which  it  is  difficult  to  collect  without  loss.  Experience  has  shown 
that  the  most  favourable  conditions  for  the  assay,  commonly  called 
the  parting,  {depart,)  consist  in  reducing  the  alloy  to  J  of  gold  and 
f  of  silver,  in  which  case  it  is  completely  acted  on,  while  the  sepa- 
rated gold  preserves  the  form  of  the  original  alloy,  and  does  not 
become  divided,  if  the  operation  be  carefully  conducted.  This 
operation  has  received  the  name  of  quartation. 

The  proportion  of  lead  to  be  added,  which  varies  with  the  standard 
of  the  alloy,  is  indicated  in  the  following  table : — 


ASSAYING  OF  ALLOYS  OF  GOLD.  337 


Standard  of  gold  alloyed  Quantity  of  lead  necessary  to  be  added  to  entirely 

with  copper.  remove  the  copper  by  cupellation. 

1000  thousandths 1"  part. 

900         "  


800 

700 

600 

500 

4001 

300 

200 

100 


10 

a 

16 

a 

22 

u 

24 

u 

26 

u 

34 


Let  us  suppose  that  the  standard  of  a  piece  of  coin  is  to  be  determin- 
ed, the  legal  standard  of  which  which  may  be  regarded  as  its  approxi- 
mate standard,  is  ■^■^^.  The  quantity  of  alloy  usually  operated  on 
being  0.500  gm.,  containing,  according  to  the  legal  standard,  0.450 
gm.  of  gold,  therefore  1.350  gm.  of  silver  and  5  gm.  of  lead  must  be 
added.  But  if  an  alloy  is  to  be  assayed  the  legal  standard  of  which 
is  entirely  uuknown,  the  first  step  is  to  ascertain  the  latter  by  ap- 
proximation, by  means  of  the  assai/  hy  the  touch-needle,  about  to 
be  described,  after  which  the  process  is  continued  as  usual. 

The  lead  is  first  placed  in  the  heated  cupel,  and  when  it  is  in 
fusion,  the  mixture  of  gold  and  silver  is  introduced,  having  been 
previously  weighed  and  wrapped  in  a  piece  of  paper.  The  cupel- 
lation is  allowed  to  go  on  as  usual,  and  requires  less  care  than  the 
cupellation  of  silver,  because  silver  alloyed  with  gold  is  not  liable 
to  blister ;  but  the  cupel  should  be  removed  immediately  after  the 
lightning  to  avoid  loss  by  volatilization.  The  lump  is  removed  after 
cooling,  flattened  under  a  hammer,  annealed  for  a  few  moments,  and 
then  rolled  between  cylinders ;  after  which  the  sheet  thus  obtained 
is  rolled  into  a  spiral  form,  and  subjected  to  the  action  of  nitric  acid 
in  a  small  assayer's  flask,  (fig.  604,)  into  which  30  grammes  of 
nitric  acid  of  22°  Baumd  are  poured,  and  boiled  for  20 
minutes.  The  acid  is  then  decanted  and  replaced  by  30  gm. 
of  pure  concentrated  nitric  acid  marking  32°,  which  is  boiled 

*\       for  10  minutes;  when  the  acid  is  decanted,  and  the  gold, 

U  which  has  preserved  the  shape  of  the  alloy,  washed  several 
Fig.  604.  times.  The  flask  being  afterward  completely  filled  with 
water,  its  mouth  is  closed  with  the  thumb,  and  it  is  inverted,  when 
the  spiral  sheet  of  gold  falls  slowly  through  the  liquid  column,  and 
is  received  in  a  small  earthen  crucible,  after  which  the  water  is 
poured  ofi",  and  the  crucible  heated  to  redness  in  the  mufile. 

The  acid  should  not  be  too  concentrated,  because  the  gold  might 
be  divided.  When  the  assay  has  been  made  with  the  precautions 
indicated,  the  gold  remains  in  the  form  of  a  spongy,  brown,  and 
very  friable  mass,  of  nearly  the  same  volume  as  the  original  alloy ; 

.  Vol.  IL— 22 


338  GOLD. 

but  it  contracts  considerably  when  heated  in  the  small  crucible, 
becoming  harder  and  assuming  the  lustre  and  colour  of  malleable 
gold.  The  calcined  gold  being  exactly  weighed,  the  standard  of 
the  alloy  is  thus  obtained  within  nearly  1  thousandth. 

Direct  assays  made  on  known  alloys  of  gold  and  silver  have 
shown  that  the  operation,  when  carefully  performed  as  just  de- 
scribed, can  give  rise  only  to  the  following  errors : — 


True  standards  of  the  alloj. 

900 

standards  found. 

900.25  

Differences. 

'  H-0.25 

800 

., 800.50   , 

-f0.50 

700 

700.00  

0.00 

600 

GOO.OO 

0.00 

500  

499.50  

—0.50 

400 

399.50  

—0.50 

300  

299.50  

—0.50 

200 

199.50  

—0.50 

100 

99.50  

-0.50 

Assaying  hy  the  touch-needle, 

§  1166.  The  assay  just  described  cannot  be  applied  to  fine 
jewelry,  because  the  article  would  be  destroyed  by  the  process,  and 
gold  jewelry  is  therefore  subjected  to  a  test  called  the  assay  by  the 
touch-needle,  which  does  not  injure  it,  and  yet  enables  a  skilful 
assayer  to  determine  its  standard  within  nearly  1  thousandth.  The 
method  consists  in  rubbing  the  object  against  a  very  hard  black- 
stone,  on  which  it  leaves  marks,  from  the  colour  of  which,  and  their 
behaviour  when  moistened  with  a  mixture  of  nitric  acid  of  a  density 
of  1.34  with  2  per  cent,  of  chlorohydric  acid,  the  assayer  forms  an 
approximate  opinion  of  the  standard  of  the  alloy.  The  black-stone 
used,  called  touch-stone,  is  a  kind  of  quartz,  coloured  with  bitumen, 
which  formerly  was  imported  from  Lydia,  but  has  likewise  been 
found  in  Bohemia,  Saxony,  and  Silesia.  The  conditions  essential 
to  a  good  touch-stone  are :  an  intense  black  colour,  incapability  of 
being  acted  on  by  acids,  hardness,  and  a  sufficient  degree  of  rough- 
ness to  retain  some  of  the  gold. 

The  assayer  is  provided  with  a  series  of  small  blades,  called  touch- 
needles,  consisting  of  alloys  of  copper  and  gold,  the  standard  of 
each  of  which  is  exactly  known,  which  enable  him  to  compare  the 
marks  they  leave  on  the  touch-stone,  before  and  after  the  action  of 
the  acid,  with  that  of  the  alloys  to  be  assa-yed. 

No  regard  should  be  paid  to  the  first  marks  left  by  the  articles 
on  the  touch-stone,  as  they  are  made  by  the  superficial  layer,  and 
always  show  a  higher  standard,  because  the  surface  consists  of  pure 
gold ;  and  several  marks  should  therefore  be  made,  the  last  of  which 
only  is  examined.  Alongside  of  these  marks  others  are  made  with 
that  touch-needle  the  composition  of  which  approaches  nearest  to 


PROPERTIES   OF   PLATINUM. 


339 


that  of  the  article ;  when  a  glass  rod,  dipped  in  the  acid,  is  drawn 
over  both,  after  which  the  colour  of  each  mark  and  the  manner  of 
action  of  the  acid  are  examined. 


PLATINUM. 

Equivalent  =  98.7  (1233.7 ;  0  =  100). 

§  1167.  Platinum,  which  was  imported  into  Europe  only  about 
the  middle  of  the  last  century,  but  was  long  known  in  America  by 
the  Spanish  name  of  platina,  a  diminutive  name  for  silver,  was  for 
a  long  time  quite  useless,  because  no  one  could  work  it.  The  pla- 
tinum of  commerce  is  nearly  pure,  as  it  commonly  contains  only  a 
small  quantity  of  iridium,  which  increases  its  hardness,  but  dimi- 
nishes its  malleability.  In  order  to  obtain  perfectly  pure  platinum, 
the  metal  of  commerce  is  dissolved  in  aqua  regia,  the  solution  fil- 
tered, and  chloride  of  potassium  is  added,  which  yields  a  copious 
yellow  precipitate  of  a  double  chloride  of  platinum  and  potassium, 
very  slightly  soluble  in  water,  but  generally  mixed  with  a  small 
quantity  of  the  corresponding  double  chloride  of  iridium  and  potas- 
sium. The  precipitate  is  mixed  with  carbonate  of  potassa  and  heated 
to  redness  in  an  earthen  crucible,  when  the  chloride  of  platinum 
gives  off  its  chlorine  to  the  potassium  of  the  carbonate  of  potassa, 
leaving  the  platinum  isolated,  while  oxygen  and  carbonic  acid  are 
disengaged.  The  double  chloride  of  iridium  is  also  decomposed, 
but  the  iridium  remains  in  the  state  of  oxide.  The  calcined  mass 
is  treated  with  hot  water,  which  dissolves  the  alkaline  salts, 
and  the  residue  is  acted  on  by  weak  aqua  regia,  which  dis- 
solves the  platinum  alone  and  leaves  the  oxide  of  iridium. 
Sal  ammoniac  is  added  to  the  solution  of  chloride  of  pla- 
tinum, when  a  yellow  crystalline  precipitate  of  double 
chloride  of  platinum  and  ammonia  PtCl34-NH3,HCl  is 
formed,  which,  on  being  calcined  to  redness  after  wash- 
ing, leaves  a  spongy  mass  of  platinum,  called  platinum 
sponge. 

In  order  to  reduce  platinum-sponge  to  the  state  of  mal- 
leable platinum,  it  is  introduced  into  a  brass  cylinder  efgh, 
(fig.  605,)  the  bottom  of  which  fits  into  a  steel  cup  abed, 
while  a  steel  piston  ik  moves  in  the  cylinder.  When  the 
cylinder  is  half-filled  with  platinum-sponge,  the  piston  is 
I  <?  introduced  and  struck  with  a  hammer,  at  first  gently, 
\l  afterward  more  powerful ;  by  which  means  a  solid  disk 
of  platinum  is  obtained  in  a  short  time,  which  is  heated 


840  PLATINUM. 

to  a  white-heat  in  a  muffle,  and  again  hammered  on  a  steel  anvil. 
By  repeating  these  operations,  a  perfectly  malleable  plate  of  plati- 
num is  obtained,  which  can  be  rolled  into  sheets  in  a  small  rolling- 
machine. 

§  1168.  Platinum  resists  the  highest  temperature  of  a  forge-fire 
without  fusing,  but  it  melts  before  the  oxyhydrogen  blowpipe,  or 
between  the  pieces  of  charcoal  terminating  the  conductors  of  a  pow- 
erful battery.  Platinum  possesses  the  property  of  being  welded 
and  soldered  on  itself  at  a  white-heat,  the  application  of  which 
property  has  just  been  mentioned  in  the  transformation  of  sponge 
platinum  into  the  malleable  metal. 

Platinum  is  of  a  grayish-white  colour,  susceptible  of  a  high  polish, 
and  possessing  great  malleability  when  pure,  while  the  presence  of 
a  very  small  quantity  of  foreign  matter  will  profoundly  affect  this 
quality.  Although  the  tenacity  of  pure  platinum  is  hardly  inferior 
to  that  of  iron,  the  platinum  of  commerce,  which  always  contains 
small  quantities  of  iridium,  is  much  less  tenacious,  for  a  wire  of  2 
millimetres  in  diameter  frequently  breaks  under  a  weight  of  126 
kilogs.     The  density  of  hammered  or  rolled  platinum  is  21.5. 

Platinum  does  not  oxidize  in  the  air  at  any  temperature,  and  ia 
acted  on  by  only  a  limited  number  of  acids.  Chlorohydric  and 
concentrated  sulphuric  acid  do  not  affect  it,  neither  does  nitric  acid 
attack  it,  although  it  is  soluble  in  this  acid  when  alloyed  with  a 
sufficient  quantity  of  silver.  Aqua  regia  is  the  true  solvent  of 
platinum. 

Platinum  is  acted  on  at  a  red-heat  by  potassa,  soda,  and  particu- 
larly by  lithia,  but  remains  unchanged  when  exposed  to  the  action 
of  the  alkaline  carbonates.  A  mixture  of  nitrate  of  potassa  and 
potassa  acts  on  it  much  more  readily  than  pure  potassa.  Sheet- 
platinum  is  acted  on,  only  after  a  long  time,  by  sulphur,  phosphorus, 
and  arsenic,  while  platinum-sponge  combines  readily  with  these 
substances,  producing  fusible  and  very  brittle  compounds.  A  mix- 
ture of  silex  and  carbon  attacks  platinum ;  in  which  manner  plati- 
num crucibles  are  frequently  rendered  useless.  As  the  surface  of 
a  platinum  crucible  becomes  rough  from  repeated  heating,  and  the 
metal  very  brittle,  it  should  never  be  heated  in  contact  with  char- 
coal, but  rather  be  placed  in  earthen  crucibles,  at  the  bottom  of 
which  a  small  quantity  of  quicklime  or  magnesia  is  deposited. 

§  1169.  Metallic  platinum  may  also  be  obtained  in  the  form  of  a 
very  finely  divided  precipitate,  called  platinum-black,  and  then  pos- 
sesses remarkable  properties,  on  which  we  shall  dwell  for  a  short 
time.  Platinum-black  is  obtained  by  reducing  platinum  in  solution 
by  an  easily  combustible  organic  substance ;  to  which  effect  a  solu- 
tion of  chloride  of  platinum  PtCl^  is  generally  boiled  with  carbonate 
of  soda  and  sugar,  when  chloride  of  sodium  is  formed,  while  the  plati- 
num is  precipitated  in  the  metallic  state  and  the  oxygen  given  off  by 
the  soda  decomposes  a  portion  of  the  sugar  into  water  and  carbonic 


PLATINUM-BLACK.  341 

acid.  The  flask  in  which  the  operation  is  performed  must  be  fre- 
quently shaken  to  prevent  the  precipitated  platinum  from  adhering 
to  its  sides.  The  precipitate  is  collected  on  a  filter  and  dried  be- 
tween tissue-paper. 

Platinum-black  is  also  prepared  by  dissolving  protochloride  of 
platinum  PtCl  in  a  concentrated  solution  of  potassa,  boiling  the 
liquid,  and  then  adding  a  small  quantity  of  alcohol ;  when  a  very 
lively  eft'ervescence  of  carbonic  acid  ensues,  while  the  platinum  is 
precipitated.  Lastly,  it  is  sometimes  obtained  by  decomposing 
sulphate  of  platinum  by  alcohol  with  the  assistance  of  heat. 

Finely  divided  metallic  platinum  possesses  the  property  of  con- 
densing gases  in  very  large  quantities.  Thus,  platinum-black  which 
is  allowed  to  remain  in  an  atmosphere  of  oxygen  gas  will  condense 
several  hundred  times  its  volume  of  the  gas  and  afterward  exhibits 
very  intense  phenomena  of  combustion.  If,  for  example,  a  drop  of 
absolute  alcohol  be  thrown  on  platinum-black  thus  charged  with 
oxygen,  the  whole  substance  becomes  incandescent ;  and  if  a  cap- 
sule containing  platinum-black  be  placed  under  a  bell-glass  filled 
with  air,  the  sides  of  which  are  moistened  with  alcohol,  the  vapours 
of  the  alcohol  undergo  a  slow  oxidation,  which  converts  them  into 
acetic  acid.  This  property  of  platinum-black  depends,  in  a  great 
measure,  on  the  method  employed  in  its  preparation ;  as  for  ex- 
ample, that  obtained  by  decomposing  sulphate  of  platinum  by  alco- 
hol is  the  most  active.  The  action  may  be  measured  in  the  following 
manner : — Having  passed  to  the  top  of  a  graduated  bell-glass  filled 
with  mercury,  a  small  quantity  of  a  solution  of  formic  acid,  (an 
organic  acid  which  is  readily  converted  in  water  and  carbonic  acid 
by  oxidizing  agencies,)  a  known  weight  of  platinum-black  wrapped 
in  tissue-paper  is  introduced  into  the  bell-glass ;  when  the  evolution 
of  carbonic  acid  immediately  begins,  but  ceases  again  in  a  few  mo- 
ments. By  ascertaining  the  volume  of  gas  disengaged,  the  quantity 
of  oxygen  condensed  by  the  platinum-black  can  be  measured. 

The  absorbing  property  of  platinum  black  is  also  perceptible, 
though  in  a  less  degree,  in  platinum  sponge,  and  even  in  sheet  pla- 
tinum. Thus,  it  has  been  shown  (§  74),  that  on  throwing  a  piece 
of  platinum-sponge  into  a  bell-glass  containing  a  detonating  mix- 
ture of  oxygen  and  hydrogen,  an  explosion  immediately  ensues :  so 
again,  if  a  current  of  hydrogen  gas  be  projected  on  platinum- 
sponge  exposed  to  the  air,  the  jet  of  hydrogen  ignites. 

■-v  Sheet-platinum  does  not  present  these  properties  at  the 

I  ordinary  temperature,  but  exhibits  them  when  heated  to 

about  390°.  If  a  coil  of  platinum  wire  (fig.  606)  be  placed 
over  the  wick  of  an  alcohol-lamp,  and  the  lamp  lighted  so 
as  to  heat  the  wire  to  redness,  the  wire  remains  incan- 
descent  for  an  indefinite  length  of  time  after  the  flame  be- 
^^*  '  neath  has  been  extinguished,  because  the  vapour  of  alco- 
hol, disengaged  from  the  wick,  burning  when  it  comes  into  contact 


342  PLATINUM. 

■with  the  wire,  develops  heat  enough  to  keep  it  incandescent.  The 
experiment  proceeds  better  by  adding  a  small  quantity  of  ether  to 
the  alcohol ;  and  the  little  apparatus  is  known  by  the  name  of 
Davy's  flameless  lamp.  In  the  same  way,  if  a  small  quantity  of 
ether  be  placed  at  the  bottom  of  a  wineglass,  (fig.  607,)  and  a  coil 
of  platinum  wire,  which  has  been  previously  heated  co 
redness,  be  fastened  to  a  pasteboard  lid  which  closes 
partly  the  mouth  of  the  glass,  the  wire  remains  incan- 
descent for  a  long  time.  In  these  experiments,  the 
vapours  of  alcohol  and  ether  are  only  imperfectly 
burned,  yielding,  as  products  of  combustion,  volatile 
substances  of  highly  suffocating  properties  and  con- 
Fig.  607.  taining  an  organic  acid;  all  of  which  shall  hereafter  be 
described. 

Deutoxide  of  nitrogen,  and  ammonia,  mixed  with  oxygen  gas,  are 
converted,  by  contact  with  platinum-sponge,  into  nitric  acid,  while 
the  compounds  of  nitrogen  and  oxygen,  on  the  contrary,  are  changed 
into  ammonia,  by  contact  with  the  sponge  in  an  atmosphere  of  hy- 
drogen. In  order  to  succeed  in  the  experiment,  it  is  better  to 
heat  the  platinum-sponge  to  a  temperature  of  300°  or  400°,  in  a 
glass  tube  traversed  by  the  gaseous  mixture. 

Platinum-sponge  loses  its  absorbing  property  after  some  time,  but 
regains  it  by  being  heated  for  a  few  moments  in  nitric  acid,  and 
then  calcined  at  a  dull  red-heat.  Platinum-black,  which  also  loses 
its  activity  after  some  time,  is  restored  to  its  former  state  by  heat- 
ing it  with  nitric  acid,  washing  it  with  water,  and  drying  it  by  a 
gentle  heat. 

COMPOUNDS  OF  PLATINUM  WITH  OXYGEN. 

§  1170.  Platinum  does  not  combine  directly  with  oxygen,  except 
at  a  red-heat,  or  when  assisted  by  the  caustic  alkalies.  Two  oxides 
of  platinum  are  known — 

The  protoxide  PtO, 

The  binoxide  PtO,2 
each  of  which  is  a  feeble  base,  forming  with  powerful  acids  a  series 
of  salts  which  are  easily  decomposed  by  heat  and  leave  metallic 
platinum. 

Protoxide  of  platinum  PtO  is  prepared  by  decomposing  the 
protochloride  PtCl  by  a  solution  of  caustic  potassa,  when  hydrated 
protoxide  remains  in  the  form  of  a  black  powder,  which  dissolves 
with  a  brown  colour,  in  a  concentrated  solution  of  potassa.  When 
heated,  it  first  gives  off  its  water,  and  then  oxygen.  Hydrated 
protoxide  of  platinum  dissolves  in  acids  and  yields  solutions  of  a 
deep  brown  colour,  which  are  not  precipitated  by  sal-ammoniac. 

Binoxide  of  platinum  PtOg  is  obtained  by  adding  to  nitrate 
of  platinum  one-half  of  the  potassa  which  would  be  necessary  to 


OXIDES   OF   PLATINUM.  343 

completely  decompose  the  salt,  when  a  voluminous  brown  precipi- 
tate is  formed,  consisting  of  hydrated  binoxide  of  platinum  PtOg 
+  2H0.  If  a  larger  quantity  of  alkali  were  added,  the  precipitate 
would  contain  potassa  in  combination.  But  this  oxide  is  more  easily 
prepared  by  adding  to  a  solution  of  perchloride  PlCl^  a  large 
excess  of  caustic  potassa,  when  at  first  a  yellow  precipitate  of  double 
chloride  of  platinum  and  potassium  is  formed,  but  again  dissolves  if 
the  liquid  be  heated.  The  platinum  then  exists  in  the  solution  in 
the  state  of  platinate  of  potassa ;  and  the  liquid  being  supersatu- 
rated by  acetic  acid,  hydrated  oxide  of  platinum  is  precipitated. 
The  hydrate  parts  with  its  water  at  a  moderate  heat  and  turns  black, 
while  it  loses  its  oxygen  when  exposed  to  higher  a  temperature.  It 
dissolves  in  the  acids,  and  yields  orange-yellow  solutions,  while  after 
calcination  it  is  insoluble.  The  hydrate  also  dissolves  very  readily 
in  a  concentrated  solution  of  caustic  potassa,  and  the  liquid  by  evapo- 
ration deposits  crystals  of  platinate  of  potassa.  Insoluble  platinate 
of  potassa  is  also  obtained  by  mixing  the  double  chloride  of  plati- 
num and  potassium  with  a  concentrated  solution  of  potassa,  drying 
the  substance  and  heating  it  until  the  alkali  is  fused.  By  treating 
it  with  water  the  alkaline  salts  are  dissolved,  and  a  brown  mass  of 
platinate  of  potassa  remains,  which,  when  treated  with  acetic  acid, 
leaves  hydrated  binoxide  of  platinum. 

By  adding  ammonia  to  a  solution  of  sulphate  of  platinum,  a  brown 
precipitate  is  obtained,  which  is  a  double  basic  salt,  and  which,  on 
being  diluted  for  some  time  with  a  weak  solution  of  caustic  soda, 
yields  a  substance  of  detonating  properties  when  heated  to  about 
410°.  This  fulminating  compound,  which,  however,  does  not  de- 
tonate by  percussion,  is  regarded  as  a  compound  of  platinum  and 
ammonia. 

SALTS  FORMED  BY  THE  PROTOXIDE  OF  PLATINUM. 

§  1171.  These  salts  present  but  little  interest,  and  have  hitherto 
been  but  little  studied.  They  form  brown  solutions  which  do  not 
crystallize,  and  from  which  potassa  does  not  precipitate  them  when 
sufficiently  diluted,  while  the  alkaline  carbonates  yield  a  brown  pre- 
cipitate, which  remains  suspended  in  the  liquid.  Sulf  hydric  acid 
and  the  sulf  hydrates  throw  down  a  black  precipitate. 

The  protoxalate,  which  is  the  only  protosalt  of  platinum  which 
has  hitherto  been  obtained  in  a  crystalline  form,  is  prepared  by 
heating  the  hydrated  binoxide  of  platinum  with  a  solution  of  oxalic 
acid,  when  the  former  is  reduced  to  the  state  of  protoxide,  which 
dissolves  in  the  excess  of  oxalic  acid,  while  carbonic  acid  is  disen- 
gaged. The- liquid,  when  evaporated,  deposits  the  protoxalate  of 
platinum  in  small  coppery-red  needles. 

SALTS  FORMED  OF  THE  BINOXIDE  OF  PLATINUM. 
§  1172.  The  salts  of  the  binoxide  of  platinum  are  of  an  orange- 


344  PLATINUM. 

yellow  colour,  and  caustic  potassa  throws  down  from  their  solutions  a 
brown  precipitate  of  the  platinate  of  potassa,  which  dissolves  in  an 
excess  of  caustic  potassa.  Sulf  hydric  acid  and  the  alkaline  sulf- 
hydrates  yield  black  precipitates  which  dissolve  in  a  large  excess  of 
sulf  hydrate.  All  the  salts  are  decomposed  by  heat  and  leave  me- 
tallic platinum  ;  and  iron  as  well  as  zinc  decomposes  their  solutions 
by  precipitating  metallic  platinum  in  the  form  of  a  black  powder. 
Chloride  of  potassium  and  chlorohydrate  of  ammonia  throw  down, 
from  solutions  of  salts  of  the  binoxide  of  platinum  double  chlorides, 
PtCl^+KCl,  PtClg+NHgHCl,  as  yellow  crystalline  precipitates, 
which  are  very  slightly  soluble  in  water,  and  nearly  insoluble  in 
a  mixture  of  alcohol  and  water.  The  double  ammoniacal  chloride 
yields,  by  calcination,  platinum-sponge ;  while  the  double  chloride 
of  platinum  and  potassium  is  decomposed  by  heat  into  metallic  pla- 
tinum and  chloride  of  potassium ;  after  which  the  substance,  by 
treatment  with  water,  yields  pure  platinum. 

Bichloride  of  platinum  is  the  solution  extensively  used  in  the 
laboratory,  and  presents  some  peculiar  reactions  which  should  be 
here  noted.  Potassa  and  ammonia,  their  carbonates,  and,  in  gene- 
ral, all  the  salts  of  potassa  and  ammonia,  precipitate  platinum  in 
the  state  of  double  chlorides,  while  soda  and  the  salts  of  soda  yield 
no  precipitates. 

Sulphate  of  Binoxide  of  Platinum. 

§  1173.  The  sulphate  of  binoxide  of  platinum  is  most  easily  pre- 
pared by  treating  the  sulphide  of  platinum  obtained  by  precipitating 
the  chloride  with  sulf  hydrate  of  ammonia,  with  fuming  nitric  acid, 
and  evaporating  the  solution  with  a  few  drops  of  sulphuric  acid  to 
drive  off  the  last  particles  of  nitric  acid ;  when  a  deep-brown  mass 
remains  which  dissolves  in  water  with  a  brown  colour. 

Nitrate  of  Binoxide  of  Platinum. 

§  1174.  The  nitrate  of  binoxide  of  platinum  is  prepared  by  care- 
fully pouring  nitrate  of  silver  into  a  solution  of  bichloride  of  pla- 
tinum until  a  precipitate  no  longer  forms;  when  the  chlorine  is 
precipitated  in  the  state  of  chloride  of  silver,  while  the  solution 
contains  nitrate  of  platinum,  which  crystallizes  with  difficulty.  The 
salt  may  also  be  obtained  by  dissolving  the  hydrated  binoxide  in 
nitric  acid. 

COMPOUND  OF  PLATINUM  WITH  SULPHUR. 

§  1175.  Platinum  combines  directly  with  sulphur,  when  the  metal  in 
a  very  finely  divided  state  is  heated  to  redness  in  vapour  of  sulphur ; 
but  a  purer  product  is  obtained  by  heating  in  a  crucible  equal  parts 
'^f  ammoniacal  chloride  of  platinum  and  sulphur  until  the  chlorohy- 
drate of  ammonia  and  the  sulphur  in  excess  are  reduced  to  vapour. 


COMPOUNDS   OP   PLATINUM   WITH    CHLORINE.  345 

The  sulphide  thus  obtained  corresponds  to  the  protoxide,  and  ap- 
pears as  a  gray  and  very  brittle  mass. 

The  sulphide  of  platinum  corresponding  to  the  binoxide  can  only 
be  prepared  by  the  humid  way,  and  is  obtained  by  passing  a  current 
of  sulf hydric  acid  gas  through  a  solution  of  the  double  chloride  of 
platinum  and  sodium.  The  bisulphide  is  a  sulphacid  which  enters 
into  combination  with  the  alkaline  sulphides. 

COMPOUNDS  OF  PLATINUM  WITH  CHLORINE. 

§  11T6.  Two  compounds  of  platinum  with  chlorine  are  known, 
corresponding  to  the  two  oxides.  The  protoehloride  PtCl  is  ob- 
tained by  heating  dried  bichloride  of  platinum  PtClg  in  an  oil-bath, 
gradually  raised  to  392°,  and  maintained  at  this  temperature  as 
long  as  any  chlorine  is  disengaged.  The  bichloride  thus  parts  with 
half  its  chlorine  and  is  converted  into  a  deep-green  powder,  which 
is  the  protoehloride  of  platinum.  The  protoehloride  can  also  be 
obtained  in  the  form  of  a  greenish-gray  precipitate,  by  passing  a 
current  of  sulphurous  acid  gas  through  a  solution  of  bichloride  of 
platinum  which  does  not  contain  an  excess  of  acid :  sulphuric  and 
chlorohydric  acids  are  formed  at  the  same  time.  The  protoehloride 
is  insoluble  in  water,  but  dissolves  in  chlorohydric  acid ;  and  if  sal- 
ammoniac  or  chloride  of  potassium  be  added  to  this  solution,  no 
precipitate  is  formed,  while,  by  evaporating  the  liquid,  beautiful 
crystals  of  double  chlorides,  of  which  the  formulae  are  PtCl+KCl 
and  PtCl  +  NH3,HCl,  are  obtained. 

The  bichloride  of  platinum  is  prepared  by  dissolving  platinum  in 
aqua  regia,  evaporating  the  liquid  at  a  moderate  heat  to  drive  off 
the  excess  of  acid,  and  then  treating  w^ith  water.  The  solution  of 
the  bichloride,  which  is  of  a  slightly-brownish  yellow  colour,  be- 
comes deeper  when  it  contains  a  small  quantity  of  protoehloride  of 
platinum.  Bichloride  of  platinum  does  not  crystallize,  but  remains 
after  evaporation  in  the  form  of  a  deliquescent  brown  mass,  readily 
soluble  in  alcohol.  It  combines  with  a  great  number  of  metallic 
chlorides ;  and  the  double  chlorides  of  platinum  with  potassium  and 
with  ammonia  present  peculiar  interest  in  chemical  analysis,  because 
they  are  very  slightly  soluble  in  water  and  insoluble  in  alcohol. 
These  compounds  have  already  been  mentioned  when  speaking  of 
the  determination  of  potassium,  (§  527.)  If  the  double  chlorides 
be  dissolved  in  a  large  quantity  of  hot  water,  and  the  liquid  allowed 
to  evaporate  spontaneously,  they  crystallize  in  well-defined,  regular 
octahedrons  of  an  orange-yellow  colour.  It  has  already  been  men- 
tioned that  their  formulae  are  PtCla+KCl  and  PtCl34-NH3,HCl. 
Chloride  of  sodium  forms  an  analogous  double  chloride  with  chloride 
of  platinum,  which  is,  contrary  to  the  corresponding  compounds 
of  potassa  and  ammonia,  very  soluble  in  water,  and  even  in  alcohol ; 
and  the  solution  of  which  yields,  by  evaporation,  beautiful  yellow 
crystals  of  the  formula  PtCl^+NaCH-eHO. 


346  PLATINUM. 

If  one  of  these  double  alkaline  chlorides  is  intimately  mixed  with 
2  or  3  times  its  weight  of  alkaline  chloride,  and  heated  slowly  in  a 
crucible,  metallic  platinum  is  separated  in  the  shape  of  brilliant, 
crystalline  lamellae,  which  are  easily  isolated  by  dissolving  the  alka- 
line chloride  in  water. 

§  1177.  If  a  solution  of  protochloride  of  platinum,  dissolved  in  an 
excess  of  chlorohydric  acid,  be  gradually  poured  into  caustic  am- 
monia, small  green  needles  of  the  formula  PtCl,NH3  are  deposited, 
forming  a  substance  called  ammoniacal  protoeJiloride  of  platinum ; 
the  simplest  way  of  preparing  which  consists  in  passing  a  current 
of  sulphurous  acid  gas  through  a  boiling  solution  of  bichloride 
of  platinum  containing  an  excess  of  chlorohydric  acid,  until  the 
liquid  no  longer  gives  a  precipitate  with  sal-ammoniac ;  by  which 
means  the  bichloride  of  platinum  is  reduced  into  protochloride. 
Ammonia  is  then  added,  and  the  solution,  on  cooling,  deposits  am- 
moniacal protochloride  of  platinum,  which  is  remarkable  for  its 
great  stability ;  as  it  is  scarcely  acted  on  by  the  most  powerful 
acids,  and  its  ammonia  can  be  driven  off  only  by  heating  it  for  a 
long  time  with  these  acids. 

Ammoniacal  protochloride  of  platinum  is  soluble  in  a  hot  solu- 
tion of  sulphate  or  nitrate  of  ammonia,  and  deposits  small  yellow 
crystals  on  cooling,  which  appear  to  be  an  isomeric  modification  of 
the  original  product.  The  combination  is  decomposed  at  a  tempera- 
ture of  570°,  leaving  metallic  platinum. 

§  1178.  By  digesting  ammoniacal  protochloride  of  platinum  for 
some  time  in  a  concentrated  solution  of  ammonia,  there  results  a 
yellowish-white  compound,  which  dissolves  in  the  hot  liquid,  and  is 
subsequently  deposited,  on  cooling,  in  large  prismatic  crystals  of  the 
formula  PtCl,N3lIg+H0.  By  pouring  nitrate  of  silver  into  a  hot 
solution  of  this  substance,  the  liquid  after  evaporation  yields  a  white 
crystallized  salt,  of  which  the  formula  is  (PtO,N2Hg),N05 ;  and  if 
sulphate  of  silver  be  substituted  for  the  nitrate,  the  chlorine  is  still 
precipitated  in  the  state  of  chloride  of  silver,  and  the  evaporated 
liquid  deposits  a  second  crystallized  salt,  of  which  the  formula  is 
(PtO,N,H8),S03.  The  compound  (PtOjNaHg)  is,  therefore,  a  true 
base,  which  forms  crystallizable  salts  with  the  acids,  and  which  may 
also  be  obtained  in  an  isolated  state  by  adding  a  solution  of  hydrate 
of  baryta  to  the  solution  of  the  sulphate  (PtO,N3Hg),S03  until  a 
precipitate  no  longer  forms ;  when  the  sulphuric  acid  is  precipitated 
in  the  state  of  sulphate  of  baryta,  while  the  liquid  remaining  exerts 
a  powerful  alkaline  reaction  on  coloured  tests,  and  when  evaporated 
under  the  receiver  of  an  air-pump,  deposits  white  crystalline  needles 
of  the  formula  (Pt0,N3Hp),H0.  This  base,  which  we  shall  call 
binammonia-oxide  of  platinum^  combines  directly  with  acids, 
even  with  carbonic,  and  is  powerful  enough  to  expel  ammonia  from 
its  saline  compounds. 


SALTS    OF    PLATINUM.  347 

The  following  compounds  have  been  obtained  in  a  crystallized 
form : 

Hydrated  base (PtO,N,He),HO. 

Sulphate (PtO,]Si3Hg),S03. 

Nitrate (PtO,N,HJ,N05. 

Neutral  carbonate (PtOjN^HeXCO^+HO. 

Sesquicarbonate 2(PtO,N,Hg),3CO,+HO. 

Bicarbonate {VtO,'NJi;),2CO^-\-iiO. 

Chloride (PtCl,N,Hg). 

Bromide (PtBrjN^H^). 

Iodide (PtI,N,Hg). 

§  1179.  The  base  (PtOjNaHg)  at  110°  loses  by  heat  one  equiva- 
lent of  water  and  one  of  ammonia,  being  converted  into  a  new  com- 
pound, insoluble  in  water,  of  which  the  formula  is  (PtOjNHg).  This 
substance,  which  we  shall  call  protammonia-oxide  of  platinum^ 
possesses  basic  properties  in  a  high  degree,  as  it  combines  directly 
with  the  acids,  and  yields  the  following  series  of  products : 

Anhydrous  base (PtO,NH3). 

Nitrate (PtO,NH3),N03. 

Sulphate (PtO,NH3),S03+HO. 

Chloride  (isomeric  with  ammonia- 

cal  protochloride  of  platinum)...  (PtCl,NH3). 

Iodide (PtI,NH3). 

Cyanide '. (PtCy,NH3). 

Salts  of  the  protammonia-oxide  of  platinum  are  readily  con- 
verted into  those  of  the  binammonia-oxide  of  platinum,  by  dis- 
solving them  in  an  excess  of  caustic  ammonia,  when  they  take  up 
1  equiv.  of  ammonia  and  reproduce  the  salts  of  the  binammonia- 
oxide  of  platinum.  Reciprocally,  salts  of  the  binammonia-oxide  of 
platinum  are  easily  converted  by  heat  in  those  of  the  protammo- 
nia-oxide of  platinum  by  losing  1  equiv.  of  ammonia. 

§  1180.  The  two  series  of  salts  just  described  are  not  the  only 
ones  which  have  been  obtained  by  means  of  the  ammoniacal  proto- 
chloride of  platinum.  If  the  chloride  (PtCl^NgHg)  of  the  binammo- 
nia  platinic  series  be  boiled  with  weak  nitric  acid,  reddish  vapours 
are  disengaged,  and,  on  cooling,  a  substance  is  deposited  of  the 
formula  (PtCl,N2Hg)0,N05,  which  may  be  regarded  as  the  nitrate 
of  a  third  base  represented  by  the  formula  (PtCl,N2Hg)0. 

If  ammoniacal  protochloride  of  platinum  be  boiled  with  a  large 
excess  of  nitric  acid  a  liquid  is  obtained  which  deposits  successively, 
by  evaporation,  two  crystallizable  compounds,  the  formula  of  the 
first  of  which  is  (PtC105,N^H,,),2N05,  which  forms  small  brilliant 
needles,  very  slightly  soluble   in  water,  and   deflagrating  when 


348  PLATINUM. 

heated.  This  compound  contains  a  fourth  base,  of  which  the  very 
complex  formula  is  (PtClO^jN^Hj,).  This  base  has  been  obtained 
in  combination  with  carbonic,  oxalic,  phosphoric,  and  chromic  acids, 
forming  salts  which  crystallize  readily,  because  they  are  very  slightly 
soluble  in  water. 

The  formula  of  the  second  compound,  which  remains  in  the  mother 
liquid,  is  (PtCl304,N^H^3),2N05,  and  it  may  be  considered  as  the  ni- 
trate of  a  fifth  base  {FtGl^O^,^JlJ. 

COMPOUND  OF  PLATINUM  WITH  CYANOGEN. 

§  1181.  By  heating  an  intjmate  mixture  of  finely  divided  platinum 
and  ferrocyanide  of  potassium  to  a  dull  red-heat  in  an  earthen  cru- 
cible, and  then  treating  the  mass,  when  cooled,  with  water,  a  solution 
is  obtained,  which  first  deposits  crystals  of  undecomposed  ferrocy- 
anide of  potassium,  but  which  yields,  after  additional  evaporation, 
a  double  cyanide  of  platinum  and  potassium.  This  substance,  after 
being  purified  by  a  second  crystallization,  appears  in  the  form  oi" 
beautiful  crystals  of  the  formula  KCy-f  PtCy+3H0.  Its  solutions 
precipitate  a  great  number  of  metallic  salts,  in  which  precipitates 
the  potassium  of  the  preceding  compound  is  replaced  by  1  equiv. 
of  the  metal,  of  which  the  salt  effects  the  precipitation. 

DETERMINATION  OF  PLATINUM,  AND  ITS  SEPARATION  FROM  THE 
METALS  PREVIOUSLY  DESCRIBED. 

§  1182.  Platinum  is  determined  in  the  metallic  state,  or  in  that 
of  dried  double  ammoniacal  chloride.  When  platinum  exists  in  a 
liquid  in  the  state  of  bichloride,  the  liquid  is  concentrated  by  eva- 
poration, and  twice  its  volume  of  alcohol  is  added,  after  which  chlo- 
rohydrate  of  ammonia  is  poured  into  the  solution,  to  completely 
precipitate  the  platinum  in  the  state  of  double  chloride  of  platinum 
and  ammonia.  The  precipitate  is  washed  with  alcohol,  and  dried 
under  the  receiver  of  an  air-pump  ;  and  the  weight  of  the  platinum 
is  subtracted  from  that  of  the  double  chloride,  which  contains  44.23 
per  cent,  of  metallic  platinum.  The  double  ammoniacal  chloride 
may  also  be  calcined  in  a  covered  crucible,  when  sal-ammoniac  is 
disengaged,  while  metallic  platinum  remains,  which  is  weighed. 
But  the  decomposition  by  heat  requires  great  care,  because  it  is 
difficult  from  preventing  some  particles  of  platinum  from  being 
carried  off  by  the  vapours  which  are  disengaged.  Platinum  may 
also  be  precipitated  in  the  state  of  double  chloride  of  platinum  and 
potassium,  by  using  the  same  precautions  as  in  the  precipitation  by 
sal-ammoniac ;  and  by  decomposing  the  double  potassic  chloride 
by  heat,  there  is  less  fear  of  the  platinum  being  carried  off  by  the 
gases ;  but  as  the  platinum  remains  mixed  with  chloride  of  potas- 
sium, the  residue  must  be  washed  several  times  to  dissolve  the  alka- 
line chloride. 

§  1183.  In  order  to  separate  platinum  from  the  metals  previously 


EXTRACTION    OF    PLATINUM.  349 

described,  either  the  insolubility  of  metallic  platinum  in  all  acids 
except  aqua,  regia  and  acid  mixtures  which  can  evolve  chlorine,  or 
the  precipitation  of  platinum  by  sulf  hydric  acid,  even  in  acid  liquids, 
or,  lastly,  its  complete  precipitation  by  chloride  of  potassium  or  chlo- 
rohydrate  of  ammonia,  is  relied  on.  It  is,  however,  important  to 
observe  that  platinum,  when  alloyed  with  a  considerable  quantity 
of  metal  soluble  in  nitric  acid,  is  itself  dissolved  in  the  acid ;  so 
that  only  isolated  platinum  can  be  considered  as  insoluble  in  nitric 
acid. 

EXTRACTION  OF  PLATINUM. 

§  1184.  Platinum  occurs  in  the  native  state  in  alluvial  sands,  re- 
sembling those  in  which  gold  is  found,  generally  in  open  valleys  or 
amid  serpentine  rocks.  The  principal  localities  of  platinum  are  in 
Colombia,  Brazil,  and  the  Ural  Mountains  in  Siberia.  It  generally 
occurs  in  small  grains,  although  pieces  weighing  10  kilogs.  have 
been  met  with.  The  platiniferous  sands,  by  washing,  ultimately 
yield  a  sand  rich  in  platinum,  but  of  a  very  complicated  composi- 
tion ;  as  it  contains,  in  addition  to  the  platinum,  the  metals  which 
constantly  accompany  it,  namely,  osmium,  iridium,  palladium,  rho- 
dium, and  ruthenium  ;  and,  moreover,  gold,  silver,  iron,  and  copper ; 
and  lastly,  many  heavy  minerals,  such  as  magnetic  oxide  of  iron, 
titanic  iron,  chromate  of  iron,  pyrites,  etc. 

When  the  platiniferous  sand  contains  any  considerable  quantity 
of  gold,  this  metal  is  first  extracted  by  amalgamation  ;  when  the  ore, 
after  being  purified  as  much  as  possible  by  mechanical  means,  is 
acted  on,  in  glass  balloons  heated  in  a  sand-bath,  by  aqua  regia  con- 
taining an  excess  of  chlorohydric  acid,  a  small  quantity  of  water 
being  added,  so  that  as  little  iridium  as  possible,  which  would  render 
the  platinum  brittle,  may  be  dissolved.  The  aqua  regia  is  renewed 
several  times  until  the  platinum  is  completely  dissolved ;  and  the 
operation  must  be  efiected  in  a  chimney  which  draws  well,  in  order 
to  carry  off  the  vapours  which  are  disengaged,  and  which  are  ren- 
dered injurious  by  the  presence  of  osmic  acid.  The  solution  of  pla- 
tinum is  decanted,  after  having  been  allowed  to  become  clear  by 
rest,  and  a  concentrated  solution  of  sal-ammoniac  is  added,  which 
precipitates  the  platinum  almost  entirely  in  the  state  of  double  chlo- 
ride of  platinum  and  ammonia.  As  the  mother  liquid  still  contains 
some  platinum  and  some  quantity  of  foreign  metals,  the  latter  are 
precipitated  by  blades  of  iron  and  zinc,  while  a  black  deposit  is  ob- 
tained, from  which  a  certain  quantity  of  platinum  may  be  extracted. 
For  this  purpose,  the  deposit  is  first  treated  with  chlorohydric  acid, 
which  dissolves  the  foreign  metals,  and  the  residue  is  then  acted  on 
by  very  weak  aqua  regia,  which  readily  dissolves  the  divided  plati- 
num, without  sensibly  afiecting  the  iridium ;  when  sal-ammoniac  is 
added,  which  precipitates  the  double  chloride  of  platinum  and  am- 
monia. 


350     .  OSMIUM. 

The  double  chloride  of  platinum  and  ammonia  is  calcined  at  a 
dull  red-heat,  and  the  platinum-sponge  which  is  thus  obtained  is 
pulverized  by  hand,  and  then  diluted  with  water  so  as  to  form  a 
homogeneous  mud,  which  is  passed  over  a  sieve,  the  grosser  particles 
remaining  on,  which  are  again  pulverized.  The  workman  must  ob- 
serve the  greatest  cleanliness  in  the  various  operations,  as  the  pre- 
sence of  dust,  or  even  a  single  hair  in  the  mud,  will  give  rise  to 
serious  defects  in  the  forged  platinum.  The  powdered  platinum  is, 
therefore,  generally  washed  several  times,  in  order  to  remove  all 
the  dust. 

The  platinum  paste  is  introduced  into  an  apparatus  resembling 
that  of  fig.  605,  only  larger,  care  being  taken  that  no  bubbles  of 
air  are  inclosed.  The  substance  is  first  compressed  with  a  wooden 
pestle,  then  with  a  metallic  piston ;  when  the  water  separates  from 
the  platinum,  while  the  latter  becomes  more  solid ;  and  the  process 
is  terminated  by  compressing  it  with  great  force.  The  platinum 
disc  is  then  heated  to  whiteness  in  an  earthen  crucible,  placed  on 
an  anvil  and  struck  with  a  heavy  hammer,  after  which  it  is  again 
heated  to  whiteness  before  being  forged. 


OSMIUM. 

Equivalent  =  99.6  (1245.9 ;  0=100). 

§  1185.  Osmium,  prepared  by  calcining  the  double  chloride  of 
osmium  and  ammonia,  is  of  a  metallic-gray  colour,  resembling  pla- 
tinum, while,  when  it  has  been  reduced  by  the  humid  way,  it  often 
shows  a  bluish  fringe.  The  metal  is  sufiiciently  malleable. to  allow 
of  its  being  rolled  into  plates  or  sheets,  although  it  is  reduced  to 
powder  by  percussion.  Osmium  neither  fuses  nor  volatilizes  in  a 
forge-fire,  and  its  density  is  about  10.  The  metal  combines  readily 
with  oxygen ;  and  when  it  has  been  reduced  by  the  humid  way,  it 
rapidly  absorbs  the  oxygen  of  the  air,  especially  when  assisted  by 
water,  and  is  converted  into  osmic  acid ;  and  when  heated  in  oxygen 
at  a  low  temperature,  it  ignites  and  is  converted  into  osmic  acid, 
which  sublimes.  Concentrated  nitric  acid  acts  readily  on  it  and 
disengages  copious  reddish  vapours,  producing  soluble  osmic  acid, 
which  product  is  also  obtained  by  the  action  of  aqua  regia  on  the 
metal.  The  caustic  alkalies  and  alkaline  nitrates  attack  it  at  a  red- 
heat,  the  osmic  acid  combining  with  the  alkalies.  Powdered  osmium, 
heated  on  a  blade  of  platinum,  in  the  flame  of  an  alcohol-lamp,  dis- 
engages vapours  of  osmic  acid,  the  characteristic  penetrating  odour 
of  which  evinces  the  presence  of  very  small  quantities  of  osmium. 


COMPOUNDS    OF    OSMIUM.  351 

COMPOUNDS  OF  OSMIUM  WITH  OXYGEN. 

§  1186.  Osmium  forms  a  large  number  of  compounds  with  oxygen, 
five  of  which  are  known,  and  are 

The  protoxide OsO. 

"    sesquioxide Os^Og. 

"    binoxide OsOa. 

"    osmious  acid OsOg. 

"    osmic  acid OsO^. 

The  two  acid  compounds  are  the  most  important,  and  the  best  un- 
derstood. 

Protoxide  of  osmium  OsO  is  prepared  by  pouring  potassa  into 
a  solution  of  the  double  protochloride  of  osmium  and  potassium, 
when  a  deep-green  precipitate  is  formed,  which  dissolves  with  a 
green  colour  in  acids,  and  which  is  easily  reduced  to  the  metallic 
state  by  deoxidizing  agencies. 

Sesquioxide  of  os7nium  OsgOg  is  obtained  by  maintaining,  for 
some  time,  at  a  temperature  of  122°,  a  mixture  of  osmic  acid  and 
ammonia,  when  a  precipitate  is  formed  which  is  a  compound  of  the 
sesquioxide  of  osmium  and  ammonia,  and  which  dissolves  in  acids, 
producing  yellow  solutions  which  do  not  crystallize. 

If  chlorine  be  passed  over  a  mixture  of  divided  osmium  and 
chloride  of  potassium,  gently  heated  in  a  glass  tube,  a  double  chlo- 
ride is  obtained,  of  which  the  formula  is  OsCl  +KC1,  and  which 
when  treated  while  hot  by  a  solution  of  carbonate  of  potassa, 
yields  a  black  precipitate  of  binoxide  of  osmium  OsOg. 

Osmic  acid  OsO^  is  formed  in  many  ways: — 1.  By  the  roasting 
of  osmium  in  the  air,  or  better  still,  in  an  atmosphere  of  oxygen  ; 
2.  By  acting  on  osmium  by  nitric  acid ;  3.  By  heating  to  redness 
metallic  osmium  with  nitrate  of  potassa,  and  decomposing  the  os- 
miate  of  potassa  by  an  acid. 

Osmic  acid  is  a  white  substance,  which  crystallizes  in  brilliant 
prisms,  and  exhales  a  very  penetrating  odour  resembling  that  of 
chloride  of  sulphur ;  and  as  its  vapour  excites  coughing  and  irri- 
tates the  eyes  and  skin,  the  substance  should  be  avoided  with  great 
care.  Osmic  acid  liquifies  at  a  temperature  below  212°,  and  boils 
below  a  red-heat.  It  is  very  soluble  in  water,  although  the  sub- 
limed acid  requires  a  long  time  for  solution;  and  it  also  dissolves 
largely  in  alcohol  and  in  ether,  but  after  some  time  is  reduced  by 
these  liquids,  especially  under  the  influence  of  polar  light.  It  is 
readily  decomposed  by  deoxidizing  agencies,  and  by  the  majority 
of  organic  substances :  it  stains  the  skin  and  linen  black.  Iron, 
zinc,  tin,  copper,  &c.  precipitate  metallic  osmium  from  its  solutions. 

Osmic  acid  is  a  weak  acid,  which  does  not  directly  redden  the 
tmcture  of  litmus,  and  does  not  decompose  the  carbonates,  but 
which  combines  with  the  alkalies,  although  the  resulting  compounds 


B52  OSMIUM. 

are  not  very  fixed,  as  solutions  of  the  alkaline  osmiates  disengage, 
when  boiled,  vapours  of  osmic  acid. 

Osmious  acid  OsOg  only  exists  in  combination  with  alkaline 
bases,  and  by  endeavouring  to  isolate  it,  it  is  decomposed  into  osmic 
acid  and  binoxide  of  osmium. 

Osmite  of  potassa  is  obtained  by  pouring  a  few  drops  of  alcohol 
into  a  solution  of  osmiate  of  potassa,  when  the  salt  is  deposited  as  a 
rose-coloured  crystalline  powder,  in  which  case  the  osmic  acid  im- 
parts a  portion  of  its  oxygen  to  the  alcohol.  Large  crystals  of  os- 
mite of  potassa  are  obtained  by  allowing  a  solution  which  contains, 
at  the  same  time,  osmiate  and  nitrite  of  potassa  to  rest ;  when  tbe 
osmic  is  slowly  decomposed  by  the  nitrous  acid,  causing  beautiful 
crystals  of  osmite  of  potassa  to  be  deposited. 

Osmite  of  soda,  which  is  prepared  in  the  same  way,  and  yields 
rose-coloured  solutions,  crystallizes  with  much  difficulty,  because  it 
is  more  soluble. 

No  osmite  of  ammonia  is  known,  and  ammonia  immediately  re- 
duces the  solutions  of  osmite  of  potassa  and  osmite  of  soda. 

We  shall  not  treat  of  the  salts  formed  by  the  oxides  of  osmium 
with  acids,  as  they  are,  as  yet,  but  little  understood. 

COMPOUNDS  OF  OSMIUM  WITH  CHLORINE. 

§  1187.  If  osmium  be  heated  in  a  current  of  chlorine,  two  chlo- 
rides are  produced :  a  bichloride  OsClg  and  a  protochloride  OsCl, 
the  latter,  which  is  the  more  volatile,  condensing  in  the  most  re- 
mote portions  of  the  tube.  It  is  an  orange-coloured,  very  fusible 
and  deliquescent  substance,  while  the  protochloride  is  of  a  beautiful 
green,  and  its  solution  in  water  soon  decomposes,  chlorohydric  and 
osmic  acids  being  formed,  while  metallic  osmium  is  precipitated. 

EXTRACTION  OF  OSMIUM. 

§  1188.  Osmium  always  accompanies  platinum-ore,  but  exists  in 
it  chiefly  in  combination  with  iridium,  forming  compounds  of  very 
variable  proportions,  called  iridosmiums.  Iridosmium  is  found  in 
small,  gray,  very  dense  spangles,  sometimes  presenting  the  form 
of  lamellae  with  six  facets  of  the  rhombohedric  system.  Being 
acted  on  with  difficulty  by  aqua  regia,  it  remains  in  the  residue  after 
the  treatment  of  platinum-ores.  Osmium  and  iridium  are  prepared 
by  heating  in  an  earthen  crucible,  for  an  hour,  at  a  strong  red-heat, 
100  parts  of  pulverized  iridosmium  and  300  parts  of  nitre,  when 
osmiate  and  iridiate  of  potassa  are  formed.  The  fused  material 
being  run  on  a  cold  metallic  plate,  is  then  broken  to  pieces,  and  intro- 
duced into  a  tubulated  retort,  with  a  large  excess  of  nitric  acid,  a 
well-cooled  receiver  being  fitted  to  the  retort  as  soon  as  heat  is  ap- 
plied. A  great  proportion  of  the  osmic  acid  volatilizes,  and  con- 
denses on  the  sides  of  the  receiver,  in  the  form  of  beautiful  white 
crystals,  which  are  subsequently  dissolved  in  a  concentrated  solu- 


IRIDIUM.  353 

tion  of  potassa,  from  which  all  the  osmium  is  afterward  precipitated 
by  alcohol,  in  the  state  of  osmite  of  potassa,  which  salt  is  used  in 
preparing  metallic  osmium  and  all  its  products. 

When  the  substances  heated  in  the  retort  no  longer  disengage 
osmic  acid,  water  is  added,  and  the  insoluble  residue  being  collected 
on  a  filter,  then  contains  a  certain  quantity  of  oxide  of  osmium  and 
a  large  quantity  of  oxide  of  iridium.  It  is  boiled  with  aqua  regia, 
which  dissolves  the  osmium  and  iridium  in  the  state  of  chlorides, 
after  which  sal-ammoniac  is  poured  into  the  solution,  when  the  double 
chloride  of  osmium  and  ammonia  is  precipitated,  together  with  the 
corresponding  compound  of  iridium  and  ammonia  IrCla+NHgHCl. 
The  double  chlorides  are  suspended  in  water  and  subjected  to  the 
action  of  a  current  of  sulphurous  acid,  when  the  double  chloride  of 
iridium  IrClgH-NHgHCl  is  transformed  into  the  double  chloride 
IrCl+NHgHGl  which  dissolves,  while  the  double  chloride  of  osmium 
remains  unchanged  and  is  precipitated.  The  latter  yields  metallic 
osmium  by  calcination,  while  the  solution  which  contains  the  double 
chloride  of  iridium  and  ammonia  deposits,  by  evaporation,  beautiful 
brown  crystals,  which  yield  iridium  when  calcined. 


IRIDIUM. 

Equivalent  =  99.0  (1237.5  j  0  =  100). 

§  1189.  Iridium  prepared  by  the  calcination  of  the  double  ammo- 
niacal  chloride  (§  1188)  presents  the  appearance  of  a  gray  spongy 
mass,  resembling  platinum.  Iridium  is  difficult  to  solder,  and 
hitherto  has  not  been  obtained  in  a  malleable  state ;  while  it  is 
still  more  difficult  of  fusion  than  platinum.  The  metal  is  obtained 
in  a  compact  mass,  very  hard,  and  capable  of  a  fine  polish  by  mois- 
tening powdered  iridium  with  water,  compressing  it,  at  first  slightly 
between  tissue-paper,  and  then  powerfully  by  means  of  a  press,  and 
calcining  it  at  a  strong  white-heat  in  a  forge-fire.  The  metal  thus 
obtained  is  very  porous,  and  its  specific  gravity  does  not  exceed  16.0, 
while  the  density  of  compact  iridium  is  probably  equal  to  that  of 
platinum ;  as  a  native  alloy  of  iridium  and  platinum  is  found,  con- 
taining 20  per  cent,  of  platinum,  and  crystallized  in  regular  octohe- 
drons,  the  density  of  which  is  22.3.  Nitric  acid  and  even  aqua 
regia  do  not  attack  iridium  when  isolated,  although  aqua  regia  dis- 
solves it  when  alloyed  with  platinum  or  other  metals.  Heated  to 
redness  with  potassa  or  nitre,  iridium  oxidizes,  and  iridiate  of 
potassa  is  formed.  It  is  attacked  by  chlorine  at  a  red-heat  and  in 
the  presence  of  chloride  of  potassium,  a  double  chloride  of  iridium 
and  potassium  being  formed. 

Vol.  11.-^23 


354  IRIDIUM. 

COMPOUNDS   OF    IRIDIUM  WITH  OXYGEN. 
§  1190.  Four  compounds  of  iridium  with  oxygen  are  known : 

The  protoxide I^gO. 

"  sesquioxide IfaOg. 

"  binoxide IrOg. 

"  trinoxide , IrOg. 

The  protoxide  of  iridium  is  obtained  by  precipitating  by  an  alka- 
line carbonate  the  double  protochloride  of  iridium  and  potassium, 
when  a  greenish-gray  precipitate  is  formed  which  dissolves  in  acids, 
yielding  green  solutions.  The  oxide  is  undecomposable  by  heat, 
but  is  easily  reduced  by  hydrogen  at  a  red-heat. 

Sesquioxide  of  iridium  is  formed  when  iridium  is  attacked  by  the 
alkalies  or  alkaline  metals,  and  appears  as  a  black  powder,  inso- 
luble in  acids,  but  combining  with  the  alkalies,  producing  brown 
solutions.     Heat  restores  this  oxide  to  the  state  of  protoxide. 

If*  the  sesquioxide  be  dissolved  in  a  solution  of  potassa,  and  the 
liquid  be  afterward  saturated  by  an  acid,  a  precipitate  is  thrown 
down,  which  turns  blue  by  absorbing  the  oxygen  of  the  air,  and  at 
last  assumes  an  indigo  colour,  when  it  has  passed  into  the  state  of 
hydrated  binoxide  of  iridium  IrOg+SHO.  The  binoxide  may  also 
be  obtained  by  pouring  potassa  into  a  solution  of  sesquichloride  of 
iridium,  when  no  precipitate  is  formed  at  first,  while  the  liquid,  on 
being  exposed  to  the  air,  deposits  ultimately  a  deep-blue  precipitate. 

Lastly,  when  the  trichloride  of  iridium  IrClg  is  precipitated  by 
an  alkali,  there  results  a  greenish-yellow  precipitate  of  trinoxide  of 
iridium  IrOg,  which,  however,  is  always  combined  with  a  certain 
quantity  of  alkali. 

If  an  oxide  of  iridium  be  digested  with  a  solution  of  formic  acid 
until  carbonic  acid  is  no  longer  disengaged,  a  very  finely  divided 
black  powder  of  iridium  is  obtained,  which  exerts  a  powerful  absorb- 
ent action  on  gases,  and  causes  the  ignition  of  an  explosive  mixture 
of  hydrogen  and  oxygen. 

COMPOUNDS  OF  IRIDIUM  WITH  CHLORINE. 

§  1191.  Four  chlorides  of  iridium,  corresponding  to  the  four 
oxides,  are  known. 

ProtoMoride  of  iridium^  which  is  obtained  by  heating  to  a  dull- 
red  very  finely  divided  iridium  in  a  current  of  chlorine,  combines 
with  the  alkaline  chlorides  and  with  chlorohydrate  of  ammonia, 
yielding  products  which  readily  crystallize.  Iridium  is  acted  on 
more  powerfully  by  chlorine  when  previously  mixed  with  chloride 
of  potassium. 

Sesquichloride  of  iridium  lrjd\  is  prepared  by  dissolving  the 
sesquioxide  in  chlorohydric  acid,  and  appears  as  a  hard,  uncrjstal- 
lizable,  and  deliquesK3ent   substance,  which   forms  soluble  double 


COMPOUNDS   OF   IRIDIUM.  355 

cMorides  with  the  alkaline  chlorides  and  with  chlorohydrate  of 
ammonia.  When  solutions  of  these  double  chlorides  are  boiled, 
they  deposit  very  slightly  soluble  double  chlorides,  which  contain 
bichloride  of  iridium  IrCla,  while  corresponding  double  compounds, 
containing  protochloride  of  iridium  IrCl,  remain  in  the  liquid.  Sul- 
phurous acid  converts  them  into  double  chlorides  containing  the 
protochloride. 

Bichloride  of  iridium  is  formed  when  finely  divided  iridium  or 
its  oxides  are  dissolved  in  aqua  regia  and  heated  to  the  boiling 
point,  when  solutions  of  a  reddish-yellow  colour  are  obtained.  If 
chloride  of  potassium  be  poured  into  the  liquid,  a  double  chloride  is 
obtained,  the  solution  of  which  is  red  and  deposits  octohedric  crys- 
tals, which  are  of  such  an  intense  red  colour  as  to  be  nearly  black, 
and  the  formula  of  which  is  IrCla+KCl  +  HO.  The  ammoniacal 
bichloride  of  iridium  is  very  slightly  soluble  in  cold  water,  but 
forms  with  boiling  water  a  solution  which  on  cooling  deposits  octo- 
hedral  crystals  of  a  deep-red  colour.  The  colouring  power  of  this 
compound  is  very  great,  as  1  part  will  sensibly  colour  40,000  parts 
of  water  j  and  it  is  a  small  quantity  of  this  double  chloride  which 
often  gives  a  red  hue  to  the  double  chloride  of  platinum  and  am- 
monia. 

Sulphurous  acid  converts  these  double  compounds  into  soluble 
double  chlorides,  containing  protochloride  of  iridium  IrCl,  and 
which  are  much  more  soluble,  (§  1188.) 

Lastly,  if  an  oxide  or  chloride  of  iridium  be  treated  with  concen- 
trated aqua  regia  not  exceeding  the  temperature  of  110°  or  120°, 
a  deep-brown  solution  is  obtained,  which  contains  trichloride  of  iri- 
dium IrClg.  This  chloride  does  not  crystallize,  but  also  forms 
double  chlorides  with  the  alkaline  chlorides. 

The  solutions  of  iridium  and  its  different  oxides  are  variously  co- 
loured, from  which  property  the  name  of  iridium  has  been  derived. 

COMPOUNDS  OF  IRIDIUM  WITH  SULPHUR. 

§  1192.  Iridium  combines  directly  with  sulphur  when  the  finely 
divided  metal  is  heated  in  a  current  of  vapour  of  sulphur,  but  it  is 
difficult  to  thus  obtain  a  perfect  sulphuration  of  the  metal.  If  sulf- 
hydric  acid  gas  be  passed  through  solutions  of  the  various  chlorides 
of  iridium,  brown  precipitates  are  obtained  which  are  sulphides  cor- 
responding to  the  chlorides.  The  most  sulphuretted  compounds  act 
the  part  of  sulphacids  with  regard  to  the  alkaline  sulphides.  The 
affinity  of  iridium  for  sulphur  is  sometimes  applied  to  the  prepara- 
tion of  the  metal,  iridosmium  being  fused  with  a  mixture  of  carbon- 
ate of  soda  and  sulphur,  when  the  material  is  acted  on,  and  sulph- 
ides of  iridium  and  osmium  are  formed,  which  are  separated  by 
means  of  water.  The  sulphides  are  easily  attacked  by  chlorine, 
and  yield  chlorides  which  are  isolated  by  the  processes  detailed  in 
§  1188. 


356  PALLADIUM. 


PALLADIUM. 
Equivalent  =  63.3  (665.2;  0  =  100). 

§  1193.  Palladium  is  a  brilliant  metal,  of  tlie  specific  gravity 
11.8,  and  of  a  white  colour  intermediate  between  silver  and  plati- 
num, and  which  begins  to  fuse  at  the  highest  temperature  of  a 
forge-fire,  and  melts  readily  before  the  flame  of  the  oxyhydrogen 
blowpipe.  It  can  be  soldered  and  forged  at  a  white-heat,  and  it  is 
malleable  and  readily  worked  into  thin  sheets  and  wire. 

Palladium  does  not  combine  directly  with  oxygen,  but  it  oxidizes 
when  fused  with  potassa,  or  better  still,  with  nitrate  of  potassa. 
Sulphuric  acid  does  not  act  upon  it,  while  nitric  acid  easily  dis- 
solves it  when  assisted  by  heat,  and  aqua  regia  dissolves  it  rapidly. 
It  combines  directly  with  chlorine,  sulphur,  and  silver. 

Palladium  has  within  the  last  few  years  been  brought  into  com- 
merce, being  obtained  as  an  accessory  product  in  the  treatment  of 
certain  gold-ores  and  the  gold-dust  of  Brazil,  (§  1154,)  which  con- 
sist chiefly  of  an  alloy  of  gold  and  palladium.  Palladium  alloyed 
with  ^  of  silver  is  used  by  dentists,  and  it  has  been  proposed  to  use 
it  for  the  construction  of  the  graduated  scales  of  astronomical  instru- 
ments, because,  while  it  is  nearly  as  white  as  silver,  it  is  not  black- 
ened by  sulf hydric  acid ;  and  the  divisions  on  one  of  the  \largest 
instruments  in  the  Paris  observatory  are  drawn  on  palladium. 

COMPOUNDS  OF  PALLADIUM  WITH  OXYGEN. 

§  1194.  Two  combinations  of  palladium  with  oxygen  are  known : 
a  protoxide  PdO,  and  a  binoxide  PdOg. 

Anhydrous  protoxide  of  palladium  is  obtained  by  decomposing 
nitrate  of  palladium  by  gentle  heat,  when  a  deep-gray,  metallic 
powder  remains,  which  loses  all  its  oxygen  at  a  higher  temperature. 
By  pouring  an  alkaline  carbonate  into  a  solution  of  protonitrate  of 
palladium,  a  deep-brown  precipitate  of  hydrated  protoxide  results, 
which  readily  dissolves  in  dilute  acids. 

Binoxide  of  palladium  has  not  yet  been  obtained  in  an  isolated 
form,  and  when  caustic  potassa  or  carbonate  of  potassa  is  added  to 
a  solution  of  bichloride  of  palladium,  the  brown  precipitate  which 
forms  always  contains  alkali.  Binoxide  of  palladium  readily  parts 
with  half  its  oxygen  at  a  slightly  elevated  temperature,  and  is  com- 
pletely reduced  at  a  higher  degree  of  heat. 

SALTS  FORMED  BY  THE  PROTOXIDE  OF  PALLADIUM. 

§  1195.  "The  protosalts  of  palladium  yield  solutions  of  a  reddish- 
brown  colour,  from  which  potassa  throws  down  a  brown  precipitate 


HALOID   COMPOUNDS   OF   PALLADIUM.  357 

which  dissolves  in  an  excess  of  alkali,  while  sulf  hydric  acid  and  the 
alkaline  sulphides  give  black  precipitates  which  do  not  dissolve  in 
an  excess  of  sulf  hydrate.  Cyanide  of  mercury  yields  a  white, 
slightly  grayish  precipitate  of  cyanide  of  palladium ;  and  iron  or 
zinc  precipitate  palladium  in  the  form  of  a  black  powder,  which 
assumes  a  metallic  lustre  when  burnished. 

Nitrate  of  palladium  is  obtained  by  dissolving  palladium  in  nitric 
acid,  but  the  evaporated  liquid  does  not  deposit  crystals,  although, 
if  ammonia  be  added,  a  crystallizable  double  nitrate  is  formed. 

COMPOUNDS  OF  PALLADIUM  WITH  CHLORINE. 

§  1196.  Two  chlorides  of  palladium,  corresponding  to  the  two 
oxides,  are  known.  Protoehloride  of  palladium  PdCl  is  obtained 
by  dissolving  palladium  in  aqua  regia,  when  a  red  solution  is 
formed,  yielding  on  evaporation  deep-red  crystals,  which  by  the 
action  of  heat  are  decomposed  and  converted  into  metal.  Proto- 
ehloride of  palladium  forms  double  chlorides  with  the  alkaline  chlo- 
rides and  chlorohydrate  of  ammonia.  The  double  chlorides  of 
potassium  and  ammonia  are  very  slightly  soluble  in  water  and  inso- 
luble in  alcohol;  their  formulae  are  PdCl+KCl,  PdCH-NH3,HCl, 
and  they  form  beautiful  crystals;  while  the  double  chloride  of 
sodium,  on  the  contrary,  is  deliquescent  and  very  soluble  in  water. 
The  colour  of  these  double  chlorides  in  small  crystals  is  of  a  slightly 
reddish-yellow. 

Protoehloride  of  palladium  is  converted  by  the  action  of  aqua 
regia  and  moderate  heat  into  the  bichloride  PdClg,  which  after  eva- 
poration under  an  air-pump  assumes  the  form  of  a  brown  crystal- 
line mass.  Bichloride  of  palladium,  which  is  not  very  fixed,  and 
the  solutions  of  which  are  readily  decomposed  by  heat,  forms  with 
chloride  of  potassium  a  double  chloride  of  the  formula  PdClg-hKCl, 
which,  being  very  slightly  soluble,  is  precipitated  in  red  crystalline 
powder,  consisting  of  small  regular  octohedrons.* 

COMPOUND  OF  PALLADIUM  WITH  CYANOGEN. 

§  1197.    Palladium  has  a  great  affinity  for   cyanogen,   and  a 

cyanide  of  palladium  is  obtained  in  the  form  of  a  slightly-grayish 

white  precipitate,  by  adding  a  soluble  cyanide  to  the  solution  of  a 

protosalt  or  of  protoehloride  of  palladium,  the  precipitation,  how- 

*  The  combination  of  palladium  with  iodine  deserves  some  notice,  as  it  is  of 
importance  in  analytical  chemistry,  being  obtained  in  the  determination  of  iodine. 
The  iodine  contained  in  any  soluble  iodide  may  be  very  exactly  determined  by 
precipitating  it  by  means  of  nitrate  or  chloride  of  palladium,  when  a  black  fleecy 
deposit  of  iodide  of  palladium  is  formed,  which  does  not  completely  settle  down 
until  after  24  hours,  and  which  is  insoluble  in  water,  alcohol,  and  ether.  It 
begins  to  lose  its  iodine  at  a  temperature  of  212°,  and  is  entirely  freed  from  it 
when  heated  to  about  580°,  when  pure  palladium  remains,  from  the  weight  of 
which  the  weight  of  the  iodine  with  which  it  was  combined  may  be  deduced.— 
W.  L.  F. 


358  RHODIUM. 

ever,  being  complete  only  when  the  liquid  does  not  contain  an 
excess  of  acid.  Cyanide  of  palladium  combines  with  the  alkaline 
cyanides  and  with  cyanohydrate  of  ammonia. 

A  hot  and  saturated  solution  of  the  double  cyanide  of  palladium 
and  potassium  deposits,  on  cooling,  small  crystalline  spangles  of  the 
formula  PdCy+KCy-fHO ;  while  the  same  solution  by  slow  eva- 
poration at  the  ordinary  temperature  yields  larger  crystals  of  the 
formula  PdCy+KCy+3H0. 

EXTRACTION  OF  PALLADIUM. 

§  1198.  Palladium  exists  in  small  quantities  in  platinum-ore,  and 
remains  in  the  mother  liquid  which  is  obtained  when  a  solution  of 
platinum-ore  in  aqua  regia  is  precipitated.  It  has  already  been 
mentioned  (§  1184)  that  the  metals  which  remain  in  this  mother 
liquid  are  generally  precipitated  by  a  blade  of  iron ;  they  are  then 
redissolved  in  aqua  regia,  and  the  excess  of  acid  being  driven  off  by 
evaporation,  the  residue  is  treated  with  water  and  poured  into  a 
solution  of  cyanide  of  mercury,  which  produces  a  solution  of  cyanide 
of  palladium,  which  by  the  application  of  heat  leaves  metallic  palla- 
dium. The  greater  proportion  of  palladium  is  obtained  from  the 
Brazil  gold-dust,  which  is  dissolved  in  aqua  regia  saturated  with 
potassa,  -and  then  treated  with  a  solution  of  cyanide  of  mercury, 
which  precipitates  the  palladium  alone.  Palladium-sponge  is  con- 
verted into  malleable  metal  by  the  same  process  as  that  described 
for  platinum. 


RHODIUM. 

Equivalent  =  52.2  (652.5 ;  0  =  100). 

§  1199.  Rhodium  exists  in  small  quantities  in  the  majority  of 
platinum-ores,  and  has  also  been  found  in  America  combined  with 
gold.  It  is  extracted  from  the  metallic  precipitate  which  is  obtained 
by  decomposing  by  a  blade  of  iron  the  mother  liquid  which  remains 
after  the  precipitation  of  the  solutions  of  platinum-ore  in  aqua  regia 
by  sal-ammoniac.  These  metals  being  dissolved  in  aqua  regia,  the 
palladium  is  precipitated  by  cyanide  of  mercury,  and  the  liquid  is 
evaporated  to  dryness,  after  having  added  common  salt  and  an 
excess  of  chlorohydric  acid ;  when  the  excess  of  cyanide  of  mercury 
is  converted  into  chloride  of  mercury,  while  double  chlorides  are 
formed  with  the  chloride  of  sodium.  The  substance,  when  dried,  is 
treated  with  alcohol,  which  dissolves  the  double  chloride  of  platinum 
and  sodium  as  well  as  that  of  iridium  and  sodium ;  the  double  chlo- 
ride of  rhodium  and  sodium,  which  is  insoluble  in  alcohol,  alone 


COMPOUNDS  OF   KHODIUM.  359 

remaining.  This  compound,  after  being  purified  by  crystallization, 
is  heated  in  a  glass  tube  in  a  current  of  hydrogen,  when  metallic 
rhodium  remains  on  dissolving  the  substance  in"  water. 

Rhodium  has  been  thus  called  on  account  of  the  rose  colour  of 
its  solutions.  It  is  a  gray  metal  of  the  specific  gravity  10.6, 
resembling  platinum,  but  more  difiicult  to  solder  and  fuse  than  this 
latter  metal. 

Rhodium  does  not  oxidize  in  the  air  at  the  ordinary  temperature, 
but  when  very  finely  divided  readily  combines  with  oxygen  at  a 
red-heat.  The  most  powerful  oxidizing  acids,  even  aqua  regia,  do 
not  act  on  the  metal  when  pure,  but  it  readily  dissolves  in  aqua 
regia  when  alloyed  with  platinum  or  other  metals.  Potassa  and 
nitre  act  on  it  at  a  red-heat,  and  convert  it  into  the  sesquioxide ;  and 
bisulphate  of  potassa  also  attacks  it  at  a  red-heat,  forming  a  double 
sulphate  of  potassa  and  sesquioxide  of  rhodium. 

COMPOUNDS  OF  RHODIUM  WITH  OXYGEN. 

§  1200.  The  existence  of  two  oxides  of  rhodium,  the  protoxide 
RhO  and  the  sesquioxide  Rh^Og,  is  admitted. 

The  protoxide  RhO  is  formed  when  very  finely  divided  rhodium 
is  roasted  in  the  air  at  a  high  temperature ;  while  if  the  temperature 
be  lower,  oxides  intermediate  between  the  protoxide  and  sesquioxide 
are  obtained. 

The  sesquioxide  Rh^Og  is  produced  when  powdered  rhodium  is 
attacked  by  a  mixture  of  nitre  and  potassa,  when,  after  treating 
the  substance  with  water  and  washing  the  residue  with  a  weak  acid, 
the  sesquioxide  remains  in  the  form  of  a  black  powder.  This  is  the 
most  important  oxide  of  rhodium,  as  it  combines  with  the  acids  and 
forms  salts  of  which  the  solutions  are  red  when  concentrated,  and 
rose-coloured  when  more  diluted.  Potassa  precipitates  the  hydrated 
sesquioxide  from  its  solutions  on  boiling  the  liquid,  while  ammonia 
throws  down,  when  cold,  a  yellow  precipitate,  which  is  not  deposited 
for  some  time,  and  which  is  a  compound  of  the  sesquioxide  with  am- 
monia. Sulfhydric  acid  and  sulf  hydrate  of  ammonia  give  brown 
precipitates.  Hydrogen  reduces  solutions  of  rhodium  when  aided 
by  solar  light,  and  precipitates  from  them  metallic  rhodium ;  and 
iron,  zinc,  and  copper  precipitate  the  metal  in  the  form  of  a  black 
powder. 

COMPOUNDS  OF  RHODIUM  WITH  CHLORINE. 

§  1201.  Two  chlorides  of  rhodium  corresponding  to  the  two 
oxides  are  known,  and  are  prepared  by  treating  the  mixture  of 
oxides  obtained  by  roasting  rhodium  in  the  air  with  chlorohydric 
acid,  when  two  chlorides  are  formed:  the  protochloride  RhCl, 
which  remains  in  the  form  of  an  insoluble  reddish  powder,  and  the 
sesquichloride  Rh^Clg,  which  dissolves.  The  sesquichloride  pro- 
duces brown  solutions,  and  does  not  crystallize,  but  forms  with 


860  RUTHENIUM. 

the  alkaline  chlorides  crystallizable  double  chlorides,  of  a  beautiful 
red  colour,  the  best  method  of  preparing  which  consists  in  heating, 
in  a  current  of  chlorine,  a  mixture  of  finely  divided  rhodium  and 
alkaline  chloride. 

The  double  chloride  of  rhodium  and  sodium  crystallizes  in  beau- 
tiful red  crystals,  of  which  the  formula  is  RhaClg+SNaCl+lSHO. 

COMPOUND  OF  RHODIUM  WITH  SULPHUR. 

§  1202.  Rhodium  combines  directly  with  sulphur  at  a  red-heat, 
forming  a  sulphide  which  is  fusible  in  a  forge-fire.  When  sulf- 
hydrate  of  ammonia  is  poured  into  a  solution  of  the  double  chloride 
of  rhodium  and  sodium,  a  brown  precipitate  of  the  sulphide  Rh^Sg 
is  obtained. 


RUTHENIUM. 
Equivalent  =  52.2  (652.5 ;  0  =  100). 

§  1203.  A  new  metal,  to  which  the  name  of  ruthenium  has  been 
given,  has  been  recently  found  in  the  platiniferous  sands,  occurring 
principally  in  iridosmium,  which  sometimes  contains  5  or  6  per 
cent,  of  it.  In  its  chemical  properties,  ruthenium  closely  resembles 
iridium,  with  which  it  was  for  a  long  time  confounded.  Ruthenium 
is  extracted  from  iridosmium  by  heating  to  redness  in  a  porcelain 
tube,  traversed  by  a  current  of  moist  chlorine,  a  mixture  of  finely 
powdered  iridosmium  with  one-half  its  weight  of  common  salt.  The 
mass,  when  cooled,  is  dissolved  in  water,  producing  a  brownish-red 
solution,  into  which  a  few  drops  of  ammonia  are  poured  after  hav- 
ing heated  it  to  about  120°,  when  a  brownish-red  precipitate  of 
sesquioxide  of  ruthenium,  mixed  with  oxide  of  osmium,  is  formed. 
The  precipitate  is  heated  in  a  retort  with  nitric  acid,  to  convert 
the  oxide  of  osmium  into  osmic  acid,  which  is  driven  off  by  boiling 
for  a  short  time.  The  residue  is  calcined  for  one  hour  in  a  silver 
crucible,  with  a  mixture  of  potassa  and  nitre,  when  the  material  is 
treated  with  water  deprived  of  air  by  boiling,  and  allowed  to  rest 
for  12  hours  in  a  bottle  closely  corked  and  wholly  filled.  The 
liquid,  which  is  of  an  orange-yellow  colour,  is  then  decanted  and 
saturated  with  nitric  acid,  when  the  sesquioxide  of  ruthenium  is 
precipitated  in  a  black  velvetlike  powder,  which,  by  calcination  in 
a  current  of  hydrogen  gas,  yields  metallic  ruthenium. 

Ruthenium  is  a  gray  metal,  of  the  specific  gravity  of  8.6,  resem- 
bling iridium ;  and  it  is  infusible,  does  not  consolidate  at  a  red-heat, 
and  is  acted  on  with  great  difficulty  by  aqua  regia. 

Several  oxides  and  corresponding  chlorides  of  ruthenium  have 
been  obtained. 


FOUETH  PAKT. 


ORGANIC  CHEMISTRY. 


INTRODUCTION. 


§  1204.  In  this  fourth  part  it  is  intended  to  give  a  description  of 
the  substances  found  in  organized  beings,  as  well  as  the  combina- 
tions derived  from  them  by  various  chemical  processes  performed  in 
the  laboratory.  The  majority  of  organic  compounds  may  be  com- 
pared with  those  comprised  under  the  head  of  inorganic  chemistry, 
and,  like  the  latter,  may  be  crystallized  by  fusion,  sublimation,  or 
solution ;  and  can  combine  either  with  acids,  or  with  bases,  or  may 
be  decomposed  into  acid  and  into  basic  elements,  their  compounds 
being  subject  to  the  laws  of  definite  proportions  in  the  same  man- 
ner as  substances  belonging  to  mineral  chemistry.  In  a  word,  they 
possess  no  peculiar  character  which  authorizes,  in  a  methodic  classi- 
fication, their  separation  from  compounds  of  mineral  chemistry, 
from  which  they  are  distinguished  by  their  origin  alone ;  the  sepa- 
ration being  only  admitted  because  it  facilitates  the  study  of  organic 
compounds,  which  are  generally  of  a  complex  character,  and  the 
properties  of  which  are  more  readily  understood  after  the  student 
has  become  familiarized  with  the  most  frequent  and  simple  reac- 
tions of  mineral  chemistry. 

There  exists,  however,  in  organized  beings,  a  certain  number  of 
substances,  the  essential  physical  properties  of  which  differ  greatly 
from  those  just  mentioned,  and  which  constitute  the  organs  of  vege- 
tables and  animals.  They  are  distinguished  by  their  insolubility  in 
solvents,  and  by  the  peculiar  forms  they  assume  under  the  influence 
of  vitality.  They  undergo,  in  organized  beings,  a  host  of  trans- 
formations, frequently  without  experiencing  any  remarkable  change 
in  their  elementary  composition,  and  thus  become  fitted  for  the  va- 
rious parts  which  they  are  destined  to  constitute  in  organic  life. 
They  can  in  no  manner  be  made  to  assume  a  crystalline  form ;  and 
whenever  they  are  crystallized  or  included  in  compounds  subjected 
to  the  ordinary  laws  of  definite  proportions  and  capable  of  crystal- 
lization, it  will  be  found  that  they  have  been  completely  changed, 
and  that  the  new  differ  very  materially  from  the  original  substances, 
although  their  elementary  composition  is  frequently  identical. 

361 


362  ORGANIC   CHEMISTRY. 

We  shall  call  these  compounds  organized  substances^  or  organized 
matter^  to  distinguish  them  from  other  substances  found  in  living 
beings,  and  often  confounded  with  them  under  the  general  name 
of  organic  substances  or  matter^  which  should  only  be  considered  as 
indicating  their  common  origin.  The  latter  name,  however,  should 
be  applied  only  to  substances  of  the  organic  kingdom  which  are  not 
also  found  in  the  mineral  kingdom. 

§  1205.  Some  organic  substances  contain  only  carbon  and  hy- 
drogen ;  and,  while  the  majority  of  substances  found  in  vegetables 
contain  carbon,  hydrogen,  and  oxygen,  those  forming  the  organs 
of  animals  consist  of  carbon,  hydrogen,  oxygen,  and  nitrogen. 
Similar  quaternary  compounds  are  found  in  almost  all  parts  of 
vegetables,  principally  in  the  cereals,  which,  thence  derive  their 
property  of  nourishing  animal  life.  Some  organized  beings  also 
contain  a  greater  number  of  simple  bodies :  thus,  some  contain 
sulphur,  others  phosphorus.  Animals  provided  with  a  stony  case, 
or  shells,  contain  a  large  proportion  of  carbonate  of  lime,  forming 
nearly  the  whole  of  their  external  envelop ;  while  the  bones  of 
vertebrated  animals  contain  a  large  quantity  of  phosphate  and  a 
small  proportion  of  carbonate  of  lime.  Lastly,  in  all  animals  and 
vegetables,  salts  are  found,  formed  by  the  mineral  bases,  combined 
either  with*  mineral  or  organic  acids,  and  which,  in  many  cases,  ap- 
pear essential  to  the  existence  and  development  of  the  organized 
being.  The  principal  mineral  bases  found  in  organized  beings  are 
potassa,  soda,  lime,  magnesia,  alumina,  oxides  of  iron  and  manga- 
nese ;  while  the  mineral  acids  are  carbonic,  phosphoric,  sulphuric, 
nitric,  and  silicic  acid.  In  addition  to  the  salts  formed  by  these 
substances,  the  chlorides  of  potassium,  sodium,  calcium,  and  magne- 
sium, and  more  rarely  their  bromides  and  iodides,  also  occur.  These 
mineral  substances,  with  the  exception  of  nitric  acid,  are  found  in 
the  ashes  of  organized  beings  after  their  combustion. 

Carbon  and  its  compounds  with  oxygen  may  be  ranked  among 
organic  substances,  as  they  are,  in  most  cases,  extracted  from  them ; 
and  with  still  greater  reason  may  ammonia  be  included  among  them, 
as  it  is  always  prepared  from  organic  matter.  We  shall  not,  how- 
fever,  recur  to  those  substances  which  have  been  considered  in  the 
preceding  parts  of  this  work. 

§  1206.  The  various  organic  compounds  may  be  divided  into — 

1.  Compounds  which  cannot  be  separated  into  several  kinds  of 
substances  without  evidently  changing  their  constitution  and  nature, 
which  we  shall  call  simple  proximate  principles  ; 

2.  Compounds  formed  of  one  or  two  proximate  principles,  united 
in  definite  proportions  ; 

3.  Compounds  formed  by  the  union,  in  indefinite  proportions^ 
either  of  proximate  principles,  or  definite  compounds  of  these  same 
principles. 

We  shall  give  the  name  of  species  to  compounds  of  the  first  two 


INTRODUCTION.  368 

classes,  while  substances  of  the. third  class  will  be  considered  as 
mixtures  of  several  species,  which  latter  it  is  always  possible  to 
separate,  either  by  mechanical  means  or  chemical  processes,  with- 
out altering  their  nature. 

The  name  of  proximate  analysis  is  given  to  the  mechanical  or 
chemical  operations,  the  objects  of  which  are  to  separate  the  species 
which  immediately  constitute  organized  beings ;  and  elementary 
analysis  is  the  operation  by  which  the  nature  and  proportions  of 
the  simple  bodies  composing  these  beings  is  determined.  Element- 
ary analysis  is  generally  applied  to  species,  because  the  knowledge 
of  their  composition  furnishes  one  of  their  most  distinctive  charac- 
teristics. 

PROXIMATE  ANALYSIS  OF  ORGANIC  SUBSTANCES. 

§  1207.  The  proximate  analysis  of  organic  substances  is  one  of 
the  most  difficult  problems  of  this  branch  of  chemistry,  because  the 
great  instability  of  organic  matter,  the  facility  with  which  it  is  al- 
tered by  chemical  agents,  and  the  great  diversity  of  its  nature,  do  not 
permit  the  establishing  of  well-defined  rules,  such  as  those  applied 
to  the  analysis  of  mineral  substances. 

Mechanical  separation  by  the  lens  and  microscope  affords  a  means 
of  separation  which  sometimes  succeeds  ;  and  in  some  cases  leviga- 
tion  may  be  used,  by  suspending  the  mixture  in  water,  when  the 
various  insoluble  species  composing  it  are  deposited,  more  or  less 
rapidly,  according  to  their  varieties  of  density  and  shape. 

Neutral  solvents,  that  is,  those  which  exert  no  chemical  action  on 
the  organic  species  to  be  separated,  afford  the  most  ordinary  means 
for  the  isolation  of  the  latter ;  and  the  substances  most  frequently 
employed  for  the  purpose  are  water,  alcohol  in  various  degrees  of 
concentration,  ether,  and  wood-spirit.  As  they  are  used  sometimes 
cold  and  sometimes  hot,  it  is  important  in  the  latter  case  to  ascer- 
tain whether  some  of  the  organic  species  are  not  modified  by  the 
temperature  at  which  the  operation  is  being  carried  on.  Soluble 
and  insoluble  organic  substances  constituting  a  mixture  may  be 
separated  by  means  of  neutral  solvents,  and  the  solutions,  when 
slowly  evaporated  at  a  proper  temperature,  frequently  deposit  the 
species  successively  in  the  form  of  crystals,  which  can  thus  be  iso- 
lated ;  and,  although  the  separation  is  generally  incompletely  effected 
by  the  first  crystallization,  by  redissolving  the  crystalline  deposits 
which  have  successively  formed  in  the  same  solvent,  as  before,  and 
recrystallizing  them,  the  species  may  be  separated  in  a  state  of 
purity. 

By  subjecting  a  mixture  of  organic  species  to  the  successive  action 
of  various  solvents,  they  can  generally  be  separated  into  several 
parts,  each  of  which  is  formed  of  a  more  simple  mixture  than  the 
original  mixture.  By  skilfully  applying  the  action  of  neutral  solv- 
ents, substances  which  do  not  even  present  great  differences  of  solu- 


364  ORGANIC   CHEMISTRY. 

bility  in  the  same  solvent  can  be  'separate,  remarkable  instances  of 
which  will  be  mentioned  when  treating  of  the  analysis  of  fat  sub- 
stances. 

Solvents  which  exert  a  chemical  action  on  the  organic  species 
composing  the  mixture,  but  without  modifying  the  species  so  that  it 
cannot  be  restored  to  its  original  .state,  are  frequently  used  with 
success ;  but  their  action  must  be  limited,  either  to  the  decomposi- 
tion of  a  compound  species  into  simple  species,  or  to  simple  combi- 
nations of  the  species  with  the  substance  of  the  solvent ;  in  which 
case  one  or  several  of  the  species  combine  with  the  substance  of  the 
solvent,  and  form  soluble  compounds,  the  simple  species  of  which 
may  be  separated  without  change.  Thus,  an  insoluble  salt,  formed 
by  an  organic  acid  with  a  mineral  or  an  organic  base,  may  be  de- 
composed by  a  solution  of  potassa  or  carbonate  of  potassa,  so  that 
the  organic  acid  shall  form  a  soluble  compound  with  the  alkalies, 
from  which  it  may  then  be  separated  without  change. 

Acid  solvents  are  also  sometimes  employed,  as,  for  example,  when 
an  insoluble  organic  base  is  combined  with  an  organic  or  mineral 
acid,  forming  an  insoluble  salt :  by  treating  the  substance  with  a 
weak  solution  of  chlorohydric  or  sulphuric  acid,  the  base  is  dissolved, 
and  may  be  precipitated  by  supersaturating  the  liquid  by  potassa  or 
ammonia. 

The  metallic  salts  are  sometimes  employed  to  effect  double  de- 
composition, in  solutions  obtained  by  treating  organic  mixtures  by 
neutral  or  alkaline  solvents.  Thus,  a  great  number  of  organic 
acids  form  insoluble  salts  with  protoxide  of  lead ;  and  by  adding 
acetate  of  lead  to  their  solutions,  previously  neutralized  by  potassa 
or  ammonia,  an  insoluble  salt,  formed  by  the  oxide  of  lead  with  the 
organic  acid,  is  precipitated ;  and  the  precipitate,  after  being  well 
washed,  is  suspended  in  water,  through  which  a  current  of  sulf  hy- 
dric  acid  gas  is  passed,  when  the  lead  is  converted  into  insoluble 
sulphide,  while  the  organic  acid  separates  and  generally  dissolves 
in  the  liquid. 

Many  organic  substances,  which  do  not  change  in  the  air  in  the 
presence  of  neutral  solvents  at  the  ordinary  temperature,  possess 
the  property  of  absorbing  oxygen  rapidly  when  in  contact  with  an 
alkaline  liquid,  in  which  case  they  are  converted  into  acids  which 
combine  with  the  alkali ;  and  it  is  therefore  important,  when  alkaline 
solvents  are  used,  to  determine  by  a  preliminary  experiment  whether 
the  phenomenon  just  mentioned  will  take  place ;  which  is  done  by 
introducing  a  small  quantity  of  the  organic  substance  and  the  alka- 
line solvent  into  a  graduated  bell-glass,  filled  with  air  over  mer- 
cury, and  to  observe  whether  the  volume  of  air  is  lessened. 

§  1208.  Certain  organic  species  are  isolated  by  distillation,  which 
process  requires  great  caution ;  and  it  is  necessary  to  ascertain 
whether  the  product  of  distillation  really  pre-existed  in  the  mixture, 
or  whether  it  has  resulted  from  changes  effected  by  heat  in  the 


INTRODUCTION.  365 

original  substances.  Distillation  or  sublimation  must,  in  many- 
cases,  be  efifected  at  a  temperature  below  that  of  the  boiling  point 
of  substances  which  volatilize  under  the  ordinary  pressure  of  the 
atmosphere,  because  the  temperature  of  ebullition  is  often  sufficiently 
elevated  to  change  the  other  organic  species  which  exist  in  the  mix- 
ture. The  substances  are  then  heated  in  a  current  of  steam,  when 
the  vapours  of  the  organic  volatile  species,  having  considerable  ten- 
sion at  the  temperature  of  212°,  are  continually  carried  over  by 
the  aqueous  vapour,  and  condensed  with  it.  By  this  process  many 
of  the  odoriferous  essential  oils  contained  in  plants  are  separated. 

By  applying  distillation  to  organic  substances,  a  mixture  of  seve- 
ral volatile  species  is  frequently  obtained,  which  are  soluble  in  each 
other,  and  cannot  be  separated  by  the  means  of  chemical  combina- 
tion. When  such  species  are  unequally  volatile,  a  separation  may 
be  effected  by  subjecting  them  to  successive  distillations  and  dividing 
the  products  into  fractions,  if  not  absolute,  at  least  sufficient  for 
the  study  of  the  properties  of  the  species.  The  difficulties  of  such 
a  separation  increase  as  the  difference  between  the  boiling  points 
is  smaller ;  and  it  is  often  more  advantageous,  instead  of  distilling 
the  mixture  under  the  ordinary  pressure  of  the  atmosphere,  to  boil 
it  under  a  much  weaker  pressure,  because,  in  that  case,  the  ratio 
between  their  elastic  forces  becomes  much  less.  We  will  endeavour 
to  explain  this  by  an  example. 

Let  us  suppose  a  mixture  of  alcohol  and  ether,  in  nearly 
equal  proportions.  Alcohol  alone  boils  at  173.3°,  and  ether  isolated 
at  94.5°,  under  the  pressure  of  29.922  inches ;  and  we  will  admit, 
although  the  supposition  is  not  entirely  exact,  that  the  mixture  of 
alcohol  and  ether  boils  at  94.5°.  The  normal  tension  of  the  va- 
pour of  ether  at  this  temperature  is  29.922  inches,  while  that  of 
alcohol  is  4.055  inches,  and  the  ratio  of  the  two  tensions  is  there- 
fore 0.136.  It  is  evident  that  the  first  portions  which  pass  over  in 
distillation  will  contain  much  more  ether  than  alcohol,  but  that  this 
will  contain,  nevertheless,  a  considerable  proportion  of  the  latter 
substance,  since  the  ratio  of  the  two  tensions  is  represented  by  0.136. 
If,  on  the  contrary,  the  mixture  be  boiled  under  a  pressure  suffi- 
ciently feeble  for  the  boiling  point  to  sink  down  to  32°,  the  normal 
tension  of  alcohol  at  this  temperature  being  0.492  inches,  while  that 
of  ether  is  7.165  inches,  the  ratio  between  the  two  elastic  forces  is 
only  0.068,  and  consequently  much  more  feeble  than  at  the  tempe- 
rature of  94.5°.  If,  therefore,  the  retort  containing  the  mixture 
be  surrounded  with  ice,  and  the  distillation  effected  by  rarefying  the 
air  by  means  of  an  air-pump,  the  proportion  of  alcohol  which  will 
pass  over  in  distillation  at  the  same  time  with  the  ether  will  scarcely 
be  one-half  of  that  which  distilled  at  the  temperature  of  94.5° ; 
and  the  proportion  will  be  still  less  if  the  retort  be  surrounded  by 
a  refrigerating  mixture  of  ice  and  common 'salt  at  14°.  In  fact,  at 
this  temnerature,  the  tension  of  the  vapour  of  alcohol  is  0.251 


366  ORGANIC   CHEMISTRY. 

inches,  while  that  of  the  vapour  of  ether  is  4.468  inches ;  and  the 
ratio  of  the  two  elastic  forces  is  only  0.056.* 

We  will  not  devote  too  much  time  to  a  general  indication  of  the 
principal  processes  employed  for  the  analysis  of  organic  mixtures, 
as  in  the  following  a  large  number  of  examples  will  be  given,  which 
are  better  adapted  to  illustrate  the  methods. 

ELEMENTARY  ANALYSIS  OF  ORGANIC  SUBSTANCES. 

§  1209.  Although,  in  the  preceding  parts  of  this  work,  the  greater 
part  of  the  processes  employed  in  chemistry,  to  determine  the  ele- 
mentary composition  of  organic  substances,  have  been  already  ex- 
plained, we  still  think  it  necessary  to  add  some  new  details,  and 
indicate  the  various  precautions  to  be  observed,  according  to  the 
nature  and  physical  properties  of  the  organic  substances  to  be 
analyzed. 

It  has  been  mentioned  (§  1205)  that  the  majority  of  substances 
extracted  from  the  vegetable  kingdom  were  composed  only  of  carbon, 
hydrogen,  and  oxygen,  while  a  certain  number  of  vegetable  species 
and  the  majority  of  animal  substances  contain  nitrogen  in  addition  ; 
and  lastly,  that  some  organic  substances  contain  sulphur  and  phos- 
phorus. But,  by  subjecting  organic  substances  to  the  various  reac- 
tions capable  of  being  performed  in  the  laboratory,  other  substances 
are  obtained,  which  are  not  organic  substances,  properly  so  called, 
because  they  have  not  been  directly  extracted  from  the  organic 
kingdom,  but  the  study  of  which  presents  great  interest.  Such  sub- 
stance, produced  by  chemical  reactions,  often  contain  elements  which 
have  not  been  met  with  in  organic  substances,  properly  so  called, 
as,  for  example,  chlorine,  bromine,  iodine,  arsenic.  Again,  organic 
species  which  act  the  part  of  acids  may  form  salts  with  mineral 
bases,  while  basic  organic  species  form  salts  with  the  mineral  acids. 

*  The  apparatus  used  for  distillation  under  reduced  pressure  consists  in  a  re- 
tort A  (fig.  608)  arranged  in  a  small  kettle  containing  ice  or  the  refrigerating  mix- 
ture. The  retort  is  fitted  to  an  or- 
dinary tubulated  receiver  B,  the 
corks  of  which  are  covered  with 
'  sealing-wax,  and  which  is  arranged 
in  a  vessel,  so  that  it  may  be  en- 
tirely covered  by  a  refrigerating 
mixture  of  crystallized  chloride  of 
calcium  and  ice  ;  the  temperature 
of  which  mixture  must  necessarily 
-be  much  lower  than  that  surround- 
ing the  retort.  To  the  second  tu- 
"       "7        ~  bulure  of  the  receiver  a  leaden- 

Fig.  608.  pipe,   having    a    stopcock  r   and 

communicating  with  an  air-pump,  is  fitted.  A  vacuum  is  made  until  the  liquid 
in  the  retort  boils,  when  the  stopcock  r  is  closed,  and  the  distillation  is  effected 
by  means  of  the  difference  of  temperature  in  the  retort  and  the  receiver.  The 
distillation  can  be  arrested  at  will,  by  allowing  air  to  enter  the  apparatus  through 
the  stopcock  r. 


INTRODUCTION.  36T 

Now,  the  study  of  these  salts  possesses  great  interest,  because  they 
are  more  easily  obtained  in  a  state  of  purity  than  the  isolated  or- 
ganic species,  and  their  analysis  furnishes  very  valuable  elements 
for  the  determination  of  the  composition  and  constitution  of  the 
species.  From  all  this  it  will  be  seen  that  the  chemist  who  devotes 
himself  to  the  investigation  of  organic  substances  must  frequently 
examine  elements  quite  different  from  those  which  exist  naturally  in 
the  substances  subjected  to  analysis,  and  that  the  presence  of  such 
new  elements  sometimes  obliges  him  to  modify  his  ordinary  pro- 
cesses. 

DETERMINATION  OF  CARBON  AND  HYDROGEN. 

§  1210.  The  carbon  and  hydrogen  of  an  organic  compound  are 
always  determined  by  completely  burning  the  substance,  either  in 
free  oxygen,  or  by  means  of  the  oxygen  contained  in  an  easily  re- 
ducible metallic  oxide ;  when  the  hydrogen  is  converted  into  water, 
which  is  absorbed  by  some  highly  hygroscopic  substance,  such  as 
chloride  of  calcium  or  concentrated  sulphuric  acid,  while  the  carbon 
passes  into  the  state  of  carbonic  acid,  which  combines  with  a  known 
quantity  of  caustic  potassa ;  the  increase  of  weight  of  the  potassa 
representing  the  weight  of  carbonic  acid  formed. 

Oxide  of  copper  CuO,  which  is  generally  used  to  effect  the  com- 
bustion, may  be  prepared  in  several  ways,  and  in  each  case  presents 
some  special  properties  on  which  it  is  proper  to  dwell. 

One  of  the  most  simple  processes  consists  in  roasting  copper 
turnings  at  a  red-heat  in  the  muffle  of  a  cupelling  furnace,  (fig.  594,) 
when,  the  surface  of  the  copper  becoming  oxidized,  the  whole  is  re- 
moved after  a  few  hours'  roasting,  and  rubbed  in  a  mortar  to  detach 
the  oxide,  or  to  pulverize  those  sheets  of  copper  which  are  entirely 
converted  into  oxide.  The  substance  is  passed  over  a  coarse  sieve 
to  separate  the  sheets  of  metal,  .which  are  again  roasted.  A  very 
coarse-grained  oxide  is  thus  obtained,  which  attracts  but  slightly  the 
moisture  of  the  air.  A  finer  oxide,  the  hygrometric  power  of  which 
is  equally  feeble,  is  prepared  by  substituting  for  the  copper  turn- 
ings, copper  precipitated  chemically,  or  produced  by  decomposing 
acetate  of  copper  by  heat. 

An  oxide  of  copper  in  fine  powder,  and  more  easily  reducible 
than  that  prepared  by  roasting,  may  be  obtained  by  dissolving  the 
metal  in  nitric  acid,  evaporating  the  solution  to  dryness,  and  cal- 
cining for  an  hour,  at  a  dull  red-heat,  the  subnitrate  of  copper  which 
remains  after  evaporation.  The  oxide,  which,  when  ground,  pre- 
sents the  appearance  of  a  fine,  velvet-black  powder,  is  well  adapted 
to  the  combustion  of  organic  substances,  but  rapidly  attracts  the 
moisture  of  the  air,  and,  on  this  account,  requires  great  caution  in 
analysis,  if  the  amount  of  hydrogen  is  to  be  accurately  determined. 

The  oxide  of  copper  produced  by  the  decomposition  of  the  car- 
bonate by  heat  is  also  well  adapted  to  the  combustion  of  organic 


368  ORGANIC   CHEMISTRY. 

substances,  but  is  at  least  as  hygrometric  as  that  prepared  by 
calcining  the  nitrate ;  which  property,  however,  may  be  lessened 
by  heating  it  longer  and  at  a  higher  temperature,  when  it  again 
becomes  more  compact,  and  is  reduced  with  greater  difficulty  by 
combustible  substances. 

Chromate  of  lead  PbO,Cr03  is  sometimes  substituted  for  oxide 
of  copper,  because  organic  substances  burn  readily  in  contact  with 
the  salt ;  and,  as  the  chromate  fuses  at  quite  a  low  temperature, 
the  heat  is  raised  toward  the  close  of  the  combustion,  so  as  to  cause 
its  fusion ;  by  which  means  the  last  particles  of  carbon  which  may 
remain  after  the  decomposition  of  the  organic  matter  are  forced 
into  contact  with  the  burning  substance,  and  their  combustion  is 
necessarily  complete.  Chromate  of  lead  possesses  another  advan- 
tage in  being  less  hygrometric  than  oxide  of  copper,  so  that  the 
determination  of  hydrogen  may  be  made  more  accurately.  The 
chromate  of  lead  should  be  previously  fused  in  an  earthen  crucible, 
rolled  into  a  plate  on  a  sheet  of  copper,  reduced  to  powder,  and  im- 
mediately preserved  in  a  well-stoppered  bottle. 

Before  using  oxide  of  copper  for  combustion,  it  is  always  heated 
to  redness  in  an  earthen  crucible,  in  order  to  destroy  the  organic 
dust  with  which  it  may  be  mixed  and  drive  oflf  its  moisture ;  and 
the  crucible,  when  removed  from  the  fire,  is  placed  under  a  bell- 
glass  containing  some  pieces  of  quicklime,  and  allowed  to  cool.  It  is 
frequently  used  before  it  is  entirely  cooled,  as  there  is  then  less 
fear  of  its  attracting  moisture. 

§  1211.  As  organic  matter  burns  under  conditions  difiering 
slightly  according  to  the  nature  of  the  substance,  we  shall  pay  at- 
tention to  several  cases. 

We  will  suppose,  in  the  first  place,  that  the  organic  substance 
contains  only  carbon,  hydrogen,  and  oxygen,  and  will  also  examine 
several  points,  according  to  the  state  of  the  substance  and  its  greater 
or  less  volatility,  assuming  the  substance  to  be  solid,  non-volatile, 
and  not  decomposable  below  212°. 

The  combustion  is  efiected  in  a  glass  tube  ah,  (fig.  609,)  made 
^  c  as  strong  as  possible,  and  of  an 

i^ •; — ^  internal   diameter  of  about   15 

^ig-  ^0^-  millimetres,   being   j-   metre    in 

length,  while  one  of  its  ends  is  drawn  out  to  a  point  c  and  turned 
upward.  The  other  end  «,  which  remains  open,  has  its  edges 
slightly  rounded,  so  as  not  to  injure  the  cork  fitted  into  it ;  which 
latter  should  be  previously  dried  in  a  stove  at  the  temperature  of 
212°,  to  prevent  it  from  giving  ofi*  moisture. 

The  glass  tube  intended  for  analysis,  and  which  we  shall  call  the 
comhustion-tuhe,  should  be  thoroughly  cleaned  by  wiping  it  out  with 
tissue-paper,  and  then  heated  throughout  its  whole  length,  while  a 
tube  open  at  both  ends,  and  fitted  to  the  nozzle  of  a  bellows,  is  in- 
troduced into  it,  when  the  current  of  air  thus  established  removes 


INTRODUCTION.  369 

all  moisture ;  after  which  the  tube  must  be  closed  "With  a  cork.  As 
the  combustion-tube  may  still  contain  some  organic  dust,  a  small 
quantity  of  hot  oxide  of  copper,  recently  calcined,  is  introduced 
into  it,  and,  after  having  shaken  the  tube,  the  oxide  is  set  aside. 

The  organic  matter  intended  for  analysis  having  been  previously 
finely  powdered,  the  portion  to  be  subjected  to  combustion,  which 
varies  in  weight  from  8.300  gm.  to  0.500  gm.,  is  very  accurately 
weighed.  Larger  quantities  are  sometimes  taken  when  the  substance 
contains  but  little  carbon  or  hydrogen  and  great  exactness  is  re- 
quii^ed  in  the  analysis.  It  is  to  be  weighed  in  a  small  glass  tube 
closed  at  one  end ;  and  if  the  matter  is  hygroscopic,  the  open  end 
of  the  tube  should  be  closed  with  a  ground-glass  stopper. 

The  mixture  of  the  organic  matter  with  oxide  of  copper  is  made 
in  a  mortar  of  glazed  porcelain  or  glass,  which  has  previously  been 
perfectly  dried  by  being  heated  in  a  stove ;  but  it  is  better  to  use 
a  metallic  mortar,  (fig.  610,)  not  very  deep,  and  highly  polished  on 
the  inside,  because  it  is  more  easily  heated,  and  be- 
cause metal  does  not  attract  moisture  like  glass. 
The  inside  of  the  mortar  should  be  cleaned,*  before 
using  it,  with  a  small  quantity  of  oxide  of  copper, 
Fig.  610.  which  is  afterward  rejected.  The  quantity  of  oxide 
of  copper  to  be  mixed  with  the  organic  matter,  and  which  should 
be  such  as  to  occupy  a  length  of  1  or  2  decimetres  in  the  combus- 
tion-tube, being  first  placed  in  the  mortar,  the  organic  matter  con- 
tained in  the  small  tube  in  which  it  has  been  weighed  is  added ;  while, 
in  order  that  none  may  adhere  to  its  sides,  a  small  quantity  of 
oxide  of  copper  is  passed  through  the  small  tube  several  times  and 
then  poured  into  the  mortar.  The  substance  is  ground  rapidly  with 
the  pestle,  in  order  to  make  a  uniform  mixture,  which  is  immediately 
introduced  into  the  combustion-tube,  at  the  bottom  of  which  a  small 
column  of  pure  oxide,  of  3  or  4  centimetres  in  length,  has  been  pre- 
viously deposited ;  for  which  purpose  the  substance  in  the  mortar 
is  dipped  up  with  the  tube,  or  first  poured  on  a  copper  spoon  C, 
(fig.  611,)  and  thence,  by  a  copper  funnel,  into  the 
combustion-tube.  A  small  quantity  of  oxide  of  cop- 
Fig.  611.  pgj.  being  rubbed  in  the  mortar  to  remove  any  par- 
ticles of  the  mixture  which  may  adhere,  and  then  dropped  into  the 
tube,  the  latter  is  then  filled  with  pure  oxide  of  copper.* 

*  As  Mitcherlich's  old  method  of  filling  combustion-tubes,  which  for  a  long  time 
was  rejected  by  the  majority  of  chemists,  seems  now  again  to  be  brought  into  use, 
it  will  be  well  to  mention  it.  The  organic  substance  is  contained  in  a  long  tube, 
the  external  diameter  of  which  is  sufficiently  small  as  to  allow  of  its  being  inserted 
into  the  combustion-tube ;  and  the  oxide  of  copper  is  used,  after  being  heated  to 
a  dull-red,  while  it  is  still  of  a  temperature  of  about  212°,  at  which  degree  of  heat 
the  organic  substance  is  supposed  not  to  decompose.  The  absorption  of  moisture 
by  the  oxide  of  copper  is  thus  prevented  during  the  filling,  which  is  done  as  fol- 
lows:— Supposing  the  combustion-tube  to  be  16  inches  long,  the  lower  2  inches 
would  be  filled  with  coarse  oxide,  and  then  a  column  of  fine  oxide  would  be  in- 
VoL.  II.— 24 


370 


ORGANIC  CHEMISTRY. 


If  the  oxide  of  copper  employed  is  very  finely  powdered,  there 
is  danger  that  the  column  will  not  be  sufficiently  porous  to  allow  an 
easy  disengagement  of  gas ;  and  a  small  canal  must  therefore  be 
made  in  the  upper  part  of  the  tube  throughout  its  whole  length, 
which  is  easily  effected  by  carefully  dropping  the  tube  lengthwise 
on  a  smooth  table,  and  perhaps  applying  a  few  slight  shocks  at  the 
ends. 

As  the  oxide  of  copper  during  this  manipulation  has  almost 
always  attracted  an  appreciable  quantity  of  moisture,  this  must  be 
removed  if  the  exact  amount  of  hydrogen  in  the  substance  is  to  be 
determined ;  which  is  effected  by  placing  the  combustion-tube  in  a  tin 
vessel  V  (fig.  612)  filled  with  hot  water,  and  made  to  communicate 

with  a  small 
air-pump  P, 
to  the  second 
tubulure  of 
which  is  fit- 
ted a  tube  T, 
filled  with 
pumice-stone 
soaked  in  sul- 
phuric acid. 
By  working 
the  pump  se- 
veral times, 
and  each  time 

allowing  the  air  to  enter  which  was  dried  by  passing  through  the 
tube  T,  the  hygroscopic  moisture  is  completely  removed ;  but  the 
process  can  only  be  employed  when  the  organic  substance  does  not 
give  off  sensibly  any  vapour,  in  vacuo,  at  a  temperature  of  212°, 
and  when  it  cannot,  under  these  circumstances,  either  give  off  water 
or  decompose.  In  any  other  case  the  process  of  desiccation  just 
mentioned  could  not  be  employed,  and  recourse  must  be  taken  to 
the  use  of  coarser  and  more  highly  calcined  oxide  of  copper,  while 


Fig.  612. 


serted,  occupying  about  6  inches ;  after  which  the  organic  substance  is  introduced, 
by  inserting  the  tube  containing  it  in  the  combustion-tube,  and  allowing  the  desired 
quantity  to  fall  out;  after  which  the  small  tube  is  corked,  and  subsequently 
weighed  to  ascertain  the  amount  of  substance  extracted.  The  combustion-tube 
is  then  filled  with  another  column  of  6  inches  of  fine  oxide  of  copper,  and  the  or- 
ganic substance  is  mixed  up  thoroughly,  by  means  of  the  spirally-twisted  end  of  a 
long  and  clean  copper  wire,  with  the  columns  of  oxide  below  and  beneath  it;  which 
is  easily  done  by  successively  screwing  the  wire  down  to  the  layer  of  coarse  oxide, 
and  working  it  backward  and  forward  for  about  5  minutes ;  the  tube  being  held 
with  a  cloth,  because  the  oxide  has  the  temperature  of  boiling  water.  Another 
inch  of  pure  fine  oxide  is  then  added,  and  the  tube  is  corked.  There  will  then  be 
contained  in  the  tube,  1st,  two  inches  of  coarse  oxide;  2dly,  twelve  inches  of  an 
intimate  mixture  of  fine  oxide  and  the  organic  substance ;  3dly,  one  inch  of  tme 
oxide ;  and,  lastly,  a  free  space  of  one  inch,  to  allow  of  rendering  the  whole  co- 
lumn porous  bj  shaking. —  W.  L.  F. 


INTRODUCTION. 


3T1 


the  mixture  must  be  made  in  the  mortar  as  rapidly  as  possible, 
taking  care  to  hold  the  breath. 

The  combustion-tube,  after  being  charged,  is  enveloped  with  a 

thin  ribbon  of  brass,  previously 

annealed,    and    fastened    with 

^^^Li^^^'H'^'^'TS^iiimiiiiiiii'iH?^^  copper-wire,  as  represented  in 

Fig-  613.  fig.  613,  after  which  the  tube, 

thus  protected,  may  be  heated  to  a  very  high  temperature  without 

danger. 

The  combustion-tube  being  placed  on  a  long  sheet-iron  furnace, 


Fig.  614. 


(fig.  614,) 
the  appa- 
ratus in- 
tended to 
absorb  wa- 
ter is  fitte^i 
to  it  by 
means  of  a 
very  well 
apparatus  con- 
with  pieces 


of  chloride  of  calcium,  arranged 
3    as  in  fig.  615,  while  plugs  of 
cotton,  placed  at  a  and  5,  pre- 
vent the  small  particles  of  chlo- 
The  cork  a  is  covered  with 


Fig.  615. 

ride  from  escaping  from  the  tube, 
sealing-wax,  in  order  that  its  weight  may  not  change  by  absorbing 
or  exhaling  moisture,  if  any  existed  in  the  air.  A  U-tube,  filled 
with  pumice-stone  soaked  in  concentrated  sulphuric  acid,  is  some- 
times substituted  for  the  tube  containing  chloride  of  calcium. 

The  carbonic  acid  formed  by  combustion  condenses  in  a  concen- 
trated solution  of  caustic  potassa,  marking  about  45°  Baum^,  and 
placed  in  the  apparatus  B  (fig.  614)  described  on  page  324,  vol.  i., 
which  is  fitted,  by  means  of  a  caoutchouc  connecter,  to  a  tube  in- 
tended to  condense  the  water.  As  it  might  be  feared  that  the 
solution  of  potassa,  notwithstanding  its  concentration,  might  part 
with  a  small  quantity  of  water  to  the  very  dry  gases  which  traverse 
it,  a  small  U-shaped  tube  C,  containing  pieces  of  caustic  potassa, 
which  absorb  at  the  same  time  the  vapour  of  water  and  the  small 
quantity  of  carbonic  acid  which  escapes  absorption  in  the  apparatus 
B,  is  affixed  to  the  latter. 

Lastly,  a  bottle  Y,  the  cork  of  which  has  a  stopcock  r,  is  fitted 
to  this  apparatus,  thus  establishing  or  interrupting  at  will  commu- 
nication with  the  outer  air.  To  the  bottle  is  permanently  fitted  a 
U-tube  filled  with  sulphuric  pumice-stone,  intended  to  prevent  the 
vapour  of  water  from  passing  from  the  bottle  V  into  the  tube  C. 
(The  U-tube  is  not  represented  in  the  figure.)    ' 


372 


ORGANIC  CHEMISTRY. 


The  drying-tiibe  A  and  the  whole  of  the  apparatus  B  and  C  hav- 
ing been  previously  exactly  weighed,  their  increase  of  weight  during 
the  experiment  gives  respectively  the  quantity  of  water  and  of  car- 
bonic acid  formed  by  combustion. 

When  the  apparatus  is  arranged,  the  anterior  portion  a  F  of  the 
combustion-tube,  which  contains  only  pure  oxide  of  copper,  is  sur- 
rounded by  burning  coals ;  and  in  order  that  the  heat  may  not 
communicate  by  radiation  to  the  parts  of  the  tube  containing  the 
mixture  of  oxide  and  organic  matter,  a  double  screen  F,  made  of 
JF  sheet-iron,  and  represented  in  fig.  616,  is  interposed.  When 
the  anterior  portion  of  the  tube  is  heated  to  redness,  the 
coals  are  gradually  moved  toward  the  part  containing  the 
mixture  of  oxide  and  organic  matter,  the  rapidity  of  moving 
Fig.  616.  the  coals  being  guided  by  the  evolution  of  gas  which  is  ob- 
served rising  in  bubbles  through  the  potash  apparatus,  and  which 
should  never  follow  so  rapidly  as  not  to  allow  the  counting  the 
bubbles  which  traverse  the  apparatus  B.  This  is  continued  until 
the  tube  is  completely  surrounded  with  coals,  when  the  combustion 
is  terminated,  and  the  evolution  of  the  gases  ceases,  and  very  soon 
the  potassa  ascends  into  the  globe  which  communicates  with  the 
drying-tube,  in  consequence  of  the  absorption  of  the  carbonic  acid 
contained  in  this  globe.     The  globe  apparatus  is  then  moved  from 

_^  the  position  of  fig.  617  to  that  of  fig. 
"  618,  and  if  the  globes  are  of  suitable 
dimensions,  the  solution  of  potassa  will 
certainly  ascend  to  the  drying-tube, 
(§  260,)  and  very  soon,  the  absorption 
of  carbonic  acid  continuing,  bubbles 
of  air  re-enter  the  apparatus,  passing 
through  the  solution  of  potassa.     The 


Fig.  617. 


Fig.  618. 


coals  surrounding  the  end  c  of  the  combustion-tube  are  then  re 

moved,  and,  when  the  ktter  is  sufficiently  cooled,  its  point  is  broken 

with  a  pincers,  (fig.  619 ;)  when  the  gas  in  the  apparatus 

being  rarefied,  the  outer  air   enters  through  the  broken 

point  and  establishes  the  equilibrium.     A  tube  S,  (fig.  620,) 

containing  pieces  of  caustic  potassa,  and  furnished  with  a 

caoutchouc  tube,  which  it  is  sufficient  to  press  against  the 

combustion-tube  to  render  the  opening  tight,  is  then  adapted 

^'       to  the  point ;  after  which  the  stopcock  r  of  the  bottle  V  is 

closed,  and  by  opening  the  stopcock  r'  the  water  in  this  bottle  is 

allowed  slowly  to  escape.  The  atmo- 
spheric air,  freed  from  moisture  and 
carbonic  acid  by  its  passage  through 
the  tube  S,  removes  the  small  quan- 
tities of  vapour  of  water  and  carbonic 
Fig.  620.  acid  which  still  remained,   and  con- 

veys them  into  the  apparatus  A,  B,  C,  where  they  are  condensed. 


INTRODUCTION.  373 

When  about  1  litre  of  water  has  escaped,  the  apparatus  is  taken 
apart,  weighed,  and  the  carbonic  acid  and  water  formed  during  com- 
bustion exactly  ascertained,  whence  the  quantity  of  carbon  and  hy- 
drogen contained  in  the  organic  matter  can  be  calculated.  As  we 
have  supposed  the  substance  subjected  to  analysis  to  contain  only 
carbon,  hydrogen,  and  oxygen,  the  oxygen  may  be  obtained  differ- 
entially, that  is,  by  subtracting  the  weight  of  hydrogen  and  carbon 
united,  from  that  of  the  substance  subjected  to  analysis. 

It  frequently  happens  that  it  is  difficult  to  completely  burn  or- 
ganic substances,  either  because  they  cannot  be  intimately  mixed 
with  the  oxide  of  copper,  or  because,  by  being  decomposed  by  heat, 
they  leave  a  charcoal  of  difficult  combustion,  which  is  sometimes  de- 
posited in  the  upper  portions  of  the  combustion-tube,  out  of  contact 
of  the  oxide  of  copper.  In  this  case,  it  becomes  necessary  to  termi- 
nate the  combustion  in  a  current  of  oxygen ;  for  which  purpose  a 
mixture  of  2  or  3  gm.  of  chlorate  of  potassa,  coarsely  powdered,  and 
15  or  20  gm.  of  oxide  of  copper,  is  introduced  into  the  bottom  of 
the  combustion-tube,  while  upon  this  is  placed  a  column  of  3  or  4 
centimetres  of  pure  oxide,  then  the  mixture  of  oxide  of  copper  and 
the  organic  substance,  and  lastly  the  tube,  is  filled  with  pure  oxide. 
The  apparatus  is  arranged  as  has  been  described.  When  the  organic 
matter  has  been  completely  burned,  and  the  hot  coals  surround  the 
tube,  even  as  far  as  the  extreme  portion  which  contains  the  chlorate 
of  potassa,  some  coals  are  carefully  moved  toward  this  end,  in  order 
to  disengage  oxygen.  The  first  portions  of  the  gas  are  absorbed  by 
the  copper  reduced  by  combustion,  and  it  is  only  after  the  entire  oxi- 
dation of  this  metal  that  free  oxygen  begins  to  pass  through  the 
tube,  and  care  must  be  taken  that  its  evolution  be  not  too  rapid. 
The  organic  matter  is  necessarily  entirely  burned  in  the  atmosphere 
of  oxygen,  and  the  carbonic  acid  produced  is  carried  by  the  current 
of  oxygen  into  the  absorbing  apparatus,  which  renders  the  aspirator 
useless. 

The  chlorate  of  potassa  should  have  been  previously  fused,  in  order 
to  free  it  from  organic  substances  and  moisture.  In  this  method  of 
operating,  it  may  be  feared  that  the  chlorate,  by  contact  with  the 
oxide  of  copper,  may  give  off  a  small  quantity  of  chlorine  which  is 
not  completely  retained  in  the  combustion-tube ;  which  difficulty, 
however,  is  remedied  by  using  a  longer  combustion-tube,  and  placing, 
in  front  of  the  oxide  of  copper,  a  length  of  8  or  10  centimetres  of 
litharge,  which,  at  a  red-heat,  retains  the  whole  of  the  chlorine. 

Sometimes  the  oxygen  is  prepared  in  a  small  separate  retort, 
which  is  made  to  connect  with  the  small  end  of  the  tube,  instead  of 
evolving  oxygen  by  means  of  the  chlorate  of  potassa  placed  in  the 
combustion-tube  itself. 

Although  the  majority  of  organic  substances  will  b^rn  completely 
by  contact  with  oxide  of  copper  alone,  it  is  always  prudent  to  per- 
form one,  at  least,  of  the  combustions  with  the  addition  of  chlorate 


•374  ORGANIC   CHEMISTRY. 

of  potassa,  in  order  to  ascertain  whether  the  amount  of  carbon  found 
has  not  been  too  small  in  the  preceding  analyses. 

§  1212.  If  the  substance  to  be  analyzed  is  liquid  and  non-volatile, 
as,  for  example,  a  fixed  oil,  it  is  weighed  in  a  small  tube,  closed  at 
one  end,  and  introduced  into  the  combustion-tube,  after  having 
poured  into  the  latter  a  column  of  oxide  of  copper  of  4  or  5  centi- 
metres in  height ;  after  which  the  tube  is  inclined  so  as  to  spread 
the  oil  over  a  certain  extent  of  its  sides,  and  then  entirely  filled 
with  oxide  of  copper.  It  frequently  happens  that  complete  combus- 
tion is  not  effected  by  the  oxide  of  copper  alone,  and  must  be  ter- 
minated in  a  current  of  oxygen. 

Greasy  and  easily  fusible  substances  should  not  be  triturated  with 
the  oxide  of  copper,  because  some  particles  might  adhere  to  the  mor- 
tar and  pestle ;  but  a  suitable  quantity  of  the  material  should,  in 
this  case,  rather  be  melted  in  a  small  glass  boat,  made  of  a  piece 
of  tube  divided  longitudinally,  and  introduced,  after  being  weighed, 
into  the  tube,  at  the  bottom  of  which  the  oxide  of  copper  is  placed. 
By  heating  that  portion  of  the  tube  which  contains  the  boat,  the 
grease  melts,  and  flows  over  a  certain  extent  of  the  tube,  which  is 
then  to  be  filled  with  oxide  of  copper.  It  is,  in  this  case,  equally 
prudent  to  terminate  the  combustion  in  a  current  of  oxygen. 

§  1213.  Volatile  liquid  substances  are  weighed  in  glass  bulbs 
(fig.  621)  hermetically  sealed,  the  manner  of  making  which  has 
^^'^^^^  been  described,  (§  699,)  and  the  manner  of 

^  filling  them  in  §  269.      It  is  essential  not 

Fig.  621.  ^Q  bring  the  bubbles  in  contact  with  the  hot 

oxide  of  copper  after  they  have  been  opened,  as  vapours  affecting 
the  accuracy  of  the  analysis  would  infallibly  be  produced.  Two 
tubes  of  nearly  the  same  capacity  are  used,  and  one  of  them  being 
filled  with  recently  calcined  and  still  hot  oxide  of  copper,  is  closed, 
and  allowed  to  cool  completely ;  while  into  the  second  tube,  which 
is  to  serve  as  a  combustion-tube,  a  column  of  4  or  5  centimetres  of 
oxide  of  copper  is  introduced,  and  afterward  the  bubbles  are  inserted, 
of  which  one  of  the  points  is  broken ;  and,  lastly,  the  second  tube 
is  filled  with  the  oxide  of  copper  which  has  been  allowed  to  cool  in 
the  first,  and  is,  consequently,  free  from  moisture.  It  is  better,  in 
such  analyses,  to  use  coarse  oxide  of  copper,  mixed  with  roasted 
turnings,  because  this  oxide,  even  when  it  completely  fills  the  sec- 
tion of  the  tube,  is  sufiiciently  porous  to  afford  an  easy  passage  for 
gases  and  vapours.  The  absorbing  apparatus  is  arranged  as  usual, 
but  the  operation  is  conducted  as  rapidly  ^s  possible,  in  order 
that  the  vapours  of  the  volatile  substance  inay  only  have  time 
to  reach  the  anterior  part  of  the  combustion-tube,  which  is  heated 
to  redness,  while  the  part  containing  the  bubbles  is  protected  by 
several  screen^.  When  the  oxide  of  copper  is  red  for  a  length  of 
several  decimetres,  some  coals  are  carefully  moved  toward  the  part 
containing  the  bubbles,  while  the  distillation  of  the  substance  is 


INTRODUCTION.  375 

regulated  by  the  position  of  the  coals.  The  vapours  burn  while 
traversing  the  oxide  of  copper ;  and  when  combustion  ceases,  the 
tube  is  surrounded  with  burning  coals,  and  heated  throughout  its 
whole  length,  after  which  the  experiment  is  terminated  as  usual. 

If  the  substance  to  be  analyzed  is  very  volatile — if  it  boils,  for 
example,  at  a  temperature  below  122°  under  the  ordinary  pressure 
of  the  atmosphere — it  is  difficult  to  obtain  an  exact  analysis  by  the 
process  just  stated.  The  vapours  of  the  substance  cannot  be  pre- 
vented from  penetrating  the  anterior  part  of  the  combustion-tube, 
before  this  part  is  heated  to  redness,  and  they  thus  escape  combus- 
tion and  render  the  analysis  inaccurate.  The  experiment  is  then 
arranged  in  the  following  manner : — The  combustion-tube  is  drawn 
out  at  its  posterior  portion,  so  as  to  form  a  tubulure  <?,  while  the 
liquid  to  be  analyzed  is  contained  in  a  globe  U  bent  into  the  form 
I  ^  of  a  retort  (fig.  622)  and  terminating  in 

^>^  two  closed  points,  one  of  which  enters  the 
uO[  tubulure  of  a  combustion-tube  previously 
V  filled  with  oxide  of  copper  and  arranged 
fig.  622.  on  its  sheet-iron  furnace.     The  globe  is 

hermetically  fastened  by  caoutchouc,  while  the  ordinary  condensers 
are  fitted  to  the  combustion-tube,  which  is  surrounded  by  burning 
coals.  When  the  whole  length  of  the  tube  is  red,  the  anterior  point 
of  the  globe  is  broken,  by  pressing  it  against  the  sides  of  the  tubu- 
lure ;  and  if  the  liquid  is  very  volatile,  it  sometimes  boils  immediately, 
and  the  analysis  may  fail  in  consequence  of  a  too  sudden  evolution 
of  gas.  If  such  an  accident  is  to  be  feared,  the  globe  should  be 
surrounded  by  a  refrigerating  mixture  before  breaking  the  point ; 
when  the  ebullition  is  easily  regulated,  either  by  heating  the  globe 
with  the  hand,  or  by  hot  coals.  When  the  whole  of  the  liquid  is 
distilled,  and  the  absorption  of  carbonic  acid  causes  the  potassa  to 
ascend  into  the  globe  apparatus,  the  second  point  b  of  the  bubble  is 
burst,  when  the  external  air,  entering  the  combustion-tube,  carries 
into  it  the  last  portions  of  vapour  which  remained  in  the  bubble. 
The  latter  is  then  detached,  replaced  by  the  tube  S  filled  with  pieces 
of  potassa,  (fig.  620,)  and  lastly,  water  is  allowed  to  escape  from  the 
aspirator-bottle  to  terminate  the  analysis  in  the  ordinary  way. 

§  1214.  We  will  suppose,  lastly,  that  the  organic  substance  to  be 
analyzed  is  gaseous,  and  that  it  cannot  be  condensed  in  a  refrige- 
rating mixture  at  —20°,  in  which  case  it  could  still  be  analyzed  by 
the^ processes  described  for  very  volatile  liquids;  and  the  proceeding 
of  the  analysis  is  then  as  follows : 

When  the  gas  contains  only  carbon  and  hydrogen,  its  analysis  can 
be  very  readily  made.  The  apparatus  is  arranged  as  for  the  analysis 
of  very  volatile  liquids,  and,  when  the  combustion-tube  is  heated  to 
redness  throughout  its  whole  length,  the  disengaging-tube  of  the 
apparatus  which  produces  the  gas  to  be  analyzed  is  fitted  to  its  tu- 
bulure by  means  of  caoutchouc.     The  gas  burns  when  in  contact 


376 


ORGANIC   CHEMISTRY. 


with  the  incandescent  oxide  of  copper,  while  the  vapour  of  watei 
and  carbonic  acid  are  arrested  in  the  ordinary  condensers ;  and, 
when  a  sufficient  quantity  of  gas  is  supposed  to  be  burned,  the  dis- 
engagement-tube which  conveys  the  gas  is  detached,  and  water  al- 
lowed to  escape  from  the  aspu-ator-bottle,  in  order  to  burn  the  last 
portions  of  gas  which  remain  in  the  combustion-tube,  and  drive  their 
products  into  the  condensers.  This  experiment  gives  the  weight  of 
carbon  and  hydrogen  contained  in  the  gas  burned ;  but  as  the  weight 
of  this  gas  is  not  known,  it  is  evident  that  only  the  ratio  between 
the  weight  of  the  hydrogen  and  carbon  can  be  inferred  from  it, 
which,  however,  will  give  a  sufficient  clue  as  to  the  composition  of 
the  gas. 

It  is  better  to  operate  so  as  to  ascertain  the  volume  of  the  gas 
subjected  to  experiment,  and,  consequently, 
also  its  weight,  if  its  density  has  been  de- 
termined by  previous  experiment,  in  which 
case  the  process  can  also  be  applied  to  gases 
containing  oxygen  and  nitrogen.  For  this 
purpose  the  apparatus  represented  in  fig.  623 
is  used.  The  pipette  ah,  containing  400  or 
500  cubic  centimetres,  terminates  at  its 
upper  part,  in  a  straght  tube  cr,  to  which 
is  luted  a  steel  tubulure,  having  a  stop- 
cock r,  while  the  lower  tube  af  of  the  pipette 
is  luted  to  one  of  the  tubulures  of  a  cast- 
iron  piece  having  a  stopcock  R,  furnished 
with  a  second  tubulure  g.  A  tube  gh,  open 
at  both  ends,  is  luted  to  the  tubulure  g,  and 
the  whole  apparatus  is  fastened  to  an  up- 
right board.  The  stopcock  R  has  three 
apertures,  as  figures  624,  625,  and  626 
show  which  represent  transverse  sections 
'of  the  stopcock,  in  the  three  principal  po- 
sitions which  may  be  given  to  it.  In 
fig.  624,  the  branches  hf  and  gh  communi- 
cate, and  in  fig.  625  the  branches  5/,  gh  communicate  with  each 
other,  and  with  the  external  air  by  the  tubulure  f,  while  mercury 
escapes ;  and  lastly,  in  fig.  626  the  branches  do  not  communicate 


Fig.  623. 


Fig.  624.  Fig.  625.  Fig.  626. 

with  each  other,  but  the  branch  bf  communicates  with  the  external 


INTRODUCTION.  377 

air  by  the  tubulure  t,  while  the  mercury  contained  in  this  branch 
alone  escapes. 

The  stopcock  R  being  in  the  position  of  fig.  624,  and  the  cock  r 
being  open,  the  apparatus  is  filled  with  mercury  through  the  tube  gh  ; 
and  when  it  begins  to  escape  through  the  tubulure  r,  the  cock  R  is 
brought  to  the  position  of  fig.  626,  and  the  mercury  which  escapes 
is  collected  in  a  bottle.  The  level  of  the  mercury  is  allowed  to 
fall  until  it  exactly  reaches  the  mark  a  on  the  tube  fa  ;  and  the 
capacity  of  the  pipette  is  then  inferred  from  the  weight  of  the  mer- 
cury. The  apparatus  is  then  again  filled  with  mercury,  and  the 
tubulure  r  made  to  communicate  with  the  apparatus  which  disengages 
the  gas  to  be  analyzed.  As  the  gas  is  produced,  mercury  is  allowed 
to  escape,  so  as  to  fill  the  pipette  with  gas  to  just  below  the  mark  a ; 
after  which  the  stopcock  r  is  closed,  the  chemical  apparatus  which 
evolves  the  gas  removed,  and,  bringing  the  cock  R  to  the  position  of 
fig.  624,  mercury  is  carefully  poured  into  the  branch  gh,  so  as  to 
bring  the  level  exactly  to  a.  By  adding  the  diff'erence  of  height  h 
between  the  levels  of  mercury  in  the  two  branches  6/,  gh,  which  is 
then  measured,  to  the  height  H  of  the  mercury  in  the  barometer, 
the  pressure  (H+A)  to  which  the  gas  is  subjected  is  obtained,  while 
the  thermometer  T  (fig.  623)  shows  its  temperature.  If,  therefore, 
the  density  of  the  gas  be  known,  its  weight  can  be  easily  calculated. 

In  order  to  burn  the  gas,  it  suffices  to  cause  the  tubulure  r  to 
communicate  with  the  pointed  tubulure  c  of  the  combustion-tube 
heated  to  redness  (fig.  614)  and  furnished  with  its  ordinary  con- 
densing apparatus.  The  stopcock  r  being  carefully  opened,  mer- 
cury is  poured  into  the  branch  gh  by  means  of  a  funnel  which  only 
allows  the  proper  quantity  of  mercury  to  escape ;  and  as  soon  as 
the  pipette  is  entirely  filled  with  mercury,  so  that  the  latter  reaches 
the  stopcock  r,  this  cock  is  closed,  the  apparatus  of  fig.  623  re- 
moved, and  the  operation  terminated  as  usual. 

§  1215.  In  the  processes  just  described,  the  weight  of  the  carbon 
is  inferred  from  that  of  the  carbonic  acid  absorbed  by  the  potassa : 
it  may  also  be  determined  by  measuring  the  volume  of  gas,  by  which 
method  the  first  exact  analyses  of  organic  substances  were  made. 

The  hydrogen  and  carbon  are  then  determined  separately,  the 
determination  of  the  former  being  made  in  the  ordinary  manner,  by 
burning  the  organic  matter  with  oxide  of  copper,  and  collecting  the 
water  produced  in  a  tube  filled  with  pieces  of  chloride  of  calcium, 
and  fitted  to  the  combustion-tube  by  means  of  a  cock.  The  determi- 
nation of  carbon  is  performed  in  an  apparatus  represented  in  fig.  627. 
The  tube  ah  contains  the  mixture  of  the  organic  substance  with 
oxide  of  copper,  and  at  its  anterior  portion  contains  pure  oxide  of  cop- 
per ;  while  a  bent  tube  cdef,  the  two  vertical  legs  of  which,  de,  ef 
descend  to  the  bottom  of  the  test-glass  AB  filled  with  mercury,  is 
fitted  by  means  of  a  cock,  to  the  combustion-tube,  which  therefore 
communicates  with  the  external  air  by  the  tube  cdef,     A  bell-glass  0, 


378 


ORGANIC   CHEMISTRY. 


divided  into  cubic  centimetres,  and  of  which  the  sides,  after  being 
wiped  with  tissue-paper,  retain  sufficient  water  to  saturate  the  air  re- 
maining in  the  bell-glass 
with  moisture,  is  passed 
over  the  leg  ef.  Before 
fitting  the  branch  c  to 
the  combustion-tube, 
the  bell-glass  C  is  made 
to  descend,  until  a  very 
small  volume  of  air  (50 
c.  c.  for  example)  alone 
remains,  the  mercury 
being  on  a  level  in  the 
bell-glass  and  the  cir- 
cular space  comprised 
between  the  bell-glass 
and  the  test-glass.  The 
cock  c  is  then  fitted,  and 
the  apparatus  allowed 
to  attain  the  tempera- 
ture of  the  surround- 


Fig.  627. 


ing  medium.  The  temperature  t  and  the  height  of  the  barometer 
Hq  being  noted  down,  we  will  designate  by  v  the  volume  of  air  in 
the  combustion-tube  and  in  the  tube  cdef ;  by /the  elastic  force  of 
the  vapour  of  water  at  the  temperatue  f,  when  the  volume  of  air  in 
the  apparatus,  supposing  it  to  be  dry,  reduced  to  32°,  and  under 
the  pressure  of  0.760  m.,  29.922  inches,  will  be 

{y-tD\j)    1^.00387. «    •      760      ' 

The  organic  matter  is  then  subjected  to  combustion  ;  and  as  car- 
bonic acid  is  disengaged,  the  bell-glass  C  is  raised,  in  order  to  keep 
the  surface  of  the  mercury  in  the  bell-glass  nearly  level  with 
that  in  the  test-glass.  When  the  combustion  is  terminated,  the 
coals  are  removed,  and  the  apparatus  allowed  to  fall  to  the  sur- 
rounding temperature  t' ;  after  which  the  mercury  inside  is  brought 
exactly  to  the  level  of  that  outside,  by  raising  or  depressing  the 
bell-glass,  or  by  pouring  mercury  into  the  test-glass.  Lastly,  the 
volume  V  occupied  by  the  gas  in  the  bell-glass  is  marked,  as  well  as 
the  height  H'^  of  the  barometer.  The  volume  of  gas  in  the  ap- 
paratus, reduced  to  dryness,  at  the  temperature  of  32°,  and  under 
a  pressure  of  0.760  m.,  will  be — 


760 


(V-j-V)     1^0.00367. «' 

and  the  volume  of  carbonic  acid  formed  by  combustion,  when  dry 
and  under  normal  conditions  of  pressure  and  temperature,  is  therefore 


(f+V) 


1+0.00367  •  V 


760    " 


(t;H-50) 


1+0.00367  .  t 


Ho-/- 

760    * 


INTRODUCTION.  370 

In  order  to  obtain  the  weight  of  carbonic  acid  furnished  by  the  or- 
ganic matter,  it  is  sufficient  to  multiply  this  volume,  in  cubic  centi- 
metres, by  the  weight  0.0019774  m.  of  1  cubic  centimetre  of  car- 
bonic acid. 

The  determination  of  carbonic  acid  by  volume  is  much  more  deli- 
cate than  that  by  weight.  It  is  essential  that  the  shape  of  the 
combustion-tube  should  not  be  altered  during  the  combustion,  as  this 
would  change  the  volume  v  ;  and  the  volume  of  gas  at  the  close  of 
the  experiment  must  not  be  measured  until  the  combustion-tube  at- 
tains tTie  surrounding  temperature,  which  often  requires  a  long  time. 
Lastly,  it  is  necessary  to  use  very  coarse  oxide  of  copper,  for  finely 
divided  and  feebly  calcined  oxide  absorbs  carbonic  acid,  in  the  pre- 
sence of  moisture,  when  it  falls  to  the  ordinary  temperature.  All 
these  difficulties  have  caused  this  method  of  analysis  to  be  neglected, 
although  its  results  are  accurate  in  the  hands  of  a  skilful  mani- 
pulator. 

§  1216.  When  the  organic  substance  contains,  at  the  same  time, 
carbon,  hydrogen,  oxygen,  and  nitrogen,  the  determination  of  carbon 
and  hydrogen  requires  peculiar  care.  A  portion  of  the  nitrogen 
which  is  set  free  during  the  combustion  of  the  substance  by  the  oxide 
of  copper,  does  not  affect  the  results  of  the  analysis,  while  another 
portion  is  converted  into  deutoxide,  which,  being  changed  into  nitrous 
gas  by  contact  with  the  oxygen  of  the  air,  condenses  partly  in  the 
tube  which  absorbs  the  water,  and  partly  in  the  potassa,  rendering 
the  analysis  inaccurate.  This  is  avoided  by  placing  near  the  orifice 
of  the  combustion-tube  a  column  of  metallic  copper  of  about  2  de- 
cimetres in  length ;  when  the  gases  which  arise  from  combustion 
traversing  the  incandescent  copper,  before  reaching  the  absorbing 
tubes,  the  oxides  of  nitrogen  are  decomposed  by  giving  off  free  ni- 
trogen, while  the  carbonic  acid  and  water  undergo  no  change.  The 
metallic  copper  used  to  decompose  the  oxide  of  nitrogen  is  prepared 
by  roasting  copper  turnings  in  the  air,  so  as  to  oxidize  its  surface, 
and  then  reducing  the  surface  to  the  metallic  state,  by  heating  the 
roasted  turnings  in  a  glass  tube  in  a  current  of  hydrogen,  by  which 
means  the  surface  of  the  metal  becomes  very  porous,  and  exerts  a 
much  more  powerful  reducing  action  than  if  it  were  smooth  and 
polished. 

If  the  organic  substance  contains  sulphur,  the  process  of  ordi- 
nary combustion  must  again  be  slightly  modified,  because  the 
sulphur,  by  burning  in  contact  with  the  oxide  of  copper,  is  largely 
converted  into  sulphurous  acid,  which  condenses  the  apparatus  con- 
taining potassa,  thus  rendering  the  determination  of  the  carbonic 
acid  inaccurate.  But  the  sulphurous  acid  is  entirely  retained  in 
the  combustion-tube,  by  placing  in  the  anterior  part  of  the  tube  a 
length  of  0.2  m.  of  litharge,  which,  at  a  red-heat,  absorbs  sulphur- 
ous acid  wholly,  provided  the  current  of  gas  be  not  too  rapid. 

It  is  also  necessary  to  place  a  column  of  litharge  in  the  tube,  in 


380  ORGANIC   CHEMISTRY. 

front  of  the  oxide  of  copper,  when  the  organic  substance  contains 
chlorine,  bromine,  or  iodine,  because,  in  that  case,  a  chloride,  bro- 
mide, or  iodide  of  copper  is  formed,  which  is  sufficiently  volatile  to 
permit  its  vapours  to  reach  the  tube  containing  the  chloride  of  cal- 
.  cium,  and  falsify  the  determination  of  water.  Litharge  decomposes 
and  perfectly  retains  these  vapours  at  a  red-heat. 

The  analysis  of  salts  formed  by  organic  acids  with  mineral  bases 
the  carbonates  of  which  are  indecomposable,  or  decompose  with  diffi- 
culty by  heat,  also  requires  peculiar  precautions.  Such  bases  are 
the  alkalies  and  alkaline  earths,  which  remain  partly  in  the  co'mbus- 
tion-tube  in  the  state  of  carbonates,  while  it  cannot  be  admitted 
that  they  do  so  entirely,  because  the  carbonates  are  partially  de- 
composed by  the  oxide  of  copper,  the  sides  of  the  tube,  and,  par- 
ticularly, by  the  mineral  acids,  chlorine,  and  other  elements  which 
may  exist  in  combination  with  the  oxide  of  copper  or  with  the 
reduced  copper.  The  carbonic  acid  may  be  completely  disengaged 
by  substituting  chromate  of  lead  for  the  oxide  of  copper,  especially 
if  a  small  quantity  of  bichromate  of  potassa  be  added  to  the 
chromate.  Otherwise,  the  combustion  is  conducted  in  the  same 
manner  as  for  the  oxide  of  copper. 

DETERMINATION  OF  NITROGEN. 

§  1217.  The  nitrogen  contained  in  organic  substances  is  deter- 
mined by  the  process  described  for  the  analysis  of  the  nitrates, 
(§  108.)  A  combustion-tube  /a,  (fig.  628,)  closed  at  one  end,  and 
about  0.8  m.  in  length,  is  used,  at  the  bottom  of  which  about  20  gm. 

of  bicarbonate  of  soda  ah 

'^^ j^  •  'f_     -^^^    are  placed,  and  above  it  a 

rm '  jn-^^^— ^ liiTi iiiiBiiiiiiiiiimiiiriinimii iiiiia  column  hc  of  pure  oxide  of 

'        Fig.  628.  •        copper,  of  five  or  six  cen- 

timetres in  length,  after- 
ward the  mixture  cd  of  the  organic  substance  with  oxide  of  copper, 
and  lastly  a  length  de  of  0.2  m.  of  pure  oxide  of  copper.  Over  the 
whole  is  superimposed  a  column  ef  of  0.2  m.  of  metallic  copper, 
prepared  from  copper  turnings  previously  roasted  in  the  air  to 
oxidize  their  surface,  and  then  reduced  in  a  current  of  hydrogen. 
The  tube  being  arranged  on  a  long  sheet-iron  furnace,  (fig.  629,) 
a  glass  tube,  which  is  made  to  communicate  with  the  tubulure  of  a 
small  air-pump  P,  is  fitted  to  its  orifice  by  means  of  a  cork,  while 
to  the  second  tubulure  d  of  the  pump  a  glass  tube  def  is  fastened, 
of  which  the  vertical  leg  ef  is  about  0.8  m.  in  length,  and  the 
curved  extremity  of  which  dips  into  the  small  mercurial  bottle  B. 
In  the  first  place,  the  air  must  be  completely  removed  from  the 
apparatus,  for  which  purpose  as  perfect  a  vacuum  as  possible  is 
made  with  the  pump,  and  the  stopcock  s  is  closed,  leaving  open 
those  at  /*,  r'.     After  a  few  moments  it  is  ascertained  whether  the 


INTRODUCTION. 


381 


apparatus  remains  empty,  in  which  case  the  column  of  mercury  in 
the  tube  ef  should  remain  absolutely  stationary.     Some  coals  are 


Fig.  629. 

brought  near  the  end  of  the  tube  containing  the  bicarbonate  of 
soda,  when  the  carbonic .  acid  disengaged  drives  the  air  from  the 
tube  ;  and  as  soon  as  the  gas  begins  to  be  evolved  under  the  mer- 
cury, the  anterior  part  of  the  tube,  which  contains  the  metallic 
mercury  and  a  length  of  some  centimetres  of  pure  oxide  of  copper, 
is  surrounded  with  hot  coals,  and  it  is  then  ascertained  whether 
the  gas  which  is  evolved  be  pure  carbonic  acid.  For  this  purpose 
it  is  sufficient  to  collect  the  gas  in  a  small  bell-glass  filled  with 
mercury,  at  the  top  of  which  a  solution  of  potassa  has  been  placed ; 
and  if  the  gas  formed  is  pure  carbonic  acid,  its  bubbles  jvill  be  im- 
mediately dissolved.  When  this  result  is  obtained,  the  coals  which 
effected  the  decomposition  of  the  bicarbonate  of  soda  are  removed, 
and  above  the  orifice  of  the  disengaging-tube  def  a  large  bell-glass 
C  is  placed,  filled  with  mercury,  and  to  the  top  of  which  fifty  or 
sixty  cubic  centimetres  of  a  concentrated  solution  of  potassa  have 
been  passed.  The  coals  are  gradually  moved  toward  the  part  con- 
taining the  organic  matter,  conducting  the  operation  as  in  the  de- 
termination of  carbon  and  hydrogen.  Carbonic  acid,  vapour  of 
water,  nitrogen  and  its  oxides,  are  formed ;  but  the  oxides  of 
nitrogen  are  restored  to  the  state  of  free  nitrogen  while  passing 


S82  ORGANIC   CHEMISTRY. 

through  the  portion  of  the  tuhe  which  contains  metallic  copper,  so 
that  only  a  mixture  of  carbonic  acid  and  nitrogen  reaches  the  bell- 
glass,  in  which  the  carbonic  acid  is  dissolved  by  the  potassa,  while 
the  nitrogen  remains  free.  When  the  combustion  is  terminated, 
the  column  of  pure  oxide  of  copper  which  separates  the  carbonate 
of  soda  from  the  original  mixture  of  oxide  and  organic  matter  is 
surrounded  with  coals ;  and  lastly,  by  again  heating  the  carbonate, 
a  new  evolution  of  carbonic  acid  is  produced,  which  completely 
drives  the  gaseous  products  of  combustion  into  the  bell-glass  C. 

It  now  only  remains  to  measure  exactly  the  nitrogen  gas  col- 
lected, for  which  purpose  the  bell-glass  is  carried  over  a  large 
vessel  filled  with  water,  when,  by  opening  the  orifice  of  the  former, 
the  mercury  contained  in  it  falls  to  the  bottom  of  the  vessel,  and  is 
replaced  by  water.  The  gas  is  poured  into  a  smaller  bell-glass, 
divided  into  cubic  centimetres,  and  held  in  a  vertical  direction  by 
means  of  a  stand,  while  the  water  on  the  inside  and  outside  of  the 
bell-glass  is  brought  to  the  same  level.  When  the  gas  has  attained 
an  equilibrium  of  temperature,  its  volume  Y,  the  temperature  f,  and 
the  height  Ho  of  the  barometer  are  marked,  and  the  weight  of 
nitrogen  gas  attained  is  therefore 

0.0012562  gm.  V ^__  .  E^, 

°  1  + 0.00367. «        760 

It  is  important  to  ascertain  whether  the  gas  contains  no  deutoxide 
of  nitrogen ;  to  which  effect  a  few  bubbles  of  air  are  introduced 
into  the  bell-glass,  when  the  gas  instantly  turns  red  if  it  contains 
any  appreciable  quantity  of  deutoxide.  We  shall  subsequently 
point  out  the  means  of  measuring  nitrogen  more  exactly,  and  of 
accurately  ascertaining  its  purity. 

When  the  nitrous  substance  is  volatile,  the  length  of  the  column 
of  pure  oxide  of  copper  between  the  mixture  of  the  oxide  with  the 
organic  matter,  and  the  bicarbonate  of  soda,  must  be  increased; 
and  before  commencing  the  combustion,  both  the  anterior  part  of 
the  tube  and  the  column  of  pure  oxide  must  be  heated  to  redness. 

Instead  of  placing  at  the  bottom  of  the  tube  the  bicarbonate  of 
soda,  intended  to  disengage  carbonic  acid,  this  end  of  the  tube 
may  be  terminated  by  a  fine  tubulure,  which  is  made  to  communi- 
cate, by  ipeans  of  caoutchouc,  with  an  apparatus  for  disengaging 
carbonic  acid,  in  which  case  the  exhaustion  by  the  air-pump  may  be 
omitted,  because  the  evolution  of  carbonic  acid  is  prolonged  until  all 
the  air  is  driven  out.  When  the  combustion  is  terminated,  the  cur- 
rent of  carbonic  acid  is  re-established,  in  order  to  drive  all  the 
nitrogen  into  the  bell-glass. 

§  1218,  Nitrogen  is  also  dosed  by  another  process,  not  of  so 
general  application  as  the  one  just  described,  because  it  is  not 
adapted  to  the  nitrates,  but  which  yields,  in  the  majority  of  cases, 
exact  results.  This  process  is  founded  on  the  fact  that  nitrous 
substances,  with  the  exception  of  those  containing  nitre  or  nitrous 


INTRODUCTION.  383 

acid,  when  heated  in  contact  with  hydrated  alkalies,  give  off  their 
nitrogen  in  the  state  of  ammonia,  which  can  be  collected  in  an 
acid,  and  determined  in  the  state  of  double  chloride  of  platinum 
and  ammonium.  In  order  to  effect  the  decomposition  of  the  nitrous 
substance,  a  mixture  of  lime  and  hydrated  caustic  soda  is  used, 
which  is  prepared  by  slaking  quicklime  in  a  solution  of  caustic 
soda  containing  a  quantity  of  soda  equal  to  nearly  half  of  that  of 
the  lime  employed,  after  which  the  substance  is  successively  ground, 
dried,  calcined  in  an  earthen  crucible,  again  pulverized,  and  then 
preserved  in  a  close  bottle.  We  shall  call  it,  for  the  sake  of  short- 
ness, 8oda-lime. 

An  accurately  weighed  quantity  of  the  organic  matter  is  mixed 
with  a  certain  quantity  of  soda  lime,  and  placed  at  the  bottom  of 
a  glass  tube  ahc  (fig.  630)  resembling  the  tubes  used  for  the  com- 

*         ^^>^jsjy^Ti-T^^^».-"°^ ;- [„  :;, :;, \,;  ~n         bustion  of  organic  substan- 

"""^         ^Tff  630~^  ^^^  apparatus  A,  contain- 

ing concentrated  chlorohy- 
dric  acid,  is  fitted  to  the  orifice  of  the  tube.  The  tube  is  gradually 
surrounded  by  hot  coals,  as  in  the  ordinary  combustions  of  organic 
substances,  the  ammonia  produced  being  dissolved  in  the  chloro- 
hydric  acid.  When  the  decomposition  is  effected,  the  point  of  the 
combustion-tube  is  broken,  and,  by  blowing  through  the  tube  e  of 
the  bulb  apparatus,  the  ammonia  still  remaining  in  the  tube  is 
driven  into  the  chlorohydric  acid.  The  apparatus  A  is  then  re- 
moved, the  acid  it  contains  poured  into  a  porcelain  capsule,  and 
the  apparatus  washed  several  times  with  a  mixture  of  two  parts  of 
alcohol  and  one  of  ether,  which  is  then  added  to  the  capsule,  into 
which  an  excess  of  bichloride  of  platinum  is  then  introduced,  to 
precipitate  the  ammonia  as  double  chloride  of  platinum  and  am- 
monium. The  precipitate  is  collected  on  a  small  filter,  washed  with 
a  mixture  of  alcohol  and  ether,  and  weighed  after  drying:  one 
gramme  of  double  chloride  of  platinum  and  ammonium  contains 
0.06349  gm.  of  nitrogen. 

This  process  of  decomposition  may  be  modified  so  as  to  obtain  a 
more  rapid,  and  yet  very  exact  analysis,  by  placing  in  the  bulb 
apparatus  ten  cubic  centimetres  of  a  standard  solution  of  sulphuric 
acid,  obtained  by  mixing  61.250  gm.  of  monohydrated  sulphuric  acid 
with  one  litre  of  water ;  so  that  100  cubic  centimetres  of  the  liquid 
will  saturate  2.12  gm.  of  ammonia,  corresponding  to  1.75  gm.  of 
nitrogen.  The  decomposition  of  the  nitrous  substance  is  effected 
in  the  usual  way,  and  the  ammonia  dissolves  in  the  sulphuric  acid  and 
weakens  its  standard.  If,  therefore,  the  new  strength  of  the  liquid 
be  ascertained  after  the  operation,  and  the  strength  of  the  original 
acid  subtracted  from  it,  a  difference  corresponding  to  the  quantity 


384  ORGANIC   CHEMISTRY. 

of  ammonia  absorbed,  and  from  which  the  latter  may  be  deduced 
by  a  very  simple  calculation,  is  obtained. 

The  standard  of  the  acid  liquid  is  determined  by  means  of  a 
solution  of  saccharate  of  lime,  that  is,  a  solution  of  caustic  lime  in 
sugar  and  water,  which  dissolves  a  much  larger  proportion  of  lime 
than  pure  water ;  and  the  solution  may  be  kept  unchanged  in  well- 
stoppered  bottles.  The  first  step  is  to  ascertain  the  number  of  cubic 
centimetres  of  the  alkaline  solution  necessary  to  exactly  saturate 
10  cubic  centimetres  of  the  normal  acid  solution ;  for  which  pur- 
pose the  10  cubic  centimetres  of  normal  acid  solution  are  poured 
into  a  beaker  containing  a  small  quantity  of  tincture  of  litmus ; 
and  then  the  solution  of  saccharate  of  lime  is  added  by  means  of  an 
alkalimeter,  until  the  liquid  turns  blue,  marking  the  number  N  of 
divisions  added.  In  order  to  be  very  accurate,  the  solution  of  lime 
must  be  sufficiently  diluted  for  the  saturation  to  require  about  100 
divisions  of  the  liquid.  The  10  cubic  centimetres  of  the  acid  solu- 
tion, which  have  absorbed  the  ammonia  disengaged  by  the  decom- 
position of  the  nitrous  substance,  are  acted  on  exactly  in  the 
same  manner.  Let  us  suppose  that  n  represents  the  number  of 
divisions  of  saccharate  of  lime  which  have  effected  the  saturation  ; ; 
then  will  0.212  gm.  represent  the  quantity  of  ammonia  absorbed. 
and  ;  0.175  gm.  the  corresponding  quantity  of  nitrogen.* 


*  Bunsen  has  recently  introduced  a  new  method  for  determining  nitrogen, 
which,  on  account  of  its  extreme  exactness,  especially  when  the  substance  is 
very  nitrogenous,  deserves  to  be  described. 

About  5  centigrammes  of  the  substance,  without  being  exactly  weighed,  are  inti- 
mately mixed  with  about  5  grammes  of  fine  oxide  of  copper,  and  a  small  quantity 
of  reduced  copper  filings,  and  introduced  into  a  very  strong  glass  tube,  difficult 
of  fusion,  of  about  5  inches  in  length  and  f  inches  internal  diameter,  one  end  of 
which,  having  previously  been  drawn  out,  is  now  connected  with  an  air-pump, 
after  the  other  end  has  been  sealed,  and  the  air  is  totally  exhausted  from  the 
tube ;  after  which  the  other  end  is  also  hermetically  sealed,  and  both  points  are 
strengthened  in  the  flame  by  thickening  the  glass.  The  tube  thus  prepared  is 
packed  with  plaster  in  a  strong  iron  box,  or  coffin,  the  lid  of  which  is  well  se- 
cured, and  the  whole  is  then  exposed  to  a  strong  white-heat  for  several  hours ; 
when  the  organic  substance  in  the  tube  is  entirely  converted  into  carbonic  acid, 
water,  and  free  nitrogen.  After  cooling,  the  tube  is  taken  out  of  the  iron  box 
and  brought  under  a  graduated  cylinder  filled  with  mercury,  in  a  mercury- 
trough,  where  one  end  of  the  tube  is  broken  ofl^,  and  the  gases,  consisting  only 
of  carbonic  acid  and  nitrogen,  are  allowed  to  pass  up  into  the  cylinder.  The 
exact  volume  of  the  two  gases  being  now  ascertained,  and  reduced  to  the  cor- 
rected volume  at  32°  and  30  inches  pressure,  the  carbonic  acid  is  removed  by 
iabsorbing  it  with  a  bullet  of  caustic  potassa,  fixed  to  the  end  of  a  platinum  wire, 
and  thus  introduced  into  the  gases  through  the  column  of  mecury.  After  all  the 
carbonic  acid  is  absorbed,  which  is  the  case  when  a  diminution  of  volume  no 
longer  ensues,  the  exact  volume  is  again  ascertained  and  reduced  to  32°  and  30 
inches,  when  the  difference  will  give  the  carbonic  acid,  while  the  gas  remaining 
in  the  cylinder,  and  measured,  is  pure  nitrogen. 

The  ratio  of  the  nitrogen  to  the  carbonic  acid,  and  consequently  to  the  carbon 
in  the  organic  substance,  being  thus  obtained,  and  the  carbon  being  previously 
determined  in  the  usual  manner  by  combustion,  the  percentage  of  nitrogen  may 
easily  be  calculated. —  W.  L.  F. 


INTRODUCTION.  385 

DETERMINATION  OF  SULPHUR. 

§  1219.  The  determination  of  the  sulphur  contained  in  organic 
substances  is  frequently  a  matter  of  great  difficulty.  Some  of  these 
substances  are  destroyed  by  contact  with  concentrated  and  boiling 
nitric  acid,  while  the  sulphur  is  converted  into  sulphuric  acid,  which 
is  precipitated  by  the  chloride  of  barium ;  but  as  many  organic  sub- 
stances resist  the  action  of  nitric  acid,  the  sulphur  cannot  always 
in  this  manner  be  converted  into  sulphuric  acid. 

When  the  organic  matter  is  not  volatile,  it  is  mixed  with  20  or 
25  times  its  weight  of  a  mixture  of  nitre  and  carbonate  of  soda,  and 
the  mixture  is  thrown,  by  small  quantities  at  a  time,  into  a  platinum 
crucible  heated  to  redness  by  an  alcohol-lamp.  The  alkaline  sub- 
stance is  then  dissolved  in  water,  supersaturated  by  chlorohydric 
acid,  and  the  sulphuric  acid  precipitated  by  chloride  of  barium. 

If  the  organic  substance  is  volatile  these  processes  are  inapplicable, 
and  the  operation  is  then  conducted  as  follows,  by  a  method  w^hich 
suits  all  cases : — The  organic  matter  is  subjected  to  combustion 
with  oxide  of  copper,  as  in  the  determination  of  carbon  and  hydro- 
gen, with  the  exception  that  the  combustion-tube  is  provided  only 
with  the  bulb  apparatus  (fig.  631)  containing  a  solution  of  caustic 

-aw . ^ ^j^^____^j^  potassa.      The  greater  part  of 

the  sulphur  is  converted  into 
sulphuric  and  sulphurous  acid, 
^^'       '  which   dissolve   in  the  potassa, 

while  a  portion  of  the  sulphur,  nevertheless,  remains  in  the  combus- 
tion-tube in  the  state  of  sulphide  and^ulphate  of  copper.  The  tube, 
after  being  allowed  to  cool,  is  broken,  and  the  pieces  of  glass  and 
the  oxide  are  thrown  into  a  flask,  where  they  are  boiled  with  a 
weak  solution  of  caustic  potassa,  which  completely  removes  the 
sulphur  and  sulphuric  acid.  The  liquid  is  filtered,  and  the  potassa 
in  the  bulb  apparatus  is  added  to  the  filtrate,  which  is  then  boiled, 
and  treated  with  a  current  of  chlorine,  which  transforms  all  the 
sulphur  into  sulphuric  acid.  The  solution  is  supersaturated  by 
chlorohydric  acid,  and  the  sulphuric  acid  precipitated  by  chloride 
of  barium. 

DETERMINATION  OF  PHOSPHORUS. 
§  1220.  When  the  phosphuretted  organic  matter  is  not  volatile, 
it  is  mixed  with  20  or  25  times  its  weight  of  a  mixture  of  carbonate 
of  soda  and  nitre,  and  the  mixture  is  thrown,  by  small  portions,  into 
a  heated  platinum  crucible,  where  the  phosphorus  passes  into  the 
phosphate  of  soda.  The  alkaline  substance  is  dissolved  in  water, 
saturated  with  chloroLydric  acid,  and  then  1  gramme  of  pure  iron 
dissolved  in  aqua  regiia,  is  added  to  the  solution.  Lastly,  the  ses- 
quioxide  of  iron  combined  with  phosphoric  acid  is  precipitated  by 
an  excess  of  ammonia;  and  by  subtracting  from  the  weight  of  this 
precipitate  the  weight  of  the  sesquioxide  of  iron  produced  by  1  gm. 

Vol.  II.— 25 


386  ORGANIC   CHEMISTRY. 

of  pure  iron,  the  weight  of  the  phosphoric  acid  is  obtained,  whence 
that  of  the  phosphorus  may  bp  deduced.  If  the  substance  is  volatile, 
it  is  first  decomposed  by  carbonate  of  soda  in  a  combustion-tube, 
and  then  dissolved  in  water,  the  analysis  being  completed  as  in  the 
preceding  case. 

DETERMINATION  OF  CHLORINE,  BROMINE,  AND  IODINE. 

§  1221.  No  organic  substances  have  as  yet  been  found  in  nature 
containing  chlorine,  bromine,  or  iodine,  but  a  great  number  of  them 
have  been  artificially  produced  in  the  laboratory.  The  determina- 
tion of  these  elements  is  very  easily  made  by  heating  the  organic 
matter  in  a  combustion-tube,  in  contact  with  quicklime,  obtained  by 
slaking  ordinary  quicklime,  washing  it  with  water  to  remove  chlorides 
arising  from  the  ashes  of  the  combustible  with  which  the  limestone 
was  originally  burned,  and  then  heating  it  to  redness  in  order  to 
expel  the  water  from  the  hydrated  lime.  The  lime  thus  prepared 
is  preserved  in  a  grqund-stoppered  bottle. 

If  the  organic  substance  is  solid  and  not  volatile,  it  is  mixed  with 
a  certain  quantity  of  quicklime,  and  the  mixture  is  introduced  into 
the  combustion-tube  which  is  to  be  filled  with  pure  lime ;  but  if  the 
substance  is  liquid  and  volatile,  it  is  weighed  in  the  glass  bubbles 
before  mentioned,  which  are  dropped,  after  breaking  their  point, 
to  the  bottom  of  the  tube,  which  is  afterward  filled  with  lime.  The 
decomposition  of  the  substance  by  heat  should  be  efi*ected  with  the 
same  precautions  as  combustion  by  the  oxide  of  copper.  The 
chlorine,  bromine,  or  iodine  remain  in  the  tube  in  the  state  of  chlo- 
ride, bromide,  or  iodide  of  calcium.  At  the  close  of  the  operation, 
the  lime,  together  with  the  fragments  of  the  tube,  is  dropped  into  a 
flask,  where  it  is  treated  with  weak  nitric  acid  until  the  lime  is  en- 
tirely dissolved.  The  liquid  is  then  filtered,  and  precipitated  by 
nitrate  of  silver ;  the  process  indicated  in  §  1131  being  followed  in 
order  to  collect  and  wash  the  chloride  of  silver. 

The  determination  of  iodine  is,  however,  rather  more  difficult,  as 
a  portion  of  this  substance  often  passes  into  the  state  of  iodic  acid, 
which,  however,  is  destroyed  by  passing  a  current  of  sulphurous 
acid  through  the  liquid  at  a  moderate  temperature,  after  having 
added  nitrate  of  silver  to  it. 

DETERMINATION  OF  OXYGEN. 

§  1222.  The  oxygen  contained  in  organic  substances  is  always 
determined  differentially,  as,  hitherto,  a  suitable  process  of  direct 
determination  has  not  been  discovered.  It  will  hence  be  seen  how 
important  it  is  to  ascertain,  with  the  greatest  care,  the  nature  of  the 
elements  composing  the  organic  substance ;  for  if  a  single  element 
escapes  the  experimenter,  the  analysis  is  inaccurate,  not  only  on 
account  of  the  omission  of  the  element  which  was  overlooked,  but 


INTRODUCTION.  387 

also  because  the  weight  of  the  elementary  substance  neglected  is 
computed  as  oxygen. 

ESTABLISHMENT  OF  THE  CHEMICAL  FORMULA  OP  AN  ORGANIC 
SUBSTANCE. 

§  1223.  The  elementary  analysis  of  an  organic  substance  is  not 
alone  sufficient  to  establish  its  chemical  formula,  because  it  indicates 
only  the  ratios  which  exist  between  the  weight  of  the  elements  which 
compose  it ;  and  as  an  infinite  number  of  formulae,  the  multiples  of 
each  other,  will  all  satisfy  the  ratios  given  by  analysis,  the  question 
is,  which  of  these  formulae  to  choose.  By  studying  the  various  com- 
binations which  the  organic  substance  can  form  with  mineral  sub- 
stances, and  the  new  organic  compounds  to  which  they  give  rise 
when  subjected  to  the  various  processes  of  the  laboratory,  the 
chemist  can  generally  collect  facts  from  which  a  formula  may  be 
deduced ;  and  it  is  only  when  the  substance  has  been  studied  under 
all  its  aspects,  and  in  the  case  that  it  forms  a  great  number  of  com- 
pounds, that  its  formula,  and,  consequently,  its  chemical  equivalent, 
presents  any  degree  of  certainty.  The  numerous  changes  which, 
in  latter  years,  the  formulae  of  organic  compounds  have  undergone 
will  therefore  not  appear  surprising,  being  occasioned  by  the  dis- 
covery of  new  compounds,  or  new  chemical  reactions,  which  deprive 
the  formulae  adopted  of  the  character  of  probability  they  had  ac- 
quired from  the  facts  previously  known. 

As  it  is  impossible  to  advance  any  general  rules  for  the  establish- 
ment of  the  formula  of  an  organic  compound,  we  shall  only  cite  a 
few  examples,  to  show  the  spirit  which  governs  such  researches. 
"We  shall  distinguish  three  cases :  1st,  that  in  which  the  organic 
substance  is  acid ;  2dly,  that  in  which  it  possesses  basic  properties ; 
and  3dly,  that  in  which  the  organic  substance  is  neutral. 

CASE  IN  WHICH  THE  ORGANIC  SUBSTANCE  IS  ACID. 

§  1224.  As  the  first  example,  we  shall  take  acetic  acid,  which 
contains  only  carbon,  hydrogen,  and  oxygen. 

At  its  maximum  point  of  concentration,  acetic  acid  is  a  colourless 
and  volatile  liquid,  which,  by  combustion  with  oxide  of  copper,  yields 
the  following  composition  :* 

Hydrogen 6.67 

Carbon 40.00 

Oxygen 53.33 

100.00 

Dividing  the  weight  of  each  of  these  elements  by  its  equivalent, 
the  quotients  will  necessarily  be  to  each  other  as  the  equivalent 

*  In  order  to  render  our  arguments  more  simple,  we  shall  always  suppose  that 
the  results  of  the  direct  analyses  are  scrupulously  exact. 


388  ORGANIC   CHEMISTRY. 

numbers  of  the  simple  elements  which  enter  into  the  compound,  and 
we  thus  obtain  : 

For  hydrogen ^  =  6.67 

"    carbon ^•:^  =  6.67 

"    oxygen W  =  ^.67 

These  quotients  being  equal,  we  shall  conclude  that  concen- 
trated acetic  acid  contains  equal  numbers  of  each  of  the  three 
elements  which  compose  it,  and  the  most  simple  formula  which  can 
represent  the  acid  is  therefore  CHO ;  while  it  is  evident  that  the 
formulae  C3H3O3,  C3H3O3,  C^H^O^,  G^Kfi^  represent  equally  the  re- 
sults of  the  analysis.  On  the  other  hand,  we  have  seen  that  the 
greater  part  of  the  mineral  acids,  when  brought  to  their  maximum 
of  concentration  without  any  essential  change  in  their  chemical  pro- 
perties, are  compounds  of  the  anhydrous  acid  with  one  or  several 
equivalents  of  water,  which  can  be  replaced  by  a  corresponding  num- 
ber of  equivalents  of  a  base,  and  it  must  therefore  be  ascertained 
whether  this  is  the  case  also  with  acetic  acid.  Moreover,  we  have 
seen,  in  the  case  of  the  mineral  acids,  that  the  knowledge  of  the 
composition  of  a  salt  formed  by  the  acid  and  a  mineral  base  of 
which  the  chemical  equivalent  had  been  previously  ascertained,  fre- 
quently gives  the  equivalent  of  the  acid  itself,  and  is  sufficient  to 
establish  its  formula.  However,  the  example  of  phosphoric  acid 
has  shown  that  the  same  base  frequently  forms  several  salts  with 
the  same  acid,  and  that  it  is  not  sufficient,  to  establish  the  formula 
of  the  acid,  to  determine  the  composition  of  one  of  these  salts,  be- 
cause the  formula  would  vary  with  the  salt  selected.  It  therefore 
becomes  necessary  to  determine  the  composition  of  all  the  salts, 
either  in  the  crystallized  state,  or  after  having  dried  them  as  much 
as  possible,  always  avoiding  such  a  change  in  their  chemical  consti- 
tution that  the  dried  salt,  when  redissolved  in  water,  will  not  pro- 
duce the  original  salt  by  crystallization.  The  study  of  these  va- 
rious compounds  furnishes  a  clue  as  to  whether  the  salt  should  be 
regarded  as  monobasic,  bibasic,  tribasic,  &c.,  and  thus  give  the  ele- 
ments necessary  to  establish  its  formula.  The  same  method  must 
be  observed  in  establishing  the  formulae  of  organic  acids ;  and  we 
thereupon  proceed  to  apply  it  to  acetic  acid. 

Protoxide  of  silver  is  distinguished  among  mineral  bases  by  the 
property  of  forming  immediately  anhydrous  salts,  which  are  in 
most  cases  easily  obtained  in  a  state  of  purity,  being  generally  inso- 
luble, or  nearly  so ;  for  which  reasons  salts  of  silver  are  very  valu- 
able in  ascertaining  the  composition  of  organic  acids,  and  the  more 
80  as  their  analysis  can  be  made  with  great  accuracy.  We  shall 
therefore  analyze  the  acetate  of  silver,  for  which  purpose  an  accu- 
rately weighed  quantity  of  the  salt  is  roasted  in  a  platinum  cruci- 
ble, when,  the  organic  matter  being  destroyed,  metallic  silver  re- 


INTRODUCTION.  389 

mains,  which  is  weighed.  The  proportion  of  protoxide  of  silver  to 
which  it  corresponds  is  then  calculated,  and  the  result  will  be  that 
acetate  of  silver  is  composed  of 

Oxide  of  silver 69.45 

Acetic  acid 30.55 

100.00 

Admitting  that  acetic  acid  is  monobasic,  that  acetate  of  silver  is 
anhydrous  and  formed  of  1  equivalent  of  oxide  of  silver  (116.0)  and 
1  equivalent  of  acetic  acid,  the  equivalent  of  acetic  acid  will  be  de- 
duced from  the  proportion : 

69.45 :  30.55 : :  116.0  :  x  whence  x  =  51.0. 
Now,  there  is  only  one  way  of  forming  the  number  51.0  with 
whole  numbers  of  equivalents  of  hydrogen,  carbon,  and  oxygen, 
and  that  is  by  giving  to  anhydrous  acetic  acid  the  formula  C^ELOj, 
and  consequently,  to  concentrated  acetic  acid,  the  formula  C4H3O3 
+H0,  which  satisfies  the  analysis  we  have  given  of  this  acid.  We 
have,  in  fact, 

3  eq.  of  hydrogen 3.0 

4  "        carbon 24.0 

3    "        oxygen 24^ 

51.0 

It  is,  moreover,  easy  to  ascertain  that  such  is,  in  reality,  the  com- 
position of  the  acetic  acid  contained  in  the  acetate  of  silver.  By 
burning  this  salt  with  oxide  of  copper,  it  will  be  found  to  contain 

Oxide  of  silver 69.45 

Hydrogen 1.80 

Carbon 14.37 

Oxygen 14.38 

100.00 
Now,  the  formula  AgOjC^HgOj  gives 

1  eq.  of  oxide  of  silver 116.0  69.45 

3  "                       hydrogen 3.0  1.80 

4  "                       carbon 24.0  14.37 

3   "                      oxygen 24.0  14.38 

167,0  100.00 

But  acetic  acid  might  possibly  be  bibasic,  and  the  salt  of  silver 
contain  2  equivalents  of  oxide  of  silver ;  in  which  case  the  formula 
of  the  salt  would  be  2AgO,C3HgOg,  that  of  the  concentrated  acetic 
acid  CgHgOg+2HO,  and  the  equivalent  of  anhydrous  acetic  acid 
would  be  102.0.  The  acetic  acid  might  be  tribasic,  and  the  formula 
of  acetate  of  silver  3AgO,Ci3Hg09,-that  of  the  concentrated  acetic 


390  ORGANIC   CHEMISTRY. 

acid  CjaHgOg+SHO,  and  the  equivalent  of  the  anhydrous  acetic 
acid  might  be  153.0. 

Now,  when  an  acid  is  bibasic,  it  forms  two  series  of  salts  with 
bases :  salts  which  contain  2  equivalents  of  base  2R0,  and  salts 
containing  1  equivalent  of  base  RO,  and  1  equivalent  of  basic 
water.  If,  therefore,  acetic  acid  were  bibasic,  two  series  of  acetates 
would  be  obtained : 

1st  series 2nO,CJlfi^, 

2d  series (R0+H0),C3He09; 

and  the  salts  of  the  second  series  could  not  lose  their  equivalent  of 
basic  water,  without  a  great  change  in  their  properties. 

If  the  acetic  acid  were  tribasic,  it  should  form  three  series  of 
salts : — 

1st  series SROjC^^HgOg, 

2d      "    (2R0+H0),C,,H,0„     • 

3d      "     (R04-2HO),C,A06; 

and  the  salts  of  the  two  last  series  again  could  not  part  with  their 
water  without  an  important  modification  of  their  properties. 

In  order  to  decide  the  question,  it  is  therefore  necessary  to  pre- 
pare a  great  number  of  acetates,  dry  them  as  much  as  possible, 
without  affecting  their  chemical  constitution,  that  is,  in  such  a  man- 
ner that  the  dried  acetate,  redissolved  in  water,  shall  reproduce  the 
original  salt  hy  crystallization ;  and  lastly,  subject  these  acetates 
to  analysis.  It  will  thus  be  found  that  several  of  these  crystallized 
acetates  contain  water  ;  but  this  should  be  considered  as  their  water 
of  crystallization,  as  it  may  be  driven  off  by  heat,  and  the  dried 
salt,  dissolved  in  water,  reproduces,  by  crystallization,  the  original 
salt.  The  dried  salts  will  present  the  composition  given  by  the 
formulae  R0,C^H303,  2RO,C,HgOe,  3R0,C,3H,05,  &c. ;  and  there 
being  consequently  no  reason  for  regarding  acetic  acid  as  polybasic, 
it  is  considered  as  a  monobasic  acid,  and  the  formula  C^HgOj  has 
been  adopted  as  that  of  the  anhydrous  acid. 

§  1225.  For  the  second  example  in  establishing  the  formula  of  an 
organic  acid,  we  shall  choose  malic  acid,  which,  when  crystallized, 
is  composed  as  follows : 

Hydrogen 4.48 

Carbon 35.82 

Oxygen 59.70 

100.00 

Dividing  the  preceding  numbers  by  their  respective  equivalents, 
there  results : 


INTRODUCTION.  891 

For  hydrogen ii?  =  4.48 

"    carbon ^^  =  5.97 

"   oxygen ^f  =  7.46 

The  quotients  follow  the  ratios  of  the  numbers  3:4:  5 ;  and  the 
most  simple  formula  adapted  to  crystallized  malic  acid  is  therefore 
C4H3O5,  while  the  true  formula  may  be  one  of  the  multiples 
CsHeO,,,  C,,H,0,3,  C,,H,,0^,  etc.,  etc. 

The  analysis  of  malate  of  silver  shows  that  this  salt  contains  : 

Oxide  of  silver 66.67 

Malic  acid 33.33 

100.00 
This  salt  does  not  give  off  water  before  decomposing,  which  leads 
to  the  supposition  that  it  is  anhydrous ;  and  if  it  be  regarded  as 
formed  of  1  equivalent  of  oxide  of  silver  and  1  equivalent  of  malic 
acid,  the  equivalent  of  malic  acid  will  therefore  be  deduced  from  the 
proportion : 

66.67  :  33.33 :  :  116.0 :  x,  whence  a;=58 

The  combustion  of  the  silver  salt  with  oxide  of  copper  gives  for 
its  composition : 

Hydrogen 1.15 

Carbon 13.79 

Oxygen 18.39 

Oxide  of  silver ^ 66.67 

100.00 

which  exactly  corresponds  to  that  given  by  the  formula  AgO,C4H204, 

as  may  be  readily  seen : 

2  eq.  of  hydrogen 2.0)  1.15 

4"         carbon 24.0^58.0 13.79 

4"         oxygen 32.0J  18.39 

1  "         oxide  of  silver. ..116.0 66.67 

174.0  100.00 

The  formula  of  crystallized  malic  acid  will  therefore  be  C^HgO 
+H0 ;  but  it  remains  to  be  seen  whether  the  acid  is  monobasic,  in 
which  case  the  formula  of  the  crystallized  acid  would  be  C^HgO^H- 
HO,  and  that  of  malate  of  silver  AgOjC^HgO^ ; 

Or,  whether  it  is  bibasic,  which  would  give  to  malate  of  silver 
the  formula  2AgO,C8H  0  ,  and  to  the  crystallized  acid  the  formula 
C3H,03+2H0; 

Or  lastly,  whether  it  is  tribasic,  in  which  case  the  formula  of 
malate  of  silver  would  be  3AgO,0i3HgO,3,  and  that  of  the  crystal- 
lized acid  C,,H80,3+3HO. 


392  ORGANIC   CHEMISTRY. 

In  order  to  decide  the  question,  other  salts  formed  by  malic  acid 
must  be  analyzed.     Now,  two  malates  of  lime  are  known : 

The  formula  of  the  first  in  the  crystallized  state  is  C&OjCJI^fi^^, 
"  second  "  "         CaO,C,H,0^. 

The  first  salt  loses  6H0  by  the  action  of  heat,  without  change ; 
for,  when  dissolved  in  water,  it  reproduces  the  original  salt  by  crys- 
tallization ;  and  the  formula  of  the  dried  salt  is  therefore  CaO,Cg 
H5O9,  which  may  be  written  CaiO,2{G^Iifi^)-\-B.O,  in  which  case  it 
is  considered  as  a  bimalate  of  lime  containing  1  eq.  of  water  of 
crystallization.  But  as  this  water  cannot  be  driven  off  without 
injury  to  the  salt,  it  must  be  regarded  as  basic  water,  and  the 
formulae  of,  the  malates  of  lime  must  be  written, 

1st  malate 2CaO,C3H^08. 

2dmalate (Ca0+H0),C,H,03. 

In  this  case,  malic  acid  is  considered  as  a  bibasic  acid. 

An  examination  of  the  other  malates  leads  to  the  same  conclusion. 
Thus,  oxide  of  zinc  forms  two  malates,  the  composition  of  which,  in 
the  crystallized  state,  is  represented  by  the  following  formulae  : 

1st  malate ZnO,C^H,Oy, 

2d  malate ZnO,C3H30,3, 

which,  when  subjected  to  the  action  of  heat,  lose  a  portion  of  their 
water  without  change,  and  become, 

The  1st ZnO,C^H,0^. 

The  2d : ZnO,C3H30,. 

If  they  be  further  heated,  they  again  lose  water,  but  are  altered. 
The  formulae  of  dried  malates  of  zinc  become  very  simple,  and 
similar  to  those  of  malates  of  lime,  if  the  malic  acid  be  regarded  as 
bibasic,  in  which  case  they  are, 

2ZnO,C3H,03. 

(ZnO+HO),C,HA. 

Again,  a  malate  of  ammonia  is  known  which  crystallizes  readily  in 
beautiful  crystals,  and  shows  the  formula  (NH3,H0),C8H^0g+H0. 
But  as  this  salt  does  not  lose  water  by  heat  before  attaining  a 
temperature  at  which  it  is  completely  altered,  the  water  it  contains 
is  therefore  basic,  and  its  formula  should  be  written  (NH3HO+HO) 

All  these  considerations  must  lead  us  to  regard  malic  acid  as  a 
bibasic  acid,  forming  two  series  of  salts,  of  which  the  formulae  are 
2I10,C3H,03  and  (RO+HO),C,H,0,. 

§1226.  An  argument  of  the  same  nature,  founded  on  the  composition 
of  the  various  series  of  salts  which  the  organic  acid  can  form  with  the 


INTRODUCTION. 

same  base,  after  the  salts  have  been  dried  as  far  as  their  chemical 
constitution  will  permit,  will  decide  if  it  be  proper  to  regard  this 
acid  as  a  tribasic  acid,  in  which  case  three  series  of  salts  will  in 
general  be  obtained,  which  may  be  represented  by  the  following 
formulae,  the  symbol  A  designating  the  equivalent  of  the  tribasic  acid : 
3R0,A,  (2R0+H0),A,  (R0+2H0),A. 
The  crystallized  salts  may  contain,  in  addition,  water  of  crystal- 
lization, which  will  be  recognised  by  the  fact  that  in  most  cases  it 
can  be  driven  off  by  heat,  without  altering  the  constitution  of  the 
salt. 

DETERMINATION  OF  THE  PROPORTION  OF  BASE  WHICH  EXISTS  IN 
COMBINATION  WITH  AN  ORGANIC  ACID. 

§  1227.  In  order  to  establish  with  any  degree  of  certainty  the 
equivalent  of  an  organic  acid,  it  is  necessary,  as  has  been  shown,  to 
analyze  a  great  number  of  the  salts  which  it  forms  with  mineral 
bases ;  and  it  is  consequently  useful  to  dwell  for  a  short  time  on  the 
processes  employed  by  chemists  for  this  purpose. 

The  proportion  of  base  which  exists  in  a  salt  formed  by  an 
organic  acid  is  almost  always  determined  by  calcining  the  salt  in  the 
air,  when  the  mineral  base  remains,  either  in  the  metallic  state  after 
the  decomposition  by  heat,  or  in  a  state  of  superior  oxidation,  when  it 
absorbs  oxygen  from  the  air ;  or  lastly,  in  the  state  of  carbonate, 
when  the  salt  is  not  decomposed  by  the  degree  of  heat  at  which  the 
incineration  took  place.  If  the  organic  acid  contains  sulphur  or  phos- 
phorus, the  base  may  remain  partly  in  the  state  of  sulphate  or 
phosphate  ;  and  if  it  contains  chlorine,  bromine,  or  iodine,  a  portion 
or  the  whole  of  the  base  may  be  converted  into  chloride,  bromide, 
or  iodide. 

The  salts  formed  by  the  organic  acids  with  the  alkalies,  leave 
after  calcination  an  alkaline  carbonate ;  but  the  base  is  never 
determined  in  this  state,  because  alkaline  carbonates  attract  too 
readily  the  moisture  of  the  air.  They  are  converted  into  sulphates 
by  pouring  into  the  crucible  in  which  the  incineration  has  been 
effected  a  weak  solution  of  sulphuric  acid,  taking  care  that  the 
effervescence  produced  does  not  project  any  of  the  substance  out  of 
the  crucible.  It  is  evaporated  to  dryness ;  and  lastly,  the  crucible 
is  heated  to  a  strong  red-heat,  in  order  to  decompose  the  bisulphate 
which  has  formed,  when  the  weight  of  the  base  is  deduced  from  that 
of  the  sulphate. 

When  the  organic  salt  contains  baryta  or  strontia,  the  base 
remains  in  the  state  of  carbonate,  and  may  be  weighed  as  such ; 
and  if  it  contains  lime,  the  base  still  remains  in  the  state  of  carbon- 
ic, if  the  incineration  has  been  effected  at  a  low  temperature  ;  but 
if  the  calcination  has  required  a  red-heat,  the  greater  portion  of 
the  base  passes  into  the  state  of  quicklime.     The  base  may  still  in  this 


394  ORGANIC   CHEMISTRY. 

case  be  determined  as  carbonate,  if  the  precaution  is  taken  to  moisten 
the  matter,  after  roasting,  with  a  solution  of  carbonate  of  ammonia, 
which  is  then  evaporated  at  a  gentle  heat.  It  is  better  to  weigh 
the  lime  in  the  state  of  sulphate,  to  which  effect  the  residue  is 
moistened  after  incineration  with  sulphuric  acid,  and,  after  having 
driven  off  the  excess  of  acid  by  heat,  the  crucible  is  heated  to  red- 
ness. The  determination  of  magnesia  in  the  state  of  sulphate 
should  be  performed  in  the  same  manner. 

If  the  base  combined  with  the  organic  acid  be  protoxide  or  ses- 
quioxide  of  iron,  the  salt  is  roasted  in  the  air ;  and  in  order  to  be 
sure  that  the  residue  is  composed  only  of  sesquioxide  of  iron,  it  is 
moistened  with  nitric  acid,  and  again  calcined ;  a  similar  process 
being  applicable  to  salts  of  copper,  in  which  case  protoxide  of  cop- 
per CuO  remains.  Zinc,  combined  with  an  organic  acid,  is  also 
determined  in  the  state  of  oxide  ZnO ;  but  the  roasting  must  be 
commenced  at  the  lowest  temperature  possible,  in  order  not  to  pro- 
duce metallic  zinc,  a  portion  of  which  might  be  lost  in  the  state  of 
vapour ;  and  the  roasted  matter  is  moistened  with  a  small  quantity 
of  nitric  acid,  and  calcined  to  redness. 

The  determination  of  manganese  combined  with  an  organic 
acid  presents  some  difficulties,  because  the  composition  of  the 
oxide  which  remains  after  the  calcination  is  never  exactly  known. 
The  salt  being  first  calcined  in  a  small  platinum  boat,  in  order  to 
destroy  the  organic  matter,  the  boat  is  introduced  into  a  porcelain 
tube  heated  to  redness,  and  traversed  by  a  current  of  hydrogen  gas, 
which  is  maintained  until  the  tube  is  completely  cooled ;  when  the 
boat,  which  then  contains  non-pyrophoric  protoxide  of  manganese, 
is  removed. 

As  the  compounds  of  the  organic  acids  with  cobalt  and  nickel 
leave  oxides  after  incineration,  the  composition  of  which  is  always 
uncertain,  it  is  best  to  roast  the  salt  in  a  platinum  boat,  and  then 
heat  it  in  a  porcelain  tube  in  a  current  of  hydrogen,  when  the  pla- 
tinum contains  the  reduced  metal,  which  is  not  pyrophoric  if  the 
calcination  has  been  effected  at  a  sufficiently  high  temperature. 

The  incineration  of  salts  formed  by  the  organic  acids  with  oxides 
of  chrome  leaves  pure  sesquioxide  of  chrome,  which  can  be  imme- 
diately weighed. 

By  incinerating  the  salts  formed  by  protoxide  of  lead  with 
organic  acids,  the  metal  frequently  remains  in  the  state  of  protoxide, 
although  a  portion  of  the  oxide  of  lead  is  also  frequently  reduced  to 
the  metallic  state,  so  that  it  is  better  never  to  make  these  incine- 
rations in  platinum  vessels,  because  they  might  be  greatly  injured. 
They  are  performed  in  porcelain  capsules  heated  by  an  alcohol- 
lamp,  so  as  not  to  attain  the  point  of  fusion  of  oxide  of  lead,  which 
in  the  fused  state  would  attack  the  glazing  of  the  porcelain.  After 
incineration,  concentrated  nitric  acid  is  poured  into  the  saucer, 
which  disengages  reddish  vapours  if  the  substance  contains  metallic 


INTRODUCTION.  395 

lead.  The  acid  is  gently  evaporated,  and  the  residue,  which  is 
composed  of  pure  protoxide  of  lead,  is  calcined  at  a  dull  red- 
heat.  The  capsule  may  also  be  weighed  after  incineration,  and 
acetic  acid  afterward  poured  into  it,  which  dissolves  the  oxide  of 
lead,  and  separates  the  metallic  lead  which  remains  in  the  form  of 
small  globules.  The  globules  are  washed  several  times,  by  decant- 
ation,  in  the  capsule,  which  is  then  dried  at  a  gentle  heat ;  the 
latter  is  then  weighed  a  second  time,  when  the  difference  gives  the 
weight  of  oxide  of  lead  formed  in  the  roasted  matter.  By  weigh- 
ing the  capsule  a  third  time,  and  subtracting  this  weight  from  that 
obtained  by  the  second  weighing,  the  quantity  of  lead  reduced  is 
found,  which  is  to  be  converted  into  oxide,  by  calculation. 

Lastly,  the  oxide  of  lead  may  be  determined  in  the  state  of 
sulphate,  in  which  case,  the  incinerated  matter  is  moistened  with 
nitric  acid,  which  is  evaporated,  and  then  with  sulphuric  acid,  which 
transforms  the  nitrate  into  a  sulphate..  The  excess  of  sulphuric  acid 
being  evaporated,  the  sulphate  is  calcined  to  redness. 

Oxide  of  bismuth  is  determined  in  the  state  of  oxide  BiOg,  and 
protoxide  of  tin  in  the  state  of  stannic  acid  SnO^,  the  operation 
being  conducted  as  in  the  case  of  oxide  of  lead ;  that  is,  the  sub- 
stance is  incinerated  in  a  porcelain  capsule,  and  the  residue,  after 
being  moistened  with  nitric  acid,  is  calcined  after  the  evaporation 
of  the  acid. 

The  exact  determination  of  oxide  of  antimony  is  very  difficult. 
The  best  method  consists  in  roasting  the  salt  in  a  porcelain  crucible, 
and,  when  the  organic  matter  is  burned,  to  cover  the  crucible  with 
a  lid  having  a  hole  in  the  centre,  through  which  is  passed  the  end 
of  a  disengaging-tube  which  conveys  dry  hydrogen  into  the  crucible ; 
when  by  heating  the  latter  to  redness,  the  oxide  of  antimony  is  re- 
duced to  the  metallic  state.  The  current  of  hydrogen  is  maintained 
until  the  crucible  is  completely  cooled,  after  which  the  metallic  an- 
timony is  weighed. 

The  salts  formed  by  the  protoxide  and  sesquioxide  of  uranium 
leave,  after  roasting,  an  oxide  of  uranium,  the  composition  of  which 
is  uncertain ;  but  if  the  residue  be  calcined,  at  a  strong  red-heat, 
by  placing  the  platinum  crucible  which  contains  it  in  an  earthen 
crucible  heated  in  a  charcoal  fire,  the  oxide  2U0,U303  (§  1025) 
remains,  although  it  is  better  to  restore,  by  means  of  hydrogen,  the 
oxide  of  uranium  to  the  state  of  protoxide,  by  operating  as  was  stated 
for  manganese. 

The  quantity  of  oxide  of  silver  found  in  combination  with  an 
organic  acid  may  be  very  accurately  ascertained  by  simple  incine- 
ration, which  leaves  the  silver  in  the  metallic  state.  If  the  salt  of 
silver  is  soluble,  it  may  be  dissolved  in  water  and  the  silver  precipi- 
tated in  the  state  of  chloride,  in  which  case  a  standard  solution  of 
common  salt  may  also  be  used,  and  the  process  explained  in  §  1144 
adopted. 


396  ORGANIC   CHEMISTRY. 

Incineration  also  gives  exactly  the  platinum  contained  in  the 
salts  formed  by  organic  acids,  when  metallic  platinum  remains,  from 
which  the  quantity  of  oxide  may  be  deduced  by  calculation. 

Salts  formed  by  the  organic  acids  with  oxides  of  mercury  are 
analyzed  by  the  general  process  described  §  1107. 

The  ammonia  combined  with  an  organic  acid  is  generally  inferred 
from  the  quantity  of  nitrogen  yielded  by  the  ammoniacal  salt  in  its 
combustion  with  oxide  of  copper,  (§§  1217  and  1218,)  although  this 
base  may  be  directly  determined  in  the  state  of  double  chloride  of  pla- 
tinum and  ammonia,  as  in  the  case  of  ammoniacal  salts  formed  by  the 
mineral  acids ;  for  which  purpose  the  ammoniacal  salt  is  dissolved 
in  a  small  quantity  of  water,  and  a  slight  excess  of  bichloride  of 
platinum  is  added,  when,  after  evaporating  to  dryness  at  a  gentle 
temperature,  and  washing  the  residue  with  a  mixture  of  alcohol  and 
ether,  the  double  chloride  of  platinum  and  ammonia  is  obtained 
isolated.  Lastly,  the  ammoniacal  salt  may  be  destroyed  by  sodic 
lime  at  a  red-heat,  the  ammonia  collected  in  an  acid  solution,  and 
the  base  determined  by  one  of  the  two  methods  described  in  §§  1217 
and  1218. 

§  1228.  The  processes  just  described  are  applicable  with  absolute 
exactness  only  when  the  organic  acid  contains  carbon,  hydrogen, 
oxygen,  and  nitrogen  alone,  and  their  results  would  be  frequently 
inaccurate  if  the  acid  contained,  in  addition,  sulphur,  phosphorus, 
or  chlorine. 

If  the  acid  contains  sulphur,  the  processes  described  may  be  em- 
ployed whenever  the  sulphate  of  the  metallic  oxide  is  easily  decom- 
posed by  heat,  and  the  metallic  sulphide  is  quickly  changed  into 
oxide  by  roasting ;  but  in  every  other  case  some  of  the  processes 
spoken  of  would  give  inexact  results.  When  the  base  of  the  salt  is 
an  alkaline  or  alkalino-earthy  oxide,  or  oxide  of  lead,  it  is  sufficient 
to  heat  the  incinerated  substance  with  sulphuric  acid,  when  the  base 
remains  in  the  state  of  sulphate,  which  is  weighed.  If  the  oxide 
forms  a  sulphate  readily  decomposable  at  a  red-heat,  the  residue 
after  roasting  is  calcined  at  this  temperature,  after  having  been 
treated  with  a  small  quantity  of  nitric  acid,  to  prevent  the  presence 
of  a  metallic  sulphide,  which  might  injure  the  platinum  crucible. 
In  all  cases  it  is  prudent  to  moisten  the  substance,  after  calcina- 
tion, with  a  small  quantity  of  carbonate  of  ammonia,  evaporate  and 
recalcine  it,  by  which  means  the  last  traces  of  sulphuric  acid  are 
more  easily  driven  off. 

If  the  organic  acid  contains  phosphorus,  all  the  processes  de- 
scribed are  faulty,  and,  in  order  to  determine  the  oxide,  the  processes 
by  the  humid  way,  described  under  the  head  of  each  metal,  must  be 
adopted. 

Lastly,  if  the  organic  acid  contains  chlorine,  bromine,  or  iodine, 
it  is  often  necessary  to  modify  the  ordinary  processes.  When  the 
base  combined  with  the  organic  acid  is  an  alkaline  or  alkalino-earthy 


INTRODUCTION.  897 

oxide,  the  residue  after  incineration  is  moistened  with  sulphuric  acid, 
which  drives  off  the  chlorine,  bromine,  or  iodine,  after  which  the 
excess  of  acid  is  evaporated  and  the  substance  calcined,  when  the 
base  remains  in  the  state  of  sulphate.  This  process  does  not  always 
succeed  easily  if  the  base  be  oxide  of  lead,  in  which  case  it  must  be 
several  times  evaporated  with  sulphuric  acid,  or  better  still,  with  a 
small  quantity  of  a  concentrated  solution  of  sulphate  of  ammonia. 

The  majority  of  the  metallic  chlorides,  bromides,  and  iodides  are 
so  volatile  at  a  red-heat  that  the  calcination,  in  the  air,  of  the  or- 
ganic salt  containing  the  chlorine  should  be  avoided ;  and,  in  order 
to  determine  the  oxide,  recourse  must  then  be  had  to  the  process 
of  determining  by  the  humid  way,  described  under  each  metal. 
The  presence  of  the  organic  acid  sometimes,  however,  prevents  the 
reactions  which  the  metallic  oxide  presents  when  combined  with 
mineral  acids,  in  which  case  the  organic  acid  must  be  destroyed, 
either  by  concentrated  nitric  acid,  when  this  is  possible,  or  by  mix- 
ing it  with  15  or  20  times  its  weight  of  a  mixture  of  carbonate  of 
soda  and  nitre,  thrown,  by  small  quantities  at  a  time,  into  a  silver 
crucible,  heated  over  an  alcohol-lamp ;  when  the  metallic  oxide  is 
found  in  the  alkaline  residue. 

CASE  IN  WHICH  THE  ORGANIC  SUBSTANCE  POSSESSES  BASIC 
PROPERTIES. 

§  1229.  All  the  basic  organic  substances,  at  present  known,  con- 
tain nitrogen.  In  order  to  ascertain  their  equivalent,  not  only  the 
isolated  bases,  but  also  a  certain  number  of  salts  which  these  bases 
form  with  mineral  acids,  must  therefore  be  analyzed,  preferring 
those  which  are  most  readily  obtained  in  the  crystallized  form,  and 
which  can  be  most  accurately  analyzed.  We  shall  take  strychnine 
as  an  example. 

The  elementary  analysis  of  strychnine  yields  the  following  results : 

Hydrogen * 6.58 

Carbon 75.45 

Nitrogen 8.38 

Oxygen 9.59 

100.00 
Dividing  the  preceding  numbers  by  the  corresponding  equivalent 
of  each  simple  substance,  there  results : 

For  hydrogen ^=    6.58 

"    carbon ^-If  =  12.57 

"    nitrogen ig  =    0.60 

"    oxygen |^  =    1.20 

The  most  simple  ratios  which  exist  between  these  quotients  are 
as  the  numbers  11 :  21 : 1 :  2.     The  most  simple  formula  of  strych- 


398  ORGANIC   CHEMISTRY. 

nine  is,  therefore,  CgjHjjNOg ;  but  as  the  multiple  of  the  formulae 
C^jHaaNgO^,  CggHggNgOg,  etc.  etc.  satisfy  equally  the  results  of  the 
analysis,  the  salts  of  strychnine  must  also  be  analyzed. 

The  organic  alkalies  combine  either  with  hydracids,  without  de- 
composing them,  or  with  oxacids ;  in  which  latter  case  they  always 
acquire  the  elements  of  1  equiv.  of  water,  which  cannot  be  driven 
off  without  injury  to  the  salt;  and,  in  this  respect,  the  organic 
bases  behave  like  ammonia,  in  their  compounds  with  hydracids  and 
oxacids. 

We  shall  first  analyze  the  chlorohydrate  of  strychnine,  after  hav- 
ing dried  it  at  212°,  in  a  current  of  dry  air,  because  the  crystallized 
salt  contains  water  of  crystallization.  The  elementary  analysis  will 
yield  for  its  composition : 

Hydrogen 6.21 

Carbon 68.02 

Nitrogen 7.56 

Oxygen 8.64 

Chlorine 9.57 

100.00 

The  determination,  for  itself,  of  the  chlorine  is  sufficient  to  esta- 
blish the  equivalent  of  strychnine,  admitting  that  the  salt  is  consti- 
tuted like  the  chlorohydrate  of  ammonia ;  that  is,  that  its  formula  is 

Sty,HCl,  the  symbol  Sty  representing  the  equivalent  of  strychnine. 
In  fact,  9.57  of  chlorine  correspond  to  9.841  of  chlorohydric  acid, 
and,  consequently,  100  of  chlorohydrate  of  strychnine  contain  9.841 
of  chlorohydric  acid,  and  90.159  of  strychnine ;  whence  the  equiva- 
lent of  strychnine  will  be  obtained  by  the  proportion, 

9.841  :  90.159  :  :  36.5  :  x,  whence  a;=334. 

Now  this  equivalent  corresponds  to  the  formula  C^H^jgNgO^,  which 
gives 

22  eq.  of  hydrogen 22.0 

42  "         carbon 252.0 

2  "         nitrogen 28.0 

4  "         oxygen 32.0 

334.0 

The  formula  of  free  strychnine  is  therefore  C^HggNgO^,  and  that 
of  the  dried  chlorohydrate  Q^J^fi^,HQ\,  The  crystallized  base 
is  anhydrous.  It  is  easy  to  ascertain,  by  calculating  the  composi- 
tion of  the  chlorohydrate  of  strychnine  in  hundredths,  from  the 
formula  just  given,  that  there  result,  for  each  element,  numbers 
identical  with  those  above  transcribed,  and  which  we  have  supposed 
to  be  obtained  by  direct  analysis. 

The  formula  of  strychnine  may  be  verified  by  the  analysis  of 


INTRODUCTION.  399 

Other  salts  of  the  base,  as,  for  example,  that  of  the  sulphate.  The 
formula  of  crystallized  sulphate  of  strychnine,  dried  at  266°,  is  thus 
found  to  be  (0,3H,,N,0„HO),S03. 

§  1230.  The  quantity  of  mineral  acid  which  exists  in  combina- 
tion with  an  organic  alkali  is  determined  by  the  same  means  as 
those  used  to  determine  the  acid  in  a  mineral  salt ;  but  the  analysis 
demands  the  greatest  care,  because  the  smallest  error  may  seriously 
affect  the  generally  very  complicated  formula  of  the  organic  alkali. 
In  order  to  determine  the  quantity  of  chlorohydric  acid  which  exists 
in  chlorohydrate  of  strychnine,  the  chlorohydric  acid  is  first  deter- 
mined by  precipitating  it  in  the  state  of  chloride  of  silver,  in  the 
manner  stated  in  §  1131.  The  weight  obtained  is  generally  too 
small.  Admitting,  for  the  moment,  the  weight  obtained  to  be 
exact,  from  this  weight  may  be  calculated  the  quantity  of  pure 
silver  which  would  exactly  precipitate  the  chlorohydric  acid  con- 
tained in  5  grammes  of  chlorohydrate  of  strychnine.  The  silver  is 
dissolved  in  nitric  acid,  and  the  liquid  poured  into  a  solution  of 
5  grammes  of  chlorohydrate  of  strychnine ;  after  which  the  solu- 
tion, when  clear,  is  filtered,  and,  by  the  assistance  of  a  decimal 
solution  of  silver,  the  quantity  of  chlorohydric  acid  which  still 
remains  in  the  liquid  is  determined,  (§  1144.)  Salts  formed  by  the 
other  mineral  acids  can  be  analyzed  by  analogous  processes. 

The  compounds  which  the  chlorohydrates  of  organic  bases  form 
with  bichloride  of  platinum  are  frequently  subjected  to  analysis,  by 
being  precipitated  in  the  form  of  small  yellow  granular  crystals. 
The  composition  of  the  double  chloride  of  platinum  and  strychnine 
is  analogous  to  that  of  the  double  chloride  of  platinum  and  am- 
monia, and  its  formula  is  (C^gHggNaOJHCH-PtClg.  By  roast- 
ing this  and  similar  compounds  in  the  air,  the  organic  matter  is 
destroyed  and  the  chlorine  disengaged,  while  the  platinum  remains ; 
which  process  is  well  adapted  to  the  determination  of  the  equiva- 
lent of  the  organic  base,  and  is  capable  of  great  exactness,  on 
account  of  the  great  weight  of  the  equivalent  of  platinum. 

CASE   IN   WHICH   THE   ORGANIC   SUBSTANCE  IS  NEITHER   ACID 
NOR  BASIC. 

§  1231.  When  the  simple  organic  substance  possesses  neither  acid 
nor  basic  properties,  there  is  no  general  rule  for  establishing  its 
equivalent  and  its  formula ;  and  chemists  are  then  guided  by  the 
composition  of  the  products  of  combination,  or  decomposition,  to 
which  the  substance  gives  rise  under  the  influence  of  various  che- 
mical agents.  They  choose,  among  all  the  equivalent  formulae, 
that  which  expresses  most  simply  the  whole  of  the  reactions,  fre- 
quently giving  preference  to  the  formula  which  establishes  an 
analogy  of  constitution  with  other  substances  presenting  similar 
reactions.  We  shall  be  satisfied  with  two  examples,  which  we  shall 
select  from  the  most  simple. 


400  ORGANIC   CHEMISTRY, 

The  method  of  preparing  bicarburetted  hydrogen  or  olefiant  gas 
has  already  been  shown,  (§  266.)  The  most  simple  formula  which 
satisfies  the  direct  analysis  of  this  gas  is  CH,  and  we  will  proceed 
to  show  why  the  formula  C^H^  has  been  assigned  to  it. 

By  mixing  in  a  large  bell-glass  equal  volumes  of  olefiant  gas 
and  chlorine,  a  liquid  substance  condenses,  of  which  the  most  sim- 
ple formula  is  CJl^Cl,  and  which,  by  treatment  with  an  alcoholic 
solution  of  caustic  potassa,  loses  one-half  of  its  chlorine,  and  one- 
fourth  of  its  hydrogen,  in  the  state  of  chlorohydric  acid,  which 
combines  with  the  potassa  (K0+HC1=KCH-H0);  while  at  the 
same  time  a  very  volatile  substance  is  formed,  of  which  the  most 
simple  formula  is  C^HgCl.  It  is  but  natural  to  regard  the  chlorine 
and  hydrogen,  which  were  separated  in  the  state  of  chlorohydric 
acid,  as  united  in  the  compound  G^Hfil,  difi'erently  from  the  other 
portions  of  chlorine  and  hydrogen  which  remain,  and  which  enter  into 
the  constitution  of  the  compound  C^HgCl ;  but  chemists  have  gone 
still  further  in  admitting  that  the  chlorine  and  hydrogen  removed  by 
the  action  of  the  potassa  existed  really  in  the  state  of  chlorohydric 
acid  in  the  substance  CaHgCl;  and,  in  order  to  avoid  fractional 
numbers  of  equivalents,  they  replace  the  formula  C3H3CI  by  the 
multiple  formula  C^H^Clg,  which  they  write  Cfifil,}lC\.  If  the 
formula  C^H^  is  assigned  to  olefiant  gas,  the  reaction  of  chlorine  on 
this  substance  is  expressed  in  the  most  simple  manner  possible,  by 
the  following  equation : 

C,H,-f2Cl=C,H3Cl,HCl. 

Now,  if  chlorine  is  made  to  act  on  the  substance  C^HgCl,  or  on 
the  compound  C^HjCljHCl,  a  new  substance  is  formed,  of  which 
the  most  simple  formula  is  C4H3CI3,  which,  when  treated  by  an 
alcoholic  solution  of  potassa,  gives  ofi"  1  equiv.  of  hydrogen  and  1 
equiv.  of  chlorine.  We  shall  regard  these  equivalents  as  existing  in 
the  state  of  chlorohydric  acid  in  the  substance  C4H3CI3,  as  we  have 
done  for  the  substance  C^H^Clg,  and  shall  write  the  formula  of  the 
new  compound  C^HgCla,!!^.  The  reactions  by  which  it  is  derived 
either  from  the  substance  C4H3CI,  or  from  the  compound  0^11301,1101, 
or  lastly,  from  the  olefiant  gas  O^H^,  are  of  the  most  simple  cha- 
racter. 

C.H^Cl        +201=C,H,01„H01. 

C,H301,H0H-201=0,H,C1„H01+HC1. 

C,H,  -f401=0,H,01„H01+H01. 

In  the  last  two  cases,  1  equiv.  of  chlorohydric  acid  is  set  free. 

The  product  O4H3CI3,  or  the  compound  04H20l2,H01,  being  sub- 
mitted, in  their  turn,  to  the  action  of  chlorine,  yields  a  new  pro- 
duct, of  which  the  most  simple  formula  is  O3HOI3.  If  we  write 
this  formula  O^H^Cl^,  and  if  we  give  it  the  form  0^11013,1101,  the 
reactions  which  produce  it  by  the  action  of  chlorine  on  the  various 


INTRODUCTION-.  401 

substances  C,H,C1„  C,H,C1„HC1,  C.H^Cl,  C.HgCl^HCl,  and  C,H„ 
are  the  following : 

C,H,C1„HC1+2C1=C,HC13,HCH-  HCl. 
C,H3C1  4-4Cl=:C,HCl3,HCl4-  HCl. 

C,H3C1,  HC1+4C1=C,HC13,HC1+2HCL 
C,H,  +6C1=C,HC13,HC1+2HC1. 

The  compound  C^HClgjHCl  is  also  decomposed  by  contact  with 
the  alcoholic  solution  of  potassa,  but  the  substance  C^HClg  has  not 
yet  been  obtained  in  a  state  of  purity,  and  seems  to  be  altered 
itself  by  the  alcoholic  solution  of  potassa.  It  cannot  the  less  be 
admitted  that  this  substance  pre-exists  in  the  compound  C4H3CI3, 
for  the  very  reason  that  this  establishes  perfect  uniformity  in  all 
the  derived  compounds — a  uniformity  which,  moreover,  has  hither- 
to been  destroyed  by  no  other  reaction. 

Lastly,  the  substance  C4HCI3HCI,  when  subjected  to  the  action 
of  chlorine,  assisted  by  solar  light,  parts  with  the  whole  of  its 
hydrogen,  which  is  disengaged  in  the  state  of  chlorohydric  acid, 
while  a  crystalline  compound,  which  is  a  simple  chloride  of  carbon, 
the  most  simple  formula  of  which  is  C3CI3,  is  formed.  Various 
chemical  reactions  show  that  one  of  the  equivalents  of  chlorine 
is  not  as  deeply  interested  in  the  compound  as  the  other  two. 
|g^.  Removing,  for  example,  this  equivalent  by  an  alcoholic  solu- 
tion of  monosulphide  of  potassium,^  a  new  chloride  of  carbon, 
of  which  the  most  simple  formula  is  CCl,  will  separate,  to  which, 
for  the  moment,  we  will  give  the  formula  C2CI3,  in  which  case 
the  first  could  be  written  C3Cl3,Cl.  But  it  would  be  more  pro- 
per to  write  their  formulae  C^Cl^  and  Cfi\,C\^,  because,  with  these 
last  formulae,  the  reactions  which  give  rise  to  the  chloride  of 
carbon  0401^,012,  by  the  action  of  chlorine  on  all  the  successive 
compounds  of  which  we  have  previously  established  the  formulae, 
are  of  the  most  simple  kind  : 

C,H2Cl3,HCl  +  4C1=C,C1,C12,+2HC1. 

CACI2  +  6C1=C,C1,C13,+2HC1. 

CJlfi\,,RC\  +  6C1=C,C1,C12,+3HC1. 

C,H3C1  +  8C1=C,C1,C12,+3HC1. 

C,H3C1,HC1  +  8C1=C,C1,C12,+4HC1. 

C,H,  +10Cl=C,Cl,Cl3,'f4HCl. 

We  will  remark,  in  addition,  that  olefiant  gas  C^H^,  and  all  the 
chlorinated  products  CJifil,  C^H^Cl^,  GJiC\,  Cfi\  derived  from 
it,  present  this  remarkable  property,  that  they  may  be  regarded  as 
one  and  a  single  molecular  grouping  C^H^,  modified  only  by  the 
successive  substitution  of  an  equal  number  of  equivalents  of  chlo- 
rine for  its  equivalents  of  hydrogen.     This  fact  is  again  corrobo- 

VoL.  IL— 26 


402     •  ORGANIC   CHEMISTRY. 

rated  by  the  following :  If  the  substances  are  operated  on  at  a  tem- 
perature sufficientli/  high  to  allow  all  of  them  to  exist  in  the  gaseous 
state,  the  formulae  CJl^,  C^H3C1,  C^H.Cl,,  C.HClg,  C,Cl3  would  re- 
present the  same  volume  of  these  various  gases  ;  each  of  these  for- 
mulae corresponding,  in  fact,  to  4  volumes  of  the  vapour  of  the 
body  to  which  it  relates. 

The  comparisons  and  similarity  of  composition  just  pointed  out 
among  all  these  substances  would  disappear,  if  for  each  of  them 
equivalent  formulae  more  simple  than  those  we  have  admitted  were 
adopted,  although  they  would  still  exist  if  equivalent  formulae  were 
admitted,  multiples  of  those  just  established ;  but  there  is  no  reason 
whatever  for  thus  complicating  the  formulae. 

§  1232.  For  the  second  example  we  shall  choose  alcohol,  which 
liquid  is  composed  as  follows  : 

Hydrogen 18.05 

Carbon 52.17 

Oxygen.. 34.78 

100.00 

Dividing  each  of  these  numbers  by  the  equivalent  of  the  sub- 
stance to  which  it  belongs,  the  following  quotients  result : 

For  hydrogen 7^=13.05 


"  carbon |r  =    8.69  .^ 

"  oxygen ^=    4.35 


The  ratio  of  these  quotients  to  each  other  being  that  of  the  num- 
bers 3 :  2:1,  the  most  simple  formula  which  can  be  given  to  alcohol 
is  C2H3O,  while  all  its  multiple  formulae  represent  equally  well  the 
results  of  the  analysis. 

Alcohol  is  a  substance  possessing  neither  acid  nor  basic  proper- 
ties ;  and  as  its  equivalent  and  chemical  formula  cannot  therefore 
be  established  by  the  methods  described  for  the  acids  and  bases, 
resort  must  be  had  to  the  chemical  reactions  which  ensue  when  al- 
cohol is  subjected  to  the  various  agents  in  the  laboratory,  and  from 
these  the  formula  which  explains  them  all  in  the  simplest  manner 
must  be  deduced. 

By  mixing  together  equal  parts  of  alcohol  and  sulphuric  acid,  and 
exposing  the  mixture  for  several  hours  to  a  temperature  of  120° 
or  140°,  a  compound  acid  is  obtained  containing  sulphuric  aeid  and 
some  of  the  elements  of  alcohol.  This  acid,  called  sulphovinie, 
forms  readily  crystallizable  salts  with  bases,  and,  as  it  is  an  acid, 
its  equivalents  and  consequently  its  formula,  can  be  determined  by 
the  methods  explained,  (§  1224.)  The  result  is  then  found  that  the 
formula  of  anhydrous  sulphovinie  acid,  that  is,  of  the  acid  as  it 
exists  in  salts  which  contain  no  water  of  crystallization,  is  C^H^O, 
2SO3 ;  and  if  the  formula  CaHjO  is  assigned  to  alcohol,  the  reaction 


INTRODUCTION.  403 

which  produces  sulphovinic  acid  is  not  explained  in  a  simple  man- 
ner, as  it  is  then  supposed  that  the  reaction  takes  place  between  2 
equivalents  of  sulphuric  acid,  and  2  equivalents  of  alcohol  CgHgO, 
one  of  which  does  not  behave  in  the  same  manner  as  the  other.  If, 
on  the  contrary,  the  equivalent  formula  C^HgO^  be  adopted  for  al- 
cohol, the  reaction  is  of  the  most  simple  kind :  1  equivalent  of  al- 
cohol gives  off  1  equivalent  of  hydrogen  and  1  equivalent  of  oxygen 
in  the  state  of  water,  while  the  product  C^H^O,  remaining  after 
this  separation,  combines  with  2  equivalents  of  sulphuric  acid  to 
form  sulphovinic  acid  €^£[30,2803,  which  retains  in  combination 
the  equivalent  of  water  separated,  •  to  form  hydrated  sulphovinic 
acid  C,H,0,2S03-f-HO. 

By  distilling  the  mixture  of  alcohol  and  sulphuric  acid  in  a  retort, 
a  very  volatile  liquid,  called  ether,  passes  over^  the  most  simple  for- 
mula of  which  is  C^H^O.  Now,  it  will  be  seen  that  if  the  formula 
C^HgOg  for  alcohol  be  adopted,  ether  is  derived  from  it  simply  by 
the  abstraction  of  1  equivalent  of  water;  and  the  facility  with 
which  alcohol  loses  1  equivalent  of  hydrogen  and  1  of  oxygen, 
which  separate  in  the  state  of  water,  has  led  many  chemists  to  ad- 
mit the  existence  in  this  body  of  1  equivalent  of  water  ready 
formed,  and  to,  consequently,  regard  alcohol  as  a  combination  of  1 
equivalent  of  ether  and  1  of  water,  and  to  write  its  formula 
C^H50,H0.*  But  is  it  more  suitable  to  adopt  for  ether  its  most 
simple  formula  C^H^O  or  an  equivalent  multiple  formula  ?  This 
question  must  be  answered  by  the  chemical  reactions  of  the  sub- 
stance. Now,  ether  combines  with  the  mineral  acids,  and  the  re- 
sulting compounds,  called  compound  ethers,  should  not  be  considered 
as  salts,  because  they  have  none  of  their  characteristic  properties, 
but  rather  as  definite  compounds,  of  which  the  composition  should 
be  simply  expressed  by  the  assistance  of  the  formula  adopted  for 
ether.     Now,  there  is  known 

A  nitric  ether C^H,0,N05, 

Acarbonic  " C^H^OjCOa, 

An  oxalic    "  ^,^s^,^2% 

An  acetic    "  Qfifi^Qfifi^i 

the  formula  C^H^O  adopted  for  ether,  gives  to  all  these  compounds 
the  most  simple  formulae  possible. 

Ether,  subjected  to  an  oxidizing  agency,  gives  off  its  water  and 
is  converted  into  a  new  substance,  called  aldehyde,  of  which  the 
most  simple  formula  is  CgH^O,  but  which  is  written  C^H^O^,  be- 

*  Since  the  original  was  written,  Mr.  Frankland  has  succeeded  in  isolating,  by 
decomposing  iodic  ether,  or  iodide  of  ethyl,  C^H.I,  with  zinc,  the  until  then  hypo- 
thetic substance  ethyl,  which  thus  must  be  considered  as  a  compound  organic 
radical,  corresponding  to  a  metal  in  mineral  chemistry,  and  of  which  ether  is  the 
oxide,  while  alcohol  then  necessarily  must  be  regarded  as  its  hydrate. —  W.  L.  F. 


404  ORGANIC   CHEMISTRY. 

cause  the  reaction  which  produces  it  is  then  expressed  in  the  most 
simple  manner  by  the  equation 

C,H30+20=C,H,0,+HO  : 

the  molecular  constitution  of  aldehyde  is  therefore  the  same  as  that 
of  ether,  there  being  simply  a  substitution  of  1  equivalent  of  oxygen 
for  1  equivalent  of  hydrogen. 

The  oxidizing  agency  being  still  continued,  aldehyde  is  converted 
into  acetic  acid,  the  formula  of  which,  from  its  acid  properties,  may 
be  determined  according  to  §  1224.  It  has  been  shown  that  an- 
hydrous acetic  acid,  as  it  exists  in  salts,  is  C4H3O3.  Now,  the  new 
reaction  is  again  expressed  in  the  most  simple  manner,  by  admitting 
the  formula  C^H^O  for  ether,  and  the  formula  C^H^Oj  for  aldehyde  ; 
and  acetic  acid  is  in  fact  derived  from  aldehyde  by  a  reaction  simi- 
lar to  that  which  transforms  ether  into  aldehyde : 

.C,H,0,+20=C,H303+HO; 

the  equivalent  of  water  formed  remaining  combined  with  the  acetic 
acid,  and  giving  to  the  latter  its  maximum  of  concentration.  In 
acetic  acid,  as  in  aldehyde,  the  molecular  constitution  of  ether  is 
preserved,  a  new  equivalent  of  hydrogen  being  merely  replaced  by 
1  equivalent  of  oxygen. 

Alcohol,  subjected  to  oxidizing  agencies,  fm-nishes  the  same  pro- 
ducts as  ether ;  that  is,  aldehyde  at  first,  and  subsequently  acetic 
acid,  which  is  one  of  the  reasons  which  have  confirmed  chemists  in 
regarding  alcohol  as  a  hydrate  of  ether. 

Lastly,  ether,  when  subjected  to  the  action  of  dry  chlorine,  and 
exposed  to  solar  light,  yields  a  series  of  products,  of  which  the 
most  simple  formulae  are  C^H^CIO,  C4H3CI3O,  C^Cl.O,  which  sub- 
stances are  derived  from  ether  C^H^O,  by  reactions  resembling 
those  which  take  place  in  the  action  of  oxygen,  and  which  are  ex- 
pressed by  the  equations : 

C,H,0+2C1=C,H,C10+HC1. 

C,H,0+4Cl=C,H3Cl20+2HCl. 

C,H3O+10Cl=C4Cl,O4-5HCl. 

The  new  substances  C^H^CIO,  C4H3CI2O,  C^Cl^O  present  the 
same  molecular  constitution  as  ether  C^H^O ;  1,  2,  or  5  equivalents 
of  hydrogen  of  the  original  ether  being  replaced  by  1,  2,  oj  5  of 
chlorine. 

Numerous  additional  examples  of  products  derived  from  ether 
under  the  influence  of  various  chemical  agents  might  be  given,  and 
in  all  cases  it  would  be  found  that  the  reactions  explain  them- 
selves in  the  most  simple  and  natural  manner,  by  adopting  the 
formula  C^H^O  for  ether,  and,  as  none  of  the  explanations  would 
become  more  simple  if  an  equivalent  multiple  formula  were  substi- 


INTRODUCTION.  405 

tuted  for  the  one  adopted,  the  formula  C^H^O  for  ether  must  be 
considered  as  established,  and  consequently  the  formula  C^HgOg  or 
C^H.OjHO  for  alcohol.  These  formulae  being  once  admitted,  those 
of  all  the  products  of  ether  and  alcohol,  which  have  just  been  men- 
tioned, are  equally  established. 

§  1233.  In  the  preceding  remarks,  the  results  of  the  chemical 
analyses  have  been  supposed  to  be  absolutely  accurate,  which,  how- 
ever, is  rarely  the  case,  as  the  most  carefully  conducted  analysis  is 
liable  to  trifling  errors,  which  frequently  Igave  the  chemist  uncertain 
as  to  the  formula  he  should  adopt  for  the  substance  analyzed,  when 
the  latter  contains  a  great  number  of  equivalents  of  its  elementary 
principles,  and  when,  consequently,  its  equivalent  is  very  high. 
This  uncertainty  can  be  removed  only  by  a  new  analysis,  more 
carefully  conducted,  operating  on  larger  quantities  of  matter,  and 
directing  the  operations  chiefly  with  the  intention  of  ascertaining 
exactly  the  element  of  which  the  number  of  equivalents  is  most 
uncertain.  It  is  also  frequently  sought  to  determine  with  most 
exactness  the  atomic  weight  of  the  compound,  by  using  the  method 
of  successive  approximation,  of  which  an  example  has  been  given 
(§  1230)  in  the  determination  of  the  chlorine  contained  in  the  chlo- 
rohydrate  of  strychnine. 

The  chemist  is  also  guided  by  the  probable  analogies  of  constitu- 
tion which  should  exist  between  the  substances  of  which  he  seeks 
the  formula,  and  other  substances  presenting  notorious  resemblances 
in  their  chemical  properties  with  the  first,  and  the  formulae  of  which 
are  already  established. 

We  shall  observe,  subsequently,  that  all  organic  compounds,  of 
which  the  composition  and  formula  are  known  with  some  degree  of 
certainty  (and  the  number  of  them  is  quite  large)  contain,  in  their 
equivalent,  an  even  number  of  equivalents  of  carbon.  This  fact  is 
certainly  not  accidental,  and  renders  it  very  probable  that  for  the 
equivalent  of  carbon,  a  number  double  of  that  which  has  been 
hitherto  admitted  must  be  adopted.  The  number  6.0  has  been 
adopted  as  the  equivalent  of  carbon,  on  account  of  the  compounds 
which  this  substance  forms  with  oxygen,  as  these  compounds  are 
thus  represented : 

Oxide  of  carbon  by  the  formula CO. 

Carbonic  acid  "  CO3.  " 

'Oxalic  acid  "  CgO,. 

Oxalic  acid  alone,  of  these  compounds,  contains  an  even  number  of 
equivalents  of  carbon,  and  consequently  belongs  to  the  category  of 
other  organic  substances.  No  means  is  known  of  fixing  directly 
the  value  of  the  equivalent  of  oxide  of  carbon,  because  this  substance 
is  neutral  and  forms  no  well-marked  compound ;  and  the  formula 
C2O2  might  therefore,  without  any  inconvenience,  be  adopted  for 


406  ORGANIC   CHEMISTRY. 

oxide  of  carbon.  The  equivalent  of  carbonic  acid  is  deduced  from 
the  analysis  of  the  carbonates.  Now,  two  series  of  carbonates  are 
known,  which,  with  the  equivalent  of  carbon  now  adopted,  are 
written  ROjCOa,  RO,2C02.  But  it  has  not  yet  been  decided  with 
certainty  which  of  this  series  should  be  considered  as  containing 
the  neutral  carbonates.  If,  contrary  to  what  the  majority  of 
chemists  have  admitted,  we  were  to  regard  the  second  series  as  that 
of  the  neutral  carbonates,  we  must  write  the  formula  of  the  two 
series  2R0,C204,  R0,C304;  and  carbonic  acid  would  then  contain 
also  an  even  number  of  equivalents  of  carbon. 

Be  this  as  it  may,  the  chemist  will  necessarily  regard  the  general 
observation  we  have  just  made,  and  avoid  adopting  a  formula  which 
contains  an  uneven  number  of  equivalents  of  carbon. 

DETERMINATION  OF  THE  DENSITY  OF  THE  VAPOURS  OF  VOLATILE 

SUBSTANCES. 

§  1234.  It  has  already  been  shown,  in  the  preceding  parts  of  this 
work,  that  in  the  combinations  of  elementary  gases  there  always 
exists  a  very  sensible  ratio  between  the  volumes  of  these  gases ;  and 
that  when  the  resulting  compound  itself  is  gaseous,  a  very  simple  ratio 
between  its  volume  and  the  sum  of  the  volumes  of  the  component 
gases  is  observed.  This  law  applies  not  only  to  substances  which 
are  gaseous  at  the  ordinary  temperature,  but  probably  to  all  vola- 
tile substances,  if  they  are  observed  at  a  temperature  sufficiently 
high  for  them  to  exist  in  the  state  of  vapour,  and  if  this  temperature 
is  sufficiently  above  the  point  of  liquefaction  to  enable  the  vapour 
to  follow,  at  least  by  approximation,  the  laws  of  expansion  and 
elasticity  admitted  for  the  permanent  gases.  It  has  been  shown, 
moreover,  that  in  the  compound  gases  to  which  similar  chemical 
formulae  are  assigned,  the  equivalents  are  represented  by  the  same 
number  of  volumes  of  vapour.  Thus  chlorohydric,  bromohydric,  and 
iodohydric  gas,  resulting  from  the  combination  of  2  volumes  of 
hydrogen  with  2  volumes  of  gaseous  chlorine,  bromine,  and  iodine, 
have,  as  their  equivalents  in  volume,  4  volumes  of  gas.  The  equi- 
valents which  we  shall  be  led  to  adopt  for  the  numerous  carburetted 
hydrogens,  if  we  are  guided  by  considerations  analogous  to  those 
advanced  in  §  1231  for  olefiant  gas,  are  all  represented  by  4 
volumes  of  vapour.  The  equivalent  of  gaseous  alcohol  is  represented 
by  4  volumes,  if  we  adopt  for  its  formula  C^HgOg.  The  chemical 
reactions  of  several  organic  substances  are  perfectly  analogous  to 
those  of  alcohol ;  and  the  formulae  which  we  are  led  to  adopt  for 
them,  from  considerations  analogous  to  those  indicated,  (§  1232,)  fix 
their  gaseous  equivalents  at  4  volumes. 

Ether,  to  which  we  assign  the  formula  C^H^O,  is  represented  by 
2  volumes  of  vapour,  and  consequently  the  organic  substances,  the 
chemical  reactions  of  which  are  analogous  to  ether,  are  also  repre- 
sented by  two  volumes  of  vapour. 


INTRODUCTION.  '  407 

It  will  from  this  be  understood  that  the  density  of  the  vapours 
of  volatile  compounds  furnishes,  in  a  great  number  of  cases,  data 
valuable  in  guiding  the  choice  of  their  chemical  formulae,  especially 
when  such  compounds  have  been  but  little  studied,  and  but  a  small 
number  of  their  chemical  reactions  (and  these  not  very  well  marked) 
are  known. 

Some  volatile  substances  yield  vapours  which  obey  the  laws  of 
permanent  gases,  starting  at  temperatures  raised  only  70°  or  100° 
above  their  boiling  point ;  while  other  vapours,  on  the  contrary, 
only  obey  these  laws  approximately,  when  they  are  heated  360°  or 
450°  above  this  point.  Now,  as  the  laws  which  govern  the  com- 
binations of  gaseous  bodies  exist  rigorously,  only  under  circum- 
stances in  which  the  gases  follow  the  law  of  Mariotte  in  their  elas- 
ticities, and  present  equal  coefficients  of  expansion,  it  will  be 
necessary,  in  determining  the  density  of  a  vapour,  compared  with 
that  of  atmospheric  air  under  the  same  circumstances  of  temperature 
and  pressure,  to  ascertain  if  the  density  found  at  one  temperature 
remains  the  same  at  temperatures  which  differ  less  than  90°  or  108° ; 
and  it  is  only  when  this  condition  is  satisfied  that  the  vapour  can 
be  admitted  to  belong  to  the  permanent  gases,  and  that  the  formula 
of  the  substance  may  be  established  on  the  density  of  its  vapour. 

We  will  adduce  a  few  examples  in  support  of  the  truth  of  what 
has  just  been  said. 

Monohydrated  acetic  acid  C4H3O3+HO  boils  at  240°  under  the 
ordinary  pressure  of  the  atmosphere  ;  and  the  density  of  its  vapour, 
compared  with  atmospheric  air  under  the  same  circumstances  of 
pressure  and  temperature,  have  been  found  at 


257° 3.180 

266  3.105 

284  2.907 

302  2.727 

320  2.604 

338  2.480 

356  2.438 

374  2.378 


392° -2.248 

428  2.132 

464  2.090 

518  2.088 

590  2.085 

608  2.083 

637  2.083 


It  will  be  seen  that  the  density  of  this  vapour  diminishes  con- 
tinually to  the  temperature  of  464°,  which  is  216°  above  the  boiling 
point  of  the  substance.  But  it  will  also  be  seen  that  from  464°  to 
637°  the  density  dges  not  sensibly  vary :  this  constant  value  of  the 
density  must  therefore  be  adopted  when  the  vapour  of  acetic  acid 
is  compared  with  the  permanent  gases. 

In  a  great  number  of  other  volatile  substances,  the  density  of  the 
vapour  attains  its  constant  value  at  a  few  degrees  above  its  boiling 
point :  thus  for  alcohol,  which  boils  at  173.3°,  the  following  densi- 
ties of  vapour  have  been  found : 


408 


ORGANIC   CHEMISTRY. 


190.4° 1.725         302° 1.604 

208.4  1.649         347  1.607 

230   1.610         392  1.602 

257   1.603 

From  230°,  which  is  only  about  5Q°  above  the  boiling  point,  the 
vapour  of  alcohol  preserves  an  almost  constant  density. 

§  1235.  The  density  of  a  vapour  is  the  ratio  between  the  weight 
of  a  certain  volume  of  this  vapour  and  that  of  the  same  volume  of 
atmospheric  air,  under  the  same  circumstances  of  temperature  and 
pressure.  The  weight  of  a  given  volume  V  of  atmospheric  air,  at 
a  known  temperature  and  under  a  known  pressure,  is  easily  deter- 
mined. If  the  temperature  is  expressed  by  T,  and  the  pressure  by 
Hp,  the  weight  P  of  the  volume  V  of  air  will  be,  supposing  V  to 
represent  the  volume  expressed  in  cubic  centimetres, 

P  =  0.0012982  gm.  V.  ^^^^^  .  ^. 

The  elastic  force  H^  is  supposed  to  be  represented  by  the  height  of 
the  column  of  mercury  at  32°,  which  will  balance  it,  expressed  in 
millimetres,  while  T  represents  the  centigrade  temperature  of  an  air 
thermometer. 

To  obtain  the  density  of  a  vapour,  it  is,  therefore,  sufficient  to 
determine  the  weight  P'  of  a  known  volume  V  of  this  vapour,  at  a 
temperature  T  and  under  a  pressure  Ho.  Two  different  methods 
are  used  for  this  purpose :  in  the  first,  the  volume  occupied  by  a 
known  weight  P'  of  the  volatile  substance,  at 
the  temperature  T  and  under  the  pressure  Ho, 
is  measured :  while  in  the  second  method,  on 
the  contrary,  the  substance  is  vaporized  in  a 
flask,  of  which  the  volume  is  known  a  priori, 
and  the  weight  of  the  vapour  which  fills  it  is 
determined  by  experiment. 

In  order  to  ascertain  the  density  of  a  vapour 
by  the  first  method,  a  large  bell-glass  C,(fig.  632,) 
accurately  divided  into  cubic  centimetres,  and 
previously  dried  with  the  greatest  care,  is  filled 
with  very  dry  mercury,  and  then  inverted  over  a 
mercurial  bath,  also  very  dry,  contained  in  a  cast- 
iron  pot  y ;  while,  on  the  other  hand,  a  small 
globe  (fig.  633)  is  filled  with  the  volatile  liquid, 
the  specific  gravity  of  which  is  to  be  ascer- 
tained; and  having  hern^etically  sealed  its 
points,  the  weight  of  the  liquid  contained  in  it 
is  exactly  determined.  The  small  globe  being 
introduced  into  the  bell-glass  C,  the  latter  is 
then  surrounded  by  a  glass  cylinder 
maintained  in  a  vertical  position,  and 
Fig.  632.  Fig.  633.  is  filled  with  water,  if  the  temperature 


INTRODUCTION.  409 

is  not  to  exceed  212°,  while  a  thermometer  t  is  so  kept  in  the 
water  that  the  mercurial  column  is  always  under  the  level  of  the 
liquid.  The  diameter  of  the  cylinder  should  be  5  or  6  centimetres 
less  than  that  of  the  pot,  so  that  the  atmospheric  pressure  may  be 
directly  exerted  on  a  circular  surface  of  mercury,  comprised  be- 
tween the  outside  of  the  cylinder  and  the  inside  of  the  pot,  and  of 
which  the  level  may  be  accurately  ascertained  by  a  double-pointed 
screw  7*,  the  lower  point  of  which  is  in  exact  contact  with  the  sur- 
face in  the  mercury. 

The  kettle  being  placed  on  the  furnace,  the  temperature  is  gradu- 
ally raised,  when  the  expansion  of  the  liquid  soon  breaks  the  glass 
globe ;  and,  when  the  temperature  is  sufficiently  elevated,  the  liquid  is 
converted  into  vapour,  which  depresses  the  mercury  in  the  bell-glass. 
The  heat  is  continued  until  the  water  in  the  cylinder  boils,  after 
which  the  volume  occupied  by  the  vapour  and  the  pressure  to  which 
it  is  subjected  are  accurately  noted  down.  In  order  to  obtain  the 
latter  datum,  the  lower  point  of  the  screw  is  brought  to  the  exact 
level  of  the  surface  of  the  mercury  between  the  cylinder  and  the 
kettle,  and,  by  means  of  a  cathetometer,  the  difference  of  level 
between  the  surface  of  the  mercury  in  the  bell-glass  and  the  upper 
point  of  the  screw  is  determined,  to  which  length  must  be  added 
that  of  the  screw  already  known  a  priori,  in  order  to  obtain  the 
height  h  of  mercury  which,  in  addition  to  the  elastic  vapour, 
balances  the  external  barometric  pressure.  The  column  h  of  mer- 
cury, reduced  by  calculation  to  82°,  being  subtracted  from  the 
height  of  the  barometer,  also  reduced  to  32°,  will  give  the  elastic 
force  H'o,  of  the  vapour. 

The  fact  that  the  cylinder  surrounding  the  bell-glass  is  rarely 
perfectly  cylindrical,  gives  rise  to  deviations  in  the  luminous  rays, 
which  may  affect  the  determination  of  the  height  h,  by  means  of  the 
cathetometer,  while  the  cylinder  is  filled  with  water.  To  be  sure 
of  this,  the  micrometric  wire  of  the  telescope  of  the  cathetometer  is 
directed  over  the  division  of  the  bell-glass  nearest  to  the  level  of . 
the  mercury  inside,  and  the  water  is  then  removed  from  the  cylin- 
der by  means  of  a  siphon ;  when  it  is  easy  to  ascertain  whether  the 
wire  of  the  micrometer  remains  over  the  division,  in  which  case  the 
interposition  of  the  liquid  filling  the  cylinder  has  certainly  pro- 
duced no  abnormal  deviation  of  the  ray.  If  there  has  been  any  dis- 
placement, the  micrometer  is  again  brought  over  the  same  division, 
and  the  distance  travelled  by  the  vernier  of  the  instrument  then 
gives  the  correction  to  be  made  in  the  height  h  observed  in  the  first 
case. 

When  no  cathometer  is  at  hand,  the  simplest  way  of  determining 
the  height  h  consists  in  carefully  marking  the  position  of  the  inner 
level  of  the  mercury  on  the  divisions  of  the  bell-glass,  and  levelling 
exactly  the  external  circular  surface  of  the  bath  with  the  lower  point 
of  the  screw  r.    The  water  is  then  entirely  removed  from  the  cylin- 


410  ORGANIC   CHEMISTRY. 

der,  the  last  drops  being  soaked  up  by  tissue-paper,  and  then  mercury 
is  poured  into  the  kettle,  so  as  again  to  bring  the  external  surface 
of  the  mercury  on  a  level  with  the  point.  As  the  mercurial  bath  is 
on  the  same  level,  both  on  the  inside  and  outside  of  the  cylinder,  it 
sufl5ces  to  mark  on  the  bell-glass  the  division  to  which  the  level 
reaches.  The  height  h  is  then  equal  to  the  distance  between  this 
division  and  that  at  which  the  level  of  the  mercury  on  the  inside 
of  the  bell-glass  stops  at  the  moment  of  measuring  the  volume  of  a 
vapour. 

If  the  substance  boils  at  a  very  low  temperature,  the  density  of 
its  vapour  is  sometimes  determined  at  a  temperature  below  212° ; 
and  it  is  then  sought  to  render  stationary  the  temperature  of  the 
water  in  the  cylinder  at  the  exact  temperature  at  which  the  volume 
of  vapour  is  to  be  observed.  By  properly  regulating  the  fire  under 
the  kettle,  a  moment  arrives  at  which  the  apparatus  receives  from 
the  furnace  a  quantity  of  heat  equal  to  that  which  it  loses  from  its 
whole  surface  by  contact  with  the  surrounding  air,  and  by  the  va- 
porization of  the  water  in  the  cylinder ;  which  period,  frequently 
lasting  8  or  10  minutes,  is  chosen  for  the  observation.  The  water 
must  be  constantly  stirred  with  the  agitator  pmn^  in  order  to  obtain 
a  uniform  temperature  throughout. 

If  it  is  required  to  observe  the  volume  of  a  vapour  at  a  tempera- 
ture above  212°,  the  water  in  the  cylinder  is  replaced  by  a  fixed 
oil,  which  should  be  as  colourless  and  transparent  as  possible ;  but 
the  experiment  is  then  more  difficult  and  the  results  less  exact. 
The  oil,  of  which  the  capacity  for  heat  is  much  less  than  that  of 
water,  cools  rapidly  in  the  air,  and,  in  order  to  obtain  a  high  sta- 
tionary temperature  in  the  oil-bath,  the  mercury  in  the  kettle  must 
be  heated  to  a  greater  degree,  and,  therefore,  evolves  copious  va- 
pours, which  must  be  avoided.  It  is  also  a  matter  of  uncertainty 
whether  the  temperature  of  the  column  of  mercury,  which  is  raised 
in  the  bell-glass,  and  stands  in  immediate  contact  with  the  vapour 
the  volume  of  which  is  to  be  found,  is  not  higher  than  that  of  the 
surrounding  oil ;  and,  lastly,  if  the  tension  of  the  mercurial  vapour 
can  be  neglected,  without  any  appreciable  error,  for  temperatures 
below  212°,  (for  at  this  temperature  it  only  reaches  a  ^  millimetre,) 
this  is  not  the  case  when  high  temperatures  are  necessary ;  and  the 
tension  of  the  mercury  must  then  also  be  taken  into  account,  by. 
being  added  to  the  elastic  force  of  the  vapour.  For  these  various 
reasons,  the  process  just  described  is  not  so  well  adapted  to  tem- 
peratures above  300°  or  350°. 

§  1236.  The  second  method  is  applicable,  on  the  contrary,  to 
any  temperature  whatever;  and  the  only  difficulty  it  presents  is 
that  of  procuring  vessels  to  hold  the  vapour,  which  are  not  mis- 
shapen, or  liable  to  injury  when  exposed  to  a  very  high  tem- 
perature. 


INTRODUCTION. 


411 


A  glass  balloon  A,  (fig.  634,)  containing  400  or  500  cubic  centi- 
metres, and  drawn  out  into  an  open  and 
curved  point,  as  represented  in  the  figure, 
is  used,  and,  in  the  first  place,  dried  per- 
fectly by  means  of  an  air-pump ;  after 
which  it  is  placed  on  the  disk  of  a  scale, 
near  a  thermometer  arranged  in  the  cage. 
In  15  minutes,  in  which  time  it  may  be 
supposed  that  the  balloon  has  attained  the 
surrounding  temperature,  its  exact  weight 
P  is  ascertained,  while  at  the  same  time, 
the  temperature  t  of  the  thermometer  and 
the  height  H  of  the  barometer.are  marked ; 
^m  the  weight  found  by  direct  weighing  being 
that  of  the  balloon  itself,  in  addition  to  the 
weight  p  of  air  it  contains.     Let  V  be  the 

capacity  of  the  balloon  expressed  in  cubic  centimetres,  then  will 

the  weight  p  of  the  air  which  it  contains  be 


Fig.  634. 


jt?=0.0012932  .  V. 


Ho 


l-h0.00367.<       760' 


and  the  weight  of  the  balloon  alone  is  therefore  (P— jt?). 

About  10  grammes  of  the  liquid,  the  density  of  whose  vapour  is  to 
be  determined,  being  introduced  into  the  balloon,  the  latter  is  fast- 
ened on  a  copper  support,  with  its  tubulure  upward,  to  facilitate  the 
escape  of  the  air  which  is  expelled  by  the  vapoiiir  developed  during 
the  experiment.  This  support  may  be  variously  shaped :  in  fig.  634 
it  is  composed  of  two  metallic  rings,  the  lower  one  of  which  ah  is 
supported  by  three  small  feet  which  keep  it  at  a  distance  of  3  cen- 
timetres from  the  floor,  while  it  is  provided  with  two  grooved  up- 
rights ae^  bf,  fastened  together  by  a  crosspiece  ef.  The  upper  ring 
cd  has  two  ears,  which  slide  in  the  grooves  of  the  uprights  ae,  bf; 
and  the  balloon  A  is  fitted  between  the  'two  rings,  and  held  firmly 
by  two  corks  h,  h\  which  are  pressed  by  two  screws  g,  g',  A  verti- 
cal piece  has  a  movable  crosspiece  mn,  serving  to  support  two  ther- 
mometers T,  T,  of  which  the  bulbs  should  be  at  the  height  of  the 
centre  of  the  balloon.  As  the  crosspiece  mn  is  movable,  various 
positions  in  the  bath  can  be  given  to  the  thermometers,  in  order  to 
ascertain  whether  the  temperature  of  the  latter  be  the  same 
throughout. 

The  liquid  bath  in  which  the  balloon  is  heated  is  contained  in 
a  cast-iron  kettle  placed  over  a  furnace.  When  the  temperature 
is  not  to  exceed  212°,  the  kettle  is  filled  with  water,  while,  if  it  is 
comprised  between  212°  and  257°,  it  should  contain  a  solution  of 
chloride  of  calcium.  When  a  temperature  of  from  257°  to  302° 
is  required,  a  fixed  oil  is  used,  giving  the  preference  to  animal  oils, 
such  as  neatsfoot  oil,  as  they  yield  less  vapour  at  the  same  temper- 
ature, and  their  vapours  are  less  acid  than  those  of  vegetable  oils. 


412 


ORGANIC   CHEMISTRY. 


Fig.  635. 


Lastly,  if  the  operation  demands  a  still  higher  temperature, 
metallic  baths,  formed  of  alloys  of  lead,  bismuth,  and  tin,  are  em- 
ployed. 

Fig.  635  represents  a  more  simple  apparatus  than  that  of  fig.  634, 
and  which  possesses  some  advantages  over  the  latter.  It  is  com- 
posed of  an  iron  rod  tp,  fastened  by  means  of  a  thumbscrew  to 
one  of  the  ears  s  of  the  kettle  V.  Along 
l  the  rod  tp  slides  a  piece  of  bent  iron  cd 
\K  terminating  below  by  a  ring  gh^  on  which 
the  balloon  A  rests ;  while  a  second  ring 
e/,  fastened  to  an  iron  rod,  slides  along  the 
rod  cd^  and  may  be  fastened  to  it  at  any 
height  by  a  thumbscrew  z,  serving  to  hold 
the  balloon  in  a  fixed  position.  It  is  suffi- 
cient to  slide  the  movable  part  cd  of  the 
support  along  the  upright  tp  to  cause  the 
balloon  to  dip  into  the  kettle  V,  w^here  it  is 
then  secured  by  the  thumbscrew  r.  When 
the  metallic  bath  is  used,  it  should  be 
brought  to  the  liquid  state  before  dipping  the  balloon  into  it. 

A  second  iron  rod  t^p\  fastened  to  the  ear  s',  holds  the  air 
thermometer  B,  resembling  that  which  will  be  described  in  a  note 
at  page  414. 

The  bath  is  gradually  heated,  taking  care  that  the  temperature 
shall  constantly  rise ;  and  when  the  liquid  contained  in  the  bal- 
loon has  boiled,  it  begins  to  distil,  and  its  vapour  drives  ofi"  the  air 
contained  in  the  vessel,  which  partly  escapes  by  the  point  a.  If 
the  substance  be  valuable,  the  greater  portion  of  that  which  is 
evolved  can  be  collected,  by  introducing  the  point  a  into  a  small 
tube  closed  at  one  end.  The  temperature  is  then  raised  until  the 
point  at  which  the  examination  is  to  be  made  is  approached,  when 
all  the  doors  of  the  furnace  are  closed,  and,  stirring  the  bath  con- 
stantly, the  moment  is  awaited  when  the  temperature  becomes  sta- 
tionary. The  temperature  being  marked,  the  flame  of  an  alcohol 
lamp  is  passed  under  that  part  of  the  stem  of  the  balloon  which 
projects  from  the  fluid,  in  order  that  no  condensed  drops  shall 
remain ;  after  which  the  point  a  is  quickly  closed,  and  the  height 
T'  of  the  barometer  noted  down.  The  balloon  is  then  removed 
from  the  bath,  and  detached  when  it  is  cooled. 

The  temperature  T  of  the  mercurial  thermometer  requires  a  cor- 
rection, which  becomes  of  great  importance  in  high  temperatures, 
and  which  is  owing  to  the  circumstance  that  a  considerable  portion 
of  the  mercurial  column,  not  being  plunged  into  the  bath,  remains 
at  a  very  low  temperature.  Let  t  be  the  temperature  indicated  by 
a  small  thermometer,  the  bulb  of  which  is  kept  in  contact  with  the 
tube  of  the  principal  thermometer,  at  the  height  of  about  one-half 
of  the  mercurial  column  which  rises  above  the  level  of  the  bath ; 


INTRODUCTION.  413 

and  e  the  division  of  the  principal  thermometer,  at  about  2  or  3 
centimetres  above  the  level  of  the  bath :  it  may  then  be  admitted 
that  (T— e)  represents  the  portion  of  the  mercurial  column  at 
the  average  temperature  t.  Now,  this  portion  would  dilate  by 
(T—e) .  ^^  if  it  were  heated  from  ^  to  T ;  for  which  reason  the 
true  temperature  T'  of  the  bath  is  obtained  by  adding  to  the  tem- 
perature observed  T  the  number  of  degrees  represented  by  the 
expression  (T-e)  >~l'  ^ 

But  as  the  temperature  T'  is  that  of  the  mercurial  thermometer, 
it  is  necessary  to  find  the  temperature  T''  which  corresponds  to  it 
on  the  air  thermometer.  Mercurial  thermometers  agree  necessarily 
from  32°  to  212°,  which  are  the  fixed  points  by  which  their  scales 
are  governed;  while  they  differ  at  a  temperature  above  212°, 
because  the  various  kinds  of  glass  of  which  the  bulbs  of  thermome- 
ters are  made  do  not  obey  the  same  law  of  expansion.  The  fol- 
lowing table  shows  the  simultaneous  temperatures  indicated,  1st, 
by  a  mercurial  thermometer,  of  which  the  bulb  is  made  of  the  ordi- 
nary glass  used  in  Paris  for  making  chemical  tubes ;  2dly,  by  a  mer- 
curial thermometer,  of  which  the  bulb  is  of  crystal  from  Choisy-le- 
Roi ;  and  3dly,  by  an  air  thermometer,  of  which  the  volume  of  air  is 
constant  and  the  pressure  variable.* 

Simultaneous  Temperatures 

Of  a  mercurial  thermo-  Of  a  mercurial  thermo-  Of  an  air- 

meter  of  ordinary  glass.  meter  of  crystal.  thermometer. 

100°   centigrade   100°  100° 

109.98 110.05 110 

119.95 120.12 120 

129.91 130.20 130 

139.85 140.29 140 

149.80 150.40 150 

159.74 160.52 160 

169.68 170.65 170 

179.63 180.80 180 

189.65 191.01 190 

199.70 201.25 200 

209,75 211.53 210 

219.80 221.82 220 

229.85 232.16 230 

239.90 242.55 240 

250.05 253.00 250 

260.20 263.44 260 

270.38 273.90 270 

280.52 284.48 280 

290.80 295.10 290 

*  This  being  a  merely  comparative  table,  the  centigrade  divisions  have  not  been 
corrected  to  the  corresponding  temperatures  of  the  Fahrenheit  scale. —  W.  L.  F. 


414 


ORGANIC   CHEMISTRY. 


Of  a  mei*curial  thermo- 
meter of  ordinary  glass. 

301.08° 

Of  a  mercurial  thermo- 
meter of  crystal. 

305.72 

Of  an  air 
.      thermometer. 

300 

311.45 

316.45 

310 

321.80 

327.25 

320 

332  40 

338.22 

330 

343.00 

349.30 

340 

354.00 

360.50 

350 

When  the  operation  is  performed  at  higher  temperatures,  above 
570°  (Fahrenheit)  for  example,  and  great  exactness  is  required,  it 
is  better  to  substitute  an  air  for  a  mercurial  thermometer  ;  which  is 
absolutely  necessary  when  660°  is  exceeded,  since  at  this  temper- 
ature mercury  boils  under  the  ordinary  pressure  of  the  atmosphere ; 
and  the  boiling  manifests  itself  even  at  somewhat  lower  tempera- 
tures in  thermometers  perfectly  freed  from  air,  unless  the  calibre  of 
the  tube  be  so  small  as  to  present  great  resistance  to  the  ascent  of 
the  metal.     In  a  note,*  at  the  bottom  of  this  page,  we  shall  explain 


*  The  air  thermometer  used  in  these  experiments  consists  of  a  simple  cylin- 
drical glass  reservoir,  of  about  2  centimetres  in  diameter  and  12  or  15  centimetres 
in  length,  and  terminating  by  a  capillary  tube,  of  which  the  calibre  is  1  or  2  milli- 
metres, and  which  is  bent  to  a  right  angle,  and  drawn  out  at  its  end.  The 
reservoir  ab  is  kept  in  the  bath,  alongside  of  the  balloon  in  which  the  vapour  is  to 
be  generated.  The  first  step  is  to  perfectly  dry  the  reservoir  ab,  by  creating  a 
vacuum  in  it  several  times,  and  allowing  air  to  entei*  which  has  been  dried,  by 
passing  through  a  tube  filled  with  pumice-stone  soaked  in  concentrated  sulphuric 
acid  ;  after  which  the  bath  is  heated,  and,  when  the  temperature  becomes  station- 
ary at  the  point  at  which  the  experiment  is  to  be  terminated,  the  point  of  the  bal- 
loon and  that  of  the  air  thermometer  are  closed  simultaneously,  by  means  of  a  lamp. 
The  air  reservoir  is  then  placed  on  the  metallic  support  represented  in  fig.  6;-'6, 
the  stem  passing  through  a  cork  which  closes  a  tubulure  made  in  the  centre  of  the 

disk  gh,  while  the  curved  point  cd  enters  a  small 
mercurial  bath.  The  extremity  of  the  point  being 
broken  with  a  pincers,  the  mercury  rises  in  tlie 
tube  and  partly  fills  the  reservoir  ab,  which  is 
surrounded  with  pounded  ice,  in  order  to  reduce 
the  temperature  of  the  air  it  contains  to  32°, 
when  the  open  point  is  closed  with  a  ball  of  soft 
wax.  In  order  to  perform  this  operation  easily, 
without  changing  the  level  of  the  mercury  in  the 
vessel  A,  a  small  iron  spoon  u  is  used,  soldered 
to  an  iron  rod  uv,  which  slides  .  along  a  hori- 
zontal bar  vs,  itself  movable  along  the  ver- 
tical foot  st ;  the  movable  rod  vs  being  fixed  at 
such  a  height  that  the  bowl  of  the  spoon,  filled 
with  soft  wax,  is  exactly  at  the  height  and  in  the 
direction  of  the  point  cd.  It  is  therefore  suflB- 
cient,  in  order  to  close  the  point,  to  slide  the  end 
uv  along  the  horizontal  rod  vs.  The  mercury  in 
the  vessel  A  is  then  exactly  levelled  to  the  point  t 
of  a  double-pointed  screw  H;  the  ice  which  sur- 
rounded the  reservoir  ab  is  removed,  and,  when 
the  mercurial  column  attains  the  temperature  of 
•  the  surrounding  air,  the  difi"erence  of  height  be- 
tween the  mercury  in  the  reservoir  ab  and  the 
upper  point  k  is  exactly  measured,  by  means  of 


Fig.  686. 


INTRODUCTION.  415 

tKe  manner  of  arranging  an  air  thermometer,  and  deducing  the 
temperature  from  it. 

The  balloon  A  having  been  well  wiped  and  washed  with  alcohol, 


a  cathetometer ;  and  by  adding  to  this  difference  the  length  of  the  screw  ki,  the 
height  h  of  the  column  of  mercury  elevated  in  the  air  thermometer  is  obtained. 
Let  /io  be  this  height  at  32°,  H,  the  height  of  the  barometer  also  at  32°,  when  the 
point  d  is  closed  with  wax;  then  will  (H^  —  h^)  represent  the  elastic  force  of  the 
air  in  the  reservoir  ab  at  the  temperature  of  32°.  The  support  is  then  inverted, 
the  air  thermometer  removed,  after  having  detached  the  spoon  u,  and  it  is  weighed 
with  the  mercury  contained :  let  its  weight  be  represented  by  Q.  The  thermome"- 
ter  is  then  filled  with  mercury,  which  is  boiled  to  drive  off  the  last  bubbles  of  air  ; 
the  point  cd  being  kept,  during  this  time,  in  a  small  capsule  filled  with  mercury. 
When  the  apparatus  is  cooled,  it  is  surrounded  with  melting  ice,  and  completely 
filled  with  mei'cury  at  32° ;  when  it  is  again  weighed,  giving  now  the  weight  Q^. 
The  weight  q  of  the  envelope  of  glass  alone  being  ascertained,  after  having  emptied 
it  of  mercury,  (Q — q)  is  therefore  the  weight  of  the  mercury  at  32°,  and  (Q — q) 
is  the  weight  of  the  mercury  in  the  thermometer  when  it  was  on  the  support. 
(Q' —  Q)  therefore  represents  the  weight  of  the  mercury  at  32°,  which  occupies  the 
same  volume  as  the  air  remaining  in  the  thermometer  when  it  is  at  32°,  and  under 
the  pressure  (H^ — h^.)     If  we  designate  by  i  the  density  of  the  mercury  at  32°, 

—7 —  represents  the  capacity  in  cubic  centimetres  of  the  thermometer,  and  —j— 
the  volume  which  the  air  occupies  in  this  apparatus  at  the  moment  of  closing  the 
point  c  with  wax. 

Now,    the  capacity  of  the   thermometer,   at  the   temperature  T,  being  ^^^ 

(I+AjT),  the  volume  of  air  ^'"7^  at  32°  and  under  the  pressure  (Hg  — AJ,  there- 
fore occupies,  when  it  is  raised  to  the  temperature  T,  and  under  the  pressure  H^, 
a  volume  ~'^  (1-|-^T).  The  volume  assumed  by  a  volume  of  air  — r —  at  32° 
and  under  the  pressure  (H^ — A^),  when  raised  to  the  temperature  T  and  under 
the  pressure  H',,,  may  be  calculated,  by  the  known  laws  of  the  expansion  of  air, 
under  changes  of  temperature  and  pressure ;  and  is  thus  found  to  be, 

^^(1+ 0.00367,T)?^°, 
which  leads  to  the  equation, 

^^(14.0.00367.T)^=^°=^^(1— A:T), 

whence 

l+fcT     _Q^— Q    Ho— ftp 

1  +  0.00367.T       Q'  — ?  *       H'o 

T  may  be  deduced  from  this  equation,  but  there  is  no  necessity  of  knowing  its 
value  in  order  to  calculate  the  density  of  the  vapour,  wnich,  in  fact,  is  represented 
by  the  expression 

0.0012932  .  V.     ^  +  ^"^      .  g^. 

1  +  0.00367.T      760 

Substituting  for  ■.  A'to^'^-f'  *^®  value  first  found,  there  results  for  the  expres- 
sion of  the  density  of  the  vapour, 

0.0012932.V.  '^~^  .  liiiz^. 
Q'— 2         760 


416 


ORGANIC   CHEMISTRY. 


if  necessary,  its  weight  P'  is  accurately  ascertained,  taking  care  to 
operate  as  much  as  possible  under  the  same  circumstances  of  tem- 
perature and  pressure  as  were  observed  in  weighing  the  empty  bal- 


The  process  described  (g  1236)  is  applicable  to  the  determination  of  the  densities 
of  the  vapour  of  all  volatile  organic  substances,  and  that  of  volatile  mineral  sub- 
stances, when  the  temperature  need  not  be  raised  above  930°  ;  but  it  is  of  difficult 
application  to  higher  temperatures,  because  the  glass  softens,  and  the  ballot  n 
becomes  misshapen  from  the  pressure  of  the  metallic  bath  in  which  it  is  heated. 
By  conducting  the  experiment  in  the  method  about  to  be  described,  exact  results 
may  be  obtained  even  at  the  temperature  of  1100°  or  1200°. 

Two  tubes  ob,  a'b\  (fig.  037,)  of  the  same  length  and  diameter,  made  of  as  hard 
glass  as  possible,  are  used,  one  of  which  serves  as  an  air  thermometer,  while  the 
second  is  intended  to  contain  the  vapour  of  the  volatile  substance.  The  latter  is 
composed  of  a  reservoir  a'b',  a  capillary  portion  b'c',  and  a  larger  portion  c'd',  in 
•which  a  portion  of  the  volatilized  substance  which  escapes  from  the  reservoir  a'b' 
is  condensed  ;  and  the  air  thermometer  terminates  in  a  capillary  tube  be,  to  the  end 
of  which  is  luted  a  small  steel  stopcock  r.  The  two  tubes  are  arranged  alongside 
of  each  other,  on  a  small  support  made  of  three  parallel  disks  of  sheet-iron,  held 

together  by  iron  rods.  The 
air  thermometer  has  previ- 
ously been  filled  with  dry 
air,  and  a  certain  quantity 
of  the  substance,  the  den- 
„.      p^-  sity  of  the  vapour  of  which 

axg.  oo/.  jg   ^^   l^g    determined,    has 

been  introduced  into  the  tube  a'h'c'.  They  are  heated  simultaneously  in  air  ap- 
paratus (fig.  638),  made  of  two  or  three  concentric  sheet-iron  tubes,  closed  at 
j^  /  one  end,  and  distant  from 
—^-—-^^^^^^^^^^^-^  each  other  about  one  centi- 
metre, the  pipes  being  intro- 
duced into  a  cast-iron  tube 
ABCD,  placed  on  a  semi- 
cylindrical  grate,  so  that  it 
may  be  surrounded  by  char- 
coal. 

The  apparatus  being  ar- 
ranged, the  grate  is  filled  with 
burning  coals,  and  the  temperature  rapidly  raised,  avoiding  all  cause  of  sudden 
cooling.  When  the  volatile  substance  is  distilled,  and  the  excess  has  condensed 
in  the  cold  portion  of  the  tube  c'd',  the  temperature  is  again  raised,  (if  the  glass 
does  not  become  misshapen,)  this  time  as  slowly  as  possible.  The  stopcock  r  of 
the  air  thermometer  is  then  closed,  while  at  the  same  time  the  capillary  tube  b'& 
which  terminates  the  vapour  reservoir  a'b'  is  sealed  by  means  of  the  flame  of  a 
lamp.  The  height  H'  of  the  barometer  being  now  noted  down,  the  support,  with 
the  two  tubes,  which  are  allowed  to  cool  completely,  is  removed. 

In  order  to  determine  the  temperature  T  to  which  the  air  thermometer  has 
been  raised,  the  latter  is  placed  in  communication  with  the  manometric  apparatus, 
(fig.  639,)  which  is  composed  of  two  tubes /^,  hi,  luted  into  a  piece  having  a  stop- 
cock R,  resembling  that  of  the  figure,  the  upper  end  of  the  tube  hi  being  open, 
while  the  tube  fg  is  terminated  by  a  bent  capillary  tube,  to  which  a  steel  tubulure 
s  has  been  luted.  Fig.  640  represents  a  section  of  the  stopcock  tubulure  r, 
mounted  on  the  air  thermometer,  and  a  section  of  the  tubulure  s  of  the  manome- 
ter. It  will  be  seen  that  the  first  tubulure  is  terminated  by  a  plain  surface  ah 
and  a  projecting  cone  o,  while  the  second  has  also  a  plain  surface  a'b'  and  a 
hollow  cone  o',  which  exactly  fits  the  plain  surface  and  projecting  cone  of  the 
other.  In  order  to  close  them  hermetically,  it  is  sufficient  to  press  the  two 
parts  against  each  other,  by  means  of  the  pincers,  (fig.  641,)  which  is  tightened 
with  screws,  after  having  poured  in  a  small  quantity  of  melted  caoutchouc. 


INTRODUCTION. 


417 


loon  ;  and  in  case  the  new  circumstances  should  differ  greatly  from 
the  former  ones,  a  correction  will  be  necessary,  which,  however,  we 
shall  not  mention,  as  in  general  it  may  be  neglected. 


Fig.  639. 


Fig.  641. 


The  mano- 
meter has  b'een 
filled  with  mer- 
cury before 
adapting  the 
thermometer  to 
it;  and  the  lat- 
ter is  then 
completely  sur- 
rounded by 
melting  ice, 
when  the  mer^ 
cury  of  the  ma- 
nometer is  al- 
lowed to  escape 
through  the 
stopcock  R  so 
as  to  produce 
a  great  differ- 
ence between 
the  level  in  the 
columns  /^,  hi. 
The  stopcock  r 
is  then  opened, 
and  a  portion 
of  the  reservoir 
ab  allowed  to 
enter  the  tube 


gh,  after  which  mercury  is  carefully  poured  into  the  tube/e,  so  as  to  bring  its 
level  accurately  to  a  mark  a  at  the  top  of  the  tube  gh.  The  next^step  is  to  mea- 
sure, by  the  cathetometer,  the  difference  h  of  the  height  of  the  mercurial  columns, 
and  to  mark  the  temperature  6  of  the  small  thermometer  at  the  side  of  the  manome- 
ter, as  well  as  the  height  H"  of  the  barometer.  The  volume  of  air  is  then  composed 
of  the  volume  V,  equal  to  the  capacity  of  the  air  thermometer  abc,  kept  at  32°, 
and  of  the  volume  v  which  the  air  occupies  in  the  manometer  at  the  tempera- 
ture d.     The  weight  of  this  air  is 

0.0012932  gm.   [V'+i;  i^o.oo367.  J  ^' 

Now  the  same  quantity  of  air  occupied,  at  the  unknown  temperature  T,  at  the  mo- 
ment of  closing  the  stopcocks,  a  volume  V  (1-|-A;T),  and  its  weight  was  expressed  by 

1-|-A;T 


so  that 


0.0012932  gm. .  T^j^^^^^^  •  ^i ; 
0.0012932  [v'+t'i+o^J  5^  =  0.0012982 .V'.j:^:^!^.,^-, 


whence 


Ho— Ao 


1-1-0.00367.  T'  L      ■"  V '  l-i-0.00367.  dj       H' 

The  second  member  of  the  equation  contains  only  known  quantities,  except, 
indeed,  the  ratio  ~,  which  is  determined  in  the  following  manner : — The  tube  abc 
being  detached  from  the  manometer,  the  tube  gh  is  completely  filled  with  mercury ; 
and  then,  bringing  the  stopcock  R  into  the  position  of  fig.  639,  the  mercury  in  the 
leg  gh  is  allowed  to  escape  until  its  level  reaches  the  mark  at,  while  the  mercury 
Vol.  XL— 27  ^ 


418  ORGANIC   CHEMISTRY. 

P'—  (P-rp)  therefore  represents  the  weight  of  the  volatile  sub- 
stance which  remains  in  the  balloon,  the  point  of  which  being 
broken  under  the  mercury,  the  atmospheric  pressure  causes  the 

which  escapes  is  collected  in  a  small  bottle  and  weighed.  Its  weight  may  be  con- 
sidered as  representing  the  volume  v.  The  mercury  is  allowed  to  escape  from  the 
leg  ffh,  it  until  its  level  reaches  another  mark  0,  on  the  tube  gh,  when  the  quantity 
thus  obtained,  being  weighed,  compounds  to  a  volume  v'  which  should  be  a  notable 
fraction  of  the  capacity  of  the  thermometer-tube.  This  being  done,  and  the  level 
of  the  mercury  reaching  the  mark  a  of  the  manometer,  under  the  pressure  of  the 
atmosphere,  the  air  thermometer  is  fitted  to  the  manometer,  the  reservoir  oibeii.g 
kept  at  the  temperature  of  the  surrounding  medium.  As  the  two  columns  of  mercury 
are  on  a  level  in  the  manometer,  thore  is  a  volume  of  air  (V'-f-t')  under  the  exter- 
nal pressure  H.  The  mercury  is  allowed  to  flow  frcm  the  two  legs  of  the  mano- 
meter, by  bringing  the  stopcock  R  into  tlie  position  in  the  figure,  and  the  level  of 
the  mercury  is  brought  to  the  mark  /S;  when  the  two  columns  are  now  no  longer 
on  a  level,  and  their  difference  of  height  //  can  be  measured.  There  is,  therefore, 
a  volume  of  air  (V'-j-v-f-^')  under  the  pressure  (H— A)  ;  and  agreeably  to  the  law 
of  Mariotte, 

Y'-\-v     __H— A 

V'-fi;-f  v'  ~~    H    ' 

whence  the  volume  V  may  be  deduced. 

It  now  only  remains  to  ascertain  the  weight  of  the  vapour  which  filled  the  re- 
servoir a'b'  at  the  moment  of  closing  it,  and  the  capacity  of  the  reservoir.  It  may 
be  admitted  that  the  reservoir  a'b'  does  not  contain  any  air,  because  there  was 
originally  introduced  into  it  a  quantity  of  volatile  matter  sufficient  to  expel  all 
the  air.  The  closed  end  of  the  tube  is,  therefore,  broken,  and  the  latter  weighed 
filled  with  air  and  the  substance  it  contains ;  after  which  its  weight  is  again  ascer- 
tained when  the  substance  has  been  removed,  the  difference  of  weight  5r  represent- 
ing the  weight  of  the  substance.  In  order  to  obtain  the  volume  V  of  the  reservoir, 
the  quantity  of  water  which  will  fill  it  is  weighed;  and  now  all  the  elements  are 
known  which  are  necessary  to  calculate  the  density  of  the  vapour,  by  means  of  the 
formula 


0.0012932  .  V.  — ^"^^        ^'^ 


l-f  0.00367.T '   760' 

the  value  ascertained  by  the  air  thermometer  being  substituted  for  ^  t  q  oo367  t* 

It  frequently  happens  that  the  substance,  the  density  of  whose  vapour  is 
to  be  determined,  is  changed  by  absorbing  oxygen  from  the  air  at  the  high  tem- 
perature at  which  it  volatilizes :  in  which  case  it  becomes  necessary  to  fill  the 
tube  a'b'  with  nitrogen  gas,  and  further,  in  order  to  prevent  the  air  from  entering 
freely,  to  fit  a  pointed  tube  by  means  of  a  cork  to  the  tube  c'd'. 

By  means  of  the  process  just  described,  the  density  of  any  vapour  might  be  de- 
termined at  very  high  temperatures,  if  it  were  possible  to  procure  glass  tubes  of 
sufficient  hardness ;  but,  unfortunately,  the  strongest  glass  softens  at  a  red-heat, 
and,  therefore,  cannot  be  used  for  higher  temperatures.  Porcelain  tubes,  how- 
ever, made  of  the  same  shape  as  the  glass  tubes,  by  the  process  described  in 
§  715,  might  answer  the  purpose.  It  is,  moreover,  unnecessary  to  hermetically 
seal  the  fine  point  c'd',  when  the  substance  boils  at  a  very  high  temperature, 
because  there  is  then  no  fear,  at  the  moment  of  withdrawing  the  tubes  from  the 
cylinders,  that  a  portion  of  the  vapours  which  escape  from  the  reservoir  might 
re-enter  the  latter. 

But  there  are  volatile  substances,  the  density  of  the  vapour  of  which  it  would 
be  very  interesting  to  know,  and  which,  at  a  high  temperature,  attack  the  alka- 
line silicates ;  in  which  case  tubes  of  glass  or  porcelain  can  no  longer  be  used, 
and  resort  must  be  then  had  to  metallic  tubes,  previously  filled  with  nitrogen  gas. 
The  portion  of  the  volatile  substance  which  remains  in  the  reservoir  intended  ta 
contain  the  vapour  is  then  determined  by  chemical  processes. 


INTRODUCTION.  419 

liquid  to  ascend,  and  completely  fill  the  balloon,  if  the  air  has  been 
entirely  driven  out  by  the  vapour,  as  we  shall  suppose  to  be  the 
case.  The  balloon  is  then  inverted,  when  the  volatile  substance,  if 
it  is  liquid,  ascends  in  the  neck,  and  may  be  removed  with  a  pipette. 
The  balloon  is  filled  with  mercury,  which  is  afterward  measured  by 
being  poured  into  a  large  bell-glass  divided  into  cubic  centimetres ; 
by  which  means  the  capacity  V  of  the  balloon,  at  the  ordinary  tem- 
perature U  is  exactly  found.  If  k  represents  the  coefficient  of  the 
average  expansion  of  glass,  between  the  temperature  t  and  T,  the 
capacity  of  the  balloon  will  be  V  (l-fA;T)  at  the  temperature  T. 
The  volume  V  (l-hA;T)  of  vapour  of  the  volatile  substance,  at  the 
temperature  T  and  under  the  pressure  H'o,  therefore  weighs  (P' — 
P-f  p),  while  the  weight  of  an  equal  volume  of  atmospheric  air, 
under  the  same  circumstances  of  temperature  and  pressure,  is 

0.0012932gm.V(l+AT)j:p5Ap3.^. 

Thus  the  density  of  the  vapour  of  the  substance  is  represented  by 
V'-V+p 

0.0012932. Va+^T).,^:,^.^. 

We  have  supposed  that  the  vapour  had  entirely  expelled  the  air 
from  the  balloon,  and  consequently  that  the  latter  was  entirely  filled 
with  mercury;  which,  however,  is  rarely  the  case,  as  most  fre- 
quently a  bubble  of  air  remains,  and  sometimes  the  remaining  vo- 
lume of  air  amounts  to  even  more  than  that,  when  the  vapour  is 
very  dense,  and  a  large  quantity  of  material  has  not  been  origin- 
ally introduced  into  the  balloon.  The  experiment  does  not  fail  on 
this  account,  for  it  is  sufficient  to  collect  this  volume  v  of  air  in  a 
small  graduated  bell-glass,  and  to  measure  it  exactly.  This  volume 
V  weighs 

0.0012932  gm..j^,i5j:^.^»=/, 

t"  and  H"o  representing  the  surrounding  temperature  and  pressure 
of  the  air  at  the  moment  of  measuring  the  volume  v. 

The  weight  of  vapour  in  the  balloon,  at  the  moment  of  closing  it, 
is  therefore  (P'— P+p— ^'^). 

The  volume  v  of  air  occupies  in  the  balloon,  at  the  moment  ot 
closing  it,  at  the  temperature  T,  and  supposed  to  be  reduced  to  th( 
pressure  H'o,  a  volume 

/__      l+0^00367J      Wo 
^  '^i-H)-00367.r*H'o  • 

The  volume  occupied  by  the  vapour  in  the  balloon,  at  the  tempera- 
ture T  and  under  the  pressure  H'^,  is  therefore  only  [V  (1+ A;T)— t;'] ; 
and  as  an  equal  volume  of  air,  under  the  same  circumstances  of  tem- 
perature and  pressure,  weighs 

0.001293  gm.  [V  (l+M)  -  t,']  i^^ij^,. 55, 


420  ORGANIC  CHEMISTRY. 

the  density  of  the  vapour  is  therefore 

F-P+jp~/ 

0.0012932  [V(l+>tT)-.']^^:^l3^.;^. 

In  accurate  experiments,  care  must  be  taken  to  leave  but  a 
very  small  quantity  of  air  in  the  balloon,  in  order  as  much  as 
possible  to  avoid  corrections,  which  always  possess  some  degree  of 
uncertainty. 

The  average  coefficient  h  of  the  expansion  of  glass,  between  the 
temperatures  0  and  T,  varies  with  the  different  kinds  of  glass ;  and 
varies,  moreover,  in  the  same  glass,  with  the  temperature  T.  We 
subjoin  its  value,  at  different  intervals  of  temperature,  for  the  ordi- 
nary glass  of  which  the  balloons  used  in  Parisian  laboratories  are 
made : 

Between  0°  and  100° A:=0.0000276 

150    0.0000284 

"  200    0.0000291 

«  250    0.0000298 

"  300    0.0000306 

"  350    0.0000313 

Organic  substances  which  boil  at  high  temperatures  are  fre- 
quently easily  altered  by  the  air,  at  the  temperature  to  which  their 
vapours  must  be  heated  in  order  to  obtain  constant  densities ;  in 
w^hich  case,  care  must  be  taken  to  fill  the  balloon  with  carbonic 
acid  gas,  when  it  is  placed  in  the  kettle,  before  heating  the  latter. 
IF  or  this  purpose,  the  point  of  the  balloon  is  made  to  communicate 
with  a  small  air-pump,  to  the  second  tubulure  of  which  an  apparatus 
disengaging  carbonic  acid  gas  is  adapted;  and  a  vacuum  being 
made  several  times,  and  carbonic  acid  gas  allowed  to  enter  each 
time,  the  rest  of  the  experiment  is  then  conducted  as  usual. 

In  many  cases  it  may  be  of  advantage  to  determine  the  density 
of  a  vapour  under  a  pressure  below  that  of  the  atmosphere,  because 
then  the  substance  boils  at  a  lower  temperature,  and  in  general  it 
is  not  necessary  to  raise  the  temperature  so  high  in  order  to  obtain 
constant  densities.  This  result  is  particularly  advantageous  when 
substances  easily  altered  by  heat  are  operated  on,  and  the  boiling 
point  of  which  is  high.  In  this  case,  a  capillary  tube  ah^  terminat- 
j  p  I  ing  in  a  larger  one  cd^  is  soldered  to  the  balloon,  (fig. 
642 ;)  and  the  latter  being  placed  in  the  bath,  the  tube 
ed  is  made  to  communicate  with  a  large  bottle  placed  in 
.„  a  water-bath  kept  at  a  constant  temperature,  approach- 
ing that  of  the  surrounding  temperature;  while  the 
second  tubulure  of  the  bottle  is  made  to  communicate 
^'  '  with  a  mercurial  manometer  which  indicates  the  inter- 
nal pressure  at  every  moment,  and  with  an  air-pump,  by  means  of 
which  the  air  in  the  bottle  and  balloon  is  reduced  to  the  desired 


INTRODUCTION.  421 

degree  of  elasticity.  The  experiment  is  then  conducted  in  the  same 
manner  as  when  the  operation  is  performed  under  the  pressure  vf 
the  atmosphere ;  it  being  sufficient  to  substitute  in  the  formula  the 
elastic  force  of  the  air  observed  on  the  manometer,  for  the  baro- 
metric pressure  H'o. 

The  second  method,  which  has  just  been  described,  to  determine 
the  densities  of  vapours  of  volatile  substances,  may  furnish  very  in- 
accurate results  when  it  is  applied  to  very  impure  substances,  for 
example,  to  those  containing  a  small  quantity  of  less  volatile  mat- 
ter, the  density  of  whose  vapour  is  very  different  from  that  of  the 
substance  being  examined.  The  error  increases  with  the  quantity 
of  the  substance  introduced  into  the  balloon,  because  the  less  vola- 
tile matter  is  necessarily  concentrated  in  it,  and  the  vapour  finally 
filling  the  balloon  contains  a  much  larger  proportion  of  the  foreign 
matter  than  the  substance  which  was  introduced  into  it.  It  is 
necessary,  whenever  any  doubt  may  be  entertained  as  to  the  purity 
of  the  substance,  the  density  of  whose  vapour  is  to  be  determined 
by  this  method,  to  carefully  collect  the  portion  of  matter  which 
remains  in  the  balloon,  and  subject  it  to  analysis,  in  order  to  ascer- 
tain if  its  composition  differs  appreciably  from  that  of  the  original 
substance. 

§  1237.  It  still  remains  to  explain  the  method  of  comparing  the 
density  of  vapour  afforded  by  experiment  with  the  theoretical  den- 
sity calculated  from  the  formula,  when  the  latter  is  determined. 
We  will  take  alcohol  as  an  example. 

The  experiments  detailed  (§  1234)  assign  1.602  for  the  density 
of  the  vapour  of  alcohol,  within  the  limits  of  temperature  in  which 
this  vapour  obeys  the  laws  of  permanent  gases.  The  formula  which 
we  have  adopted  for  the  equivalent  of  alcohol  is  CJIqO^.  Now,  as 
the  density  of  hydrogen  is  known  to  be  0.0692,  and  2  volumes  have 
been  adopted  as  its  gaseous  equivalent,  the  6  equivs.  of  hydrogen 
are  therefore  represented  by  12  volumes  of  this  gas,  which  weigh 
12  +  0.0692=0.8304. 

The  hypothetic  density  of  the  vapour  of  carbon  being  0.8290, 
(§  203,)  and  its  gaseous  equivalent  being  represented  by  1  vol.,  the 
4  equivs.  of  carbon?  are  therefore  represented  by  4  vols,  of  vapour 
of  carbon,  which  weigh  4x0.8290  =  3.3160. 

The  density  of  oxygen  gas  is  1.1056,  and  its  equivalent  is  repre- 
sented by  1  vol. ;  and  2  equivs.  of  oxygen  are  therefore  represented 
by  2x1.1056  =  2.2112. 

The  formula  C^HgOg  therefore  gives 

4  eq.  of  carbon 3.3160 

6    "         hydrogen 0.8304 

2    "         oxygen .• 2.2112 

6.3576 

Now,  since  -^  =  1.5894  differs  but  little  from  the  number  1.602, 


422  ORGANIC   CHEMISTRY. 

which  has  been  found  by  direct  experiment,  the  conclusion  may. be 
drawn  that  the  equivalent  C^HgOa  of  alcohol  is  represented  by  4 
volumes  of  vapour. 

The  difference  between  the  theoretical  number  1.5894  and  the 
number  1.602  found  by  experiment,  may  be  partly  attributed  to 
slight  errors  which  always  occur  in  determinations  of  this  kind ; 
and  similar,  and  even  greater  differences  are  observed,  when  the 
experiments  are  conducted  with  the  greatest  exactness.  This  is 
owing  to  the  fact  that  the  laws  of  elasticity  of  gases,  and  their  expan- 
sion by  heat,  which  we  have  admitted  as  being  strictly  the  same  for 
all  the  gases  above  taken  into  account,  are  not  really  so  under  the  cir- 
cumstances accessible  to  our  means  of  observation.  The  gases  which 
have  not  yet  been  liquefied  differ  from  it  themselves  very  widely,  at 
the  ordinary  temperature ;  and  it  is,  therefore,  very  probable  that 
the  differences  are  greater  for  the  majority  of  vapours,  even  under 
the  most  favourable  circumstances  of  temperature  and  pressure. 

OF  THE  ANALYSIS  OF  GASES. 

§  1238.  We  have  frequently  had  occasion  to  refer  to  the  analysis 
of  gaseous  substances  in  the  first  part  of  this  work,  either  for  the 
sake  of  determining  the  composition  of  definite  gases,  or  the  pro- 
portions in  which  such  gases  existed  in  mixtures.  We  have  described 
the  most  simple  processes  used  by  chemists,  but  as  the  processes  do 
not  afford  the  degree  of  precision  demanded  by  the  subject,  we  shall 
now  describe  other  processes  by  which  a  precision  can  be  attained, 
in  the  analysis  of  gases,  which  is  not  exceeded  by  any  of  the  most 
exact  manipulations  of  chemical  analysis.  We  shall,  in  the^  first 
place,  suppose  that  it  is  required  to  analyze  a  mixture  of  atmo- 
spheric air  and  carbonic  acid ;  and,  while  applying  the  processes 
already  described,  we  shall  discuss  the  causes  of  error  to  which 
they  are  subject. 

It  will  be  recollected  that  a  certain  volume  of  this  mixture  is 
measured  over  mercury  in  a  graduated  cylinder,  and  that  in  order 
to  be  more  certain  of  the  degree  of  moisture  of  the  gas,  the  latter 
was  saturated  with  moisture  by  leaving  the  sides  of  the  cylinder 
slightly  damp.  •" 

The  first  difficulty  which  presents  itself  is.  What  is  the  tempera- 
ture of  the  gas,  and  what  its  elastic  force  ?  The  temperature  of  the 
gas  is  generally  assumed  as  that  indicated  by  a  thermometer  placed 
in  the  vicinity  of  the  cylinder ;  but  is  it  always  certain  that  the  two 
temperatures  are  identical?  As  to  the  pressure,  it  is  generally 
reduced  to  an  equality  with  that  of  the  atmosphere,  by  properly 
sinking  the  cylinder  into  the  mercury-bath ;  a  process  which  pos- 
sesses but  little  accuracy ;  or,*  indeed,  when  the  operation  is  effected 
more  exactly,  a  certain  column  of  mercury  is  left  upraised,  and 
measured  by  a  graduated  scale,  or  better  still,  by  the  process  de- 
scribed in  the  note  to  page  414. 


INTRODUCTION. 


423 


In  order  to  absorb  the  carbonic  acid,  a  small  quantity  of  a  con- 
centrated solution  of  caustic  potassa  is  introduced  into  the  bell-glass, 
and  the  latter  is  shaken ;  after  which  the  proportion  of  carbonic 
acid  is  determined  by  again  measuring  the  gaseous  volume.  But 
the  second  measuring  is  still  more  uncertain  than  the  first,  for,  to 
the  difficulties  already  pointed  out,  is  added  that  of  ascertaining 
the  degree  of  moisture  of  the  gas  in  the  presence  of  the  solution  of 
potassa  ;  in  addition  to  which,  the  form  of  the  meniscus  of  the 
liquid  is  now  changed  from  convex  to  concave ;  and  the  sides  of  the 
bell-glass  are  moistened  with  a  viscous  liquid,  which  diminishes  ap- 
preciably its  diameter. 

These  difficulties  are  overcome  by  replacing  the  solution  of  potassa 
by  a  small  ball  of  potassa  affixed  to  a  platinum  wire,  by  which  it  is 
introduced  into  the  bell-glass  through  the  mercury ;  but  in  this  case 
the  carbonic  acid  is  very  slowly  absorbed,  which  renders  it  neces- 
sary to  wait,  not 
only  until  the 
absorption  of 
carbonic  acid  is 
complete,  but 
also  until  the 
potassa  has  ab- 
sorbed all  the 
vapour  of  water 
which  existed  in 
the  gas  or  on 
the  sides  of  the 
bell-glass ;  be- 
cause it  would 
otherwise  be  im- 
possible to  as- 
certain its  state 
of  saturation. 
In  order  to  be 
sure  that  this 
condition  is  ful- 
filled, the  gas 
^^^^^  must  be  exactly 
measured  alter 


Fig.  643.  Fig.  644.  .       . 

havmg  with- 
drawn the  ball  of  potassa,  and  the  latter  must  be  again  introduced 
and  allowed  to  remain  for  at  least  12  hours ;  when  the  result  of  a 
second  measurement  of  the  gas  should  be  identical  with  the  first. 

The  proportion  of  oxygen  in  the  remaining  gas  is  determined, 
either  from  the  gaseous  volume  which  disappears  when  this  gas  is 
burned  with  an  excess  of  hydrogen,  or  by  the  diminution  of  ^ 
volume  of  the  gas  when  left  for  a  sufficient  length  of  time  in  con- 


424 


ORGANIC   CHEMISTRY. 


tact  with  a  substance  which  combines  with  oxygen.  The  manner 
of  eiFecting  this  absorption  by  phosphorus  has  already  been  ex- 
plained, (§  946 ;)  and  in  §  83  the  eudiometer  in  which  the  analysis  is 
made  by  combustion  was  described ;  but  the  process  is  always  liable, 
without  regard  to  the  method  adopted,  to  some  of  the  causes  of 
error  pointed  out  above. 

§  1239.  With  the  eudiometric  apparatus  about  to  be  described 

these  analyses  can,  on  the 
other  hand,  be  performed 
very  rapidly,  and  without 
any  danger  of  the  uncer- 
tainties just  mentioned. 
Fig.  643  represents  the 
geometrical  projection  of 
the  anterior  surface,  and 
fig.  644  gives  a  vertical 
section  made  through  a 
plane  perpendicular  to 
this  face ;  while  lastly, 
fig.  645  shows  a  perspec- 
tive view  of  the  whole. 

The  apparatus  is  com- 
posed of  two  parts,  which 
may  be  separated  and 
united  at  pleasure;  and, 
while  the  first,  or  the 
measurer,  serves  to  mea- 
sure the  gas  under  given 
conditions  of  temperature 
and  moisture,  in  the  se- 
cond the  gas  is  subjected 
to  various  absorbent  re- 
agents, on  which  account 
we  shall  call  it  the  ahsorption-tuhe. 

The  measurer  is  composed  of  a  tube  ah  of  15  to  20  millimetres 
diameter  internally,  divided  into  millimetres,  and  terminating  above 
by  a  curved  capillary  tube  bcr',  while  the  lower  end  is  luted  into  a 
cast-iron  piece  p'q\  having  two  tubulures  a,  ^,  and  a  stopcock  R. 
To  the  second  tubulure  i  is  luted  a  straight  tube  ih,  open  at  both 
ends,  of  tht  same  diameter  as  the  tube  ab,  and  also  divided  into 
millimetres.  The  stopcock  R  has  three  openings,  and  resembles 
precisely  that  of  which  sections  are  seen  in  figs.  624,  625,  and  626, 
in  the  three  principal  positions  in  which  the  key  may  be  turned. 
A  communication  can  therefore  be  established  at  will  between  the 
tubes  ab,  ih,  or  one  or  other -of  these  tubes  only  may  be  opened  to 
he  external  air. 
The  two  vertical  tubes  and  the  cast-iron  piece  form  a  manometric 


INTRODUCTION.  425 

apparatus  contained  in  a  glass  cylinder  pqp'q'  filled  with  water, 
which  is  maintained  at  a  constant  temperature,  marked  by  the 
thermometer  T,  during  the  whole  time  of  the  analysis.  The  mano- 
metric  apparatus  is  fixed  on  a  cast-iron  stand  ZZ'  furnished  with 
adjusting  screws. 

The  absorption-tube  is  composed  of  a  bell-glass  gf^  open  at  the 
bottom,  and  terminated  above  by  a  curved  capillary  tube /e  r.    The 
bell-glass  dips  into  a  small  mercurial  bath  U,  of  cast-iron,  exactly 
represented  in  figs.  646  and  647 ;  while  the  basin  U  is  fixed  on  a 
Fig.  646.       plate  which  can  be  raised  at  will  along  the  vertical 
support  ZZ',  by  means  of  the  toothed  rack  vw^  which 
works    with    the    toothed    pinion   o   set    in    motion 
by  the  crank  B.     The  ratchet  r  arrests  the  toothed- 
racks  and  consequently  keeps  the  basin  U  in  any  given 
position.     A  counterpoise  affixed  to  the  ratchet  facili- 
tates its  working,  and,  as  it  is  turned  to  one  side  or  the 
other,  the  ratchet  is  thrown  in  or  out  of  gear  with  the 
pinion. 

The  ends  of  the  capillary  tubes  which  terminate  the 

absorption-tube  and  measurer  are  luted  to  two  small 

steel   stopcocks  r,  r',  the  ends  of  which  exactly  fit 

Fig.  647.      each  other,  and  which  have  the  same  shape  as  those 

represented  in  fig.  639,  sections  of  which  are  seen  in  figs.  640 

and  641. 

The  absorption-tube  is  maintained  in  a  vertical  position  by  means 
of  pincers  u  lined  with  cork,  which  are  easily  opened  or  closed 
when  the  tube  is  to  be  removed  or  replaced.  The  measurer  ah  is 
traversed  at  h  by  two  platinum  wires  opposite  to  each  other,  the 
ends  of  which  approach  to  the  distance  of  a  few  millimetres  from 
the  inside  of  the  bell-glass,  and  of  which  the  other  ends  are  fast- 
ened with  wax  to  the  lower  edge  of  the  large  cylinder.  The  elec- 
tric spark  is  passed  into  the  bell-glass  by  means  of  these  wires ;  and 
the  water  in  the  cylinder  is  no  obstacle  if  the  spark  be  furnished  by 
a  Leyden  jar. 

§  1240.  Let  us  suppose  that  in  this  apparatus  a  mixture  of  atmo- 
spheric air  and  carbonic  acid  is  to  be  analyzed. 

Through  the  tube  ih  the  measure  ah  is  filled  with  mercury,  until 
the  latter  escapes  through  the  stopcock  r ,  which  is  then  closed ;  and 
at  the  same  time  the  absorption-tube  gf  is  filled  with  mercury ;  to 
eifect  which  the  tube  gf  is  detached  from  the  pincers  w,  and  plunged 
into  the  bath  U,  the  stopcock  r  being  open ;  and  the  operator 
sucks  with  a  glass  tube  furnished  with  a  caoutchouc  tubulure,  the 
edge  of  which  is  applied  to  the  plane  part  of  the  tubulure  r.  When 
the  mercury  begins  to  escape,  the  stopcock  r  is  closed. 

The  gas  to  be  analyzed,  which  has  been  collected  under  a  small 
bell-glass,  is  then  introduced  into  the  absorption-tube,  and  the  extra- 
vasation is  easily  performed  in  the  bath  U,  on  account  of  the  shape 


426  ORGANIC   CHEMISTRY. 

given  to  tlie  latter.  The  absorption-tube  being  then  replaced  by 
the  pincers  u,  the  two  tubulures  r,  r'  are  fitted  to  each  other :  then, 
elevating  one  end  of  the  bath  U,  and  allowing  the  mercury  of  the 
measurer  to  flow  from  the  other  through  the  cock  R,  and  lastly, 
opening  the  stopcocks  r,  r',  the  gas  is  caused  to  pass  from  the 
absorption-tube  into  the  measurer.  When  the  mercury  begins  to 
rise  in  the  capillary  tube  /<?,  its  escape  through  the  stopcock  R  is 
slackened,  so  as  to  cause  the  mercury  to  rise  very  gently  in  the 
tube/er,  and  the  cock  r  is  closed  when  the  mercurial  column  reaches 
a  mark  a,  on  the  horizontal  leg  er,  at  a  small  distance  from  the 
tubulure  r.  The  level  of  the  mercury  is  then  brought  to  a  given 
division  m  of  the  tube  ah,  and  the  difference  in  height  of  the  two 
columns  can  immediately  be  read  on  the  scale  of  the  tube  ih.  The 
water  in  the  cylinder  has  been  several  times  agitated,  throughout, 
by  blowing  air  into  it  by  means  of  a  tube  which  descends  to  the 
bottom. 

Let  ^  be  the  temperature  of  the  water,  which  is  to  be  stationary 
during  the  analysis,  /  the  elastic  force  of  the  aqueous  vapour  satu- 
rated at  this  temperature,  V  the  volume  of  the  gas,  H  the  height 
of  the  barometer,  and  lastly,  h  the  height  of  the  mercury  elevated : 
then  will  H  +  A— /  be  the  elastic  force  of  the  gas  when  supposed 
dry.  The  temperature  of  the  water  in  the  cylinder  should  be  nearly 
that  of  the  surrounding  air,  which  does  not  vary  sensibly  during 
the  short  duration  of  the  experiment ;  and  it  is  therefore  unnecessary 
to  reduce  to  32°,  by  calculation,  the  height  of  the  barometer,  and 
that  of  the  mercury  elevated  in  the  manometric  apparatus  ahih. 
The  gas  collected  in  the  measurer  is  moreover  always  saturated  with 
moisture,  because  the  sides  of  the  tube  ah  are  moistened  with  a  small 
quantity  of  water ;  and  this  is  constantly  the  same,  since  it  is  that 
which  the  mercury  does  not  remove  when  the  tube  is  filled  with  it. 

When  this  is  done,  the  mercury  is  again  allowed  to  flow  through 
the  stopcock  R,  and  the  cock  r  is  opened  in  order  to  allow  all  the 
gas  as  well  as  a  column  of  mercury  to  pass  into  the  tube  rch,  after 
which  the  stopcock  r'  is  closed.  The  absorption-tube  is  then 
detached ;  and  a  drop  of  a  concentrated  solution  of  potassa  is  passed 
up  by  means  of  a  curved  pipette  ;  when  the  absorption-tube  is  again 
fitted  to  the  measurer,  and  the  bath  U  allowed  to  fall  to  its  full 
extent ;  and  then,  after  having  poured  a  large  quantity  of  mercury 
into  the  tube  hi,  the  stopcocks  r,  r'  are  successively  opened.  The 
gas  thus  passes  from  the  measurer  into  the  absorption-tube,  and  the 
small  quantity  of  solution  of  potassa  completely  moistens  the  sides 
of  the  bell-glass.  The  cock  r  is  closed  when  the  mercury  begins  to 
fall  in  from  the  measurer  into  the  vertical  leg  ef  of  the  absorption- 
tube  ;  and  after  waiting  for  a  few  moments,  in  order  to  give  time 
for  the  absorbing  action  of  the  potassa,  the  gas  is  passed  from  the 
absorption-tube  back  into  the  measurer,  by  causing  the  bath  U  to 
ascend,  and  the  mercury  to  flow  through  the  cock  R.     As  soon  as 


INTRODUCTION.  427 

the  alkaline  solution  begins  to  rise  in  the  tube  /e,  an  inverse  move- 
ment is  caused  by  closing  the  stopcock  r ;  that  is,  the  gas  is  again 
passed  from  the  measurer  into  the  absorption-tube,  by  lowering  the 
bath  U,  and  again  pouring  mercury  into  the  tube  ih.  The  inten- 
tion of  this  operation  is  to  again  moisten  the  sides  of  the  bell-glass 
fg  with  the  solution  of  potassa,  and  subject  the  gas  to  the  absorbing 
action  of  the  new  layer  of  potassa. 

If  it  be  deemed  necessary,  these  operations  may  be  repeated 
several  times ;  although,  after  the  second,  the  whole  of  the  carbonic 
acid  is  generally  absorbed.  The  gas  is  then  passed  for  the  last  time 
from  the  absorption-tube  into  the  measurer,  and  the  cock  r  is  closed 
when  the  top  of  the  alkaline  column  reaches  the  mark  a.  The  level 
of  the  mercury  in  the  tube  ah  being  brought  to  m^  the  difference  of 
height  h'  of  the  mercury  in  the  two  legs  ah  and  ih  is  measured,  and 
the  height  H'  of  the  barometer  is  noted  down.  We  shall  suppose 
that  the  temperature  of  the  water  in  the  cylinder  has  not  changed : 
if  otherwise,  it  must  be  restored  to  the  temperature  %  by  the  addi- 
tion of  hot  or  cold  water. 

The  elastic  force  of  the  gas,  dry  and  deprived  of  carbonic  acid, 
is  therefore  (H'-f  A'-/) ;  and  consequently  (H+A-/)-(H'+A'-/) 
=H-— HM-A— A'  is  the  diminution  of  elastic  force  caused  by  the 
absorption  of  the  carbonic  acid ;  and  "~^T^7^'  represents  the  pro- 
portion of  carbonic  acid  in  the  gas  when  supposed  dry. 

§  1241.  The  proportion  of  oxygen  which  exists  in  the  gas 
remaining  must  now  be  determined ;  for  which  purpose  the  absorp- 
tion-tube is  detached  and  washed  several  times  with  water.  It  is 
dried,  first  with  tissue-paper,  and  then  by  bringing  it  into  combina- 
tion with  an  air-pump ;  and  lastly,  after  having  filled  it  with  mercury, 
it  is  fitted  to  the  measurer.  The  bath  U  being  raised  as  high  as 
possible,  the  mercury  is  allowed  to  run  through  the  stopcock  R : 
then,  opening  carefully  the  cocks  r  and  r',  the  mercury  of  the 
absorption-tube  is  passed  into  the  tube  ar'  of  the  measurer,  taking 
care  to  close  the  cock  r'  when  the  extremity  of  the  mercurial 
column  reaches  a  second  mark  B  on  the  vertical  leg  he.  The  mer- 
cury in  the  measurer  is  again  brought  to  the  level  tw,  and  the 
difference  of  level  h!'  and  the  height  W  of  the  barometer  is  ascer- 
tained. lA." -rhi'—f  is  therefore  the  elastic  force  of  the  dry  gas, 
the  quantity  of  which  is  somewhat  smaller  than  in  the  measure  made 
immediately  after  the  absorption  of  the  carbonic  acid,  because  a 
small  quantity  (about  ^^^  has  been  lost  by  detaching  the  absorption- 
tube  from  the  measurer.  This  small  loss  does  not  affect  the  result 
of  the  analysis,  because  the  gas  is  again  measured. 

The  absorption-tube  being  once  more  detached  from  the  measurer, 
the  hydrogen  gas  intended  to  burn  the  oxygen  is  now  introduced 
into  the  latter  by  arresting  the  ascending  mercury  at  the  mark  B. 
The  mercury  is  again  levelled  to  w,  the  difference  of  height  h!"  of 


428  ORGANIC   CHEMISTRY. 

the  two  columns  of  mercury  measured,  and  the  height  H'"  of  the 
barometer  observed.  H'''  +  A'''— /is  therefore  the  elastic  force  of 
the  mixture  of  hydrogen  and  oxygen  to  be  analyzed.  As  some 
time  is  required  for  the  perfect  admixture  of  the  gases,  combustion 
by  the  electric  spark  cannot  be  immediately  effected.  The  gas 
must  again  be  passed  from  the  measurer  into  the  absorption-tube, 
and  a  small  quantity  of  mercury,  which  produces  an  agitation  in  the 
gas,  allowed  to  flow  through  the  tube  cdef',  and  lastly,  the  mixture 
is  passed  back  into  the  measurer,  this  time  allowing  the  mercury  to 
entirely  fill  the  tube  r'ch^  in  order  that  the  whole  volume  of  gas 
may  be  subjected  to  combustion. 

The  electric  spark  is  then  applied,  and  after  having  established 
an  excess  of  pressure  in  the  measurer  a5,  the  stopcocks  r,  r'  are 
carefully  opened,  in  order  to  allow  the  mercurial  column  to  retro- 
grade into  the  tube  her' ;  and  it  is  stopped  when  it  reaches  the 
mark  6.  The  elastic  force  of  the  gas  remaining  is  again  measured, 
after  having  levelled  the  mercury  to  w;  and  W"-\-h""—f\&  then 
the  elastic  force.     Consequently, 

{W"+h'"-f)-{W"+h""-f)=W"-W"'-^h"'-h""  is  the 
elastic  force  of  the  gaseous  mixture  which  disappeared  during  com- 
bustion ; 

l{R'''—'R""  +  h'"—h"")  is  the  elastic  force  of  the  oxygen  con- 
tained in  the  dry  gas,  of  which  the  elastic  force  is  (H''+A''— /), 

and  J H//_iJ/_/^ —  IS  the  proportion  of  oxygen  contamed  m  the  gas, 

when  freed  from  carbonic  acid ;  whence  the  proportion  of  oxygen 
in  the  original  mixture  may  be  easily  deduced. 

§  1242.  The  example  chosen  shows  the  mode  of  operating  with 
the  apparatus :  the  manipulations  are  of  such  a  simple  character, 
that  the  operator  requires  no  assistant ;  and  lastly,  the  operation  is 
so  rapid,  that  less  than  three  quarters  of  an  hour  is  required  for 
that  just  described ;  the  greater  portion  of  which  time  is  consumed 
by  the  absorption  of  the  carbonic  acid  and  the  cleansing  of  the 
bell-glass  after  the  experiment.  Air,  freed  from  carbonic  acid,  can 
be  analyzed  in  less  than  20  minutes. 

We  will  remark,  that  in  this  manner  of  operating,  there  is  no 
necessity  of  any  gauging  capacity,  which  is  always  a  very  delicate 
operation  ;  but  as  the  volume  of  the  gas  is  constantly  the  same,  only 
its  elastic  force,  after  each  operation,  is  determined.  It  is  gene- 
rally sufficient  to  measure  the  elastic  forces  of  the  gas  by  reading 
directly  on  the  graduated  tubes  ah,  ih,  the  divisions  to  which  the 
columns  of  mercury  correspond ;  but  in  order  to  avoid  errors  of 
parallax,  the  divisions  are  read  by  means  of  a  horizontal  glass, 
(fig.  645,)  thus  allowing  no  error  greater  than  ^  of  a  millimetre. 
Although  this  is  sufficiently  precise,  tlje  cathetometer  furnishes  a 
still  greater  degree  of  accuracy. 

The  same  apparatus  may  also  be  used  in  another  way ;  and  in- 


INTRODUCTION.  429 

stead  of  maintaining  the  volume  of  gas  constant,  and  measuring  its 
elastic  forces,  the  inverse  may  be  done,  by  making  the  elastic  force 
constant  and  measuring  the  volume.  In  this  case,  the  tube  ah 
should  be  accurately  gauged,  for  which  purpose  it  is  sufficient  to 
fill  the  measure  accurately  with  mercury  ;  then  keeping  the  temper- 
ature of  the  surrounding  water  constant,  the  mercury  is  allowed 
gradually  to  escape  by  bringing  the  stopcock  R  into  the  position 
necessary  for  the  escape  of  the  metal  in  the  tube  C  alone.  The 
mercury  which  runs  out  is  weighed,  and  the  division  on  the  scale  of 
the  tube,  reached  by  the  level  of  the  mercury,  each  time,  is  marked. 

§  1243.  The  analysis  of  gases  by  combustion  is  exact  only  when 
the  ignfiable  and  combustible  gases  exist  between  certain  limits. 
When  the  detonating  mixture  forms  only  a  small  portion  of  the 
total  volume,  it  is  no  longer  inflamed  by  the  passage  of  the  elec- 
tric spark,  or,  at  least,  the  combustion  is  but  partial.  Experi- 
ment has  shown  that,  in  mixtures  of  hydrogen  and  oxygen  in  which 
the  hydrogen  is  in  excess,  there  is  no  combustion  when  the  deto- 
nating mixture  forms  a  less  fraction  than  0.08  of  the  whole  gas ; 
and  when  it  exceeds  this,  the  inflammation  and  combustion  are 
complete. 

The  limits  difier  when  oxygen  predominates  in  the  mixture :  com 
bustion  is  complete  as  long  as  the  volume  of  the  detonating  mix- 
ture does  not  form  a  less  fraction  than  0.17  of  the  whole  gas;  but 
when  this  fraction  is  included  between  0.17  and  0.10,  the  combus- 
tion is  only  partial ;  and  lastly,  below  this  there  is  no  inflammation. 
The  presence  of  an  excess  of  oxygen  therefore  opposes  the  combus- 
tion of  the  mixture  more  powerfully  than  an  excess  of  hydrogen. 
Whatever,  moreover,  may  be  the  excess  of  oxygen  in  the  mixture, 
there  is  no  fear  of  a  'portion  of  this  gas  disappearing  from  com- 
bining with  the  mercury. 

By  operating  on  mixtures  of  various  proportions  of  carbonic  acid 
and  detonating  gas,  (2  volumes  of  hydrogen,  1  of  oxygen,)  it  is  easy 
to  ascertain  that  carbonic  acid  prevents  the  combustion  of  the  de- 
tonating mixture  more  effectually  than  oxygen. 

If  the  mixture  contains,  at  the  same  time,  nitrogen,  oxygen,  and 
hydrogen,  the  oxygen  predominating  over  the  hydrogen,  the  ana- 
lysis may  be  inaccurate,  because  subnitrate  of  mercury  is  formed. 
But  during  the  formation  of  this  substance,  a  high  temperature 
must  be  developed  at  the  moment  of  combustion,  producing  a  co- 
pious volatilization  of  mercury,  and  this  condition  is  fulfilled  only 
when  the  volume  of  the  detonating  mixture  is  at  least  0.8  of  the 
gas  which  remains  after  explosion,  or  0.45  of  the  whole  volume.* 

These  limits  of  explosibility  vary  sensibly  with  the  diameters  of 

*^  Bunsen  gives  as  the  best  proportion  30.0  volumes  of  combustible  gas  to  187.3 
volumes  of  nitrogen  and  41.0  volumes  of  oxygen,  which  ratio  may  easily  be  ob- 
tained by  the  admission  of  atmospheric  air,  oxygen,  or  hydrogen.  My  own  expe- 
rience also  proves  the  above  proportion  to  be  the  safest. —  W.  L.  F. 


430  OKGANIC   CHEMISTRY. 

the  eudiometric  tubes ;  and  the  variations  are  particularly  observable 
in  mixtures  of  detonating  gas  and  carbonic  acid. 

In  exploding  a  mixture  of  hydrogen,  carbonic  acid,  and  oxygen 
or  atmospheric  air,  the  hydrogen  being  in  excess,  a  portion  of  the 
carbonic  acid  is  always  converted  into  carbonic  oxide,  for  which 
reason  this  gas  must  be  first  absorbed  by  potassa,  when  the  propor- 
tion of  oxygen  in  a  mixture  of  gases  containing  carbonic  acid  is  to 
be  determined  by  combustion. 

Reciprocally,  when  operating  with  a  detonating  mixture  contain- 
ing an  excess  of  hydrogen  and  some  carbonic  oxide,  a  quantity  of 
the  latter  gas  in  proportion  to  the  excess  of  oxide  of  carbon  over  hy- 
drogen, is  always  converted  into  carbonic  acid. 

Use  of  Absorbing  Reagents. 

§  1244.  Absorbing  reagents  may  often  be  advantageously  used 
in  the  analysis  of  gaseous  mixtures.  The  use  of  the  solution  of 
potassa  for  the  absorption  of  carbonic  acid  having  been  previously 
(§  1240)  explained,  we  will  now  review  the  reagents  which  may  be 
used  for  the  absorption  of  oxygen. 

Phosphorus  absorbs  oxygen  very  slowly  at  a  low  temperature, 
the  absorption  being  often  still  incomplete  after  several  days ;  and 
toward  the  close,  in  order  to  hasten  it,  the  tube  should  be  placed  in 
the  sun.  When  a  ball  of  phosphorus  has  been  introduced  into  a 
gas  deprived  of  oxygen,  and  contained  in  a  bell-glass  of  which  the 
sides  are  moistened  by  an  alkaline  solution,  the  gas  is  constantly 
observed  to  increase  in  volume,  probably  owing  to  the  fact  that  by 
the  contact  of  the  phosphorus  with  the  alkaline  solution,  hypophos- 
phite  of  potassa  is  formed,  and  hydrogen  or  phosphuretted  hydro- 
gen is  evolved ;  which  must  be  carefully  avoided  in  analyses. 

The  alkaline  sulphides,  sulphites,  and  hyposulphites  absorb  oxygen 
so  slowly  that  it  is  impossible  to  employ  them  in  analysis ;  for  it 
becomes  necessary  to  use  a  considerable  quantity  of  the  absorbent 
liquid ;  and  if  this  be  allowed  to  act  for  an  indefinite  length  of  time, 
an  absorption  greater  than  that  corresponding  to  the  oxygen  con- 
tained in  the  gaseous  mixture  often  ensues.   " 

Protosulphate  of  iron  saturated  with  deutoxide  of  nitrogen  ob- 
sorbs  oxygen  more  rapidly,  but  does  not  afford  exact  results.  After 
the  absorption,  the  gas  must  be  brought  into  contact  with  a  solution 
of  pure  protoxide  of  iron,  in  order  to  absorb  the  deutoxide  of  ni- 
trogen which  the  first  liquid  may  have  given  off.  The  gas  is  there- 
fore brought  into  contact  with  considerable  volumes  of  liquid,  and 
it  is  always  to  be  feared  that  its  composition  may  be  altered  by  an 
absorption  or  evolution  of  gas  effected  by  these  liquids. 

Hydrated  protoxide  of  iron,  suspended  in  an  alkaline  solution, 
absorbs  oxygen  rapidly ;  and  in  order  to  use  this  reagent,  several 
narrow  tubes,  open  at  both  ends,  are  first  placed  in  the  absorption- 
tube,  and  then  1  or  2  cubic  centimetres  of  the  liquid  are  intro- 


INTRODUCTION.  431 

duced  ;  and  when  the  gas  is  subsequently  passed  into  the  absorption- 
tube  it  is  exposed  to  a  large  absorbing-surface,  because  the  sides  of 
the  tube  are  covered  by  the  hydrated  protoxide  of  iron.  The  tubes 
inside  may  also  be  dispensed  with  if  only  the  absorption-tube  be 
shaken  frequently  after  having  separated  it  from  the  apparatus ; 
but  then  the  viscous  liquid  frequently  produces  a  large  quantity  of 
froth,  and  requires  a  long  time  for  settling. 

Protochloride  of  copper  dissolved  in  ammonia,  and  the  ammonia- 
cal  protosulphite  of  copper,  also  absorb  oxygen  very  rapidly.  The 
tube  containing  the  gas  and  absorbent  liquid  must  be  frequently 
shaken ;  but,  as  the  gas  then  contains  necessarily  a  small  quantity 
of  ammoniacal  gas  given  off  by  the  liquid,  it  becomes  necessary,  be- 
fore passing  it  into  the  measurer-tube,  to  collect  it  in  a  second  ab- 
sorption-tube containing  a  few  drops  of  dilute  sulphuric  acid. 
Pipettes  for  gas,  such  as  are  represented  in  fig.  648,  may  also  be 
used.  The  bulb  A  being  filled  with  mercury,  and  con- 
taining the  absorbent  liquid  at  its  upper  part,  and  the 
leg  ahc  being  also  filled  with  mercury,  which  is  easily 
done  by  dipping  the  end  a  into  mercury  and  sucking 
through  the  end  o,  the  leg  ah  is  introduced  into  the  bell- 
glass  containing  the  gas,  and,  by  sucking  through  the 
opening  o,  the  gas  is  made  to  pass  into  the  bulb  A.  The 
leg  abc  being  filled  with  mercury,  the  apparatus  is  shaken, 
^^'  '  so  as  to  cause  the  absorbing  liquid  to  act  on  th^  gas. 
When  the  absorption  is  terminated,  the  gas  is  again  passed  into  the 
absorption-tube,  to  effect  which  the  end  a  is  dipped  into  the  mer- 
cury, when,  by  sucking  at  o,  a  large  quantity  of  mercury  is  made 
to  pass  into  the  bulb  B,  so  that  the  mercurial  column  is  higher  in  the 
leg  d^o  ;  after  which  the  opening  o,  is  immediately  closed  with  the 
finger  slightly  moistened,  and,  by  introducing  the  leg  ah  into  the 
absorption-tube,  and  then  gradually  and  carefully  unclosing  the 
opening  o^  all  the  gas  is  made  to  pass  back  into  the  absorption-tube 
by  arresting  the  flow  at  the  moment  that  the  absorbing  liquid 
reaches  the  extremity  a.  There  has  been  also  previously  intro- 
duced into  the  absorption-tube  a  drop  of  dilute  sulphuric  acid  to 
absorb  the  ammonia  contained  in  the  gas. 

The  use  of  absorbing  liquids  in  the  analysis  of  gases  is  liable  to 
a  source  of  error  which  is  not  always  easily  avoided.  As  a  con- 
siderable volume  of  it  must  be  used,  an  alteration  of  the  composi- 
tion of  the  gaseous  residue  by  the  small  quantities  of  gas  which 
the  liquid  can  dissolve  or  exhale  is  to  be  feared.  When  it  is  used 
only  for  the  analysis  of  mixtures  of  oxygen  and  nitrogen,  this  error 
is  less  to  be  feared,  if  care  be  taken  never  to  introduce  into  the  ap- 
paratus any  thing  but  a  solution  of  protochloride  of  copper  which 
has  been  for  some  time  exposed  to  an  atmosphere  of  pure  nitrogen ; 
which  condition  is  naturally  fulfilled  when  this  liquid  is  preserved 
in  a  well-stoppered  bottle  which  is  not  opened  too  frequently,  or  in 


432  ORGANIC   CHEMISTRY. 

the  pipettes  (fig.  648)  before  mentioned.    But  this  would  not  be  the 
case  if  the  gaseous  residue  contained  other  gases  besides  nitrogen.'* 

The  analysis  of  air  by  absorbent  reagents  is  longer  than  that 
by  combustion  with  hydrogen.  In  order  not  to  be  uneasy  as  to  tlie 
exactness  of  the  analysis,  it  is  necessary  to  ascertain  that  the 
volume  of  the  gaseous  residue  is  not  again  diminished  by  remainin  o 
for  a  long  time  in  contact  with  the  absorbent  reagent.  Combustion 
by  hydrogen  is,  on  the  contrary,  always  immediately  complete,  if 
indeed  care  has  been  taken  to  mix  the  gases  well  by  passing  them 
twice  from  the  absorption-tube  to  the  measurer,  and  if  the  propor- 
tion of  combustible  gas  to  the  mixture  exceeds  the  limit  above 
mentioned,  (§  1243,)  which  is  readily  known  when  the  analysis  is 
terminated. 

In  some  special  cases,  which  will  subsequently  be  pointed  out, 
combustion  cannot  be  employed,  and  absorbing  reagents  must  be  re- 
sorted to  for  the  determination  of  the  oxygen. 

Sulphurous  acid  gas  is  absorbed  by  potassa,  and  when  it  is  mixed 
with  carbonic  acid,  the  mixture  can  be  analyzed  by  means  of  red 
oxide  of  mercury  or  peroxide  of  lead,  which  absorb  the  sulphurous 
acid  alone.  For  this  purpose,  the  oxides  are  applied,  made  into  a 
thick  paste  with  a  small  quantity  of  water,  to  a  rod  of  unglazed 
porcelain,  which  is  introduced  into  the  absorption-tube  containing 
the  gaseous  mixture,  where  it  is  allowed  to  remain  until  the  absorp- 
tion is  complete.  The  separation  of  the  two  gases  is  more  readily 
effected  by  means  of  a  concentrated  solution  of  bichromate  of  po- 
tassa mixed  with  sulphuric  acid,  which  absorbs  the  sulphurous  acid 
alone. 

Cyanogen  is  immediately  absorbed  by  potassa ;  and  may  also  be 
absorbed  by  oxide  of  mercury  suspended  in  water,  but  the  absorp- 
tion is  very  slow. 

Sulf hydric  acid  is  absorbed  by  a  small  quantity  of  a  solution  of 
sulphate  of  copper  or  acetate  of  lead. 

Bicarburetted  hydrogen  is  absorbed  by  Nordhausen  sulphuric 
acid  strongly  charged  with  anhydrous  sulphuric  ■  acid.  This  solu- 
tion is  prepared  by  pouring  a  small  quantity  of  concentrated  sul- 
phuric acid  into  a  tube  in  which  anhydrous  sulphuric  acid  has  been 
condensed ;  and  a  small  quantity  of  the  fuming  acid  may  be  intro- 
duced, by  means  of  a  curved  pipette,  into  the  absorption-tube  con- 
taining the  gaseous  mixture ;  but  then  a  considerable  quantity  of 

*  Since  the  original  was  written,  a  new  and  excellent  method  for  determining 
oxygen  has  been  discovered  by  Liebig.  The  air  to  be  analyzed  is  passed  into  a 
graduated  tube  filled  with  mercury,  over  a  mercury-bath,  and  after  having  read 
off  the  volumes,  without  regard  to  temperature,  pressure,  or  tension,  a  small  quan- 
tity of  a  most  concentrated  solution  of  caustic  potassa  is  introduced,  and  the 
volume  again  read  off  immediately,  to  ascertain  the  proportion  of  carbonic  acid. 
A  few  drops  of  pyrogallic  acid  are  then  passed  into  the  tube,  by  which  means  the 
oxygen  is  totally  absorbed  at  once ;  and  the  diminution  of  volume  shows  directly 
the  proportion  of  oxygen. —  W.  L.  F. 


INTRODUCTION.  433 

sulphurous  acid,  arising  from  the  reaction  of  the  mercury  on  the 
anhydrous  sulphuric  acid,  is  formed.  It  is  better  to  soak  a  piece 
of  platinum-sponge  or  coke  fastened  to  a  platinum  wire  in  it,  and 
then  introduce  it  into  the  gas.  In  all  cases,  before  passing  the  gas 
into  the  measurer,  it  is  necessary  to  allow  it  to  remain  in  a  second 
tube,  in  contact  with  an  alkaline  solution ;  and  it  is  also  essential 
that  the  gaseous  mixture  subjected  to  the  action  of  fuming  sulphuric 
acid  should  contain  no  oxygen ;  as,  by  contact  with  the  acid,  the 
mercury  might  readily  absorb  a  portion  of  that  gas. 

The  methods  by  absorption  may  frequently  be  advantageously 
combined  with  those  by  combustion  in  the  analysis  of  gases ;  but 
they  must  be  used  with  great  caution,  as  they  can  readily  lead  into 
error,  particularly  when  the  gas  to  be  analyzed  exists  in  very  small 
quantity. 

APPLICATION  OF  THESE  METHODS  TO  THE  ANALYSIS  OF  A  FEW 
GASEOUS  MIXTURES. 

§  1245.  In  the  following  pages  we  shall  explain  the  application 
of  the  methods  just  described  to  the  analysis  of  the  various  gaseous 
mixtures  which  may  occur ;  but  we  shall  only  consider  the  mixtures 
into  which  oxygen,  hydrogen,  nitrogen,  oxide  of  carbon,  protocar- 
buretted  and  bicarburetted  hydrogen  enter,  since  these  are  the 
compounds  which  most  frequently  occur.  If,  in  addition,  carbonic 
acid,  cyanogen,  sulf hydric  acid,  or  sulphurous  acid,  exist  in  such 
mixtures,  they  must  first  be  absorbed  by  the  absorbing  reagents 
mentioned  in  §  1244. 

We  shall  suppose  that  the  gaseous  mixtures  have  been  previously 
freed  from  the  latter  gases,  and  particularly  from  carbonic  acid. 

Mixtures  of  Oxygen  and  Nitrogen. 

I  1246.  Mixtures  of  oxygen  and  nitrogen  are  analyzed  by  combustion  in  the 
eudiometer  by  the  process  detailed,  (§  1241.)  We  shall  now  consider  only  the 
two  extreme  cases: 

1st.  When  the  mixture  contains  very  little  oxygen. 

2dly.  When,  on  the  contrary,  it  contains  very  little  nitrogen. 

When  the  gaseous  mixture  contains  very  little  oxygen,  combustion  cannot  be 
effected,  or  if,  after  having  mixed  it  with  an  excess  of  hydrogen,  the  electric 
spark  be  passed  through  it,  combustion  is  imperfect.  A  certain  quantity  of  gas 
from  the  battery  is  then  added,  and,  after  having  made  a  homogeneous  mixture 
by  passing  the  gas  several  times  from  the  measurer  to  the  absorption-tube,  the 
spark  is  passed  through;  when  combustion  is  perfectly  eflFected,  and  the  de- 
crease of  volume  of  the  mixture  gives  the  sum  of  the  oxygen  and  hydrogen  which 
combined  together,  ^  of  which  is  due  to  the  oxygen,  while  the  hydrogen  occupied  f . 
The  gas  from  the  battery  need  not  be  taken  into  account,  because  it  disappears 
totally  during  combustion.  It  is,  moreover,  evident  that  it  must  always  be  as- 
certained if  the  volume  of  hydrogen  added  is  greater  than  the  |  of  a  volume  which 
disappeared  ;  for  if  it  were  otherwise,  it  would  be  owing  to  a  portion  still  remain- 
ing in  the  gaseous  residue. 

In  order  to  prepare  gas  from  the  battery,  freshly  boiled  water,  to  which  a 

a  small  quantity  of  sulphuric  acid  has  been  added,  is  introduced  into  a  large  tube 

closed  at  one  end ;  and  two  slips  of  platinum  foil  terminating  the  wires  of  the 

battery,  which  pass  through  the  cork  in  the  tube,  are  plunged  into  the  water. 

Vol.  II.— 2a 


434  ORGANIC   CHEMISTRY. 

The  same  tube  is  traversed  by  a  discharging-tube,  by  means  of  which  the  gases 
are  collected  over  mercury.  Four  of  Bunsen's  elements,  moderately  charged,  are 
sufficient  to  afford  a  copious  evolution  of  gas;  and  the  latter  is  allowed  to  per- 
meate the  mercury  for  several  hours,  in  order  to  be  sure  that  the  water  has  dis- 
solved both  gases  in  proper  proportions,  under  an  atmosphere  formed  of  1  volume 
of  oxygen  and  2  volumes  of  hydrogen.  The  gas  is  then  collected  in  bell-glasses, 
and  before  using  it,  an  experiment  is  made  to  ascertain  that  it  leaves  no  residue 
on  combustio'n.  For  this  purpose,  a  certain  volume  of  atmospheric  air  being 
exactly  measured  in  the  eudiometer,  and  a  nearly  equal  volume  of  gas  from  the 
battery  introduced  and  perfectly  mixed  with  the  air,  the  spark  is  passed  through. 
If  the  gas  from  the  battery  contains  the  two  gases  in  the  exact  proportions  which 
form  water,  the  atmospheric  air  occupies,  after  combustion,  exactly  the  same 
volume  a-s  before. 

When,  on  the  contrary,  the  mixture  contains  a  large  quantity  of  oxygen,  com- 
bustion, is  easily  effected,  and  the  analysis  is  exact,  provided  there  be  an  excess 
of  hydrogen.  But  when  the  approximate  composition  of  the  gas  is  unknown,  it  is 
sometimes  necessary  to  add  so  great  a  quantity  of  hydrogen  that  this  quantity 
can  be  no  longer  measured  by  reducing  the  gas  to  the  same  volume,  because  the 
column  of  mercury  which  balances  it  would  exceed  the  upper  end  of  the  tube  cd. 
This,  indeed,  might  be  avoided  by  operating  on  a  smaller  quantity  of  the  gas  to 
be  analyzed  ;  but  the  analysis  can  be  continued  by  bringing  the  mixture  of  gas 
and  hydrogen  to  a  mark  m'  placed  lower  than  the  mark  m.  The  electric  spark  is 
passed  after  having  reduced  the  gas  nearly  to  an  equilibrium  with  the  external 
pressure,  and  the  elastic  force  of  the  residue  is  measured,  either  at  the  level 
m,  or  the  level  m'.  It  is  easy  to  determine  by  calculation,  and  by  the  assist- 
ance of  another  measurement  with  the  apparatus,  the  elastic  forces  which  the 
gaseous  mixture  would  present,  if,  instead  of  reaching  the  level  m',  they  had  con- 
stantly remained  at  m.  It  will  frequently  happen  that  the  gaseous  residue  of 
combustion,  levelled  successively  to  the  marks  m  and  vi,  corresponds  to  elastic 
forces  measurable  on  the  tube  ih ;  but  should  it  be  otherwise,  a  portion  of  the 
gas  is  allowed  to  escape,  and  a  small  quantity  of  atmospheric  air  to  enter,  in 
order  to  fulfil  this  condition.  Let  H'  and  H"  be  the  elastic  forces  which  corre- 
spond to  the  same  gas  when  it  is  necessarily  levelled  to  the  marks  m  and  7n' ;  H 
the  elastic  force  of  the  mixture  of  gas  and  hydrogen  which,  not  being  able  to  be 
levelled  at  m,  has  reached  the  mark  m' ;  and  x  the  elastic  forin  of  the  gas  had  it 
been  levelled  at  m :  we  shall  then  evidently  have 

The  inverse  inconvenience  frequently  occurs  when  the  gaseous  residue  is  too 
small  to  be  measured  at  the  mark  m ;  and  it  is  then  measured  at  a  higher  mark, 
and,  by  a  calculation  similar  to  that  just  made,  the  elastic  force  which  the  gas 
would  present  if  the  level  were  made  at  m  is  determined. 

The  difficulty  may  also  be  avoided  in  another  way.  After  having  passed  the 
gaseous  residue,  of  which  the  volume  is  too  small  to  be  measured,  into  the  absorp- 
tion-tube at  the  ordinary  mark,  a  certain  quantity  of  air  is  introduced  into  the 
measurer,  the  elastic  force  of  which  is  determined  after  having  levelled  the  mer- 
cury to  the  marks  m  and  C;  after  which  the  gas  collected  in  the  absorption-tube 
is  introduced,  and  the  increase  it  produces  in  the  elastic  force  is  determined. 

If  the  proportion  of  nitrogen  in  the  mixture  is  very  small,  and  if  no  great  excess 
of  hydrogen  has  been  introduced,  it  may  happen  that  the  residue  of  combustion 
can  only  be  measured  by  reducing  it  to  a  very  small  volume ;  in  which  case  it  is 
proper,  if  great  exactness  is  required,  to  regard  this  analysis  merely  as  approxima- 
tive, and  to  mark  a  new  one  in  which  a  larger  proportion  of  hydrogen  must  be 
used.    > 

Mixture  of  Hydrogen  and  Nitrogen. 

§  1247.  In  order  to  analyze  this  mixture,  it  is  burned  in  the  eudiometer  with  an 
excess  of  oxygen  ;  and  the  volume  of  hydrogen  is  then  f  of  the  volume  disap- 
peared. In  this  experiment  it  is  necessary  to  observe  that  the  volume  of  the  de- 
tonating gas  does  not  form  more  than  0.8  of  the  gaseous  residue  which  remains 


INTRODUCTION.  485 

after  combustion,  as  otherwise  nitrate  of  mercury  would  be  formed,  (^  1243.) 
It  is  always  easy  to  avoid  this  accident  by  increasing  the  quantity  of  oxygen,  of 
which  the  greater  or  less  excess  does  not  affect  the  accuracy  of  the  analysis.  The 
combustion  may  also  be  made  at  two  periods,  by  adding  in  the  first  place  an  in- 
sufficient quantity  of  oxygen,  which  is  exactly  measured,  passing  the  spark  and 
measuring  the  residue ;  and  then  adding  an  excess  of  oxygen  accurately  deter- 
mined, and  effecting  a  new  combustion.  This  method  should  always  be  employed 
when  the  gas  contains  but  very  little  nitrogen,  because  it  then  becomes  necessary 
to  add  a  great  excess  of  oxygen  in  order  to  be  able  to  measure  the  residue  after 
combustion.  It  is  also  practicable  to  increase  the  residue,  by  adding  to  the  mix- 
ture to  be  analyzed  atmospheric  air  accurately  measured,  and  then  oxygen,  in 
order  to  have  an  excess  of  the  latter  gas. 

If  the  proportion  of  hydrogen,  on  the  contrary,  is  very  small,  an  jnexplosive 
mixture  is  obtained  after  the  addition  of  oxygen,  and,  in  order  to  effect  combustion, 
gas  from  the  battery  must  be  added. 

Mixture  of  Oxygen  and  Hydrogen. 
§  1248.  After  having  measured  the  gas  in  the  eudiometer,  an  electric  spark  is 
passed  through,  when  f  of  the  volume  disappeared  are  hydrogen,  and  J  oxygen. 
As  the  gaseous  residue  must  be  either  hydrogen  or  oxygen,  it  is  sufficient  to  as- 
certain its  nature.  If  the  residue  is  too  small  to  be  measured,  it  is  necessary, 
after  ascertaining  its  nature,  to  make  a  second  analysis  after  adding  to  the  mix- 
ture an  excess  of  one  or  the  other  gas  exactly  measured ;  or  to  employ  the  method 
described  I  1246. 

Mixture  of  Nitrogen,  Oxygen,  and  Hydrogen. 
§  1249.  This  mixture  is  analyzed  like  the  preceding,  with  the  only  difference,  that 
after  having  effected  combustion  by  the  electric  spark,  and  ascertained  if  hydro- 
gen or  oxygen  remains  in  the  residue,  an  excess  of  the  gas  wanting  is  added,  and 
another  combustion  effected,  after  the  addition  of  gas  from  the  battery,  if  it  be 
necessary.  The  same  precautions  as  in  the  analysis  of  the  mixture  of  hydrogen 
and  oxygen  are  used,  care  being  also  taken,  that  if  either  of  these  combustions' 
take  place  in  the  presence  of  an  excess  of  oxygen,  the  volume  of  detonating  gas 
shall  never  form  more  than  0.8  of  the  residue  after  combustion,  to  prevent  the 
forming  of  nitric  products ;  which  accident  may,  however,  always  be  avoided 
by  the  addition  of  a  certain  quantity  of  atmospheric  air,  which  must  then  not  be 
omitted  in  the  calculation. 

Mixture  of  Oxygen  and  Oxide  of  Carbon. 

§  1250.  The  electric  spark  being  passed  through,  and  the  residue  being  mea- 
sured, the  latter  is  passed  into  the  absorption-tube,  and  brought  in  contact  with 
the  solution  of  potassa,  in  order  to  absorb  the  carbonic  acid  formed.  Now,  since 
1  volume  of  oxide  of  carbon  consumes  ^  volume  of  oxygen,  and  yields  1  volume 
of  carbonic  acid,  the  volume  of  oxide  of  carbon  sought  is  precisely  equal  to  that 
of  the  carbonic  acid  formed ;  and  it  is  also  double  of  the  decrease  of  volume  in 
the  gas  by  combustion. 

If  the  proportion  of  oxide  of  carbon  is  small,  combustion  is  either  imperfect 
or  null,  in  which  case  gas  from  the  battery  must  be  added.  The  addition  of  this 
gas  is  very  useful  in  all  cases,  because,  as  the  heat  developed  by  the  combustion 
of  the  oxide  of  carbon  is  not  very  great,  combustion  is  frequently  incomplete. 

Mixture  of  Nitrogen  and  Oxide  of  Carbon. 
1 1251.  In  the  case  of  this  mixture  the  explosion  is  effected  after  adding  an  ex- 
,  cess  of  oxygen  Avhich  is  exactly  measured,  and  then  a  certain  quantity  of  gas 
from  the  battery ;  after  which  the  volume  of  the  oxide  of  carbon  is  double  of  that 
which  disappears  by  combustion,  and  equal  to  the  volume  of  carbonic  acid  formed, 
which  is  ascertained  exactly  by  absorbing  it  by  potassa.  Care  must  be  taken  that 
the  proportion  of  the  combustible  mixture  to  the  inert  gas  be  not  great  enough  to 
form  nitric  products,  which  accident  is,  indeed,  only  to  be  feared  when  a  large 
quantity  of  gas  from  the  battery  has  been  added,  becnuse  then  the  temperature 
rises  sufficiently  high  to  produce  a  free  volatilization  of  the  mercury.    It  is  avoided 


436  ORGANIC   CHEMISTRY. 

in  all  cases,  by  adding  to  the  gas  a  proper  quantity  of  atmospheric  air,  which 
must  not  be  neglected  in  the  calculation  of  the  results. 

Mixture  of  Hydrogen  and  Oxide  of  Carbon. 
§1252.  A  volume  of  oxygen  somewhat  greater  than  its  own  being  added  to  this  mix- 
ture, the  explosion  is  effected  and  the  absorption  m  marked ;  and  lastly,  the  carbonic 
acid  is  absorbed  by  potassa.  Let  n  be  the  proportion  of  carbonic  acid  thus  found, 
X  the  proportion  of  hydrogen,  z  that  of  the  oxide  of  carbon.  The  hydrogen,  by 
burning,  consumes  half  of  its  volume  of  oxygen ;  and  thus,  in  consequence  of 
the  combustion  of  the  hydrogen,  there  is  a  decrease  of  volume  fa;.  The  oxide 
of  carbon  consumes  half  of  its  volume  of  oxygen,  and  produces  a  volume  of  car- 
bonic acid  equal  to  its  own;  ^nd  the  absorption  produced  by  the  combustion  of 
this  gas  is  therefore  \z.    Thus  we  have, 

f  z-f  lz=m, 
whence 


3 

It  is  necessary  to  add  a  considerable  volume  of  oxygen,  in  order  that  there 
shall  remain,  after  explosion,  enough  gas  to  allow  it  to  be  accurately  measured. 
If  the  original  mixture  contained  very  little  hydrogen,  it  would  be  prudent,  after 
combustion,  to  introduce  gas  from  the  battery,  and  effect  a  new  explosion,  in 
order  to  be  sure  of  completely  burning  the  oxide  of  carbon. 

Mixture  of  Nitrogen,  Oxygen,  and  Oxide  of  Carbon. 

§  1253,  If  this  mixture  contains  a  large  amount  of  nitrogen,  a  small  quantity 
of  oxide  of  carbon,  and  oxygen  more  than  sufficient  to  convert  the  oxide  of  carbon 
into  carbonic  acid,  gas  from  the  battery  is  added  to  the  mixture,  and  an  explosion 
effected.  Let  m  be  the  absorption  produced  by  the  combustion:  the  volume  n  of 
carbonic  acid  formed  is  then  determined.  Let  V  be  the  volume  of  the  original 
mixture,  y  the  volume  of  oxygen,  z  that  of  oxide  of  carbon,  and  lastly  u  that  of 
the  nitrogen ;  there  will  then  result,  in  the  first  place,  the  two  equations : 

1=771,     whence    n=2m, 

which  should  give  the  same  value  for  z ;  proving  that  it  was  in  fact  oxide  of  car- 
bon which  existed  in  the  mixture. 

An  excess  of  hydrogen  is  then  added,  and  a  certain  quantity  of  gas  from  the  bat- 
tery if  it  is  probable  that  but  very  little  oxygen  remains  in  the  mixture :  let  m'  be 
the  new  absorption  effected  by  the  combustion,  and  there  results, 

If  the  oxide  of  carbon  predominates  over  the  oxygen,  an  excess  of  oxygen  a 
must  be  immediately  added,  and  then  the  equations  are  as  follows : 

.      z=:2m, 

-^       2    '     3  ' 

w=:V— y— «=V— 3m— y+a. 

If  the  nitrogen  existed  in  small  quantity,  it  would  be  necessary  to  add  for  the 
first  combustion  a  large  quantity  of  oxygen  in  case  the  oxide  of  carbon  should 
predominate,  and,  for  the  second  combustion,  a  large  excess  of  hydrogen,  in  order 
to  have,  after  each  of  these  combustions,  a  gaseous  residue  sufficient  to  enable  its 
accorate  measurement  in  the  apparatus.    If  one  or  the  other  of  these  combustions 


INTRODUCTION.  437 

appear  feeble,  gas  from  the  battery  must  be  introduced  before  passing  the  spark, 
and  it  must  be  ascertained  if  the  volume  is  altered  by  this  new  explosion. 

Mixture  of  Nitrogen,  Oxygen,  Hydrogen,  and  Oxide  of  Carbon. 

2  1254.  Several  cases  of  this  mixture  may  occur,  according  as  one  or  the  other 
gas  predominates.  We  shall,  in  the  first  place,  suppose  that  the  oxygen  exists  in 
greater  quantity  than  that  necessary  to  completely  burn  the  hydrogen  and  oxide 
of  carbon :  combustion  is  immediately  effected  by  the  spark,  if  the  combustible 
mixture  forms  a  considerable  proportion  of  the  inert  gas ;  but  if  otherwise,  the 
spark  is  passed  only  after  having  added  the  gas  from  the  battery.  Let  m  be  the 
volume  which  disappears  by  the  combustion,  x  the  volume  of  hydrogen ;  then,  re- 
taining for  the  other  gases  the  same  characters  as  above,  we  shall  have 

8     ,  1 

The  carbonic  acid  is  absorbed  by  potassa,  causing  a  diminution  of  volume  n, 
which  gives : 

2=n. 

An  excess  of  hydrogen  being  then  introduced  and  the  explosion  effected,  a  new 
absorption  m'  is  observed,  whence 

lastly,  «=V — x— y— 2: 

whence  follows 

2OT-n, 
3 

3 

Z=zn, 

.,— V      3m+m^+3n 
«_v  g  . 

The  quantity  u  can  be  verified  by  exploding  the  last  gaseous  residue,  consisting 
only  of  nitrogen  and  oxygen,  with  an  excess  of  hydrogen. 

If  oxygen  exists  in  the  mixture  in  a  quantity  insufficient  to  completely  burn 
the  hydrogen  and  oxide  of  carbon,  a  certain  quantity  a  of  it  is  added,  and  for  the 
moment  this  new  mixture  is  regarded  as  that  to  be  analyzed :  the  equations  of 
the  preceding  case  are  consequently  applicable,  and  it  is  sufficient,  at  the  end  of 
the  analysis,  to  diminish  the  oxygen  y  by  the  quantity  a  which  had  been  added. 

Lastly,  if  the  nitrogen  be  present  in  very  small  quantity,  the  same  method 
could  be  employed ;  and  it  would  suffice  to  add,  before  each  combustion,  a  suffi- 
ciently large  excess  of  the  gas  which  is  to  effect  it,  in  order  that  the  gaseous  re- 
sidue may  be  exactly  and  easily  measured  in  the  apparatus.  A  certain  quantity 
of  atmospheric  air  may  also,  in  this  case,  be  added  to  the  original  mixture,  which 
is  to  be  brought  into  the  final  calculation. 

Mixture  of  Oxygen  and  Frotocarburetted  Hydrogen. 

\  1255.  If  the  oxygen  does  not  exist  in  a  quantity  more  than  sufficient  to  com- 
pletely burn  the  protocarburetted  hydrogen,  a  quantity  a  of  oxygen  must  be  added, 
which  is  to  be  afterward  remembered  in  the  calculation.  Let  m  be  the  diminution 
of  volume  produced  by  the  explosion,  and  n  that  effected  by  the  absorption  by 
potassa. 

As  1  volume  of  protocarburetted  hydrogen  consumes  2  vols,  of  oxygen  and  yields 
1  vol.  of  carbonic  acid,  we  shall  have,  designating  by  v  the  volume  of  protocar- 
buretted hydrogen, 

2v=m, 
«=n,     whence     2n=m ; 

which  two  relations  should  give  the  same  value  for  v,  if  the  gas  is  protocarbu- 
retted hydrogen. 


438  ORGANIC   CHEMISTRY. 

Mixture  of  Hydrogen  and  Protocarhuretted  Hydrogen. 

§1256.  To  this  mixture  a  large  excess  of  oxygen  is  added,  in  order  that,  after 
the  combustion  and  absorption  of  the  carbonic  acid,  there  shall  remain  a  volume 
which  can  be  exactly  measured  in  the  apparatus.  After  passing  the  electric 
spark,  and  observing  the  absorption  m,  the  carbonic  acid  is  absorbed  by  potassa. 
Let  us  always  designate  the  hydrogen  by  x,  the  protocarhuretted  hydrogen  by  v, 
and  by  n  the  carbonic  acid  formed  ;  we  shall  have, 

|a;-f2v=m, 
r=n, 

whence  a:=H2i=:i^, 

3 

and  V=:a;-f-w ; 

which  result  may  also  be  verified  by  determining  the  quantity  a  of  oxygen  con- 
sumed in  the  combustion,  giving 

|+2t;=a. 

Hence  is  deduced  the  equation : 

which  moreover  exists  for  carburetted  hydrogens,  their  mixtures  with  hydrogen, 
the  mixtures  of  hydrogen  with  oxide  of  carbon,  and,  consequently,  for  all  the  mix- 
tures of  these  various  gases. 

Mixture  of  Oxide  of  Carbon  and  Protocarhuretted  Hydrogen* 

§  1257.  This  mixture  is  exploded  with  a  large  excess  of  oxygen,  in  order  to  be 
able  to  measure  exactly  the  last  gaseous  residue ;  there  is  again  observed  a  de- 
crease of  volume  m,  and,  by  means  of  potassa,  it  is  ascertained  that  a  quantity  n 
of  carbonic  acid  has  formed.  If  z  and  v  still  represent  the  proportions  of  oxide 
of  carbon  and  hydrogen,  we  shall  have 

|  +  2t;=m, 
2-\-v=n, 
whence 

4n— 2m  2m— n  . 

or,  to  verify  it. 

By  ascertaining  the  quantity  of  oxygen  which  has  disappeared,  there  results 

|  +  2.=a; 

whence  is  again  deduced 

Y-\-a=m-{-n. 

A  certain  quantity  k  of  atmospheric  air,  and  then  an  excess  of  oxygen,  may  also 
be  added  to  the  gas,  taking  care  to  avoid  the  condition  in  which  nitrous  products 
may  be  formed ;  but  the  first  plan  is  preferable. 

Mixture  of  Nitrogen,  Oxygen,  and  Protocarhuretted  Hydrogen. 
§  1258.  A  quantity  b  of  oxygen  being  added  to  the  mixture  in  order  that  this 
gas  may  be  in  excess,  the  explosion  is  effected  and  the  decrease  of  volume  m 
marked ;  after  which  the  volume  n  of  carbonic  acid,  produced  by  absorption  by 
potassa,  is  ascertained.     Then  is 

2v=7», 
vs=n, 
V=y-fv-ftt. 

The  next  step  is  to  determine,  by  means  of  combustion  with  an  excess  of  hydro- 
gen, the  quantity  y'  of  oxygen  which  remains  in  the  residue.  If  m'  represents  the 
decrease  of  volume  eflfected  by  this  combustion,  we  have 

,      m' 


INTRODUCTION.  489 

We  hare,  moreover,  for  the  quantity  of  a  of  oxygen  consumed  in  the  first  com- 
bustion, 

2v=a, 
consequently, 

y=a4-y'  — 6=a-f.-g 6, 

whence  may  be  deduced 

-IT     I        I  *'*' 

M=V4-*  —  a — 3- — «. 

Mixture  of  Nitrogen,  Oxygen,  Hydrogen,  and  Protocarburelted  Hydrogen. 

1 1259,  This  mixture  frequently  exists  in  air  which  has  passed  through  the 
lungs ;  in  which  case  the  nitrogen  predominates,  and  oxygen  is  present  in  much 
larger  quantity  than  would  be  necessary  to  completely  byrn  the  combustible  gases ; 
but  the  mixture  cannot  be  exploded.  After  adding  gas  from  the  battery,  and  ob- 
serving the  decrease  of  volume  m  which  results,  the  quantity  n  of  carbonic  acid 
formed  is  ascertained,  and  these  operations  furnish 

2-+2u=m, 
v=n; 
whence 

2m  — in 

The  quantity  y'  of  oxygen  consumed  by  this  combustion  is 

After  these  operations  there  remains  a  mixture  of  y"  of  oxygen  and  u  of  nitro- 
gen, referred  to  the  original  volume,  which  is  analyzed  by  the  process  explained 
in  §  1246.     The  whole  quantity  1/  of  oxygen  contained  in  the  mixture  is 

y=y'-\-y". 

As  a  measure  of  greater  certainty,  it  is  well  to  determine  directly,  by  absorp- 
tion, in  another  portion  of  the  original  gas,  the  whole  quantity  y  of  oxygen  con- 
tained in  the  gaseous  mixture,  which  thus  affords  a  verification,  proving  the 
combustible  mixture  to  be  formed  of  hydrogen  and  protocarburetted  hydrogen. 

If  the  oxygen  contained  in  the  mixture  were  not  sufficient  to  completely  burn 
the  hydrogen  and  protocarburetted  hydrogen,  a  certain  quantity  a  of  oxygen,  to 
be  taken  into  account  at  the  close  of  the  experiment,  would  be  added,  and  to  this 
new  mixture  the  process  just  described  would  be  applied. 

Mixture  of  Nitrogen,  Oxygen,  Oxide  of  Carbon,  Hydrogen,  and  Protocarburetted  Hydrogen. 

§  1260,  We  shall  again  suppose  that  the  oxygen  is  present  in  sufficient  quantity 
to  completely  burn  all  the  combustible  gases ;  for,  if  it  were  otherwise,  a  sufficient 
quantity  of  oxygen  must  be  added,  and  the  new  mixture  then  be  considered  as 
the  original  gas. 

The  mixture  is  exploded  in  the  eudiometer,  either  alone  or  after  the  addition 
of  the  gas  from  the  battery ;  and  the  absorption  m  being  marked,  and  the  quantity 
n  of  carboni^  acid  produced  determined,  there  results,  - 

I.       1+1+ 2.=™, 

II.  2-\-v=n, 

III.  2/'=|4-|4-2t^. 

The  gas  which  remains  after  these  operations  is  composed  only  of  nitrogen  and 
Oxygen,  of  which  the  quantities  u  and  y",  which  may  from  this  time  be  considered 
as  fixed,  are  next  ascertained. 


440  ORGANIC   CHEMISTRY. 

Lastly,  in  a  fresh  quantity  of  the  original  gaseous  mixture,  the  whole  quantity 
y  of  oxygen  which  exists  in  it  is  determined  by  absorption,  which  gives 
IV.  y'-=.y  —  y". 

The  equations  I.  II.  III.,  which  are  then  sufficient  for  the  calculation  of  the 
three  unknown  quantities  z,  y,  and  u,  give 

x=m  —  y\     v=y' —,     z—-\ y'. 

Mixture  of  Oxygen  and  Bicarburettcd  Hydrogen. 

^  1261.  If  this  mixture  does  not  contain  a  sufficient  quantity  of  oxygen,  it  is  to 
be  added  in  such  a  proportion,  that  after  the  explosion  and  absorption  of  the  car- 
bonic acid  by  potassa,  there  shall  remain  a  residue  of  oxygen  which  can  be  exactly 
measured.  It  is,  moreover,  necessary  that  there  should  exist  in  the  mixture  a 
considerable  proportion  of  inert  gas,  as,  otherwise,  the  eudiometric  tube  might  be 
broken  by  the  violence  of  the  explosion.  If  the  proportion  of  bicarburetted  hy- 
drogen is  very  great,  it  is  preferable  to  first  measure  in  the  apparatus  a  certain 
quantity  of  atmospheric  air,  and  then  introduce  the  gas  to  be  analyzed,  and,  if 
it  be  necessary,  a  certain  quantity  of  oxygen,  but  not  enough  to  completely  burn 
the  combustible  gas.  After  having  effected  the  explosion,  which  is  much  less  vivid 
than  if  the  combustion  were  complete,  an  excess  of  oxygen  is  introduced  and  ex- 
actly measured,  after  which  the  mixture  is  again  exploded  in  order  to  perfect  the 
combustion ;  and,  if  the  latter  be  feeble,  it  would  be  prudent  again  to  pass  the 
electric  spark,  after  having  added  gas  from  the  battery.  Let  m  be  the  volume 
which  has  disappeared  in  the  successive  combustions,  and  n  the  volume  of  carbonic 
acid  absorbed  by  the  potassa ;  then,  as  1  volume  of  bicarburetted  hydrogen  con- 
sumes 3  vols,  of  oxygen  and  produces  2  vols,  of  carbonic  acid,  we  have,  desig- 
nating by  w  the  volume  of  bicarburetted  hydrogen, 

2w=ni, 

2w=zn,     whence     7n=n. 

In  the  last  mode  of  operating  there  is  less  danger  of  bursting  the  eudiometer, 
and  the  formation  of  nitrous  products  is  also  avoided ;  for  it  would  only  take 
place  in  the  second  combustion,  which  generally  disengages  but  little  heat. 

Mixture  of  Hydrogen  and  Bicarburetted  Hydrogen. 

§  1262.  In  order  to  analyze  this  mixture,  when  the  bicarburetted  hydrogen  is  in 
small  quantity,  it  is  sufficient  to  mix  it  with  a  large  excess  of  oxygen,  explode  it, 
and  ascertain  the  volume  of  gas  which  has  disappeared,  and  that  of  the  carbonic 
acid  absorbed  by  the  potassa.  The  only  precaution  necessary  is  to  add  enough 
oxygen  to  enable  the  last  gaseous  residue  to  be  measured.     There  then  results 

?54-  2w=zm,     whence    v:=:  Vl 

2 
2«?=:n,  *=3  {'"^  —  ♦*)• 

If  the  bicarburetted  hydrogen  exist  in  large  quantities,  it  is  better  to  eflFect  the 
combustion  at  two  periods,  and  in  atmospheric  air.  In  this  case,  a  certain  quan- 
tity of  atmospheric  air  is  first  measured,  to  which  the  gas  to  be  analyzed,  the 
volume  of  which  is  exactly  determined,  and  then  a  quantity  of  oxygen,  is  added, 
so  that,  with  the  oxygen  contained  in  the  air,  there  shall  not  be  enough  of  that  gas 
to  effect  complete  combustion.  The  electric  spark  being  passed,  an  excess  of 
oxygen  is  added,  with  a  sinall  quantity  of  gas  from  the  battery,  if  this  be  deemed 
useful,  and  the  mixture  is  exploded  a  second  time.  The  analysis  may  be  verified 
by  determining  the  quantity  of  oxygen  which  remains  in  the  eudiometer  after  the 
combustion ;  after  which  the  whole  quantity  y  of  oxygen  consumed  is  known, 
furnishing  the  equation: 

A  verification  is  always  useful,  and  becomes  indispensable  when  it  is  not  certain 
that  the  gaseous  mixture  is  composed  only  of  hydrogen  and  bicarburetted  hydrogen. 


INTRODUCTION.  ,  4^ 

Mixture  of  Oxide  of  Carbon  and  Carburetted  Hydrogen. 

1 1263.  This  analysis  is  made  like  the  preceding,  and  with  similar  precautions. 
The  relations  giving  the  proportion  of  the  two  gases  are 

z 

2-{-2w=:m,     whence    z=2(n  —  wi), 

z-\-2w=n,  w=m  —  -. 

2 

If  a  represent  the  volume  of  oxygen  consumed,  the  following  relations  again 
exist; 

2-fw=V,     |4-3w=:a,    whence    V-f-a=m-fn. 

Mixture  of  Protocarburetted  and  Bicarburetted  Hydrogen. 

§  1264.  The  analysis  will  be  conducted  as  in  the  preceding  cases ;  and  the  fol- 
lowing equations  will  be  found : 

2v-\-2w=:mt    whence    v=:2(n  —  m), 

v4-2w=n  ^^,— .2wt— «  . 

2      ' 

to  which  the  other  relations  must  be  added,  from  which  are  deduced  the  verifica- 
tions, 

2v-^Sw=zaf 
which  again  give  V4-  a = m  -j-  n. 

Mixture  of  Hydrogen,  Protocarburetted  and  Bicarburetted  Hydrogen. 

\  1265.  The  analysis  is  conducted  as  in  the  preceding  case ;  but  it  now  becomes 
necessary  to  determine  the  volume  a  of  oxygen  consumed  in  the  combustion, 
which  furnishes 

^4-2«4-2M>=m,     whence    a;=2(m-f  2«  — 2a), 

v-\-2wz=n,  t>=6a  —  In  —  2wt, 

|._|_  2u4- 3w=a,  w=m-\-An  —  3a. 

There  remains  only  one  verification  given  by  the  relation 

\=X-\-V-\-Wf 

but  which  is  reduced  to  the  equation 

Y-\-a=m-\-n. 

Mixture  of  Oxygen,  Protocarburetted  and  Bicarburetted  Hydrogen. 

1 1266.  The  analysis  is  conducted  as  in  the  preceding  cases ;  and  the  following 
equations  result : 

2v-\-2w=m,    whence    t;=m  —  n, 
v  +  2w=n,  w=^^, 

A  verification  is  obtained  by  determining  the  quantity  a  of  oxygen  added,  which 
has  been  used  in  combustion ;  which  will  give  the  relation 

2v  -f-  3w=a  +  y  ' 
leading  to  the  equation 

Mixture  of  Nitrogen,  Protocarburetted  and  Bicarburetted  Hydrogen. 
^  1267.  The  analysis  will  be  conducted  as  in  the  preceding  cases ;  and  we  shall 
nave  the  relations 


442  ORGANIC   CHEMISTRY. 

2v-\-2w=m,     whence     vs^m  —  n, 
v-\-2w=n,  w=^21, 

Vrith  a  verification  given  by  the  relation 

2v-{-Sw=ia; 
which  is  again  reduced  to 

Y-\-a=:m-{-n. 

Mixture  of  Nitrogen,  Oxygen,  Protocarburetted  and  Bicarburetted  Hydrogen. 

§  1268.  The  analysis  is  made  in  the  same  way,  taking  care  to  determine,  at  the 
close  of  the  experiment,  the  portion  a  of  oxygen  added,  which  has  disappeared  in 
combustions ;  and  the  relations  are  as  follows  : 

2v-\-2w=:m,     whence     v:=m  —  n, 
-        ,    v-{-2w=n,  ^,^2n-m 

2v-\-'3rw      y=a,  y  ^z^m-^-n  —  a, 

i/-\-u-\-v-]-w=:Yy  M  =s  V-j- a  —  m  —  n. 

Eudiometric  analysis  furnishes  no  verification;,  but  the  quantity  y  may  be 
directly  determined  by  absorption. 

Mixture  of  Oxygen,  Hydrogen,  Protocarburetted  and  Bicarburetted  Hydrogen. 

^  1269.  The  analysis  is  again  conducted  as  in  the  preceding  cases,  and  the  rela- 
tions are  the  following : 


I. 

^+2v  +  2w=.m, 

II. 

v-\-2ws=n, 

III. 

^+2v-\-3iv  —  y=a, 

IV. 

x-{-y-{-v-{-w=Y. 

These  four  equations  are  not  sufl&cient  to  determine  the  four  unknown  quanti- 
ties ;  and  in  fact  it  is  easily  seen  that  one  of  them  is  a  consequence  of  the  othei 
three,  on  account  of  a  peculiar  relation  introduced  by  the  data  of  the  problem 
By  adding  together  III.  and  IV.  there  results 

which  becomes,  on  account  of  II., 

^4-2t>-[-2w=V+a  — n; 
^ving  rise,  in  consequence  of  the  chemical  composition  of  the  mixed  gases,  to  the 
equation:  Y-{.  a-n=:m,     or,     Y+a=m  +  n, 

which  includes  the  equation  I.  in  the  other  three. 

In  order  to  solve  the  question,  the  quantity  y  of  oxygen  must  be  determined 
directly  by  absorption,  after  which  we  have  for  the  determination  of  the  three 
other  unknown  quantities, 

— -|_2t)-f-2M?=m,     whence    a;=2(m+2n  —  2a  —  2y), 

t>-f-2w=w,  v=6a-j-6y  —  7n  —  2m, 

^-{-2v-\-Sw=za-{-yy  «;=m-|-4n  —  3a  —  3y. 

Mixture  of  Oxygen,  Oxide  of  Carbon,  Protocarburetted  and  Bicarburetted  Hydrogen. 

§  1270.  The  analysis  is  conducted  as  in  the  preceding  cases,  and  from  it  are 
deduced  the  relations, 


INTRODUCTION.  443 

2 
z-{-v-\-  2w=n, 

which  four  equations  are  not  sufficient  to  determine  the  unknown  quantities, 
because  they  are  connected  together  by  the  condition 

Y  -\-  a:^m-{-n. 

The  quantity  y  of  oxygen  must  be  determined  directly  by  absorption,  which 
furnishes  the  equations 

z=^{2n+m—2a  —  2y), 
v=:  i  (4OT  — n  —  2a  —  2y). 

Mixture  of  Oxygen,  Nitrogen,  Oxide  of  Carbon,  Protocarburetted  and  Bicarburetted 

Hydrogen. 

^  1271.  The  analytic  operations  having  been  conducted  as  in  the  preceding 
cases,  and  the  oxygen  y=6  having  been  determined  by  absorption,  and  lastly,  the 
whole  quantity  a'  of  oxygen  consumed  in  combustion  having  been  equally  ascer* 
tained,  the  following  relations  are  established : 

^-\-2v-{-2w=m,    whence    y=r6, 

2-f»-f  2«;=:n,  2=  |(m4-2n  — 2a'), 

2-f  2t;4-3«>=a',  v=  ~{im  —  n—2a'), 

w=:a' — m, 
'       2-ry+«+«+«'=V,  w=(V— 6)  +  a'— (m+n). 

Eudiometric  analysis  furnishes  no  verification. 

Mixture  of  Oxygen,  Hydrogen,  Oxide  of  Carbon,  Protocarburetted  and  Bicarburetted 

Hydrogen. 

1 1272.  The.  analysis  having  been  made  as  in  the  preceding  cases,  the  oxygen 
y=zb  having  been  determined  by  absorbent  reagents,  and  lastly  the  whole  quan- 
tity a'  of  oxygen  consumed  having  been  equally  determSfned,  we  have  the  relations 

z-{-v-\-2w=:n, 

|  +  |  +  2t;4-3«;=a', 

x-\-z-{-v-\-  w= V  —  b ; 

which  four  equations  are  not  sufficient  to  determine  the  four  unknown  quanti- 
ties X,  z,  u,  and  w,  because  the  constant  quantities  are  connected  together  by  the 
relation 

m-t-n=(V— 5)4-a', 

which  reduces  the  four  equations  to  the  four  really  distinct  ones.  A  new  relation 
between  the  unknown  quantities  must  therefore  be  sought  experimentally  ;  and 
one  can  be  obtained  by  determining  exactly  the  specific  gravity  D  of  the  mixture. 
By  designating  by  d^.  d^.  d^,  d^,  c?„„  the  respective  densities  of  hydrogen,  oxygen, 
oxide  of  carbon,  protocarburetted  and  bicarburetted  hydrogen,  there  results  the 
relation 

D=xc?^  -|-  yd  -j-  2c?j,  -j-  vd^  -}-  ^^«.  5  ' 


444  ORGANIC   CHEMISTRY. 

which  new  equation,  added  to  the  first  four,  renders  the  problem  algebraieatly 
determinate. 

A  given  quantity  of  the  gaseous  mixture  may  also  be  burned  with  oxide  of  copper, 
and  the  water  formed  weighed  by  using  the  apparatus  described  in  §  1214.  If  p 
be  the  weight  of  the  water  obtained,  W  the  volume  of  gas  formed  by  the  oxide  of 
copper,  t  and  H  its  temperature  and  pressure  at  the  moment  of  being  weighed ; 
then  will  the  weight  of  the  gas  burned  be 

W.0.001293.D.,-;5^,.4, 

and  the  ratio  of  the  weight  of  water  formed  to  the  weight  of  gas  burned  will  be 

P • 

W. 0.001293.  D.j:poio367l-^ 

On  the  other  hand,  let  U  be  the  constant  volume  to  which  the  gas  has  been  re- 
duced by  eudiometric  analysis,  6  the  equally  constant  temperature  of  the  water  in 
the  cylinder,  the  elastic  force  of  the  original  gas  being  V,  we  have,  for  the  weight 
of  the  gas, 

1  V 

U .  0.001293  .  D .  1+0.00367.0 '  765* 

If  jr  designate  the  weight  of  water  yielded  by  the  gas  when  completely  burned, 
we  should  have,  for  the  ratio  between  this  weight  and  that  of  the  gas, 


U.  0.001293.  D.  ^ 


1  +  0.00367.0    760 
whence  the  equation, 

P  _ 


W. 0.001293. D.  1+00036^,,-^      U . 0.001293 . D . ^qroiseTTe *  7^ 


OP  simply, 


whence 


W. t H      U. 


1+0.00367. <  1  +  0.00367.0 


■^'W '1+0.00367.0*  h' 


Now  the  weight  of  the  water  is  equally  expressed  by 

3a; 


U.  0.001293.  0.622- 


1  2+^  +  «' 


1+0.00367.0  760  ' 

giving  rise  to 

Zx   .         .  ». 760(1 +  0.00367.0). 

2  T  "^  T-  "^  —     U  .0.001293 . 0.622     * 

which  new  relation  may  be  introduced  into  the  calculation. 

Mixture  of  Oxygen^  Nitrogen^  Hydrogen,  Oxide  of  Carhon,  Proto  and  Bicarhuretted 

Hydrogen. 

§  1273.  This  is  the  most  complex  mixture  which  will  fall  under  our  notice. 
Its  eudiometric  analysis  will  be  conducted  as  in  the  preceding  cases  :  after  having 
determined  directly  the  quantity  y=b  of  oxygen  by  absorption,  and  burned  a 
certain  quantity  of  gas  by  oxide  of  copper  to  ascertain  its  weight  of  water 
formed,  the  carbonic  acid  formed  during  this  combustion  may  also  be  collected 
and  determined,  which  furnishes  no  new  relation,  but  only  a  verification  of  the 


INTRODUCTION.  445 

quantity  of  carbonic  acid  n  found  in  the  eudiometric  analysis.     The  relations  are 
the  following ; 


^-\-l-\-2v+2w^m, 


z-\-v4-2tv=n, 

2^2  '  •  ' 

Z-\'Z-\-U-\-V-{-Wz=s:Y  —  5, 

3x.         .       _7r.760(l-f  0.00367.0)  _  a 
2    "r^"r^  U. 0.001293. 0.622  * 

to  which  may  be  added,  if  the  density  D  of  the  gaseous  mixture  has  been  deter- 
mined, the  relation 

zd^  +  y^v  "i"  ^^8  4"  ^^^  4-  ^<4  +  «^<C=I>. 

The  problem  is  thus  algebraically  determined.  It  each  of  the  numerical  deter- 
minations were  made  with  mathematical  precision,  the  values  of  the  unknown  quan- 
tities, reduced  by  calculation,  would  be  strictly  correct.  But,  however  carefully 
the  operation  may  be  conducted,  each  of  these  determinations  is  liable  to  slight 
error.  Now,  it  is  easy  to  be  certain  that  by  varying,  by  a  very  small  quantity, 
each  of  the  experimental  data,  h,  m,  n,  a',  V,  A,  and  D,  the  value  of  the  unknown 
quantities  vary  often  by  much  larger  quantities ;  and,  by  marking  certain  hypo- 
theses, properly  selected,  on  the  composition  of  the  gaseous  mixture,  it  will  be  seen 
that  by  applying  to  the  formulae  numerical  data  which  differ  very  slightly,  the 
calculated  composition  of  the  gaseous  mixture  ranges  often  between  very  extended 
limits.  This  observation  is  particularly  applicable  to  the  relation  afforded  by 
the  density  of  the  gaseous  mixture,  because  the  latter  is  composed  of  gases  of 
which  the  individual  densities,  in  general,  differ  but  slightly.  This  relation  must 
therefore  be  used  with  great  caution. 

We  have  supposed,  in  the  preceding  observations,  that  the  nature  of  the  ele- 
mentary gases  composing  the  mixture  was  known;  but  the  question  becomes 
much  more  difl&cult  when  this  is  not  the  case,  and  can,  most  frequently,  only  be 
answered  by  analysis,  which  must  be  most  carefully  conducted,  and  repeated 
several  times  ;  and  the  operator  must  satisfy  himself  that  the  relations  which  fre- 
quently exist  between  the  experimental  data,  and  which  we  have  given  in  each 
case,  are  fulfilled.  If  the  experimental  data  were  mathematically  exact,  the 
formulae  suitable  to  the  most  complicated  mixture  might  be  applied  to  them  at 
once,  and  the  calculation  would  give  no  values  for  the  gases  which  do  not 
exist  in  the  mixture.  But,  as  these  data  are  liable  to  trifling  errors,  small  values 
for  the  gases  which  do  not  exist  will  generally  be  found,  which  values  the  operator 
must  then  examine  with  great  care,  and  particularly  the  equations  which  often 
exist  between  the  numerical  data,  in  order  lo  ascertain  if  these  equations  would 
not  be  rigorously  fulfilled  by  the  experimental  data,  by  altering  the  latter  by  quan- 
tities equal  to  the  extent  of  error  to  which  each  one  is  liable.  None  of  the  me- 
thods of  analysis  by  absorption  indicated  (^  1244)  should  be  neglected  while 
examining  the  errors  which  each  may  have  produced  on  the  gaseous  residue,  by 
the  solvent  action  which  the  reagents  exert  on  the  gas  composing  this  residue. 
Lastly,  if  the  analyst  is  provided  with  large  quantities  of  gas,  he  may,  by  sub- 
jecting them  to  suitably  selected  chemical  reactions,  obtain  some  light  on  the 
nature  of  the  component  gases.* 

*  The  method  for  analyzing  complicated  gaseous  mixtures  is  due  to  Bunsen, 
who  first  employed  them  in  his  masterly  investigation  of  the  gases  issuing  from 
-^    blast  furnaces.— TT.  L.  F. 


446 


PROXIMATE    PRINCIPLES   OF   PLANTS. 


ESSENTIAL  IMMEDIATE  PRINCIPLES  OF  PLANTS. 

§  1274.  A  microscopic  examination  of  the  various  component 
parts  of  plants  shows  them  all  to  be  constituted  of  cellular  tissue, 
varying  in  form  according  to  the  part  of  the  vegetable  subjected  to 
inspection.  The  cavities  of  the  tissue  are  filled  with  very  diversified 
matter  ;  sometimes,  as  in  the  case  of  wood,  the  parietes  of  the  cells 
are  covered  by  a  hard  and  brittle  substance,  called  lignine^  or  woody 
fibre,  which  frequently  almost  completely  fills  their  interstices; 
while  at  other  times,  as  in  the  grains  of  the  cerealia,  potatoes,  and 
other  tubers,  the  cells  contain  a  quantity  of  small  ovoidal  globules, 
varying  in  size,  constituting  fecula,  or  starch;  and  lastly,  in  the 
case  of  the  young  organs  of  plants,  the  cells  contain  only  a  more 
or  less  viscous  fluid,  holding  in  solution  mineral  salts  and  various 
organic  substances,  the  principal  of  which  are  gums,  gelatinous  sub- 
stances, and  certain  nitrogenous  combinations,  designated  by  the 
general  name  of  albuminous  substances.  Oils  or  fat  substances  are 
frequently  found  in  the  cells,  as  in  the  oleaginous  grains,  some- 
times in  large  quantities. 

We  shall  begin  by  the  study  of  these  various  substances,  which 
are  found  in  all  members  of  the  vegetable  world,  and  which  are 
essential  to  the  existence  of  plants. 

CELLULAR  TISSUE,  OR  CELLULOSE,  C,,H,oO„ 

§  1275.  The  cellular  tissue  is  particularly  evident  in  the  young 
organs  of  vegetables.  The  cell  is  formed  in  the  liquids  which  cir- 
culate through  the  plant,  and 
grows  by  successive  agglutina- 
tion with  the  cells  previously 
formed,  which  occasions  a  modi- 
fication in  the  original  forms 
of  the  cells.  Sometimes  they 
are  rounded,  and  show  a  cer- 
tain regularity,  as  in  the  pith  of 
the  elder,  (fig.  649,)  and  in  the 
potato,  in  which  case  they  con- 
stitute the  cellular  tissue  pro-_ 
perly  so  called.  At  other  times 
the  cells  form  elongated  tubuli, 
communicating  by  their  con- 
tracted  extremities,  as  seen  in 
^^'       '  fig.  650,  which  represents  the 

longitudinal  section  of  a  stalk  of  asparagus,  of  which  a  transverse 
section  is  seen  in  fig.  651 ;  and  in  figs.  652  and  653,  which  exhibit 


CELLULOSE. 


447 


(fig.  653)  a  fibre  of  flax  or  hemp,  and  (fig.  t)52)  a  fibre  of  cot- 
ton :  the  tissue  is  then  called  a  vascular  tissue.     As  the  vegetable 
portions  grow  old  on  the  living  plant,  the 
vascular  vessels  are  filled  with  woody  fibre, 
which  increases  gradually  in  thickness,  and 
leaves  only  very  narrow  canals  for  the  cir- 
culation of  the  sap. 
The  whole  of  this 
mechanism    consti- 
tutes wood. 

Among  all  the 
substances  entering 
into  the  composi- 
tion of  plants,  the 
cellular  tissue  is  dis- 
^^*       '  tinguished    by    its 

great  resistance  to  chemical  agents — a  resistance  which  allows  its 
separation  in  a  state  of  purity  sufficiently  perfect  to  permit  the 

study  of  its  chemical  proper- 
ties, and  to  ascertain  its  ele- 
mentary composition.    It  has 
thus  been  found  to  be  identi- 
cal, in  this  respect,  not  only 
in  all  parts  of  the  same  plant, 
but  also  in  all  different  vege- 
tables.   Chemists  have  given 
the  name  of  cellulose  to  that 
constant  substance  which 
they  regard  as  forming 
the  cellular  tissue  of  all 
plants. 

Cellulose  is  nearly 
pure  in  cotton,  in  which  case  it  consists  of  the  down  of  the  cotton- 
seed ;  and  in  hemp  and  flax,  that  is  in  the  textile  fibres  extracted 
from  the  plants  of  these  names.  Cellulose  is  also  nearly  pure  in 
paper  and  old  linen,  which  are  made  of  the  substances  just  men- 
tioned, and  which,  during  their  prepartion  and  use,  have  been  sub- 
jected to  various  chemical  reactions,  which  have  gradually  effected 
the  entire  destruction  of  the  more  changeable  foreign  substances, 
mixed  with  the  cellular  tissue  properly  so  called. 

Cellulose  is  extracted  from  various  parts  of  plants  by  subjecting 
them  to  successive  chemical  reactions  which  destroy  the  more  altera- 
ble woody  fibre,  the  preparation  being  longer  and  more  difficult  in 
proportion  to  the  quantity  of  woody  fibre.  The  substance,  when 
obtained  in  as  disaggregated  a  form  as  possible,  is  digested  with 
hot  solutions  of  caustic  potassa  or  soda,  and,  after  washing  the 
residue,  is  treated  with  weak  chlorohydric  acid,  and  washed  with 


Fig.  653. 


448  PROXIMATE   PRINCIPLES   OF   PLANTS. 

water.  By  a  repetition  of  this  process  for  a  certain  number  of 
times,  the  woody  fibre  may  be  completely  removed ;  although  the 
same  result  may  be  obtained  more  quickly  by  subjecting  the  sub- 
stance to  more  powerful  oxidizing  reagents,  such  as  a  weak  solution 
of  chlorine  or  hypochlorite  of  lime,  and  following  each  of  these 
treatments  with  an  alkaline  solution  and  dilute  chlorohydric  acid. 
Although  these  various  reagents  attack  the  cellular  tissue  itself, 
the  action  on  it  is  much  less  active  than  on  the  substances  surround- 
ing it ;  so  that  if  the  operation  be  carefully  conducted,  and  reagents 
diluted  with  water  be  alone  used,  the  greater  portion  of  the  cellu- 
lose escapes  destruction.  It  is  washed  successively  with  alcohol 
and  ether  to  dissolve  the  fatty  matter. 

Pure  cellulose,  which  is  white  and  transparent,  is  insoluble  in 
water,  alcohol,  ether,  and  the  fixed  or  volatile  oils.  Dilute  acid 
solutions  have  but  little  effect  upon  it,  even  at  the  boiling  point,  which 
is  also  true  of  sufficiently  diluted  alkaline  solutions.  The  resistance 
which  cellulose  presents  to  these  reagents  varies  with  its  cohesion ; 
recently  formed  cellulose  being  much  more  easily  changed  than  that 
of  older  date.  Concentrated  sulphuric  and  phosphoric  acid  attack 
cellulose,  and  cause  it  to  undergo  a  remarkable  metamorphosis :  after 
converting  it  into  a  soluble  substance,  called  dextrine,  they  change 
it  to  a  sugary  substance,  or  glucose.  Fuming  nitric  acid  combines, 
when  cold,  with  cellulose,  and  converts  it  into  an  insoluble  sub- 
stance, eminently  combustible  and  explosive,  and  which  will  be  de- 
scribed hereafter.  At  the  boiling  point,  nitric  acid  dissolves  it,  and 
oxalic  acid  is  formed.  Acetic  acid,  even  in  \  concentrated  state, 
has  no  action  on  cellulose. 

Cellulose,  as  it  exists  in  the  untouched  cellular  tissue  of  plants, 
is  not  coloured  by  an  aqueous  solution  of  iodine ;  but  when  it  has 
commenced  to  be  disaggregated  by  sulphuric  acid,  it  assumes  a  beau- 
tiful blue  colour ;  which  reaction  is  frequently  used  in  the  study  of 
vegetables  under  the  microscope,  because  it  distinguishes  the  cellu- 
lar tissue  from  certain  nitrogenous  membranes,  which  do  not  possess 
this  property. 

After  some  time,  a  solution  of  chlorine,  or  a  hypochlorite,  com- 
pletely burns  cellulose,  forming  water  and  carbonic  acid;  which 
combustion  is  rapid  in  a  concentrated  and  hot  solution  of  hypochlorite. 

The  elemetary  composition  of  cellulose  is, 

Carbon 44.44 

Hydrogen 6.18 

Oxygen 49.38 

100.00 

The  formula  (j-^^^fi^^  is  generally  assigned  to  it ;  but  as  there 
are  no  means  of  determining  its  chemical  equivalent,  the  formula 
representing  its  molecular  composition  may  be  a  multiple  of  the 


LIGNIN.  449 

above.     It  will  be  remarked  that  hydrogen  and  oxygen  exist  in  it 
in  the  proportions  constituting  water. 


Fig.  654. 


LIGNIN. 

§  1276.  It  has  been  mentioned  that  the  sides  of  the  cells  become 
generally  in  crusted  with  a  substance  formed  at  the  expense  of  the 
organic  substances  dissolved   in  the  sap;    which  constitution   of 

ligneous  matter  is  very  well  exhibited 
in  fig.  654,  representing  a  transverse 
section  of  a  piece  of  oak-wood,  as  seen 
through  the  microscope.     The  black 
spaces  are  the  canals  which  still  re- 
main  in   the  cells;    some   of  which 
former,  as  a,  are  larger,  and  appear 
to  be  principally  used  for  the  circula- 
tion of  the  sap.     As  the  wood  grows 
by  annual   concentric  layers,  easily 
counted  in  old  trees,  the  centre  layers 
^    ^.^^^.  *^-.^*-^^^-     ^^6  older  than  the  external  ones,  and 
iSB^EMWBy48KBy      their  cells  are  also  much  more  incrust- 
y^^JtfjSSS^^w        6d  with  ligneous  matter  than  the  latter. 
^^B'^WHWW^  The  central  layers  of  the  trunk  of  a 

tree,  constituting  the  heart,  are  there- 
fore firmer  and  harder  than  the  outer 
layers,  forming  the  sap-wood;  and  they  are  also  less  subject  to 
change,  because  they  contain  less  sap  and  albuminous  matter,  which 
are  the  principal  causes  of  the  changes  and  rotting  of  wood. 

Although  pure  ligneous  matter  is  sometimes  deposited  in  the  cells, 
resinous  substances,  which  colour  the  wood  and  increase  its  combus- 
tibility, are  generally  precipitated  at  the  same  time ;  while  pellicles 
of  nitrogenous  matter  are  also  formed. 

No  way  of  isolating  the  ligneous  matter  in  a  state  of  purity  being 
known,  it  has  hitherto  remained  undecided  whether  the  chemical 
composition  of  this  substance  is  always  identical;  but  sensible  dif- 
ferences, which  are  observable  in  chemical  reactions  on  the  ligneous 
matter  of  various  parts  of  vegetables,  may  possibly  be  produced  by 
greater  or  less  aggregation  of  the  substance.  Sawdust,  successively 
subjected  to  the  action  of  water,  alcohol,  and  etner,  presents  a  mix- 
ture of  cellulose,  lignine,  a  small  quantity  of  nitrogenous  matter, 
and  several  insoluble  mineral  salts ;  and  by  analysis  it  is  found  to 
contain  more  carbon  and  hydrogen  than  pure  cellulose :  thus,  lig- 
nine contains  more  carbon  than  cellulose,  and  hydrogen  exists  in  it 
in  a  proportion  larger  than  that  which  would  form  water  with 
oxygen.  The  following  tables  exhibit  the  elementary  composition 
of  several  kinds  of  wood,  previously  dried  in  vacuo  at  a  temperature 
of  212°: 

Vol.  II.-r29 


450  PROXIMATE   PRINCIPLES   OF  PLANTS. 

Wood  from  the  Trunk  of  the  Tree. 

Beech.  Oak.  Birch.  Aspen.  Willow. 

Carbon 49.46 49.58 50.29 49.26 49.93 

Hydrogen....     5.96 5.78 6.23 6.18 6.07 

Oxygen 42.36 41.38 41.02 41.74 39.38 

Nitrogen 1.22 1.23 1.43 0.96 0.95 

Ashes 1.00 2.03 1.03 1.86 3.67 

100.00 100.00 100.00. .....100.00 100.00 

Wood  from  the  Branches. 

Beech.  Oak.  Tirch.  Aspen.  Willow. 

Carbon 50.37 50.08 51.29 49.59 51.39 

Hydrogen....     6.21 6.14 6.17 6.20 6.18 

Oxygen 41.14 41.38 40.41 40.23 36.45 

Nitrogen 0.78 0.95 0.87 1.00 1.41 

Ashes 1.50 1.45 1.26 2.98 4.57 

100.00 100.00 100.00 100.00 100.00 

§  1277.  Wood  is  decomposed  after  some  time,  when  subjected  to 
the  simultaneous  influence  of  air  aiid  moisture,  by  the  influence  of 
a  species  of  fermentation  owing  to  the  presence  of  nitrogenous  albu- 
minous substances,  and  carbonic  acid  is  disengaged,  while  the  wood 
is  converted  into  a  brown  or  black  substance,  called  humus,  or  mould; 
an  alteration  which  is  the  more  rapid  when  the  w^ood  is  of  recent 
formation,  because  its  canals,  being  less  incrusted  with  woody  fibre, 
contain  more  sap,  and,  consequently,  more  albuminous  nitrous  mat- 
ter, which  is  the  principal  cause  of  the  change.  This  substance, 
by  its  alteration,  gives  rise  to  true  ferments,  and  serves  as  food  for 
various  insects  which  lodge  in  the  wood  and  ultimately  destroy  it. 
If  this  be  the  cause  of  the  rotting  of  wood,  it  might  readily  be  pre- 
vented, if,  by  certain  chemical  agents,  the  alteration  of  the  nitro- 
genous matter  could  be  prevented,  thus  rendering  it  unfit  for  the 
food  of  animals.  All  poisonous  substances  which  prevent  the  putre- 
faction of  animal  matter  produce  this  effect ;  but  the  difficulty  con- 
sists in  making  it  penetrate  all  the  vessels  and  cells  of  the  wood. 
This  question  has  attracted  a  good  deal  of  attention  in  latter  years, 
and  several  processes  have  been  invented  for  its  economical  deter- 
mination on  a  large*  scale. 

The  liquid  containing  the  antiseptic  substance  has  been  made  to 
penetrate  the  smallest  vessels  of  the  wood,  by  immersing  one  end 
of  the  trunk  of  a  tree,  of  2  to  4  metres  in  length,  in  a  tub  contain- 
ing the  solution,  while  to  the  other  end  is  fitted  a  cast-iron  vessel, 
in  which  a  vacuum  is  produced  by  the  combustion  of  tow  soaked  in 
alcohol.  By  repeating  this  operation  2  or  3  times,  the  liquid  is 
forced  by  the  pressure  of  the  atmosphere  to  traverse  the  whole 
length  of  the  trunk. 


ALBUMINOID    SUBSTANCES.  45i 

Advantage  may  also  be  taken  of  the  vital  circulation  to  cause 
the  antiseptic  fluid  to  penetrate  trees  when  standing  or  when  re- 
cently felled.  When  the  tree  is  standing,  it  is  sufficient  to  make  at 
its  foot  two  incisions,  separated  by  an  interval  of  a  few  centime- 
tres, and  wrap  around  it  a  bandage  of  water-tight  stuff,  which  re- 
ceives from  a  tub  the  liquid  to  be  imbibed  by  the  tree.  The  sap- 
wood,  of  which  the  canals  are  very  open,  is  soon  injected  with  the 
liquid,  which,  however,  penetrates  with  more  difficulty  into  the 
heart  and  the  parts  thickly  incrusted  with  lignine.  When  the 
liquid  is  coloured,  this  irregular  impregnation  is  manifested  by  the 
differences  of  shade  and  by  veins,  which  often  gives  to  the  boards 
an  appearance  rendered  very  beautiful  by  polishing. 

Lastly,  a  process  called  displacement  is  sometimes  used  success- 
fully, which  consists  in  placing  the  recently  felled  tree  in  a  hori- 
zontal position  and  surrounding  the  trunk  near  its  butt  with  a  water- 
tight bag,  held  in  place  by  a  band  over  a  pad  of  clay,  and  pouring 
into  the  bag  the  antiseptic  liquid  by  means  of  a  tube  entering  a  tub 
placed  somewhere  near.  The  liquid  displaces  the  sap  and  takes 
its  place.  In  this  way,  the  delicate  woods,  such  as  the  pines  and 
firs,  may  be  rapidly  and  uniformly  injected,  but  it  is  not  so  in  the 
case  of  hard  woods  ;  as,  although  the  sap-wood  is  soon  injected,  the 
liquid  penetrates  with  difficulty  and  irregularity  into  the  heart  of 
the  tree.  This  process  has  been  greatly  improved,  for  railroad 
sleepers,  -in  the  following  manner :— A  piece  of  wood,  of  twice  the 
length  of  the  sleeper,  being  sawed  in  the  middle  to  within  3  or  4 
centimetres  of  the  opposite  side,  and  the  crack  opened  with  a 
wedge,  between  the  vertical  sides  of  the  crack  a  tarred  rope  is  in- 
terposed, which,  being  strongly  compressed  when  the  wedge  is  re- 
moved, closes  the  sides  hermetically  and  forms  a  small  narrow  re- 
servoir in  the  middle  of  the  piece  of  wood.  The  antiseptic  liquid, 
being  then  poured  into  this  reservoir,  ultimately  penetrates  the 
whole  piece  of  wood. 

Of  the  many  chemical  substances  which  may  be  used  for  this 
purpose,  the  pyrolignite  of  iron  or  impure  acetate  of  the  protoxide 
of  iron  is  generally  preferred,  on  account  of  its  efficiency  and  low 
price.  This  substance,  which  is  obtained  by  means  of  the  acid 
liquid  produced  by  the  distillation  of  wood  in  close  vessels,  contains, 
in  addition  to  the  acetate  of  iron,  creasote  and  tar,  which  assist  in 
the  preservation  of  the  wood. 

Wood  is  frequently  covered  with  tar  and  a  substance  called  ma- 
rine glue,  made  by  melting  together  1  part  of  gum  shellac  and  2 
parts  of  essence  of  coal-tar. 

NITROGENOUS  OR  ALBUMINOUS  VEGETABLE  SUBSTANCES. 

§  1278.  The  nitrogenous  matter  of  plants,  designated  under  the 
general  name  of  albuminoid  substances,  play  an  important  part  in 
vegetable  physiology ;  but  as  they  have  hitherto  been  but  imper- 


452  PROXIMATE   PRINCIPLES   OF   PLANTS. 

fectly  studied,  we  shall  only  state  what  is  with  certainty  known  con- 
cerning them. 

All  these  substances  are  solid ;  some  being  soluble  in  water,  as 
albumen,  vegetable  casein,  and  legumin ;  while  others  are  insoluble, 
as  gluten.  They  are  decomposed  by  heat,  |ind  exhale  an  odour 
similar  to  that  peculiar  to  burnt  feathers,  giving  rise  to  empyreu- 
matic  gases  and  products,  and  leaving  as  an  ultimate  residue  a 
black  and  brilliant  spongy  coal,  the  separation  of  which  has  been 
preceded  by  the  fusion  and  swelling  of  the  original  matter.  These 
substances  may  be  indefinitely  preserved  after  being  perfectly  dried; 
and  in  the  moist  state  they  can  be  preserved  for  a  long  time,  if  pro- 
tected from  the  air ;  while,  when  placed  under  the  simultaneous  in- 
fluence of  air  and  water,  they  soon  decompose,  rot,  and  call  into 
existence  a  host  of  microscopic  animalculse. 

All  albuminous  substances  dissolve  in  caustic  potassa  and  soda, 
and,  on  adding  an  acid  to  the  solution,  a  nitrogenous  substance  sepa 
rates,  in  the  form  of  grayish  flakes,  which  contract,  on  drying,  into 
a  hard  and  brittle  mass,  while  at  the  same  time  a  decided  smell  of 
sulf  hydric  acid  is  disengaged,  and  the  liquid-  contains  a  certair 
quantity  of  phosphoric  acid.  The  name  of  protein  has  been  given 
to  this  nitrogenous  substance,  which  appears  to  form  the  essential 
principle  of  all  albuminous  matter.  It  is  not  yet  known  with  cer- 
tainty in  what  state  the  sulphur  and  phosphorus  exist  in  these  sub- 
stances ;  but  some  chemists  suppose  albuminous  substances  to  be 
compounds  of  protein  with  difierent  proportions  of  sulphimide 
NHjS,  and  phosphimide  NH^Ph.  These  sulphuretted  and  phos- 
phuretted  substances  are  moreover  found  in  very  minute  quantities 
jn  them. 

In  order  to  separate  protein  from  the  alkaline  liquid,  acetic  acid 
must  be  used,  because  the  majority  of  the  mineral  acids  combine 
with  that  substance.  Protein  is  tasteless  and  inodorous ;  soluble  in 
water,  alcohol,  ether,  and  the  essential  oils ;  soluble  with  alteration 
after  some  time  in  boiling  water ;  and  its  composition  is  represented 
by  the  formula  CggHg^N^Ojo. 

Protein  combines  with  acids,  forming  compounds  soluble  in  water, 
but  which  are  precipitated  by  the  addition  of  a  great  excess  of 
acid,  and  which  are  decomposed  by  the  alkalies  with  the  precipita- 
tion of  the  protein,  which  is  again  dissolved  if  an  excess  of  alkali 
be  added.  Chlorohydric  acid  yields  with  protein,  and,  in  general, 
with  all  albuminous  substances,  a  blue  liquid.  Weak  sulphuric  acid 
destroys  protein  at  the  temperature  of  212°,  forming  several  new 
products,  among  which  is  distinguished  a  white  crystallizable  sub- 
stance, called  leucin. 

Nitric  acid  acts  powerfully  on  protein,  forming  a  yellow  acid, 
called  xanthoproteic,  which  combines,  at  the  moment  of  its  forma- 
tion, with  a  portion  of  the  nitric  acid ;  but  the  compound  is  destroyed 
by  boiling  water  and  the  xanthoproteic  acid  is  precipitated.     The 


ALBUMEN:  453 

acid,  which,  when  pure,  is  of  an  orange-yellow  colour,  pulverulent, 
and  tasteless,  combines  with  mineral  bases  and  acids,  yielding  com- 
pounds of  a  more  or  less  deep  yellow  colour.  The  xanthoproteates 
of  potassa,  soda,  and  ammonia  are  soluble ;  and  the  other  salts, 
which  are  all  insoluble,  are  easily  obtained  by  double  decomposition. 

This  reaction  of  nitric  acid  on  protein  is  frequently  applied  in  the 
study  of  vegetable  anatomy  to  detect  albuminous  substances,  since 
they  are  the  only  ones  which  turn  yellow  by  contact  with  nitric 
acid.  There  is  a  still  more  delicate  test  in  the  reddish  colour  as- 
sumed by  albuminous  solutions  when  in  contact  with  a  mixture  of 
nitrate  and  nitrite  of  mercury,  which  is  easily  obtained  by  dissolv- 
ing mercury  in  an  equal  weight  of  nitric  acid  containing  4J  equi- 
valents of  water,  and  then  diluting  the  liquid  with  twice  its  volume 
of  water.  This  liquid  reacts,  when  cold,  on  albuminoid  substances, 
and  the  discoloration  is  more  rapid  when  it  is  heated  to  212°. 

Chlorine  attacks  protein  suspended  in  water,  and  converts  it  into 
a  white  flaky  substance,  regarded  as  a  chlorite  of  protein,  because 
its  composition  is  represented  by  the  formula  CggH^jN^OjoClOa. 
This  substance,  treated  with  an  alkaline  solution,  loses  its  chlorine, 
disengages  ammonia,  and  is  converted  into  a  soluble  substance, 
called  tritoxide  of  protein,  because  its  composition  corresponds  to 
the  formula  CggH^^N^OjgHO.  Chlorine  produces  a  similar  reaction 
on  all  albuminous  matter;  and  the  same  substance  is  also  formed 
when  water  containing  albumen  in  suspension  is  boiled  for  several 
days. 

Protein  also  combines  with  the  alkaline  earths,  forming  a  pitchy 
substance,  which  becomes  very  hard  by  drying ;  which  property  is 
applied  to  the  manufacture  of  a  luting  made  of  white  of  egg  and 
slaked  lime,  (§  661.) 

Albumen. 

§  1279.  Albumen  is  a  principle  widely  disseminated  throughout 
plants,  and  existing  in  them  either  coagulated  in  their  tissues  or 
dissolved  in  the  liquids  which  circulate  through  their  vessels.  It  is 
also  largely  found  in  the  animal  economy :  the  serum  of  the  blood 
and  the  white  of  the  egg  are  essentially  composed  of  a  solution  of 
albumen  in  water.  Animal  albumen  appears  to  be  identical  in  com- 
position and  chemical  qualities  with  vegetable  albumen,,  and  many 
physiologists  admit  that  this  substance  is  furnished  immediately  to 
animals  by  the  plants  on  which  they  feed. 

Albumen  assumes  two  very  distinct  forms :  soluble  albumen,  and 
coagulated  or  insoluble  albumen  ;  and  in  both  states,  its  chemical 
composition  is  the  same.  They  will  be  easily  understood  by  com- 
paring the  albumen  of  a  raw  egg  to  that  of  one  when  cooked.  The 
albumen  of  an  egg  begins  to  coagulate  at  about  140°,  while  that  of 
human  serum  remains  unchanged  until  about  158° ;  and  as  a  gene- 
ral rule,  albumen  coagulates  with  greater  difficulty  in  proportion  to 


454  PROXIMATE   PRINCIPLES    OF   PLANTS. 

the  quantity  of  water  in  which  it  is  dissolved.  Coagulated  albumen 
no  longer  dissolves  in  water,  but  merely  swells  in  it ;  while  the  sub- 
stance obtained  by  evaporation,  at  a  low  temperature,  from  an  al- 
buminous fluid,  dissolves,  on  the  contrary,  in  cold  water,  yielding  a 
stringy  liquid.  Liquid  albumen  generally  presents  an  alkaline  reac- 
tion, and  turns  the  plane  of  polarization  of  luminous  rays  toward 
the  left ;  serum  of  the  blood  and  all  albuminous  liquids  exhibiting  the 
same  property.* 

*  A  large  number  of  substances  in  the  organic  kingdom  exhibit  a  physical  pecu- 
liarity belonging  to  their  molecular  constitution,  which  appears  to  be  a  special 
effect  of  organization,  as  it  has  hitherto  not  been  observed  in  any  inorganic  sub- 
stance. It  consists  in  the  property  possessed  by  their  molecules  of  impressing 
modifications  on  polarized  light,  which  are  analogous,  in  many  respects,  to  those 
it  experiences  when  passing  through  non-symmetrical  crystallized  bodies,  which 
faculty  has  been  called  the  rotatory  power,  from  the  character  of  the  effects  which 
it  produces.  In  this  note  we  shall  endeavour  to  explain  its  mode  of  manifesta- 
tion and  the  method  of  measuring  its  principal  peculiarities ;  and  the  idea  we 
shall  give  it  will  suffice  to  attach  it,  from  this  time,  as  a  specific  character,  to 
substances  which  possess  it,  as  they  will  be  described.  We  shall  subsequently 
explain  one  of  its  practical  applications  in  detail,  and  show  how  it  may  be  applied 
to  the  exact  determination,  in  a  solution,  of  the  proportion  of  matter  in  it  which 
exerts  the  rotatory  power.  But,  in  order  that  these  phenomena  may  be  under- 
stood by  persons  who  have  not  made  a  special  study  of  optics,  it  is  necessary  to 
recapitulate  a  few  of  the  chief  laws  of  this  science,  on  which  the  theory  of  these 
phenomena  is  based. 

When  a  simple  ray  of  light,  emanating  directly  from  a  luminous  source,  falls, 
at  an  angle  i,  on  the  surface  of  a  transparent  medium,  a  greater  or  less  portion 
of  the  ray  is  reflected ;  and,  if  the  medium  is  perfectly  transparent  and  its  sur- 
face polished,  the  portion  of  light  not  reflected  traverses  the  medium.  The  plane 
containing  the  incident  ray  is  called  the  plane  of  incidence,  and  the  reflecting  sur- 
face at  the  point  of  incidence  is  called  the  normal.  The  reflected  ray  remains  in 
the  plane  of  incidence,  and  its  direction  makes  an  angle  i  with  the  normal,  equal 
to  that  which  the  incident  ray  makes  with  the  same  normal.  The  laws  which  the 
transmitted  ray  obeys,  when  the  medium  traversed  is  homogeneous  in  all  direc- 
tions, are  the  following: — If  the  transmitted  ray  is  simple,  it  remains  in  the  plane 
of  incidence,  and  makes,  with  the  normal,  an  angle  r,  so  that  there  always  exists 

between  the  angle  of  incidence  i  and  that  of  refraction  r  the  relation  -^ — =7?i, 

"  sin  r  ' 

m  being  a  constant  quantity  for  the  same  medium,  and  called  the  index  of  refraction 
of  the  medium. 

The  same  laws  apply  to  the  case  in  which  the  ray  of  light,  instead  of  falling 
from  empty  space  on  the  medium,  reaches  it  after  having  traversed  a  first  medium 
equally  homogeneous ;  and  the  constant  quantity  m  is  then  the  relative  index  of  re- 
fraction of  the  two  media,  and  equal  to  the  ratio  of  the  indices  of  refraction  of 
these  media  with  regard  to  the  space. 

The  light  of  the  sun  is  composed  of  an  infinity  of  variously  coloured  rays,  each 
of  which  has  its  own  index  of  refraction ;  and  if  therefore  a  mass  of  solar  light  be 
passed  through  a  transparent  prism,  the  rays  separate  and  yield  a  coloured  image, 
the  solar  spectrum,  elongated  in  the  direction  of  the  refraction ;  the  rays  which  have 
the  greatest  index  of  refraction  being  the  farthest  removed  from  the  direction  of 
the  incident  ray.  The  light  of  burning  bodies  affords  a  similar  spectrum,  which 
differs  from  the  solar  spectrum  in  the  ratio  of  intensity  of  the  various  coloured 
parts. 

The  portion  of  light  reflected  at  the  surface  of  separation  of  two  medi|rfvaries 
with  the  angle  of  incidence,  and  is  smallest  when  this  angle  is  0,  that  is,  Ai^en  the 
incident  ray  is  normal  to  the  surface ;  while  it  increases  with  the  value  of  this 
angle,  and  is  equal  to  the  incident  light,  when  the  angle  of  incidence  is  equal  to 
90°,  in  which  case  the  light  is  wholly  reflected.     However,  when  the  ray  passes 


ALBUMEN. 


455 


Many  chemical  reagents  coagulate  albumen  when  cold.  Alcohol 
reduces  it  immediately  to  the  insoluble  state ;  and  ether  produces 
the  same  effect,  though  more  slowly.  » 


from  a  first  medium  into  a  second,  of  which  the  index  of  refraction  is  more  feeble, 
in  which  case  the  value  of  m  is  smaller  than  1,  the  total  reflection  of  the  incident 
ray  commences  before  the  rasant  ray ;  which  occurs  at  all  the  incidences  for  which 

the  relation  ^^. —  =  m  gives  values  for  the  sin  r  greater  than  1.     Thus,  the  total 

reflection  begins  at  the  angle  I,  for  which  we  have  sin  I:^m ;  that  is,  the  angle  of 
total  reflection. 

By  being  reflected  at  the  surface  of  separation  of  two  media,  the  nature  of  light 
is  remarkably  modified ;  which  is  readily  demonstrated  by  the  apparatus,  (fig.  655,) 

ab  and  cd  are  two  polished 
transparent  mirrors  which 
revolve  around  horizontal 
axes  0,  o\  perpendicular  to 
the  plane  of  the  figure.  The 
axes  are  supported  by  frames 
om,  o'm',  mounted  on  drums 
ef,  e'f,  which  turn  around  the 
hollow  cylinder  gh,  to  which 
r(S^    "*'^^*CS^^!>»^  I  ^^y   inclination    around    the 

^j-s5^  horizontal  axis/?  can  be  given. 
A  narrow  bundle  of  rays  is 
received  on  the  first  mirror 
ab,  at  an  incidence  i,  and  the 
whole  instrument  is  arranged 
J    ^  80  that  the  reflected  ray  shall 

^^^^^^^^^^  follow  the   direction    of   the 

Fig.  655.  axis  of  the  cylinder  gh.    This 

reflected  ray  is  received  on 
the  second  mirror  cd  at  the  same  angle  of  incidence  i;  and  by  turning  the  drum 
e'f  around  the  cylinder  gh,  all  possible  angles  can  be  made  on  the  second  plane 
of  reflection  with  the  plane  of  reflection  on  the  first  mirror,  without  changing  the 
angle  of  incidence  i.  Now,  if  the  light  reflected  by  the  first  mirror  were  still  na- 
tural light,  it  would  be  always  reflected  in  the  same  proportion  on  the  second, 
whatever  might  be  the  azimuth  of  the  plane  of  the  second  reflection  compared 
with  that  of  the  first.  But  this  is  not  the  case,  and  the  intensity  of  the  light  re- 
flected by  the  second  mirror  diminishes  in  proportion  as  the  azimuth  of  the  second 
plane  of  reflection  increases,  and  is  a  minimum  when  the  azimuth  is  90° ;  its 
variations  being  moreover  symmetrical  around  the  azimuths  0  and  90°.  By  vary- 
ing the  common  angle  of  incidence  i,  it  can  be  ascertained  that  the  variations  of 
intensity  of  the  light  reflected  on  the  second  mirror  in  the  various  azimuths  in- 
crease as  we  approach  nearer  the  value  of  i  given  by  the  formula  tang  i=m,  m 
being  the  index  of  refraction  of  the  glass. 

Light  which  possesses  this  property  is  said  to  be  polarized,  and  the  angle  at 
which  it  must  be  reflected  from  a  transparent  medium  to  acquire  it  is  called  the 
angle  of  polarization :  it  will  be  seen  that  this  angle  depends  on  the  index  of  refrac- 
tion of  the  substance  composing  the  mirror.  Polarized  light  differs  therefore 
from  natural  light  in  this,  that  while  the  latter  is  always  reflected  in  the  same 
proportion  from  a  mirror  inclined  at  the  angle  i  with  the  incident  ray,  for  all  azi- 
muths of  the  plane  of  reflection,  polarized  light  is  reflected  in  proportions  varying 
with  the  azimuth  of  the  plane  of  polarization ;  and,  if  the  angle  i  satisfies  the  rela- 
tion tang  i=nj,  there  is  a  position  of  the  plane  of  reflection  in  which  the  reflected 
ray  is  null.  The  plane  perpendicular  to  this  particular  direction  of  the  plane  of 
reflection  is  called  the  plane  of  polarization. 

When  a  ray  of  light  falls  on  a  mirror  at  the  angle  of  polarization,  the  portion 
reflected  is  polarized  in  the  plane  of  incidence ;  and  if  the  properties  of  the  re- 
fracted ray  be  examined  by  means  of  a  second  mirror  which  receives  it  at  the 


456  PROXIMATE   PRINCIPLES   OP   PLANTS. 

Albumen  is  extracted  from  flour  by  rubbing  it  with  ten  times  its 
weight  of  cold  water,  allowing  it  to  digest  for  several  hours,  de- 
canting off  the  water,  and  digesting  with  an  additional  quantity  of 

angle  of  polarization,  it  is  ascertained  that  the  transmitted  ray  presents  the  pro- 
perties of  a  ray  partially  polarized,  or  of  a  mixture  of  natural  and  polarized  light; 
but  the  plane  of  polarization  of  the  polarized  portion  is  perpendicular  to  the  plane 
of  polarization  of  the  reflected  portion.  It  may  therefore  be  admitted  that  when 
a  ray  of  natural  light  falls  on  a  mirror  at  the  angle  of  polarization,  a  portion  of 
the  light  traverses  the  mirror  without  modification,  but  that  the  other  portion  is 
divided  into  two  bundles  polarized  in  planes  perpendicular  to  each  other ;  and 
while  the  first  bundle,  which  is  polarized  in  the  direction  of  the  plane  of  incidence, 
is  reflected,  the  second,  polarized  perpendicularly  to  this  plane,  is  refracted.  We 
recognise,  moreover,  that  these  two  rectangularly  polarized  bundles  are  equal  to 
each  other,  and  that  their  union  produces  natural  light ;  which  may  therefore  be 
regarded  as  formed  by  the  union  of  two  equal  bundles,  polarized  at  right  angles. 

When  the  bundle  of  light  which  has  traversed  a  first  mirror  at  the  angle  of 
polarization  traverses  a  second  at  the  same  angle,  a  portion  of  the  natural  light 
is  divided  into  two  bundles  rectangularly  polarized ;  and  the  bundle  polarized  in 
the  direction  of  the  plane  of  reflection  is  reflected,  while  the  bundle  polarized 
perpendicularly  to  this  plane  is  refracted  and  joins  the  portion  polarized  by  the 
first  refraction.  After  its  passage  through  the  second  mirror,  the  bundle  con- 
tains a  portion  of  polarized  light  much  greater  than  when  it  left  the  first.  Trans- 
mission through  a  third  mirror  again  increases  the  polarized  portion ;  so  that 
after  passing  through  a  sufiicient  number  of  mirrors,  at  the  angle  of  polarization, 
the  bundle  of  natural  light  is  entirely  separated  into  light  polarized  in  the  direc- 
tion of  the  plane  of  incidence  which  is  reflected,  and  into  light  polarized  perpen- 
dicularly to  the  plane  of  incidence  which  traverses  the  mirrors. 

Crystallized  media  which  do  not  belong  to  the  regular  system,  effect  imme- 
diately the  separation  of  natural  light  into  its  two  rectangularly  polarized  bundles. 
A  bundle  of  natural  light  which  falls  on  a  rhomboid  of  Iceland  spar,  is  divided  in 
the  crystal  into  two  bundles,  of  equal  intensity,  polarized  rectangularly,  and  which 
separate  because  they  obey  different  laws  of  refraction.  One  of  these  bundles  is 
polarized  in  the  direction  of  the  plane  of  the  principal  section  of  the  rhombohe- 
dron ;  while  the  plane  of  polarization  of  the  second  is  perpendicular  to  the  plane 
of  the  principal  section.     The  first  obeys  the  ordinary  laws  of  the  refraction  of 

light  in  homogeneous  media,  and  remains  in  the  plane  of  incidence,  the  law  -: — =w» 
being  satisfied  for  all  incidences;  for  which  reason  it  is  called  the  ordinary  ray. 

The  second  ray  obeys  very  different  laws  :  it  remains  in  the  plane  of  incidence 
only  when  this  plane  coincides  or  is  perpendicular  to  the  plane  of  the  principal 

section,  and  it  is  only  in  this  case  that  it  satisfies  a  law  -r— -;=??i'  similar  to  that 

*'  sin  r 

which  the  ordinary  ray  obeys.  In  all  other  directions  of  the  incident  ray  the  law 
of  the  second  refracted  ray  is  more  complex ;  on  which  account  this  ray  has  been 
called  the  extraordinary  ray. 

These  two  rays  do  not  separate  sufficiently  to  form  two  isolated  images,  except 
when  the  rhomb  of  spar  is  very  thick ;  but  a  great  separation  may  be  produced 
by  replacing  the  rhomb  of  spar  by  a  prism  cut  out  of  this  mineral ;  so  that  the 
edges  of  the  prism  shall  be  perpendicular  to  the  principal  section  of  the  rhombo- 
hedron.  When  the  refracting  angle  of  the  prism  is  only  5°  or  10°,  the  two. 
bundles  separate  sufficiently,  but  the  images  are  coloured  if  the  incident  ray  is 
not  simple.  This  discoloration  is  avoided  by  gluing  to  the  prism  of  spar  a  glass 
prism  of  a  proper  angle,  the  refraction  of  which,  acting  in  a  direction  contj^ry 
to  that  of  the  prism  of  spar,  almost  entirely  destroys  the  dispersion  of  colors. 
This  apparatus,  which  is  frequently  used  in  the  study  of  polarized  light,  is  called 
an  achromatic  birefracting  prism ;  and  it  enables  us  to  examine,  with  ease,  the  pro- 
perties of  light  polarized  by  reflection  from  a  mirror:  when  used  for  this  purpose, 
it  is  often  called  an  analyzing  prism.  If  the  light  is  completely  polarized  in  the 
direction  of  the  plane  of  reflection,  it  is  evident  that  when  the  plane  of  the  prin- 
cipal section  of  the  birefracting  prism  coincides  with  the  plane  of  reflection,  all 


ALBUMEN. 


457 


flour.  After  having  repeated  this  operation  three  or  four  times,  a 
liquid  is  obtained  containing  a  certain  quantity  of  albumen,  which 
can  be  separated  by  evaporation  at  a  low  temperature. 


the  light  will  traverse  the  prism  in  the  state  of  an  ordinary  ray,  and  the  extra- 
ordinary ray  will  be  extinguished.  When,  on  the  contrary,  the  plane  of  the 
principal  section  is  perpendicular  to  the  plane  of  polarization  of  the  ray,  the  light 
will  pass  wholly  in  the  extraordinary  ray,  and  the  ordinary  ray  will  be  null.  Jn 
all  the  intermediate  azimuths  of  the  principal  section  of  the  birefracting  prism, 
there  will  be  an  ordinary  and  an  extraordinary  image;  and  their  relative  intensities 
will  vary  according  to  the  position  of  the  principal  section.  The  law  of  these  varia- 
tions is  very  simple  :  let  Cbe  the  angle  which  tlie  plane  of  the  principal  section  of 
the  birefracting  prism  makes  with  the  plane  of  original  polarization ;  and  I  the 
intensity  of  the  polarized  ray  which  falls  on  this  prism  :  the  intensity  of  the  ordi- 
nary ray  is  I  cos  X,  and  that  of  the  extraordinary  ray  I  sin  X:  in  all  cases  the 
rays  are  complements  of  each  other,  for  we  always  have  I  cos  ^S4-Isin  X=l. 

The  birefracting  prism  is  very  convenient  for  determining  the  direction  of  the 
plane  of  polarization  of  a  polarized  ray ;  as  it  is  sufficient  to  find  the  direction  to 
be  given  to  the  plane  of  the  principal  section  of  the  prism,  in  order  that  the  extra- 
ordinary fasciculus  furnished  by  the  normal  incident  ray  may  become  null. 

In  order  to  understand  the  modifications  experienced  by  polarized  light  when  it 
traverses  various  media,  the  apparatus  represented  in  fig.  656  is  frequently  used ; 
in  which  ab  represents  a  polished  mirror,  receiving  the  luminous  rays  at  the  angle 
of  polarization,  and  reflecting  them  in  the  line  cd,  while  at  n  is  an  achromatic  bi- 


Fig.  656. 

refracting  prism,  mounted  on  the  centre  of  a  movable  index  mn,  which  moves  on 
a  graduated  circle  pq  perpendicular  to  the  line  cd.  The  plane  of  polarization  of 
the  ray  reflected  by  the  mirror  being  vertical,  the  extraordinary  image  aiForded 
by  the  birefracting  prism  will  vanish  when  its  principal  section  is  in  the  vertical 
plane,  and  the  alidade  will  then  correspond  to  0  of  the  division.  AB  is  a  support 
,^on  which  various  transparent  media,  which  will  be  traversed  by  the  polarized  ray, 
.  as,  for  example,  fluids  contained  in  tubes,  can  be  placed.  Fig.  657  represents  the 
longitudinal  section  of  one  of  these  tubes ;  which  is  composed  of  a  tube  of  thick 

glass,  generally  enclosed  in  a 
metallic  tube  to  which  are 
fitted  the  two  ferrules  m,  n, 
which  support  the  glass  plates 
closing  the  ends  of  the  tubes. 
Fig.  657.  If  AB,  one  of  those  tubes,  filled 

with  water,  alcohol,  or  ether, 
be  placed  on  the  support,  so  that  the  ray  of  polarized  light  may  be  obliged  to  tra- 


\p//////2^/////y//yyyy/yy^//^^^^^ 


'':^i':'~:'^^''~f^^^^^^^^^ 


458  PROXIMATE   PRINCIPLES    OF   PLANTS. 

In  order  to  extract  albumen  from  potatoes,  they  are  cut  into  thin 
slices,  which  are  digested  in  water  containing  two  per  cent,  of  sul- 
phuric acid.     The  water  is  decanted  after  twenty-four  hours,  and 

verse  the  liquid  before  reaching  the  birefracting  prism,  it  will  be  seen  that  the 
ray  has  suffered  no  essential  change  in  its  properties  by  its  passage  through  the 
fluid ;  it  is  still  completely  polarized,  and  its  plane  of  polarization  remains  ver- 
tical. But,  on  substituting  for  pure  water  several  other  liquids,  as,  for  example, 
a  solution  of  cane-sugar,  the  properties  of  the  polarized  light  are  completely 
modified.  Thus,  before  the  interposition  of  the  tube  containing  the  solution  of 
sugar,  the  extraordinary  image  of  the  birefracting  prism  is  null  when  the  index 
marks  0°;  and  the  image  reappears  if  the  tube  be  interposed.  Nevertheless,  the 
light  has  not  been  depolarized  by  its  passage  through  the  solution  of  sugar,  and 
remains  completely  polarized  ;  but  its  plane  of  polarization  is  no  longer  vertical, 
and  it  has  been  deviated  by  a  certain  angle  toward  the  right  of  the  obserA'er 
who  looks  through  the  birefracting  prism ;  and,  in  fact,  if  the  index  be  turned 
to  the  right  by  a  certain  angle  at,  the  extraordinary  image  disappears  entirely. 
The  solution  of  sugar  has,  therefore,  turned  toward  the  right,  by  an  angle  at,  the 
plane  of  polarization  of  the  light.  If  tubes  of  different  lengths  be  filled  with  the 
same  solution  of  sugar,  it  will  be  found  that  the  angles  of  deviation  are  in  pro- 
portion to  the  lengths  of  the  tubes.  On  filling  a  tube  of  uniform  length,  successively, 
with  solutions  more  and  more  rich  in  sugar,  it  is  found  that  the  angles  of  deviation 
t  are  in  proportion  to  the  quantities  of  sugar  contained  in  the  same  volume  of  liquid.  It 
may,  therefore,  be  said  in  general  terms  that  the  deviations,  or  rotations,  of  the  plane 
of  polarizatioti  are  in  proportion  to  the  number  of  molecules  of  sugar  which  the  luminous 
ray  meets  in  its  passage.  Let  a  be  the  deviation  impressed  by  a  homogeneous  liquid 
on  the  plane  of  polarization  of  the  simple  ray,  acting  on  it  under  the  same  cir- 
cumstances, through  units  of  space  and  with  an  imaginary  density  equal  to  unity. 
The  density  becoming/,  without  any  change  in  the  energy  of  the  molecular  action, 
the  deviation,  through  the  unity  of  thickness,  will  be  [at]  J:  then,  the  length 
becoming  I  for  the  same  density,  the  total  deviation  will  be  [at]  IS.  If,  therefore, 
tt  represent  the  deviation  observed  experimentally,  we  shall  have 

[ct']U=A,     whence     [at]  =  ^. 

The  quantity  [jt]  is  characteristic  of  the  active  substance ;  and  is  the  same,  at 
equal  temperatures,  for  all  the  values  of  I  and  /,  and  may  be  considered  as  the 
molecular  or  specific  rotatory  power  of  the  homogeneous  liquid  observed. 

We  have  supposed  that  the  polarized  ray  was  simple  light ;  which  condition, 
though  strictly  fulfilled  with  difficulty,  can  nevertheless  be  sufficiently  satisfied  by 
placing  between  the  birefracting  prism  and  the  eye  a  glass  coloured  red  by  sub- 
oxide of  copper,  which  allows  the  red  rays  only  to  pass,  and  extinguishes  all  the 
others. 

When  the  polarized  ray  is  composed  of  white  light,  and  traverses  a  medium 
endowed  with  a  moderately  powerful  rotatory  power,  the  extraordinay  ray  is  not 
extinguished  in  any  position  of  the  birefracting  prism ;  and  the  two  bundles  dis- 
play very  beautiful  colours,  which  are  always  complementary  in  the  two  images: 
that  is  to  say,  which  are  such  that  they  reproduce  white  light  when  superimposed 
on  each  other.  It  is  easy  to  calculate  these  discolorations  d,  priori,  when  the  de- 
viations «!,  at,,  at,  are  known  which  the  medium  exerts  on  the  plane  iif  polarization 
of  each  simple  ray,  and  the  intensities  i„  4)  h  of  these  rays  in  wffte  light.  Let 
us  suppose,  in  fact,  that  the  plane  of  the  principal  section  makes  an  angle  e  with 
the  vertical  plane  of  the  primitive  polarization  of  all  the  rays.  This  plane  will 
make  an  angle  at, — e  with  the  plane  of  polarization  deviated  from  the  first  ray, 
and,  if  the  medium  possessing  the  rotatory  power  is  colourless,  that  is,  if  it  al- 
lows the  simple  rays  to  pass  precisely  in  the  proportion  in  which  these  rays  exist 
in  white  light,  the  intensity  of  the  first  ray  in  the  ordinary  image  will  be  ?,cos 
'(at — t),  and  the  intensity  of  the  same  ray  in  the  extraordinary  image  will  be  2,sin 
\a — «) ;  so  again  the  second  ray  will  give  in  the  ordinary  image  i^cos^(a^ —  ), 
and  in  the  extraordinary  image  fc,sin'(«, — i) ;  while  the  third  ray  will  give  in  the 


ALBUMINOUS    SUBSTANCES.  459 

allowed  to  rest  for  the  same  space  of  time  on  fresh  slices  of  pota- 
toes ;  whe'n,  after  several  similar  operations,  a  yellowish  liquid  is  ob- 
tained, which  must  then  be  saturated  with  a  small  quantity  of  po- 
tassa,  taking  care  to  preserve  a  slight  acid  reaction.  The  liquids, 
evaporated  at  a  low  temperature,  yield  soluble  albumen,  mixed  with 
salts,  and  probably  with  dextrin ;  but  if  the  liquid  be  boiled,  the 

ordinary  image  ZjC0S^(je3  — «),  and  in  the  extraordinary  image  iasiri*[ui — «),  and 
80  on. 

The  ordinary  image  will  therefore  be  formed  by  the  superposition  of  a  portion 
tiCos^(!t, — ()  of  the  colour  of  the  first  ray,  a  portion  i^cos^ltt^ — «)  of  the  colour  of 
the  second  ray,  a  portion  »3Cos*(flt, — «)  of  the  colour  of  the  third  ray,  and  so  on. 
The  colour  resulting  from  the  ordinary  image,  and  its  intensity,  may  be  calculated, 
by  means  of  these  elements,  by  a  peculiar  law  established  by  Newton. 

The  colour  and  intensity  of  the  extraordinary  image  will  be  calculated  in  the 
same  way,  by  means  of  the  constituent  parts  i,sin'(3ti — «),  ta8in'*(a2 — «),  i,sin' 
(stj — i)  of  each  of  the  simple  rays  which  compose  it. 

Now,  it  has  been  observed,  that  for  all  media  endowed  with  rotatory  power, 
with  the  exception  of  tartaric  acid,  the  relative  deviations  of  the  simple  rays  which 
constitute  white  light  obey  very  nearly  the  same  law :  in  other  words,  the  deviations 
of  the  planes  of  polarization  of  the  various  simple  rays  are  always  proportional 
to  each  other.  So  that,  instead  of  measuring  the  deviations  produced  by  media 
endowed  with  rotatory  power  upon  one  simple  ray,  the  red  ray,  for  example,  the 
deviations  may  be  measured  for  which  the  ordinary  and  extraordinary  image  pre- 
sent identical  hues.  But  all  these  hues  cannot  be  measured  with  equal  precision, 
because  they  are  not  all  subject  to  variations  equally  sensible  to  the  eye,  for  they 
have  very  small  variations  of  the  azimuth  t  of  the  principal  section  of  the  analy- 
zing prism.  The  variations  of  tint  are  most  sensible  in  a  certain  violaceous  hue  of 
the  extraordinary  image  ;  because,  however  slightly  the  index  may  be  turned  to 
the  right  or  left,  the  image  passes  suddenly  from  blue  to  red  and  from  red  to  blue. 
This  particular  tint  has  been  adopted  by  all  experimenters,  and  is  generally  called 
the  tint  of  passage,  or  sensible  tint. 

The  white  light  of  the  sun,  and  particularly  that  transmitted  through  whitish 
clouds,  can  therefore  be  used ;  and  in  the  comparison  of  the  molecular  rotatory 
powers  of  various  active  media,  the  formula 

can  be  applied,  in  which  at  is  the  deviation  of  the  index,  in  which  the  tint  of  pas- 
sage has  been  observed.  It  is  important,  however,  to  remark  that  these  measures 
will  be  exact  only  if  the  white  light  used  in  the  observation  is  always  composed  of 
exactly  the  same  materials,  and  this  proposition  is  not  rigorously  accurate,  at  all 
times,  as  regards  the  light  transmitted  by  the  vault  of  heaven,  in  which  blue  light 
more  or  less  predominates.  It  would  be  still  more  inaccurate  to  substitute  for  this 
the  light  of  a  lamp,  the  composition  of  which  diflfers  greatly  from  that  of  solar  light. 
The  result  might  also  be  very  erroneous  if  the  media  were  coloured;  for,  in  that 
case,  they  would  not  allow  the  simple  rays  to  pass  in  the  proportions  in  which  they 
exist  in  white  light,  and  it  then  becomes  necessary  to  make  the  observation  with 
homogeneous  light. 

It  is  always  useful,  when  the  molecular  rotatory  powers  of  substances  are  to  be 
measured  by  observing  the  tint  of  passage,  to  operate  with  tubes  of  suitable  length, 
or  with  solutions  so  diluted  that  the  angular  deviations  corresponding  to  the  tint 
of  passage  shall  differ  but  slightly;  because  the  composition  of  the  sensible  tint 
differs  remarkably  in  very  diverse  absolute  deviations. 

We  have  endeavoured,  in  the  preceding  note,  to  give  a  general  idea  of  the  special 
action  which  certain  organic  substances  exert  on  polarized  light.  The  reader  who 
may  desire  to  study  this  subject  more  deeply  should  consult  the  memoirs  of  M. 
Biot,  to  whom  the  discovery  of  these  interesting  phenomena,  and  their  application 
to  the  study  of  a  vast  number  of  chemical  phenomena,  is  due.  (See  Annates  de 
Chimie  et  de  Physique,  3e  serie,  tomes  x.  et  xi.) 


460  ESSENTIAL   PRINCIPLES   OF  VEGETABLES. 

albumen  is  precipitated,  on  the  contrary,  in  flakes,  and  is  then  pure, 
but  has  become  insoluble  in  water. 

It  is  more  easy  to  prepare  albumen  from  animal  liquids — for  ex- 
ample, from  serum  of  the  blood  or  white  of  egg — as  it  is  then  suffi- 
cient to  evaporate  these  liquids  at  a  temperature  below  122°  to 
obtain  it  in  the  form  of  a  transparent  layer  resembling  paste.  This 
substance,  finely  powdered,  should  be  treated  with  ether,  and  then 
with  alcohol,  which  dissolves  the  fatty  substances,  after  which  the 
residue  is  composed  of  soluble  albumen  mixed  with  salts.  A  purer 
albumen  is  obtained  by  pouring  into  the  white  of  egg,  or  the  serum, 
chlorohydric  acid,  which  precipitates  the  albumen,  by  forming  with 
it  a  scarcely  soluble  compound.  The  precipitate  being  separated 
and  treated  with  a  large  quantity  of  water,  which  redissolves  it, 
carbonate  of  ammonia,  which  precipitates  the  coagulated  albumen 
in  the  form  of  white  flakes,  is  poured  into  the  liquid,  and  the  preci- 
pitate, after  being  washed  in  water,  dried,  and  then  treated  suc- 
cessively with  water  and  alcohol,  furnishes  pure,  but  insoluble  al- 
bumen. 

The  action  of  acids  and  alkalies  on  albumen  is  inferred  from  what 
has  been  said  touching  the  action  of  the  same  substances  on  protein. 
We  shall  merely  mention  the  difference  of  action  exhibited  by  phos- 
phoric acid  in  different  degrees  of  hydration.  Monohydric  phos- 
phoric acid  P05,H0  coagulates  albumen  immediately,  while  the 
trihydric  acid  P05,3HO  not  only  does  not  coagulate  it,  but  will  even 
dissolve  the  substance  precipitated  by  the  monohydric  acid. 

Albumen  forms  insoluble  compounds  with  several  metallic  salts, 
particularly  with  corrosive  sublimate,  for  which  reason  the  white  of 
eggs  is  used  as  an  antidote  in  cases  of  poisoning  by  this  medicine.  On 
account  of  this  property,  also,  corrosive  sublimate  is  used  in  the  pre- 
servation of  anatomical  specimens,  as,  by  combining  with  the  albumen, 
it  prevents  it  from  putrefying,  and  keeps  worms  from  attacking  them. 

Grluten,  Vegetable  Fibrine,  Glutin,  Vegetable  Casein. 

§  1280.  Gluten  is  most  easily  extracted  from  the  cerealia,  and 
principally  from  wheat,  by  making  a  thick  paste  with  wheat  flour, 
and  kneading  it  under  a  stream  of  water  until  the  water  is  no  longer 
milky ;  when  the  water  carries  off"  the  fecula  and  soluble  matter, 
while  a  glutinous  and  elastic  substance  remains,  which,  when  dried, 
is  converted  into  a  yellowish,  translucid,  and  brittle  mass,  consisting 
chiefly  of  gluten,  but  containing  likewise  cellulose,  some  grains  of 
fecula  which  have  not  been  removed  by  the  water,  and  fatty  sub- 
stances which  can  be  dissolved  in  ether  after  the  dried  matter  has 
been  finely  powdered.  There  are,  in  addition,  substances  which 
can  be  removed  by  treating  them,  when  hot,  first  with  concentrated, 
and  subsequently  with  weak  alcohol.  The  alcoholic  liquors  deposit, 
on  cooling,  a  substance  which  resembles,  in  its  composition  and  che- 
mical properties,  the  casein  of  cheese,  for  which  reason  it  has  re- 


AMYLACEOUS    MATTER. 


461 


celved  the  name  of  vegetable  casein.  The  alcoholic  liquors,  on 
cooling,  deposit  after  evaporation  a  substance  called  glutin,  having 
the  same  composition  as  albumen,  and  scarcely  differing  from  it  in 
its  chemical  properties. 

To  the  substance  left  by  gluten  after  these  various  processes,  the 
name  of  vegetable  fibrin  has  been  given,  which  substance,  in  fact,  pre- 
sents the  same  composition  as  animal  fibrin,  which  it  closely  resembles 
in  its  chemical  properties.  Vegetable  fibrin  combines  with  sul- 
phuric acid,  producing  a  compound  soluble  in  pure  water,  and  which 
dissolves  in  a  weak  solution  of  caustic  potassa,  furnishing  a  liquor 
resembling  in  its  properties  that  produced  by  animal  fibrin  under 
the  same  circumstances. 

Legumin. 

§  1281.  Legumin  is  extracted  from  peas,  beans,  and  lentils,  which 
contain  about  18  per  cent,  of  it.  They  are  chopped,  and  digested 
for  two  or  three  hours  with  tepid  water,  when  the  greater  part  of 
the  legumin  dissolves.  In  order  to  extract  that  which  remains  in 
the  pulp,  the  latter  is  washed  and  again  macerated  with  hot  water, 
and  the  substance  being  expressed  in  a  cloth  and  the  liquid  filtered, 
the  legumin  is  precipitated  from  it  by  the  addition  of  acetic  acid. 
Some  of  the  fatty  substances  are  removed  by  treating  the  dried 
matter  with  ether  and  alcohol. 

The  substance  thus  obtained  resembles  starch,  when  it  has  been 
precipitated  by  acetic  acid ;  and  when  dried,  it  forms  a  brilliant  and 
transparent  mass.  Its  aqueous  solution  is  precipitated  by  alcohol 
and  the  acids  ;  and  it  dissolves  in  the  caustic  alkalies,  which  appear 
to  have  no  effect  upon  it.  Its  composition  corresponds  to  the  for- 
mula CgoHy^NjjOgy ;  but  the  substance  to  which  the  name  of  legumin 
has  been  given  is  probably  a  mixture  of  several  substances,  which 
have  not  yet  been  separated. 

AMYLACEOUS  MATTER  C,Jl,,0,o. 

§  1282.  The  name  of  amylaceous 
matter  is  given  to  a  substance  which 
forms  rounded  grains,  varying  in 
appearance,  with  which  the  cells 
of  certain  parts  of  plants  are  filled. 
That  extracted  from  potatoes  is 
commonly  called  fecula^  and  that 
obtained  from  the  grains  of  the 
cerealia  is  known  by  the  name  of 
starch.  When  the  fecula  of  the 
potato  is  examined  by  the  micro- 
scope, it  will  be  found  to  consist  of 
ovoidal  granules,  the  surface  of  each 
Fig.  658.  of  which  exhibits  a  particular  point 


462 


ESSENTIAL   PRINCIPLES   OF  VEGETABLES. 


«,  the  hilum,  around  which  the  substance  is  arranged  in  concen- 
tric layers.  " 

On  the  surface  of  each  granule  curves  can  be  perceived,  which  sur- 
round the  hilum  concentrically,  and  with  apparent  regularity.     If 


Fig.  659. 


Fig.  tibO. 


one  of  these  grains  be  strongly  compressed  between  two  plates  of 
glass,  it  breaks  into  several  pieces,  (fig.  659,)  and  all  the  planes  of 
rupture  generally  pass  through  the  hilum,  as  if  the  substance  were 
less  resistant  at  this  point.  Each  grain  is  formed  by  the  superpo- 
sition of  a  great  number  of  very  thin  pellicles,  which  sometimes  ap- 
pear immediately  in  the  broken 
granules.  They  can  always  be 
shown  by  heating  the  fecula  to 
392°,  a  temperature  which  effects 
its  disaggregation,  and  then 
moistening  them  with  water,when 
the  granules  swell  considerably, 
and  the  pellicles  which  compose 
them  separate.  Fig.  660  repre- 
sents a  grain  of  potato  feciiia 
which  has  begun  to  exfoliate. 
The  pellicles  may  be  rendered 
still  more  visible  under  the  mi- 
croscope, by  moistening  them 
with  an  aqueous  solution  of  io- 
dine, which  turns  them  intensely 
blue.  Two  grains  are  frequent- 
ly united  together,  and  new  pel- 
licles of  amylaceous  matter  are 
deposited  on  the  united  grains, 
thus  forming  a  single  irregular 
grain,  having  two  hila. 

By  triturating  a  small  quantity 
of  fecula,  for  a  long  time,  in  a 
rough  mortar,  the  greater  part 
of  the  granules  are  burst,  and  if 
the  broken  grains  be  examined 
by  the  microscope,  no  appearance 
of  liquid  can  be  recognised,  and 


PECULA   AND    STARCH. 


463 


no  portion  of  the  substance  can  be  dissolved  in  cold  water.  The 
entire  grain  is,  therefore,  formed  of  solid  matter,  and  contains  no 
gummy  fluid,  as  was  long  supposed. 

The  hilum  is  not  always  as  apparent  in  the  amylaceous  gra- 
nules of  other  vegetables  as  in  those  of  the  potato,  and  can  fire- 
quently  only  be  shown  by  desiccation,  which  produces,  at  this  point 
of  the  granules,  a  greater  contraction  than  at  the  other  points, 
and  a  depression  which  can  be  immediately  recognised.  The  sym- 
metrical arrangement  of  the  amylaceous  molecules  around  the  hilum 
is  particularly  evident  on  examining  by  the  microscope  potato  fecula 
illuminated  by  polarized  light,  (fig.  661,)  and  interposing  a  rhomb  of 
Iceland  spar  between  the  object  and  the  eye,  when  a  Mack  cross,  of 
which  the  centre  is  lost  in  the  hilum,  is  observed,  analogous  to  that 
produced  under  the  same  circumstances  by  thin  plates  of  crystal 
of  the  same  axis,  cut  perpendicularly  to  this  axis.  Fig.  661  repre- 
sents the  same  grains  of  fecula  as  fig.  658,  but  seen  with  polarized 
light. 

The  amylaceous  grains  of  se- 
veral vegetables  exhibit  a  pecu- 
liar appearance  which  enables  an 
experienced  eye  to  recognise 
immediately  the  vegetable  to 
which  they  belong.  This  fact 
is  easily  proved  by  figs.  658,  662, 
663,  and  664,  which  represent 
amylaceous  grains  of  various 
kinds,  seen  by  the  microscope 
and  illuminated  by  natural  light. 
In  fig.  658  there  are  grains  of  po- 
tato fecula ;  in  fig.  662,  grains  of 
wheat  starch ;  in  fig.  663  are  seen 
the  amylaceous  grains  of  peas, 
(the  grains  a  belonging  to  dried 
peas,  and  the  grains  h  to  green 
peas ;)  and  lastly,  fig.  664  repre- 
sents the  starch  from  Indian 
corn.  Potato  fecula  is  still  more 
easily  distinguished  from  other 
fecula  when  seen  by  polarized 
light,  as  it  is  the  only  one  which 
exhibits  in  this  case  a  well- 
marked  black  cross,  (fig.  661.) 
By  this  character  it  is  possible  to 
discover  by  the  microscope  if 
wheat  flour  has  been  adulterated 
with  potato  starch. 
Fig.  664.  The  absolute  size  of  amyla- 


464  ESSENTIAL   PRINCIPLES   OF  VEGETABLES. 

ceous  grains  varies  greatly  in  different  vegetables ;  and  the  follow- 
ing table  gives  the  extreme  length  of  the  granules  extracted  from 
some  of  them : 

Granules  of  potato 0.185  mm. 

"  beans 0.075 

"  sago 0.050 

"  wheat 0.045 

"  sweet-potato 0.040, 

"  Indian  corn 0.025 

"  millet 0.010 

"  parsnip O.OOT 

"  mangel-wurzel 0.004 

The  grains  of  potato  starch  are  collected  in  particular  cells,  nearly 
as  is  seen  in  fig.  Q^b^  which  represents  some  full  cells. 

§  1283.  The  amylaceous  matter  extracted  from  various  vegeta- 
bles presents  exactly  the  same  chemical  composition,  which  is  iden- 
tical with  cellulose,  when  the  two  substances  have  been  dried  undpr 
the  same  circumstances.  Amylaceous  matter,  dried  in  vacuo  at 
284°,  contains 

Carbon 44.44 

Hydrogen 6.18 

Oxygen 49.38 

100.00 

which  composition  corresponds  to  the  formula  O^^^fi^^;  although 

it    is    generally     admitted 
„       ^^^^^^^  that  1  equivalent  of  oxygen 

.^i^-  .]J^^^^  ^^^  -^  equivalent  of  hydro- 

)^m^:^^mk  gen  exist  in  it  in  the  state 

of   water,   notwithstanding 
that  this  water  cannot  be 
fitO^.  '^^^BT-^WfT^WS^K^^m^^  driven  off  without  injuring 
,      ^  winm^MHii^mr—  r^^lJt^^MlEl^^^      amylaceous      matter. 
'^'^^l^jm^^^S^^^^^mMtOBs)^^^^^^^^  ^^^^  therefore  as- 
jM^rS^^Kjl^^HE^^^^^^  signed  to  the  substance  sup- 
^^^^uJH^mf/     posed  to  be  anhydrous  the 
'^^^^jM^  "^S^Bjg^^       formula   C12H9O9,  and   the 
''^     "  formula  CjgHjoOjo  to  those 

^ig-  666.  dried  in  vacuo  at  284°. 

Amylaceous  matter  may  exist  in  different  states  of  hydration ; 
and  fecula,  with  only  1  equivalent  of  water,  forms  a  very  light 
powder,  rapidly  attracting  the  moisture  of  the  air;  but  when  ex- 
posed for  some  time  to  air  which  is  far  from  its  state  of  saturation, 
it  increases  11  per  cent.,  by  absorbing  2  equivalents  of  water.  The 
same  state  of  hydration  is  obtained  by  drying  the  most  hydrated 
fecula  in  vacuo,  at  the  ordinary  temperature.     In  naoister  air,  it  ab- 


FECULA   AND   STARCH.  465 

sorbs  still  2  equivalents  of  water,  and  then  contains  18  per  cent,  of 
it ;  and  lastly,  in  air  saturated  with  moisture  it  may  still  absorb  6 
equivalents,  so  that  it  will  contain  in  all  6  equivalents  or  35  per  cent, 
of  water.  In  this  state  of  hydration  the  grains  adhere  remarkably 
to  each  other,  and  the  substance  is  easily  compressed  into  balls. 
Moist  fecula,  recently  extracted  from  the  tubers,  and  merely  sepa- 
rated from  its  water  of  combination  by  the  absorbent  action  of 
plaster,  retains  45  per  cent,  of  water,  and  is  called,  in  commerce, 
green  fecula. 

Fecula  perfectly  dried  in  vacuo,  and  then  exposed  to  a  tempera- 
ture of  536°,  assumes  an  amber  colour  without  losing  any  of  its 
weight ;  but  not  without  being  greatly  modified,  and  transformed 
into  a  substance  of  the  same  chemical  composition,  but  very  soluble 
in  water,  and  known  by  the  name  of  dextrin.  When  the  fecula 
has  not  been  previously  dried,  this  transformation  is  effected  at  a 
lower  temperature,  and  it  is  still  more  rapid  when  heated  in  a  tube 
hermetically  sealed,  preventing  the  evaporation  of  the  water. 

If  water  containing  1  or  2  hundredths  of  fecula  be  boiled,  the 
latter  swells  and  separates  so  as  to  appear  to  dissolve  in  the  water ; 
but  if  the  liquid  be  then  exposed  to  a  temperature  below  32°,  it 
freezes,  and  the  amylaceous  matter  becomes  to  a  certain  degree  ag- 
gregated, and  separates  from  the  liquid  in  the  form  of  small  pelli- 
cles. When  fecula  is  diluted  with  12  or  15  times  its  weight  of 
water,  the  temperature  of  which  is  slowly  raised,  all  the  grains  ex- 
foliate on  approaching  the  boiling  point,  and  swell  to  such  a  degree 
as  to  occupy  nearly  the  whole  volume  of  the  liquid,  thus  converting 
the  latter  into  a  gelatinous  paste,  which  is  used  for  pasting  paper. 
The  fecula  swells  also,  even  in  cold  water,  if  1  or  2  hundredths  of 
caustic  potassa  or  soda  be  added  to  it. 

Sulphuric,  chlorohydric,  phosphoric,  and  nitric  acid  also  produce, 
when  cold,  the  swelling  and  disaggregation  of  the  amylaceous  gra- 
nules ;  the  disaggregation  being  very  rapid  if  the  acid  liquid  con- 
tains at  least  0.2  of  real  acid,  while  it  follows  in  time,  even  when 
the  quantity  of  acid  is  very  small.  When  dilute  acids  are  made  to 
act  on  starch,  at  the  temperature  of  212°,  the  amylaceous  matter 
is  soon  disaggregated,  being  converted  first  into  dextrin,  and  then 
into  a  sugar-like  substance,  glucose,  which  both  exert  rotation  to- 
ward the  right.     We  shall  again  recur  to  this  remarkable  action. 

When  an  aqueous  solution  of  iodine  is  poured  upon  fecula,  the 
latter  turns  of  a  beautiful  blue  colour  ;  and  the  same  discoloration 
is  produced  on  starch  in  the  state  of  paste,  and  even  in  the  water 
in  which  it  has  been  boiled.  The  colour  changes  with  the  more  or 
less  advanced  stage  of  disaggregation  of  the  fecula,  and  becomes 
insensible  when  the  fecula  has  assumed  the  condition  of  dextrin 
soluble  in  water,  even  when  cold.  When  water  is  heated  contain- 
ing fecula  coloured  by  iodine,  the  blue  colour  disappears  com- 
pletely as  soon  as  the  temperature  reaches  150.8°,  and  does  not 

Vol.  IL— 30 


466  ESSENTIAL   PRINCIPLES   OF   VEGETABLES. 

reappear  at  a  higher  temperature ;  but  on  allowing  it  to  cool,  the 
colour  reappears.  These  effects  may  be  reproduced  several  times ; 
but  the  intensity  of  colour  lessens  each  time,  because  a  portion  of 
the  iodine  is  vaporized. 

lodinated  starch,  suspended  in  water,  is  bleached  by  the  action 
of  solar  light,  the  iodine  being  then  converted  into  iodic  and  hy- 
driodic  acid.  A  few  drops  of  chlorine  will  cause  the  colour  to  re- 
appear, because  they  decompose  the  hydriodic  acid,  and  set  at  liberty 
the  iodine,  which  again  seeks  the  starch.  Alkaline  solutions  all 
bleach  iodinated  starch,  by  attacking  the  iodine,  and  the  addition 
of  an  acid  restores  the  colour. 

Neither  acetic  acid  nor  ammonia  act  on  fecula;  while  fuming 
nitric  acid  combines  with  amylaceous  matter,  and  forms  a  compound 
insoluble  in  water,  called  xyloidiii,  which  is  regarded  as  a  combi- 
nation of  1  equivalent  of  amylaceous  matter  and  1  equivalent  of 
nitric  acid.  If  the  nitric  acid  be  hot,  oxalic  acid  is  immediately- 
obtained. 

When  fecula  is  ground  with  a  concentrated  solution  of  caustic 
potassa,  it  is  converted  into  a  substance  which  dissolves  in  cold 
water;  and  when  a  soluble  salt  of  baryta  or  lime  is  poured  into  tl:e 
solution,  precipitates  are  obtained,  which  are  compounds  of  the 
amylaceous  matter  with  baryta  or  lime.  By  treating  the  precipi- 
tates with  an  acid,  the  amylaceous  matter  is  again  isolated,  and  the 
latter,  in  however  separated  a  form  it  may  exist,  is  again  coloured 
blue  by  iodine. 

Chlorine,  in  the  presence  of  water,  acts  powerfully  on  fecula,  and 
ultimately  transforms  it  into  carbonic  acid  and  water.  Concen- 
trated solutions  of  the  hypochlorites  produce  the  same  effect  at  a 
temperature  of  212°. 

Cellulose,  the  chemical  composition  of  which  is  the  same  as  that 
of  amylaceous  matter,  is  not  coloured  blue  by  a  solution  of  iodine ; 
which  reaction  easily  distinguishes  the  two  substances  in  the  micro- 
scopic study  of  the  organs  of  vegetables.  But  when  cellulose  has 
been  brought  into  contact  for  a  few  moments  with  sulphuric  acid,  it 
has  acquired  the  property  of  turning  blue  by  iodine ;  a  fact  which 
seems  to  prove  that,  by  the  influence  of  sulphuric  acid,  cellulose 
passes  into  a  state  in  which  it  exhibits  the  properties  of  amylaceous 
matter. 

§  1284.  In  order  to  extract  fecula  from  potatoes,  the  tubers  are  first 
reduced  to  a  pulp,  by  means  of  a  grater,  which  destroys  their  cells, 
and  the  pulp  is  then  exposed  to  a  current  of  water,  which  removes 
the  fecula  and  conveys  it  into  a  proper  receiver.  The  fecula  is 
mixed  with  a  small  quantity  of  cellular  tissue,  which  is  easily 
removed  by  fresh  levigation ;  for  the  grains  of  fecula,  on  account 
of  their  rounded  form,  fall  to  the  bottom  of  the  water,  while  the 
pellicles  of  cellulose,  remaining  longer  in  suspension,  form  the  su- 
perficial layer  of  the  deposit. 


INULIN  AND   LICHENIN.  467 

Wheat  starch  is  made  in  the  same  manner,  by  working  a  paste 
of  flour  under  a  stream  of  water,  as  in  the  method  of  separating  the 
gluten,  (§  1280 ;)  when  the  water,  after  being  allowed  to  rest,  de- 
posits the  starch  it  held  in  suspension.  If  flour  moistened  with 
water  be  exposed  to  the  air,  it  soon  putrefies,  but  the  nitrogenous 
matter  alone  is  decomposed  and  changed  into  soluble  products ;  so 
that,  if  the  deposit  be  washed  after  some  time,  the  starch,  mixed 
with  a  small  quantity  of  cellular  tissue,  only  remains.  The  putre- 
faction of  the  gluten  is  hastened  by  pouring  on  the  flour  the  water 
arising  from  a  previous  operation,  which  is  called  the  mother  liquid 
by  manufacturers  of  starch. 

Inulin  Cj^HjoOio. 

§  1285.  Certain  roots  contain  a  peculiar  substance,  inulin^  having 
the  same  composition  as  amylaceous  matter,  and  appearing  to  play 
the  same  part,  while  its  rotatory  power  is  toward  the  left,  contrary 
to  that  of  amylaceous  matter.  Inulin  is  generally  extracted  from 
the  root  of  the  elecampane,  {inula  helenium ;)  for  which  purpose 
the  bruised  roots  are  digested  with  boiling  water,  and  the  solution 
clarified  with  white  of  egg ;  when  the  liquid  deposits  inulin  on  cool- 
ing, in  the  shape  of  a  white  powder.  This  substance,  which  is 
almost  insoluble  in  cold,  dissolves  freely  in  boiling  water ;  and  if 
the  water  be  boiled  for  a  long  time,  the  inulin  is  changed  into  a 
sugar-like  substance.  Inulin  dissolves  readily  in  acids,  but,  at  the 
boiling  point,  it  is  more  rapidly  converted  into  sugar,  without  any 
change  in  the  direction  of  the  rotatory  power.  Boiling  nitric  acid 
converts  it  into  oxalic  acid,  which  transformation  is  probably  ef- 
fected only  after  intermediate  stages  of  condition  which  have- not 
yet  been  observed. 

Lichenin  G^^^fi^Q, 

§  1286.  Several  species  of  moss  and  lichen  contain  a  substance, 
called  lichenin^  of  the  same  composition  as  amylaceous  matter,  but 
differing  from  it  in  several  points.  It  is  generally  obtained  from 
Iceland  moss,  by  digesting  the  chopped  moss  for  24  hours  with  20 
times  its  weight  of  cold  water,  to  which  a  small  quantity  of  car- 
bonate of  soda  has  been  added,  and  repeating  the  washing  until  the 
water  is  altogether  free  from  bitterness.  The  moss  is  then  boiled 
with  ten  times  its  weight  of  water,  and  the  boiling  liquid  expressed 
in  a  cloth ;  when,  on  cooling,  it  becomes  a  transparent  jelly,  which, 
after  being  dried,  is  a  transparent,  hard,  and  brittle  mass,  soluble  in 
boiling  water,  from  which  alcohol  precipitates  it.  If  a  solution  of 
lichenin  be  boiled  for  a  long  time,  it  is  no  longer  precipitated  by 
cooling,  and  is  converted  into  a  gummy  substance.  Lichenin  dis- 
solves readily  in  acids,  which  convert  it  into  sugar  at  the  boiling 
point ;  and  when  heated  with  dilute  nitric  acid,  it  yields  oxalic  acid. 

Gelatinous  lichenin  is  coloured  blue  by  iodine. 


468  ESSENTIAL   PRINCIPLES  OF  VEGETABLES. 

Gums  C,2H,oO,o. 

§  1287.  Certain  substances,  as  yet  imperfectly  understood,  which 
issue  from  trees,  are  called  gums.  Their  elementary  composition  is 
the  same  as  that  of  amylaceous  matter,  but  they  differ  from  it  in 
several  of  their  chemical  properties :  thus  amylaceous  matter  forms 
oxalic  with  nitric  acid,  while,  under  the  same  circumstances,  gums 
produce  both  oxalic  and  a  peculiar  acid  called  mucic  acid. 

Gums  may  be  divided  in  three  species : 

1.  Gum  arabic,  or  arahin. 

2.  The  gum  of  our  indigenous  fruit-trees,  or  cerasin. 

3.  Gum  tragacanth,  of  which  the  essential  principle  has  received 
the  name  of  hassorin. 

Gum  arabic  issues,  in  the  form  of  a  viscous  solution,  from  certain 
species  of  acacia,  and  after  some  time  the  substance  coagulates  and 
dries  on  the  tree.  Large  quantities  of  this  gum  are  imported  from 
Senegal. 

Gum  arabic  is  found  in  small  round  masses,  having  a  conchoidal 
and  vitreous  fracture ;  and  its  taste  is  sweetish  and  nearly  insipid. 
It  dissolves,  in  indefinite  proportions,  in  water,  imparting  to  it  a 
peculiar  consistence,  called  gummy.  It  dissolves  slowly  in  cold, 
and  rapidly  in  boiling  water ;  and  the  liquid,  when  evaporated,  be- 
comes more  and  more  thick,  and  finally  solidifies  into  a  transparent 
mass,  which  presents  no  traces  of  crystallization. 

The  purest  gum  arabic  of  commerce  has  always  a  slightly  yellow- 
ish tinge;  but  it  may  be  made  perfectly  colourless  by  passing 
chlorine  through  a  boiling  solution  of  gum  and  drying  the  substance. 
Gum  arabic,  being  insoluble  in  alcohol  and  ether,  is  precipitated 
from  its  aqueous  solutions  when  alcohol  is  added ;  which  method  is 
sometimes  adopted  in  proximate  analysis  to  separate  gum  from 
sugars,  which  dissolve,  on  the  contrary,  very  readily  in  dilute  alco- 
hol. The  aqueous  solution  of  gum  arabic  exerts  a  rotatory  power 
toward  the  left. 

Gum  arabic,  dried  in  vacuo  at  266°,  exhibits  the  same  elementary 
composition  as  amylaceous  matter  dried  under  the  same  circum- 
stances, and  its  formula  is  therefore  C^g  H^q  O^q,  or  a  multiple  of 
it.  Caustic  potassa  coagulates  a  concentrated  solution  of  gum 
arabic;  but  if  the  solution  is  diluted,  no  precipitate  is  formed, 
although,  by  afterward  adding  alcohol,  a  compound  of  gum  with 
potassa  is  formed.  Subacetate  of  lead,  poured  into  a  solution  of 
gum  arabic,  yields  a  white  precipitate,  of  which  the  formula  is 
PbO,Ci3HjoOio.  Under  these  circumstances,  therefore,  gum  arabic 
behaves  like  an  acid. 

Cold  sulphuric  acid,  introduced  into  an  aqueous  solution  of  gum 
arabic,  slowly  inverts  its  primitive  rotatory  power,  and  changes  it 
from  the  left  to  the  right ;  the  inversion  ensuing  more  rapidly  when 
assisted  by  heat ;  and  if  the  liquor  be  boiled,  the  gum  thus  modified 


SUGARS.  469 

IS  finally  converted  into  a  fermentable  sugar,  wlilch  also  exerts  a 
rotatory  power  in  the  latter  direction.  The  transformation  is 
effected  by  passing  through  a  series  of  intermediate  states,  which 
may  be  observed,  by  saturating  the  acid  with  chalk,  and  precipitat- 
ing by  alcohol  the  already  partially  modified  substance. 

Cherry-trees,  plum-trees,  and  various  other  fruit-trees  exude  a 
viscous  matter,  which  solidifies  in  the  air,  and  produces  a  gum 
called  cerasin,  probably  a  mixture  of  several  substances.  It  swells 
in  cold  water,  and  dissolves  with  diSiculty ;  but  when  boiled  for  a 
long  time,  a  considerable  portion  of  it  dissolves,  and  the  dissolved 
portion  closely  resembles  arabin. 

Gum  tragacanth  flows  from  certain  vegetables  of  the  genus  astra- 
galus, which  are  cultivated  chiefly  in  the  East :  it  exudes  in  the 
shape  of  a  very  thick  gummy  juice,  which,  on  solidifying,  forms 
small  contorted  strips.  This  gum  is  also  probably  a  mixture  of 
several  substances ;  and  the  name  of  hassorin  has  been  given  to 
that  which  predominates  and  is  regarded  as  its  essential  principle. 
Bassorin  does  not  dissolve  in  water,  even  at  the  boiling  point ;  but 
it  swells  and  is  converted  into  a  gelatinous  substance.  It  dissolves 
rapidly  in  the  alkalies ;  while  dilute  sulphuric  acid,  at  the  boiling 
point,  converts  it  into  glucose. 

Cerasin  and  bassorin,  when  treated  with  nitric  acid,  yield  a  mix- 
ture of  oxalic  and  mucic  acid ;  the  formation  of  which  latter,  which 
is  easily  proved,  because  the  acid  is  insoluble  in  cold  water,  is  a  very 
well-marked  characteristic,  by  which  gums  may  be  distinguished 
from  amylaceous  matter. 

Iodine  does  not  colour  gums  when  they  are  pure  ;  and  when  gum 
tragacanth  assumes  a  blue  tinge,  it  is  easily  seen  that  this  arises 
from  the  presence  of  a  small  quantity  of  fecula. 

Vegetable  Mucilage, 

§  1288.  Many  grains,  such  as  flaxseed,  and  many  leaves,  stems, 
and  roots  of  vegetables,  as  the  mallow,  marsh-mallow,  borage,  etc. 
etc.,  when  macerated  in  cold,  or  better  still,  in  boiling  water,  yield 
gummy  and  stringy  liquids,  in  which  alcohol  produces  a  gelatinous 
precipitate,  the  nature  of  which  has  not  been  well  ascertained.  The 
general  name  of  vegetable  mucilage  has  been  given  to  these  sub- 
stances. The  mucilage  of  flaxseed  presents,  when  dried,  the  same 
elementary  composition  as  amylaceous  matter  and  gums. 

SUGARS. 

§  1289.  Sugars  are  substances  soluble  in  water,  having  a  sweet 
taste,  and  possessing  the  property  of  being  converted  into  alcohol 
and  carbonic  acid,  when  left  in  contact  with  certain  nitrogenous 
organic  substances,  called  yeasts,  or  leaven.  Sugars  are  widely 
diffused  through  the  vegetable  kingdom ;  and  three  principal  spe- 
cies have  been  distinguished  by  chemists. 


470  ESSENTIAL   PRINCIPLES  OF  VEGETABLES. 

1.  Cane-sugar. 

2.  Grapersugar. 

3.  The  uncrystallizable  sugar  of  fruits. 

The  first  species  is  perfectly  well  known,  while  the  others  are  lesa 
so;  and  when  their  properties  are  more  accurately  ascertained, 
they  will  probably  be  subdivided.  A  crystallizable  substance, 
sugar  of  milk,  is  also  found  in  the  milk  of  animals,  and  should  be 
classed  among  the  sugars,  from  the  definition  we  have  just  given  of 
these  substances  ;  but  we  shall  reserve  its  examination  until  the 
study  of  the  fluids  of  the  animal  economy  shall  occupy  our  atten- 
tion. In  their  composition,  sugars  present  this  remarkable  fact, 
al^eady  remarked  in  other  substances,  that  their  hydrogen  and 
oxygen  exist  in  exactly  the  proportions  which  form  water. 

Cane-sugar  Q^fi^fi^^. 

§  1290.  Cane  sugar  exists  in  solution  in  the  juice  of  a  large  num- 
ber of  vegetables ;  and  may  be  said  to  be  found  in  all  vegetables 
the  juice  of  which  is  not  acid,  as  acids  react  powerfully  on  cane- 
sugar,  and  convert  it  into  fruit-sugar.  Cane-sugar  is  also  abun- 
dantly found  in  the  sugar-cane,  the  sugar-beet,  melons,  turnips, 
carrots,  the  stalk  of  Indian  corn,  the  ascending  sap  of  the  maple, 
the  descending  sap  of  the  birch,  and  in  a  great  number  of  tropical 
fruits,  as  the  cocoa-nut,  pineapple,  etc.  etc.  It  is  principally 
derived  from  the  sugar-cane  and  sugar-beet ;  and  large  quantities 
are  also  extracted  from  the  sugar-maple. 

Very  pure  cane-sugar  is  found  in  commerce,  either  in  the  form 
of  large  colourless  and  transparent  crystals,  constituting  sugar- 
candy,  or  in  that  of  small  crystals  adhering  to  each  other,  as  in  our 
common  loaves  of  sugar.  Cane-sugar  is  inodorous,  possesses  a  very 
sweet  taste,  and  its  density  is  about  1.60.  It  dissolves  in  J  of  its 
weight  of  cold  and  in  a  still  smaller  quantity  of  boiling  water  ;  and 
the  solution,  when  concentrated,  produces,  by  evaporation  at  a  low 
temperature,  beautiful  crystals.  It  dissolves  in  80  times  its  weight 
of  boiling  absolute  alcohol,  but  the -greater  portion  of  it  is  deposited 
during  cooling ;  and  it  may  be  said  to  be  nearly  insoluble  in  cold 
alcohol.  Sugar  dissolves  much  more  easily  in  shghtly  diluted  alco- 
hol, for  4  parts  of  alcohol  at  181.5°  will  dissolve  1  of  sugar.  Cane- 
sugar  melted  or  dissolved  in  water  turns  the  plane  of  polarization 
of  polarized  light  toward  the  right. 

Cane-sugar  fuses  when  heated  above  320°,  forming  a  viscous 
mass,  flowing  with  difiiculty,  which  solidifies  into  a  transparent  mass 
having  a  vitreous  fracture.  This  mass,  rolled  out  on  marble  tables, 
is  sold  under  the  name  of  barley-sugar ;  in  making  which  article, 
confectioners  are  in  the  habit  of  adding  a  small  quantity  of  vine- 
gar before  melting  the  sugar.  In  this  state,  the  sugar  is  vitreous 
and  transparent,  but  in  a  short  time,  especially  if  the  air  have  ac- 
cess to  it,  the  outer  layers  become  opake  and  fall  in  consequence 


CANE-SUGAR.  471 

of  the  crystallization  which  takes  place.  Melted  sugar,  kept  for 
Bome  time  at  the  temperature  of  356°,  loses  the  property  of  crys- 
tallizing when  redissolved  in  water ;  and  its  constitution  is,  in  that 
case,  deeply  altered. 

The  composition  of  crystallized  cane-sugar  and  that  of  barley- 
sugar  corresponds  to  the  formula  C^^H^fi^y 

If  cane-sugar  be  heated  to  410°  or  428°,  it  loses  2  equiv.  of 
water,  and  is  converted  into  a  black  substance  called  caramel,  of 
which  the  formula  is  consequently  Cj^HgOg.  This  substance  is  deli- 
quescent, no  longer  tastes  of  sugar,  is  very  soluble  in  water,  which 
it  turns  of  a  deep  brown  colour,  and  acts  the  part  of  a  weak  acid, 
dissolving  in  the  alkalies,  and  forming  black  precipitates  with 
baryta  and  oxide  of  lead. 

On  continuing  to  heat  caramel,  it  parts  with  more  water,  and  is 
converted  into  a  black  insoluble  product ;  and,  lastly,  if  the  tem- 
perature be  still  raised,  acid  products  and  inflammable  gases  are 
disengaged,  while  a  puffy  black  coal  remains.  All  these  products 
are  obtained  mixed  when  sugar  is  suddenly  heated. 

When  pounded  or  rubbed  in  the  dark,  sugar  becomes  phospho- 
rescent ;  and  when  grated  it  has  a  slight  taste  of  burnt  sugar,  owing 
to  the  production  of  a  small  quantity  of  caramel  by  the  elevation 
of  the  local  temperature. 

When  a  solution  of  cane-sugar  is  boiled  for  a  long  time,  the  sugar 
undergoes  alteratiou,  which  may  be  readily  observed  by  examining 
the  successive  effects  of  the  liquid  on  polarized  light.  It  first  loses 
the  property  of  crystallizing,  and  closely  resembles  sugar  which  has 
been  heated  for  some  time  to  356°  ;  which  alteration  is  effectually 
prevented  by  the  presence  of  a  small  quantity  of  alkali. 

The  mineral  acids,  even  when  very  dilute,  and  the  greater  part 
of  the  organic  acids,  alter  cane-sugar  and  transform  it  into  a  sugar 
which  no  longer  crystallizes  as  formerly  by  evaporation,  and  which 
turns  the  plane  of  polarization  of  polarized  rays  toward  the  left. 
This  new  sugar  may  be  called  sugar  inverted  hy  acids,  and  in  its 
chemical  properties  it  closely  resembles  fruit-sugar.  Acids  which 
produce  the  same  transformation  undergo  no  change  themselves, 
and  are  found  intact  in  the  liquor ;  and  the  transformation  takes 
place  with  the  mineral  acids  even  when  cold,  and  much  more 
rapidly  if  the  temperature  be  raised. 

§  1291.  Cane-sugar  combines  with  bases,  and  forms,  in  certain 
cases,  crystallizable  compounds,  called  saccharates.  If  concentrated 
water  of  baryta  be  poured  into  a  concentrated  boiling  solution  of 
Bugar,  a  crystalline  mass  of  saccharate  of  baryta  is  deposited  on 
cooling,  having  for  its  formula 

BaO+C^H,,0,,. 

This  salt  bears  a  temperature  of  392°  without  decomposing  or 


472  SUGARS. 

losing  its  water;  but  carbonic  acid  readily 'decomposes  it,  the  sugar 
being  redissolved  and  carbonate  of  baryta  precipitated. 

Two  compounds  of  cane-sugar  with  lime  may  be  obtained,  the 
first  of  which  is  produced  by  pouring  a  solution  of  sugar  upon  an 
excess  of  slaked  lime,  when  a  compound,  very  soluble  when  cold,  is 
formed,  and  can  be  separated  by  filtering.  If  the  liquid  be  heated 
to  boiling,  the  greater  part  of  this  compound  is  precipitated,  since 
it  presents  the  remarkable  property  of  being  much  less  soluble  in 
hot  than  in  cold  water ;  so  much  so,  that  it  may  even  be  washed  in 
hot  and  then  redissolved  in  cold  water.  The  formula  of  this  sac- 
charate,  when  dried  at  212°,  is 

8CaO,2(C^H„0„). 

If,  on  the  contrary,  hydrate  of  lime  be  added,  by  small  quan- 
tities at  a  time,  to  a  concentrated  solution  of  cane-sugar,  until  no 
more  will  dissolve,  and  then  alcohol  be  poured  into  the  liquor  at 
185°,  a  saccharate  of  lime  is  precipitated,  of  which  the  formula  is 

CaO,C^H„0„. 

Solutions  of  saccharate  of  lime  have  a  strong  alkaline  reaction ; 
and  they  rapidly  attract  the  carbonic  acid  of  the  air,  causing  the 
formation  of  small  transparent  crystals  of  carbonate  of  lime,  resem- 
bling those  of  the  native  'crystals  of  the  substance,  which  are  depo- 
sited on  the  sides  of  the  vessel  containing  them. 

If  finely  divided  protoxide  of  lead  be  digested  with  a  concen- 
trated solution  of  sugar  in  excess,  an  insoluble  saccharate  of  lead  is 
formed ;  and  the  liquid  contains  a  small  quantity  of  oxide  of  lead 
in  solution.  The  same  insoluble  compound  is  obtained  by  pouring 
into  a  solution  of  sugar  acetate  of  lead,  which  forms  no  precipitate, 
and  then  ammonia,  which  precipitates  the  saccharate  of  lead; 
when,  by  allowing  the  liquid  and  the  precipitate  to  rest  for  some 
time  in  a  hot  place,  they  assume  a  crystalline  appearance.  The 
composition  of  saccharate  of  lead  dried  in  vacuo  corresponds  to  the 
formula 

2PbO,C„H,„0,,. 

By  being  heated  to  320°,  it  loses  1  equiv.  of  water,  and  its  for- 
mula becomes  2PbO,Ci2H909;  and  in  both  states  of  desiccation  it 
yields,  when  decomposed  by  sulf  hydric  acid,  a  sugary  liquor,  which 
by  evaporation  produces  sugar.  The  sugary  substance  has  there- 
fore undergone  no  permanent  alteration  by  losing  2  equiv.  of  water, 
and  it  is  reasonable  to  suppose  then  the  formula  of  anhydrous  cane- 
sugar  to  be 

C12H9O9, 

which  would  give  for  that  of  crystallized  sugar 

C^H„0„2H0; 


CANE   SUGAR.  473^ 

and  the  formulae  of  the  saccharates  are 

C,fifi,,  BaO+2HO, 

C,.H,0„  CaO+2HO, 

2(C,;H90,),3Ca04-4HO. 

"Bj  evaporating  a  concentrated  solution  of  1  part  of  sea-salt  and 
4  parts  of  cane-sugar,  crystals  of  sugar-candy  are  first  formed,  but 
the  mother  liquid  subsequently  deposits  crystals  having  at  the  same 
time  a  sweet  and  a  saline  taste,  of  a  deliquescent  combination,  of 
which  the  formula  is 

NaCl,2(C^H„0„). 

Chloride  of  potassium  and  chlorohydrate  of  ammonia  form  simi- 
lar compounds,  which  often  cause  the  loss  of  a  large  quantity  of 
sugar,  in  the  manufacture  of  beet-sugar,  when  the  roots  contain 
much  sea-salt,  as  is  the  case  when  they  have  grown  near  the  sea. 
As  these  compounds  are  deliquescent,  they  remain  in  the  mother 
liquid  or  in  the  molasses. 

The  presence  of  sugar  prevents  the  precipitation  of  several  me- 
tallic oxides  by  alkalies,  which  is  especially  evident  in  the  ses- 
quisalts  of  iron  and  those  of  oxide  of  copper  CuO,  and  which  is 
readily  explained,  as  the  hydrates  of  the  sesquioxide  of  iron  and 
oxide  of  copper  dissolve  in  a  solution  of  sugar  to  which  a  certain 
quantity  of  potassa  has  been  added. 

Concentrated  sulphuric  acid  blackens  cane-sugar,  and  yields 
complicated  products ;  its  action  when  very  dilute  has  already  been 
described,  (§  1290.)  Monohydrated  nitric  acid  produces  with  sugar 
an  insoluble,  very  combustible  substance,  analogous  to  that  yielded 
by  starch.  The  ordinary  nitric  acid  of  commerce  attacks  sugar 
when  hot,  and  transforms  it  into  a  very  soluble  and  deliquescent 
acid,  to  which  the  names  of  oxalhydric  and  oxysaccJiaric  acid  have 
been  given.  If  the  action  of  the  nitric  acid  be  much  prolonged,  a 
great  deal  of  oxalic  acid,  which  is  finally  converted  into  carbonic 
acid,  is  formed  in  the  liquor. 

At  the  boiling  point  sugar  reduces  several  metallic  salts ;  it  pre- 
cipitates suboxide  of  copper  Cu^O  from  the  acetate  of  copper,  and 
metallic  copper  from  the  sulphate  and  nitrate  of  this  metal ;  and  it 
precipitates  metallic  silver  from  the  solution  of  nitrate  of  silver,  at 
the  same  time  disengaging  products  of  the  oxidation  of  sugar,  such 
as  formic,  carbonic  acid,  etc.  etc. 

By  distilling  a  mixture  of  1  part  of  cane-sugar  and  8  parts  of 
quicklime,  in  a  glass  retort  scarcely  filled  to  one-half  at  a  certain 
temperature,  the  mixture  swells,  gases  are  disengaged,  and  an  oily 
liquid  can  be  collected  in  a  receiver  properly  cooled.  The  liquid, 
shaken  with  water,  parts  to  it  with  a  product  C3H3O  which  is  copi- 
ously obtained  in  the  distillation  of  the  acetates,  and  is  known  by 
the  name  of  acetone.     The  liquid,  exhausted  by  water,  decomposes 


474  ^  SUGARS. 

nearly  wholly,  into  an  oily  liquid  CgH^O,  boiling  at  183.2°,  and 
called  metacetone, 

Sugar  of  Acid  Fruits  C^fi.^fl^^, 

§  1292.  The  second  kind  of  sugar  found  in  vegetables,  and  which 
is  often  called  uncrystallizahle  or  fruit-sugar,  possesses  the  property 
of  turning  the  plane  of  polarization  to  the  left ;  and  exists  exclu- 
sively in  the  sour  juices  of  vegetables,  principally  in  fruits,  as 
grapes,  currants,  cherries,  plums,  etc.  etc.  In  order  to  extract  it, 
the  juice  must  be  expressed,  the  acids  saturated  with  chalk,  the 
juice  boiled  with  white  of  egg,  which,  by  coagulating,  removes  the 
mucilaginous  substances,  and  lastly,  the  liquid  evaporated  at  a 
gentle  heat.  The  substance  thus  obtained  presents,  when  dried, 
the  appearance  of  gum,  being  very  deliquescent,  dissolving  largely 
in  water,  and  even  in  alcohol  at  91.40°,  while  it  is  insoluble  in  abso- 
lute alcohol.  In  contact  with  yeast  it  ferments  immediately,  and 
produces  alcohol  and  carbonic  acid.  It  is  found  already  formed 
in  the  ascending  sap  of  the  birch  and  in  the  descending  sap  pf  the 
maple. 

Cane-sugar  is  readily  converted  into  this  second  species  of  sugar 
by  boiling  its  solutions  with  dilute  acids,  which  transformation  also 
takes  place,  in  the  presence  of  these  acids,  when  cold,  as  well  as  in 
that  of  organic  acids,  such  as  tartaric,  citric,  malic,  and  oxalic,  but 
it  requires  a  much  longer  time.  Cane-sugar  always  undergoes  this 
first  transformation,  under  the  influence  of  yeast,  before  that  of  fer- 
mentation properly  so  called,  that  is  to  say,  before  being  converted 
into  alcohol  and  carbonic  acid.  It  is  generally  admitted  that  the 
uncrystallizahle  sugar  of  all  fruits  is  identical,  although  this  is  by 
no  means  clearly  proved,  and  several  varieties  will  probably  be 
found  hereafter. 

The  chemical  composition  of  sugar  fuming  to  the  left,  dried  in  a 
water  bath,  corresponds  to  the  formula  Q^^^Jd^^, 

When  a  syrupy  solution  of  this  sugar  is  allowed  to  rest  for  some 
time,  it  deposits  small  crystalline  grains  of  a  sugary  substance,  which 
has  been  called,  improperly,  grape-sugar,  being  very  different  from 
the  sugar  which  produced  it,  as  its  composition  differs  in  contain- 
ing, in  addition,  the  elements  of  2  equiv.  of  water,  thus  making  its 
formula  Q^Jl^fi^^.  By  dissolving  it  in  water  a  liquor  is  obtained 
which  is  also  very  different  from  that  afforded  by  the  non-crystalline 
sugar  which  produced  it :  thus,  while  a  solution  of  the  latter  turned 
the  plane  of  polarization  toward  the  left,  a  solution  of  the  crystalline 
sugar  turns  it  toward  the  right,  like  cane-sugar.  This  granular 
sugar  differs,  moreover,  from  cane-sugar,  not  only  in  its  crystalline 
appearance,  but  also  in  the  manner  in  which  it  behaves  with  various 
chemical  agents,  and  by  the  intensity  of  its  rotatory  power.  One 
of  the  most  striking  differences,  and  one  of  the  most  easy  to  prove, 
is,  that  cane-sugar,  boiled  with  dilute  acids,  is  converted  into  sugar 


GRAPE   SUGAR.  475 

turning  the  plane  of  polarization  toward  the  left ;  while  under  the 
same  conditions,  grape-sugar  undergoes  no  change,  and  continues 
to  turn  toward  the  right. 

Grape-sugar  C^^H^fi^^. 

§  1293.  We  have  just  seen  that  the  syrupy  solution  of  sugar, 
turning  to  the  right,  yielded  hy  sour  fruits,  as  well  as  the  liquor 
obtained  by  boiling  cane-sugar  with  dilute  acids,  deposit,  after  a 
time,  a  sugary  substance  in  crystalline  grains,  to  which  the  name 
of  grape-sugar  has  been  given.  It  is  the  same  substance  which 
forms  the  white  powder  on  dry  grapes,  or  raisins,  and  which  con- 
stitutes the  grains  of  sugar  found  in  the  inside.  If  the  pulp  of 
these  fruits,  freed  as  much  as  possible  from  their  crystalline 
granules,  be  treated  with  water,  a  solution  is  obtained  which  still 
contains  a  large  quantity  of  sugar  turning  to  the  left. 

The  urine  of  patients  labouring  under  a  peculiar  disease,  called 
diabetes  melUtus,  or  saccharine  diabetes,  contains  sometimes  10  per 
cent,  of  a  sugar,  the  chemical  properties  of  which  appear  to  be  iden- 
tical with  those  of  grape-sugar.  A  precisely  similar  sugar  is  ob- 
tained when  starch  is  boiled  with  a  weak  solution  of  sulphuric  acid, 
and  the  solution  is  evaporated  after  having  been  saturated  with 
chalk ;  which  species  is  generally  called  glucose.  The  granular 
sugar  found  in  honey  appears  to  be  identical  with  grape-sugar  ; 
and  lastly,  the  same  sugar  is  frequently  separated  from  preserves 
made  of  acid  fruits,  in  the  form  of  crystalline  crusts ;  in  which  case 
it  has  been  produced  by  the  alteration  of  the  cane-sugar  used  in 
their  manufacture,  which,  by  virtue  of  the  acids  of  the  fruit,  is  con- 
verted into  uncrystallizable  sugar  turning  to  the  left,  the  latter 
product  itself,  in  time,  changing  into  grape-sugar. 

Grape-sugar  crystallizes  with  much  more  difficulty  than  cane- 
sugar,  always  producing  a  compound  crystallization ;  and  it  is  less 
soluble  in  water  than  cane-sugar,  for  it  requires  IJ  parts  of  cold 
water  to  dissolve  1  of  grape-sugar.  Its  taste  is  also  less  sweet. 
Grape-sugar,  on  the  contrary,  dissolves  somewhat  more  freely  in 
alcohol  than  cane-sugar ;  as  1  part  of  it  dissolves  in  60  parts  of  boil- 
ing absolute  alcohol,  and  in  5  or  6  parts  of  alcohol  at  181.40. 
Solutions  of  grape-sugar  turn  the  plane  of  polarization  to  the  right. 

The  composition  of  crystallized  grape-sugar  corresponds  to  the 
formula  C^^H.^O,^. 

This  sugar  softens  at  about  140°,  and  is  completely  liquefied  at 
212°,  at  which  temperature  it  loses  2  equiv.  of  water,  and  is  con- 
verted into  a  new  sugar  of  which  the  formula  is  C^fi^fi^^,  and 
which  then  presents  the  composition  of  the  fruit-sugar  just  described, 
although  it  continues  to  turn  polarized  light  to  the  right.  This 
latter  sugar  leaves,  after  evaporation,  a  pitch-like  mass ;  but  if  this 
be  allowed  to  rest  for  some  time  in  contact  witt  water,  crystals  of 


476  SUGARS. 

grape-sugar  are  formed.  If  grape-sugar  be  further  heated,  it  becomes 
brown  and  converted  into  caramel. 

§  1294.  Grape-sugar  combines  less  readily  with  bases  than  cane- 
sugar;  and,  when  boiled  with  alkaline  solutions,  the  liquor  turns 
brown  and  exhales  a  smell  of  burnt  sugar,  acid  products  being 
formed  which  combine  with  the  alkali.  If  slaked  lime  be  poured 
into  a  solution  of  grape-sugar,  a  large  quantity  of  the  lime  is 
dissolved,  and  the  liquor  first  exerts  an  alkaline  reaction,  but  at 
a  later  period  becomes  neutral,  and  carbonic  acid  no  longer  forms 
a  precipitate.  The  sugar  is  then  converted  into  a  powerful  acid 
called  ghicic,  of  which  the  formula  is  CJlfi^,  and  which  forms 
soluble  salts  with  nearly  all  the  bases ;  the  formula  of  glucate  of 
lime  being  CaO,2C3H505-fHO.  The  acid  may  be  isolated  by  pour- 
ing oxalic  acid  into  glucate  of  lime  until  no  precipitate  is  thrown 
down ;  when,  by  evaporating  the  solution,  a  white  acid  is  obtained, 
of  a  gummy  appearance,  very  soluble  in  water  and  deliquescent. 
The  acid  forms  with  oxide  of  lead  an  insoluble  salt  of  the  formula 
2PbO,C8H303,  which  is  prepared  by  pouring  subacetate  of  lead 
into  a  solution  of  glucate  of  lime.  The  glucate  of  lead,  suspended 
in  water,  is  readily  decomposed  by  sulf hydric  acid,  and  yields  free 
glucic  acid. 

Glucic  acid  is  also  formed  when  a  solution  of  cane  or  grape-sugar 
is  boiled  for  a  long  time  with  sulphuric  or  hydrochloric  acid. 

When  a  solution  of  glucic  acid  is  boiled  in  the  air,  the  liquid 
turns  brown,  and  a  new  acid,  called  apoglucic,  is  formed ;  and  by 
saturating  the  liquor  with  chalk,  after  some  time,  acid  glucates  and 
apoglucates  of  lime  are  formed ;  after  which  the  liquid  is  reduced 
to  the  consistence  of  syrup  and  treated  with  alcohol,  which  dissolves 
the  acid  glucate  and  leaves  the  apoglucate  of  lime.  The  latter  salt, 
being  redissolved  in  water,  is  treated  with  acetate  of  lead,  which 
yields  a  precipitate  of  apoglucate  of  lead,  which,  while  suspended 
in  water,  is  decomposed  by  sulfhydric  acid,  and  yields  free  apo- 
glucic  acid.  Apoglucic  acid  is  a  brown,  non-deliquescent  substance, 
which  readily  dissolves  in  water,  but  very  feebly  in  alcohol ;  and  its 
formula,  when  dried  at  248°,  is  G^Ji^fi^Q,  while  that  of  apoglucate 
of  lead  is  PbO,Cj8Hg08.  The  same  acid  is  formed  when  solutions  of 
the  alkaline  glucates  are  boiled  in  the  air. 

By  pouring  IJ  part  of  concentrated  sulphuric  acid  gradually, 
and  by  small  quantities  at  a  time,  upon  1  part  of  grape-sugar  melted 
at  212°,  treating  it  with  water,  and  lastly  saturating  the  liquor  with 
carbonate  of  baryta,  a  large  proportion  of  the  baryta  remains  in  the 
state  of  insoluble  sulphate  of  baryta,  while  the  liquid  contains  a 
soluble  salt  of  baryta,  the  sulphosaecharate.  If  subacetate  of  ba- 
ryta be  poured  into  this  liquid,  a  precipitate  of  sulphosaccharate  of 
lead  is  formed,  of  which  the  formula,  when  it  has  been  dried  at 
338°,  is  4PbO,C2^H3o03oS03.  The  sulphosaccharic  acid  is  easily 
separated  by  decomposing  the  sulphosaccharate  of  lead,  suspended 


GRAPE-SUGAR.  477 

in  water,  by  sulf  hydric  acid ;  but  it  is  not  ver^  fixed,  and  is  easily 
decomposed  by  a  slight  elevation  of  temperature. 

Grape-sugar  forms  a  crystallizable  compound  with  sea-salt,  ob- 
tained by  dissolving  in  water  6  parts  of  sugar  and  1  of  salt,  and 
allowing  the  liquid  to  evaporate  spontaneously,  when  beautiful 
well  terminated  crystals  are  deposited,  of  which  the  formula  is 
NaCl,2(Ci2Hj^Oj3)H-2HO.  In  a  dry  vacuum,  or  under  the  influ- 
ence of  heat,  these  crystals  part  with  2  equivalents  of  water  and 
fall  to  dust. 

§  1295.  A  boiling  solution  of  grape-sugar  reduces  immediately 
the  blue  liquor  obtained  by  pouring  potassa  and  tartrate  of  potassa 
into  salts  of  the  oxide  of  copper  CuO,  and  precipitates  from  it  the 
red  suboxide  of  copper  CUgO  ;  which  reaction  is  extremely  sensible, 
because  these  cupreous  compounds  possess  considerable  colouring 
power ;  and  it  enables  the  chemist  to  detect  the  presence  of  very  small 
quantities  of  sugar  in  a  liquor,  besides  affording  an  easy  means  of 
distinguishing  grape-sugar  from  cane-sugar,  which  produces  no 
similar  effect. 

It  has  been  proposed  to  apply  this  reaction  to  the  purpose  of 
ascertaining  the  quantity  of  grape-sugar  existing  in  a  fluid.  The 
cupreous  liquor  is  prepared  by  dissolving  together  sulphate  of  cop- 
per, tartrate  of  potassa,  and  caustic  potassa,  which  produce  an  in- 
tensely blue  liquor ;  after  which  the  solution  is  reduced  to  a  certain 
standard,  such,  for  example,  that  100  cubic  centimetres  of  it  shall 
be  exactly  discoloured  when  boiled  with  1  gm.  of  grape-sugar.* 
In  order  to  use  the  standard  solution,  100  cubic  centimetres  of  it 
are  boiled  in  a  porcelain  capsule,  and  the  liquor  to  be  tested  is 
gradually  added  to  it  by  means  of  an  alkalimeter.  The  volume  of 
liquor  which  produces  the  exact  effect  contains  precisely  1  gm.  of 
sugar. 

This  process  will  also  serve  to  determine  the  quantity  of  cane- 
sugar  contained  in  a  liquid,  as  it  sufl&ces  to  convert  the  sugar,  by 
boiling  it  with  an  acid,  into  sugar  turning  to  the  left,  which  pro- 
duces the  same  effect  on  the  cupreous  liquid,  and  then  to  operate 
with  this  liquid  as  has  been  stated,  after  having  saturated  the  excess 
of  acid. 

Lastly,  the  process  may  also  be  applied  to  the  determination  of 
the  proportions  of  cane-sugar  and  grape-sugar  which  may  be  mixed, 
by  first  ascertaining  the  discolouring  power  of  a  simple  solution  of 


*  The  solution  which  has  been  found  most  efl&cient  is  prepared  by  first  dis- 
solving 20  gm.  sulphate  of  copper  in  80  cubic  centimetres  of  water ;  and  then 
adding  343.8  gm.  of  a  solution  of  caustic  potassa,  of  the  specific  gravity  1.12,  to 
a  solution  of  80  gm.  neutral  tartrate  of  potassa  in  80  cubic  centimetres  of  water. 
Mix  the  two  solutions  by  pouring  the  cupreous  solution  into  the  alkaline  liquid,  by 
small  quantities  at  a  time,  and  dilute  the  whole  to  the  volume  of  1  litre.  When 
thus  prepared  the  solution  will  keep  unchanged  for  years. —  W.  L.  F' 


478  V  SUGARS. 

the  mixture,  and  then  that  of  an  equal  quantity  of  the  mixture 
after  the  cane-sugar  has  been  changed  by  boiling  with  an  acid.* 

GELATINOUS  PRINCIPLES  OF  FRUITS. 

§  1296.  The  juices  of  all  ripe  fleshy  fruits  yield,  by  continued 
boiling  under  certain  conditions,  gelatinous  substances,  which  are 
derived  from  an  immediate  principle,  insoluble  in  water,  which  ex- 
ists in  greater  or  less  proportion  in  all  vegetables,  and  to  which  the 
name  o^  pectose  has  been  given. 

Pectose,  which  is  chiefly  found  in  the  pulp  of  unripe  fruits  and 
certain  roots,  such  as  carrots  and  turnips,  is  intimately  mixed  with 
the  cellulose  which  composes  the  cells.  As  it  is  entirely  insoluble 
in  water  and  all  other  solvents,  and  moreover  very  easily  changeable, 
it  has  hitherto  not  been  isolated,  and  its  chemical  composition  has 
not  been  ascertained ;  but  we  are  led  to  admit  its  existence  from 
the  peculiar  products  which  it  affords  under  the  influence  of  various 

*  By  measuring  the  deviations  produced  on  the  plane  of  polarization,  the  quan- 
tity of  cane-sugar  contained  in  solutions  can  be  ascertained  with  great  exactness, 
•when  the  liquid  to  be  tested  contains  no  other  principles  which  cause  the  plane 
of  polarization  to  deviate. 

For  this  purpose  a  preparatory  experiment  is  made,  on  a  known  weight,  for 
example,  20  gm,  of  very  pure  cane-sugar,  by  dissolving  them  in  a  quantity  of 
water  such  that  the  solution  shall  occupy  a  given  volume,  which  we  will  call  V, 
and  using  of  this  solution  as  much  as  is  necessary  to  fill  a  tube  the  constant 
length  of  which  shall  be,  for  example,  0.3  m, :  let  N  be  the  deviation  observed 
through  the  tube,  under  these  circumstances.  On  now  making,  with  other  weights 
of  the  same  sugar,  solutions  of  equal  volume  V,  and  filling,  the  same  proof- tube 
with  them,  they  will  produce  deviations  n,  n',  n",  and  the  weight  of  sugar  con- 
tained in  the  volume  V  of  these  solutions  will  be  respectively  20  gm.  -rr,  20  gm.  —» 

n"  N  .N 

20  gm.  — ,  etc.     From  this,  if  the  sugar  thus  tested  be  impure,  but  only  mixed 

with  substances  deprived  of  the  rotatory  power,  the  same  products  20  gm.  — ,  etc., 

will  express  the  absolute  weight  of  pure  sugar  contained  in  the  gross  weight  used 
to  form  V. 

Tubes  of  different  lengths  may  also  be  used,  and  the  deviations  observed  re- 
duced by  calculation  to  that  which  they  would  have  been  if  they  had  been  mea- 
sured in  the  same  tube. 

As  the  sugar  of  acid  fruits  turns  the  plane  of  polarization  to  the  left,  the  quan- 
tity of  this  sugar  formed,  either  in  its  artificial  solutions  or  in  the  juices  of  fruits 
which  do  not  contain  other  substances  acting  on  the  plane  of  polarization,  may 
be  ascertained  by  analogous  processes ;  the  molecular  rotatory  power  of  the  fruit- 
sugar,  or  the  deviation  produced  in  the  tube  of  0.3  m.  by  the  solution  containing 
20  gm.  of  the  sugar  in  a  volume  of  100  cub.  cent.,  having  been  equally  determined 
d  priori.  It  is  necessary  to  operate  always  at  the  same  temperature,  for  the 
molecular  rotatory  power  of  this  kind  of  sugar  varies  considerably  with  the  tem- 
perature. 

The  crystalline  sugar  of  grapes  and  glucose  turn  the  plane  of  polarization  toward 
the  right ;  and  the  preceding  methods  are  therefore  applicable  to  the  determina- 
tion of  those  sugars  which  exist  in  solutions  containing  no  other  active  ingre- 
dients. 

When  cane-sugar  is  mixed  with  the  sugar  of  acid  fruits  it  is  evident  that  the 
deviation  n  observed  is  only  the  difference  between  the  deviation  n'  to  the  right  of 
cane-sugar,  and  the  deviation  n"  to  the  left  of  the  sugar  of  acid  fruits  ;  but  even  in 
this  case  the  quantities  of  the  two  species  of  sugar  which  exist  in  the  solution  can 


PECTIN.  479 

chemical  agents.  The  characteristic  property  of  pectose  is  that  of 
being  transformed,  under  the  simultaneous  influence  of  acids  and 
heat,  into  a  substance  soluble  in  water,  and  called  pectin^  which 
distinguishes  pectose  from  cellulose,  as  the  latter  yields  no  similar 
product. 

Pectin,  which  is  found  ready  formed  in  ripe  fruits,  is  developed 
in  green  fruits  by  the  action  of  heat,  their  pectose  being  converted 
into  pectin  by  the  vegetable  acids  which  they  contain.  Pectin  is 
also  obtained  by  boiling  carrots  and  turnips  with  feebly  acidulated 
water ;  but  the  most  simple  process  consists  in  extracting  it  from 
ripe  fruits.  By  expressing,  for  example,  the  pulp  of  ripe  pears, 
and,  after  having  filtered  the  juice,  adding  carefully  oxalic  acid, 
which  precipitates  the  lime,  and  then  a  concentrated  solution  of 
tannin,  which  precipitates  the  albuijiinous  matter,  and,  lastly,  by 
pouring  in  alcohol,  the  pectin  is  precipitated  in  the  form  of  long 
gelatinous  filaments.     This,  being  washed  with  alcohol  and  redis- 

be  determined.  After  having  measured  the  deviation  n  produced  by  the  mixed 
solution,  exactly  y'^  of  its  volume  of  chlorohydric  acid  is  added,  and  the  liquid, 
having  been  well  mixed,  is  maintained  for  10  minutes  at  a  temperature  of  140°  or 
150°,  by  which  means  the  cane-sugar  is  entirely  changed  into  sugar  turning  to  the 
left.  After  having  reduced  the  temperature  to  exactly  59°,  the  deviation  n  of  the 
new  solution  is  again  observed ;  and  it  now  consists  of  the  deviation  n'  of  the 
original  sugar  of  the  acid  fruits,  and  the  deviation  n"  of  the  inverted  sugar  pro- 
duced by  the  cane-sugar.  But  the  state  of  saturation  of  the  liquor  has  been 
changed  by  the  addition  of  the  chlorohydric  acid,  and  in  order  to  take  it  into 
account,  the  deviation  observed  n'  must  be  replaced  by  the  deviation  ^n,  which 
would  have  been  observed  had  it  not  been  necessary  to  add  the  acid  in  order  to 
produce  the  inversion.  We  have  evidently,  by  admitting  that  a  quantity  of  cane- 
sugar  producing  a  deviation  n'  to  the  right  yields  a  quantity  of  fruit-sugar  devi- 
ating by  Kw'  to  the  left, 

n  =  n'  —  n" 
jy-ni=n"4-Kn'; 

■which  two  equations  will  serve  to  determine  the  unknown  deviations  n'  and  n", 
from  which  may  be  calculated  the  proportions  of  the  two  kinds  of  sugar.  The 
proportional  coefficient  K  is  determined,  once  for  all,  by  a  first  experiment,  made 
with  very  pure  crystallized  cane-sugar,  at  the  temperature  at  which  the  test  is  to 
be  made. 

If  the  cane-sugar  were  mixed  with  grape-sugar  or  glucose,  the  solution  of  the 
solution  n  would  still  be  observed,  and  would  be  the  sum  of  the  separate  rota- 
tions n'  and  n"  of  the  cane-sugar  and  glucose.  By  then  heating  the  liquor  with 
jij  of  its  weight  of  chlorohydric  acid,  the  cane-sugar  alone  would  be  changed  into 
sugar  turning  to  the  left,  while  the  glucose  would  remain  unchanged.  Supposing 
n'  to  be  the  rotation  of  the  new  liquor  in  a  tube  of  the  same  length,  there  would 
exist  for  the  determination  of  the  unknown  n',  n"  the  two  equations 

nz=zn'-\-n" 
J^ni  =  n"  —  Kn'. 

If  the  glucose  were  mixed  with  fruit-sugar  the  problem  would  be  undeter- 
mined, because  neither  of  these  substances  could  be  inverted  in  its  action  on  the 
plane  of  polarization. 

These  methods  may  be  successfully  used  to  determine  in  solutions  several 
other  substances  which  turn  the  plane  of  polarization,  and  to  study  in  these  sub- 
stances chemical  phenomena  which  are  with  difficulty  explained  by  ordinary 
chemical  experiments. 


480  aELATINOUS   PRINCIPLES   OF  FRUITS. 

solved  in  water,  is  again  precipitated  by  alcohol  and  dissolved  in 
water,  which  processes  are  repeated  until  reagents  no  longer  indicate 
the  presence  of  sugar  or  any  organic  acid. 

Pectin  thus  obtained  is  an  uncrystallizable  white  substance,  though 
soluble  in  water,  from  which  alcohol  precipitates  it  in  a  jelly;  or, 
when  this  solution  is  somewhat  concentrated,  in  the  shape  of  long 
filaments.  Pectin  behaves  like  a  neutral  substance  to  coloured  re- 
agents, and  is  not  precipitated  by  the  neutral  acetate  of  lead,  whi'e 
the  subacetate,  on  the  contrary,  throws  it  down  from  its  solutions  in 
combination  with  the  oxide  of  lead.  It  exerts  no  action  on  polarized 
light ;  and  its  composition  corresponds  to  the  formula  Cg^H^Og^. 

An  aqueous  solution  of  pectin  is  converted,  by  boiling  for  several 
hours,  into  a  new  white  substance,  called  parapectin,  presenting  the 
same  chemical  composition  as  pectin,  and,  being  neutral  with  colour- 
ed reagents,  very  soluble  in  water,  uncrystallizable,  and  insoluble 
in  alcohol,  which  precipitates  it  in  a  transparent  jelly.  It  therefore 
closely  resembles  pectin,  but  is  distinguished  from  it  by  being  pre- 
cipitated by  neutral  acetate  of  lead.  The  composition  of  parapectin, 
dried  at  212°,  is  the  same  as  that  of  pectin ;  but  it  affords  two  com- 
pounds with  oxide  of  lead,  which  are  obtained  by  precipitating  its 
solutions  by  the  neutral  acetate  and  subacetate.  The  formulae  of 
these  compounds  are 

PbO,C„,H„0,,HO, 
2PbO,C„H,„0^. 

Parapectin,  when  heated  to  ebullition  with  very  dilute  acids,  is 
converted  into  a  new  isomeric  modification,  called  metapectin  ;  which 
is  distinguished  from  pectin  and  parapectin  by  sensibly  reddening 
the  tincture  of  litmus,  and,  being  precipitated  by  chloride  of  barium ; 
properties  possessed  neither  by  pectin  nor  parapectin.  Metapectin 
is  soluble  in  water  and  uncrystallizable.  It  is  precipitated  by  al- 
cohol, and  combines  with  acids,  forming  compounds  soluble  in  water, 
but  precipitable  by  alcohol. 

Pectin,  parapectin,  and  metapectin  are  converted  into  an  insoluble 
acid,  called  pectic  acid,  by  contact  with  the  alkalies  and  alkaline 
earths. 

§  1297.  The  vegetable  parts  which  contain  pectose,  contain  also 
a  peculiar  substance  called  pectase,  which  exerts  quite  a  special  in- 
fluence on  pectin  and  its  isomerics,  analogous  to  that  of  beer-yeast 
on  sugars.  This  substance  may  be  separated  by  precipitating  the 
juice  of  fresh  carrots  by  alcohol;  and  after  the  precipitation  the 
pectase  has  become  insoluble  in  water,  without  losing  its  power  of 
action  on  pectin. 

Pectase  possesses  the  remarkable  property  of  transforming,  in  a 
short  time,  pectin  into  a  gelatinous  substance,  insoluble  in  cold  water, 
without  any  apparent  chemical  intervention  of  its  elements  in  the 
transformation.     This  phenomena,  which  is  called  pectic  fermenta- 


PECTIC   ACID.  481 

tion^  resembles  other  phenomena  of  fermentation,  which  shall  soon 
be  described  in  detail.  The  reaction  may  be  effected  when  protected 
from  the  air,  is  accompanied  by  no  evolution  of  gas,  and  is  particu- 
larly easily  performed  at  the  temperature  of  86°. 

Pectase  is  uncrystallizable,  and,  when  left  in  water  for  2  or  3 
days,  decomposes  rapidly,  becoming  covered  with  mould,  and  no 
longer  acting  as  pectin  leaven.  Its  action  on  pectin  is  also  de- 
stroyed by  heating  it  for  some  time  in  boiling  water.  Pectase  exists 
in  vegetables,  sometimes  in  its  soluble  and  sometimes  in  its  insolu- 
ble modification ;  while  acid  fruits,  on  the  contrary,  contain  it  only 
in  its  insoluble  modification. 

§  1298.  By  introducing  pectase  into  a  solution  of  pectin,  the  latter 
is  converted  into  an  acid  called  peetosie  acid,  very  slightly  soluble 
in  cold  water,  and  which  is  precipitated  in  the  gelatinous  state. 
The  acid  is  also  obtained  by  causing  cold  and  very  dilute  solutions 
of  potassa,  soda,  ammonia,  or  the  alkaline  carbonates,  to  act  on 
pectin;  when  pectosates  are  formed,  from  which  the  peetosie  acid 
may  be  precipitated  by  an  acid.  It  is  essential  that  the  alkaline 
liquids  should  not  be  concentrated,  nor  act  for  too  long  a  time,  for 
the  peetosie  acid  would  be  transformed  into  a  new  acid,  called  pectic. 

Peetosie  acid  is  gelatinous,  almost  insoluble  in  cold,  but  soluble  in 
boiling  water ;  and  the  solution  made  when  hot  becomes  gelatinous 
on  cooling.  Pectosates  are  gelatinous  and  uncrystallizable;  and 
the  formula  of  the  lead-salt  is  2PbO,C32H3^02g. 

§  1299.  If  the  action  of  pectase  on  pectin  be  continued  for  a  suf- 
ficient length  of  time,  the  latter  is  converted  first  into  peetosie 
and  then  into  pectic  acid ;  which  latter  transformation  pectin  also 
undergoes  when  it  is  treated  with  dilute  solutions  of  the  alkalies  or 
alkaline  carbonates,  or  with  lime  and  baryta.  By  treating  the 
pectates  with  chlorohydric  acid,  the  pectic  acid  is  precipitated. 

Pectic  acid  is  generally  obtained  from  carrots  or  turnips,  by 
washing  the  pulp  of  the  roots  until  the  water  is  colourless  and  taste- 
less ;  after  which  it  is  heated  for  15  minutes  with  a  weak  solution 
of  carbonate  of  soda,  which  converts  the  pectin  into  pectic  acid, 
forming  a  soluble  pectate  of  soda.  The  liquor  is  separated,  and 
chlorohydric  acid  added,  which  precipitates  the  impure  pectic 
acid  in  the  state  of  jelly.  It  is  washed  as  completely  as  possible, 
and  redissolved  in  ammonia ;  and,  after  boiling  the  liquid,  a  few 
drops  of  subacetate  of  lead  are  poured  in,  which  precipitate  a  small 
quantity  of  pectic  acid,  with  some  albuminous  matter  which  perti- 
naceously  follows  the  pectic  acid;  after  which  the  pectic  acid  re- 
maining in  the  solution  is  precipitated  by  chlorohydric  acid. 

Pectic  acid  is  quite  insoluble  in  cold,  and  nearly  so  in  boiling 
water,  which  distinguishes  it  from  peetosie  acid,  which  dissolves, 
on  the  contrary,  largely  in  hot  water.  Pectic  acid  dissolves  readily 
in  alkaline  solutions,  even  when  very  dilute.  The  pectates  of  the 
alkalies  and  that  of  ammonia  alone  are  soluble,  while  all  other  pec- 

VoL.  II.— 31 


i82  GELATINOUS  PRINCIPLES   OF  FRUITS. 

tates  are  insoluble,  and  precipitate  in  very  voluminous  gelatinous 
masses.  No  soluble  pectate  crystallizes,  but  remains,  after  evapora- 
tion, in  the  form  of  a  gummy  mass.  It  is  very  difficult  to  obtain 
well-defined  salts,  as  the  composition  of  those  procured  by  double 
decomposition  varies  greatly  with  that  of  the  soluble  pectate  and 
the  circumstances  under  which  the  precipitation  takes  place.  The 
formula  of  pectic  acid  has  been  deduced  from  the  analysis  of  the 
pectate  of  baryta  obtained  by  treating,  when  cold  and  protected 
from  the  air,  a  solution  of  pectin  with  a  large  excess  of  water  of 
baryta,  when  at  first  a  precipitate  of  pectosate  of  baryta  forms, 
which,  under  the  influence  of  the  excess  of  base,  is  converted  into 
pectate  of  baryta.  The  salt,  first  dried  in  vacuo,  then  in  an  air- 
bath  at  248°,  presents  the  composition 

2BaO,C3AoO^. 

When  pectic  acid  is  boiled  for  a  long  time  in  water  it  dissolves 
in  it  completely ;  but  is  then  converted  into  a  new  soluble  acid, 
called  parapectie.  Pectates  kept  for  a  long  time  at  a  temperature 
of  302°  are  also  changed  into  parapectates ;  the  same  transforma- 
tion taking  place  as  when  their  solutions  are  boiled  for  a  long  time. 

Parapectic  acid,  which  is  very  soluble  in  water  and  uncrystalliz- 
able,  exerts  an  acid  reaction  on  coloured  tinctures,  and  forms  soluble 
salts  with  potassa,  soda,  and  ammonia;  while  its  other  salts  are  in 
soluble,  and  prepared  by  double  decomposition.  The  formula  of 
the  parapectate  of  lead,  dried  at  302°,  is 

§  1300.  A  solution  of  pectin  left  to  itself  for  several  days  becometi 
strongly  acid,  and  loses  the  property  of  being  precipitated  by  alco 
hoi ;  after  which  it  contains  a  new  acid,  called  metapectic ;  the 
transformation  taking  place  much  more  rapidly  in  the  presence  of 
pectose,  or  the  pulp  of  green  fruits.  Pectin  undergoes  the  same 
changes  in  a  very  short  time,  when  boiled  with  dilute  acids,  or  with 
slightly  concentrated  alkaline  solutions ;  and  lastly,  pectic  and  para- 
pectic acids  are  converted  into  metapectic  acid  when  they  are 
boiled  with  dilute  acids,  and  even  undergo  this  change,  after  a  length 
of  time,  in  cold  water. 

Metapectic  acid,  which  is  very  soluble  in  cold  water,  is  uncrys- 
tallizable,  and  forms  soluble  salts,  which  do  not  crystallize,  with  a 
great  number  of  bases.  Its  solutions  are  not  precipitated  by  waters 
of  lime  and  baryta,  but  they  afford  precipitates  with  the  subacetate 
of  lead.  Two  metapec tates  of  lead  are  known,  of  which  the  formulae 
are 

2PbO,C,H,Oy  and  3PbO,C,H,0,. 

Metapectic  acid  is  as  powerful  an  acid  as  the  majority  of  acids 
found  in  fruits. 


PECTIN.  483 

At  the  boiling  point,  parapectic  and  metapectic  acids  decompose 
the  double  tartrate  of  potassa  and  copper,  and  precipitate  from  it 
red  suboxide  of  copper ;  in  which  respect  they  behave  like  grape- 
sugar,  and  sugar  turning  to  the  left ;  while  these  acids,  like  all  the 
products  derived  from  pectin,  are  distinguished  from  sugars  by  ex- 
erting no  action  on  polarized  light. 

§  1301.  The  following  table  shows  the  composition  of  the  various 
substances  derived  from  pectose,  and  exhibits  the  relations  between 
their  formulae : 

Formula  of  the  Formula  of  the  compound 

free  substance.  with  oxide  of  lead. 

Pectose unknown,  unknown. 

Pectin Cg^H^oOggjSHO,  unknown. 

Parapectin C,JI,fi,„SRO,  PbO, C,JI,,0,,,mO, 

Metapectin C3,H^O,3,8HO,  2PbO,C,,H,,03e,6HO. 

Pectosic  acid C33H^O,3,3HO,  2PbO,C3,H,,0^,HO. 

Pectic  acid C32H^0,3,2H0,  2PbO,C33H^O,3. 

Parapectic  acid :C,,H,50,„2HO,  2PbO,C^H,,0,,. 

Metapectic  acid C,H30„2HO.  2FhO,CJlfi,. 

From  this  manner  of  writing  the  formulae,  it  will  be  seen  that 
they  are  all  multiples  of  the  most  simple  formula,  CgH^Oy,  if  cer- 
tain quantities  of  hydrogen  and  oxygen  be  neglected,  which  we 
have  separated  from  the  formulae,  as  if  they  existed  in  the  state  of 
water.  If  these  relations  are  correct,  it  may  be  said  that  all  the 
substances  are  derived  from  the  first,  pectin,  by  simple  molecular 
partitions,  and  by  separations  or  absorptions  of  water.  Pectin 
is  a  neutral  substance,  and  in  its  modifications  acquires  more  and 
more  decided  acid  properties,  the  last  transformation  being  an  acid 
as  powerful  as  the  majority  of  those  of  the  vegetable  kingdom. 
But  it  is  important  to  remark  that  the  determination  of  the  formulae 
of  uncrystallizable  substances  as  unstable  as  those  first  described, 
and  of  which  the  acid  properties  are  so  slightly  marked,  presents 
great  difficulties,  and  too  much  importance  must  not  be  attached  to 
them. 

§  1302.  The  successive  transformations  of  pectin  under  the  influ- 
ence of  pectase  and  the  acids  explain  readily  the  modifications  of 
this"  substance  during  the  ripening  of  fruits,  and  during  the  process 
of  cooking  which  yields  jellies. 

Vegetable  jellies  are  produced  by  the  transformation  of  pectose 
or  pectic  acid  under  the  influence  of  pectase,  which  transformation 
most  frequently  stops  at  pectosic  acid ;  for  jellies  generally  disap- 
pear when  they  are  heated  to  212°,  because  the  pectosic  acid  is 
then  dissolved ;  whi,le  the  syrupy  juice  again  sets  into  a  jelly  on 
cooling,  on  account  of  the  separation  of  gelatinous  pectosic  acid. 
It  must  be  admitted  that,  under  the  influence  of  heat  and  the  vege- 


484  MANNITE. 

table  acids  which  exist  in  the  pulp,  pectose  is  first  converted  into 
pectin,  and  that  the  latter,  under  the  influence  of  pectase,  is  con- 
verted into  pectosic  acid;  and  that  it  may  even  be  changed  into 
pectic  acid  if  the  action  of  the  pectase  be  sufficiently  prolonged. 
It  is  important  to  raise  the  temperature  slowly,  because,  if  the  fruit 
were  suddenly  exposed  to  a  temperature  of  212°,  the  action  of  the 
pectase  would  be  paralyzed,  and  the  pectic  fermentation  would  no 
longer  be  produced ;  which  happens  in  preserving  fruits :  they  are 
dipped  only  for  a  few  moments  in  boiling  water,  and  the  pectase  is 
thus  rendered  inactive. 

Mannite  CgHyOg. 

§  1303.  Mannite,  which  is  a  substance  widely  scattered  through 
the  vegetable  organization,  exists  in  the  proportion  of  60  per  cent, 
in  manna,  the  dried  juice  which  flows  spontaneously  from  certain 
species  of  ash-trees  in  the  south  of  Europe,  and  from  which  man- 
nite is  easily  extracted  by  boiling  it  with  concentrated  alcohol,  which 
dissolves  the  mannite  and  again  deposits  it  on  cooling.  Mannitr- 
also  exists  in  the  juice  of  onions,  asparagus,  celery,  and  mushrooms 
together  with  sugar  and  other  soluble  vegetable  substances,  and  h 
obtained  from  them  by  first  destroying  the  sugar  by  fermentation^ 
which  does  not  alter  the  mannite,  and  then  evaporating  the  liquor 
to  dryness  and  treating  it  with  boiling  alcohol,  which  dissolves  the 
mannite.  "  The  juice  of  sugar-beets,  which  after  fermentation  con- 
tains a  large  quantity  of  mannite,  is  evaporated  to  the  consistence 
of  syrup,  and  treated  with  alcohol  to  dissolve  the  mannite. 

Mannite,  crystallized  in  alcohol,  presents  the  appearance  of  long 
acicular  crystals  :  it  dissolves  in  5  parts  of  cold,  and  in  a  smaller 
quantity  of  boiling  water ;  and  its  aqueous  solution,  slowly  evapo- 
rated, yields  larger  and  better-defined  prismatic  crystals.  Heated 
slightly  above  212°,  it  melts  into  a  colourless  liquid  which,  on  cool- 
ing, assumes  a  crystalline  texture ;  but  if  heated  still  further,  it  is 
decomposed  and  yields  products  analogous  to  those  of  the  sugars. 

Mannite  is  distinguished  from  the  sugars  by  exerting  no  rota- 
tory power  on  polarized  light,  by  yielding  no  sugar  turning  to  the 
left  when  treated  with  acids,  and  by  not  fermenting  by  contact  with 
the  leaven  of  sugar-like  substances.  Fuming  nitric  acid  transforms 
it  into  an  explosive  substance,  resembling  that  produced  under  the 
same  circumstances  by  lignin,  starch,  and  sugar ;  while  the  nitric 
acid  of  commerce  yields,  when  hot,  oxysaccharic  and  oxalic  acids. 
The  formula  admitted  for  mannite  is  CgHyOg,  but  it  should  be  pro- 
bably doubled  or  trebled. 

Mannite  combines  with  oxide  of  lead,  when  a  very  concentrated 
aqueous  solution  of  it  is  poured  into  a  hot  solution  of  ammoniacal 
acetate  of  lead ;  when  the  compound  separates,  on  cooling,  into 
small  crystalline  lamellae  of  the  formula  2PbO,CgH.O^.     The  com- 


DEXTRIN.  485 

position  of  this  product  indicates  that  the  formula  of  mannite  should 
be  written  C^B..0^,2}10. 

PRODUCTS  OF  THE  ACTION  OF  ACIDS  ON  LIGNIN,  CELLULOSE, 
AMYLACEOUS  MATTER,  AND  THE  SUGARS. 

ACTION  OF  DILUTE  ACIDS  ON  STARCH. 
Dextrin  C^Ji^fi^Q. 

§  1304.  It  has  been  mentioned  (§  1283)  that  fecula,  when  boiled 
for  some  time  with  water  containing  some  hundredths  of  sulphuric 
acid,  is  soon  completely  dissolved,  being  first  converted  into  a  sub- 
stance closely  resembling  gum  arabic,  and  then,  if  the  ebullition  be 
continued,  changing  into  a  sugar  turning  the  plane  of  polarization 
of  polarized  light  to  the  right.  The  first  product  of  transformation 
of  the  amylaceous  matter  has  received  the  name  of  dextrin,  be- 
cause it  possesses  the  property  of  deviating  polarized  light  more 
powerfully  to  the  right  than  any  other 'known  substance.  As  the 
elementary  composition  of  dextrin  is  the  same  as  that  of  amyla- 
ceous matter,  this  transformation  can  only  be  owing  to  disaggrega- 
tion ;  the  sulphuric  acid  by  which  it  has  been  effected  being  found 
unchanged  in  the  liquid. 

Dextrin  is  very  soluble  in  water,  and  dissolves  also  in  dilute 
alcohol,  but  is  insoluble  in  absolute  alcohol.  As  it  dissolves  but 
sparingly  in  concentrated  alcohol,  which  dissolves  a  much  larger 
proportion  of  sugar  turning  to  the  left  and  grape-sugar,  this  solv- 
ent is  frequently  employed  to  separate  dextrin  from  those  sugars 
with  which  it  is  ordinarily  mixed  when  prepared  by  the  process  just 
indicated.  Dextrin  separated  from  its  solutions  by  evaporation 
assumes  the  form  of  a  colourless,  transparent  substance,  without  any 
appearance  of  crystallization,  closely  resembling  gum  arabic,  but 
possessing  an  opposite  rotatory  power.  Heated  with  the  nitric  acid 
of  commerce,  it  yields  oxalic  acid,  but  not  mucic  acid,  thus  distin- 
guishing  it  chemically  from  the  gums.  Iodine  does  not  colour  so-  j  . 
lutions  of  dextrin,  which  affords  an  easy  method  for  ascertaining  when  '  ' 
the  transformation  of  the  amylaceous  matter  is  completed,  and  which 
exhibits  the  action  of  sulphuric  acid  in  the  preparation  just  indi- 
cated. By  pouring  into  a  small  quantity  of  the  hot  liquor,  previous 
to  boiling,  a  few  drops  of  an  aqueous  solution  of  iodine,  the  beau- 
tiful indigo-blue  colour  peculiar  to  the  pure  amylaceous  matter  is 
produced;  while,  if  the  same  experiment  be  repeated  some  time 
after,  the  iodine  produces  a  violet  tinge,  and,  at  a  still  later  period, 
a  purplish  or  reddish  hue :  lastly,  no  change  of  colour  is  eftected ; 
the  yellowish  tinge  being  merely  due  to  the  aqueous  solution  of 
/oiine.  But  at  this  period  a  portion  of  the  dextrin  formed  has 
generally  undergone  a  more  advanced  transformation,  and  is  changed 


486  ACTION   OF  ACIDS   ON   STARCH. 

into  sugar  turning  to  the  right,  but  of  which  the  rotatory  power  is 
less  than  its  own. 

Solutions  of  dextrin  possess  some  properties  of  solutions  of  gum, 
and  may  be  substituted  for  them  occasionally  in  the  arts. 

One  method  of  preparing  dextrin  consists  in  heating  fecula  to  a 
temperature  of  about  410°,  when  it  becomes  disaggregated  and 
converted  into  dextrin ;  the  dried  fecula  being  spread  in  layers  of 
3  or  4  centimetres  in  thickness,  on  sheet-iron  tables  in  a  furnace 
heated  by  a  regular  circulation  of  hot  air,  the  temperature  of  which 
must  not  exceed  410°. 

The  product  thus  obtained  is  called  torrefied  starchy  or  le'iocomme, 
and  exhibits  the  pulverulent  appearance  of  fecula,  while  its  colour 
is  slightly  yellowish,  owing  to  a  more  advanced  decomposition. 

Another  process  consists  in  moistening  1000  kilogs.  of  fecula  with 
300  of  water,  containing  2  kilogs.  of  nitric  acid,  and,  after  allowing 
the  substance  to  dry  spontaneously,  heating  it  for  1  or  2  hours  in  a 
stove  at  212°  or  230°  ;  when  the  transformation  is  perfected  and 
the  acid  is  evaporated. 

§  1305.  Diastase. — A  peculiar  nitrogenous  substance,  called  dias- 
tase, which  possesses  the  property  of  converting  a  large  proportion 
of  fecula  into  dextrin,  and  even  into  sugar  when  its  action  is  suf- 
ficiently prolonged,  exists  in  the  germ  of  the  cerealia  and  tubercular 
vegetables.  It  appears  to  be  formed  at  the  moment  of  germination, 
probably  at  the  expense  of  the  albuminous  matter  contained  in  the 
grain,  as  it  resides  in  the  very  origin  of  the  germ,  and  in  the  eye  of 
the  tuber ;  and  its  use  in  the  vegetable  economy  appears  to  be  that  of 
disaggregating  the  amylaceous  matter  and  transforming  it  into  an 
isomeric  soluble  substance,  which  the  vital  forces  then  change  into 
other  isomeric,  but  insoluble  substances,  such  as  cellulose,  which  is 
to  form  the  frame-work  of  the  growing  plant. 

Diastase  is  generally  extracted  from  barley  which  has  sprouted, 
by  digesting  the  powdered  grain  in  water  at  77°  or  86°,  and,  after 
several  hours,  compressing  the  paste  in  a  cloth  and  filtering ;  when 
the  liquid  contains  diastase  in  solution,  and  may  be  used  immediately 
to  effect  the  solution  of  starch.  If  the  active  principle  is  to  be  sepa- 
rated from  it,  it  must  be  heated  to  167°,  a  temperature  which  does 
not  alter  the  diastase,  but  at  which  an  albuminoid  substance  mixed 
with  it  coagulates.  Anhydrous  alcohol  is  then  poured  into  the 
liquor  as  long  as  any  precipitate  is  formed,  when  the  diastase  is 
precipitated  in  flakes,  which  are  redissolved  in  water  and  again 
precipitated  by  alcohol.  The  substance,  dried  in  vacuo,  is  white, 
amorphous,  soluble  in  water  and  weak  alcohol,  but  insoluble  in  con- 
centrated alcohol.  The  aqueous  solution  is  neutral  and  tasteless, 
and  is  not  precipitated  by  acetate  of  lead.  Diastase  may  be  pre- 
served for  a  long  time  in  dry  air,  but  soon  putrefies  in  dampness ;  and 
a  temperature  of  212°  deprives  it  entirely  of  its  action  on  starch, 
which  is  very  powerful,  for  1  part  of  diastase  is  sufficient  to  trans- 


GLUCOSE.  487 

form  into  dextrin,  and  subsequently  into  sugar,  2000  parts  of  fecula ; 
to  produce  which  effect  by  the  action  of  acid,  it  would  require  30 
times  the  weight  of  sulphuric  acid.  It  cannot  be  supposed,  on  ac- 
count of  the  small  proportion  of  diastase,  that  any  ordinary  chemical 
reaction  takes  place ;  and  the  phenomenon  must  rather  be  com- 
pared to  those  mysterious  actions,  called  actions  hy  contact^  of  which 
several  examples  have  been  pointed  out  in  mineral  chemistry ;  and 
it  may  also  be  assimilated  to  other  phenomena,  also  imperfectly  ex- 
plained, known  by  the  name  oi  fermentation^  of  which  we  have  seen 
the  first  instance  in  the  action  of  pectase  on  pectin. 

Diastase  appears  to  be  most  active  between  the  temperatures  of 
149°  and  167°,  the  action  ceasing  at  a  higher  degree.  .  At  32°  it 
still  converts  starch  into  dextrin  and  sugar,  but  at  10.4°  dextrin 
only  is  formed.  Diastase  exerts  no  action  on  cellulose,  lignin,  nor 
even  on  cane-sugar,  which  is  so  easily  changed  by  dilute  acids. 

The  action  of  diastase  is  likewise  applied  in  the  arts  to  the  purpose 
of  obtaining  dextrin  with  more  or  less  sugar,  the  transformation 
being  effected  in  a  double  boiler,  between  the  sides  of  which  steam 
is  made  to  circulate.  The  ground  barley,  called  malt^  being  sus- 
pended in  water  heated  to  167°,  the  fecula  is  added  to  it  by  small 
quantities  as  it  dissolves.  The  operation  is  watched,  and  the  liquor 
tested  from  time  to  time  with  the  aqueous  solution  of  iodine,  and, 
when  a  vinous  colour  is  produced,  the  action  of  the  diastase  must 
be  quickly  paralyzed,  as,  otherwise,  a  large  quantity  of  sugar  would 
be  formed ;  and  it  is  done  by  rapidly  heating  the  liquor  to  212°,  by 
passing  steam  through  it.  It  is  then  decanted  and  evaporated  to 
the  consistence  of  syrup. 

The  dextrin  thus  prepared  is  used  in  the  baking  of  pastry,  or  in 
the  manufacture  of  beer,  cider,  alcohol,  and  various  other  alcoholic 
liquors ;  while  that  arising  from  the  torrefied  fecula,  or  the  action 
of  acids,  is  used  in  the  finishing  of  muslins,  the  thickening  of  mor- 
dants in  dyeing  and  calico  printing  and  wall-paper  printing,  etc.  etc. 
Of  later  years  it  has  been  used  in  surgery,  in  what  is  called  the 
immovable  treatment  of  fractures : — Muslin  bandages,  soaked  in  a 
mucilaginous  preparation,  obtained  by  dissolving  100  gm.  of  dex- 
trin in  50  of  camphorated  brandy,  and  adding,  soon  after,  40  gm. 
of  water,  are  rolled  around  the  limb,  and  the  apparatus  becomes 
immovable  when  the  dextrin  is  dry.  They  are  easily  removed, 
when  necessary,  by  softening  the  dextrin  with  warm  water, 

G-lucose  C^aHj^Oi^. 

§  1306.  If  the  action  of  diastase,  or  that  of  the  acids  on  starch,  be 
prolonged,  the  dextrin  which  is  first  formed  is  converted  into  sugar ; 
and  the  solution,  when  evaporated,  sets  into  a  crystalline  mass  re- 
sembling that  formed  by  grape-sugar.  This  sugar  is  called  glucose^ 
and  its  identity  with  grape-sugar  is  generally  admitted.  In  the 
transformation  the  amylaceous  matter  (j^^^qO^q  absorbs  4  equiv. 


488  ACTION   OF   ACIDS    ON   STARCH. 

of  w'lter  to  constitute  glucose  C^Ji^fi^^;  and  it  is  important  to 
remark  that  cane-sugar  C^Ji^fi^^^  is  intermediate  between  these 
two  substances,  while  it  has  hitherto  been  impossible  to  arrest  the 
absorption  of  water  at  1  equiv. ;  for  it  would  be  of  immense  com- 
mercial value  if  the  intermediate  product  were  cane-sugar,  which  is 
much  more  valuable  than  glucose. 

Glucose  is  found  in  commerce  under  three  different  forms :  syrup 
of  fecula,  glucose  in  mass,  and  granulated  glucose. 

The  saccharification  is  generally  effected  by  sulphuric  acid,  di- 
luted with  33  times  its  weight  of  water,  and  heated  to  a  tempera- 
ture slightly  above  212°,  the  operation  being  performed  in  large 
wooden  tubs,  at  the  bottom  of  which  a  leaden  tube,  having  a  great 
number  of  holes,  is  placed.  The  tube  may  be  made  to  communicate 
with  a  high  pressure  steam-generator,  which  drives  steam  imme- 
diately into  the  water  in  the  tub,  which,  being  f  filled  with  acidu- 
lated water,  is  thus  rapidly  heated  to  212°.  The  fecula  previously 
diluted  with  water  is  gradually  added,  and  in  30  or  40  minutes 
after  the  last  addition  of  fecula  the  conversion  into  sugar  is  com- 
pleted. In  order  to  ascertain  this,  a  few  drops  of  the  liquid  are 
allowed  to  cool  on  a  plate,  and  then  treated  with  a  small  quantity 
of  a  solution  of  iodine,  which  should  produce  no  change  of  colour. 
When  this  result  is  obtained,  the  flow  of  steam  is  arrested,  and  the 
acid  is  saturated  with  powdered  chalk,  which  should  be  gradually 
added,  lest  the  effervescence  produced  should  cause  the  liquid  to 
overflow  ;  and  the  moment  of  saturation  is  ascertained  by  means 
of  the  tincture  of  litmus.  The  liquor  is  allowed  to  rest  for  12  hours, 
after  which  it  is  decanted  and  bleached  by  filtration  through  animal 
black,  and  it  is  then  evaporated  in  order  to  reduce  it  to  the  degree 
of  concentration  required.  If  solid  glucose  is  to  be  obtained,  the 
syrup  is  concentrated  until  it  marks  40°  or  42°  of  Baume,  and 
then,  when  sufficiently  cool,  it  is  run  into  barrels,  in  which  it  soli- 
difies. In  order  to  granulate  it,  it  is  evaporated  to  only  32°  B.,  and 
then  allowed  to  remain  for  24  hours  in  reservoirs,  in  which  it  cools 
as  rapidly  as  possible,  while  the  calcareous  salts  are  deposited  ; 
after  which  the  syrup  is  brought  into  vats,  the  bottoms  of  which  are 
pierced  with  small  holes  closed  with  pins  ;  fermentation  being  pre- 
vented by  pouring  into  each  vat  2  decilitres  of  an  aqueous  solution 
of  sulphurous  acid.  Crystallization  does  not  commence  for  8  days : 
when  f  of  the  mass  are  solidified  the  pins  are  removed  and  the 
liquid  flows  out.  The  crystals  are  then  dried  on  cakes  of  plaster, 
in  a  drying  machine,  of  which  the  temperature  should  not  exceed 
77°,  in  order  to  prevent  the  fusion  of  the  grains. 

Glucose  in  grains  is  rarely  made,  except  for  the  purpose  of  adul- 
terating brown  sugar. 

Glucose,  in  syrup  or  in  bulk,  is  used  in  the  manufacture  of  beer 
ttnd  alcohol,  and  for  the  improvement  of  common  wines. 


ULMIN.  489 

ACTION  OF  ACIDS  ON  SUGARS. 

§  1307.  It  has  been  mentioned  that  cane-sugar,  by  being  boiled 
with  acids,  is  readily  converted  in  sugar  turning  to  the  left,  which 
itself,  after  some  time,  undergoes  a' change,  and  separates  from  its 
solutions  in  the  form  of  grape-sugar  or  glucose.  If  the  action  of 
the  acids  be  continued,  and  especially  if  they  be  highly  concen- 
trated, the  reactions  produced  are  much  more  complicated.  Fruit- 
sugar  and  glucose  should,  moreover,  evidently  yield  the  same  products. 

On  dissolving  100  parts  of  cane-sugar  in  300  parts  of  water,  to 
which  30  parts  of  sulphuric  acid  are  added,  and  heating  the  liquor, 
it  will  soon  be  seen  to  turn  brown.  The  new  products  formed  vary 
with  the  temperature  of  the  liquor;  and  if  the  experiment  be  made 
in  a  retort  communicating  with  a  receiver  in  which  a  vacuum  has 
been  effected,  the  liquor  boils  at  a  low  temperature ;  while  if  the 
operation  be  arrested  after  the  distillation  of  a  portion  of  the  water, 
the  residue  is  found  to  contain  glucic  acid,  in  larger  quantity 
according  to  the  prolongation  of  the  action ;  besides  a  small  quan- 
tity of  apoglucic  acid.  If,  on  the  contrary,  the  liquor  be  boiled, 
under  the  pressure  of  the  atmosphere,  after  having  previously  filled 
the  apparatus  with  carbonic  acid  or  hydrogen  gas,  in  order  to  pre- 
vent the  oxygen  of  the  air  from  affecting  the  reaction,  it  turns 
brown,  and  soon  deposits  black  flakes,  formed  by  the  admixture  of 
two  new  substances,  ulmm  and  ulmic  acid.  These  substances  are 
separated  by  means  of  potassa,  which  forms  a  soluble  salt  with  ulmic 
acid,  while  the  ulmin  is  isolated.  The  formula  of  ulmin,  dried  at 
284°,  is  C^oHjgOj^;  and  the  solution  of  ulmate  of  potassa,  which  is 
of  a  deep  red  colour,  deposits,  when  saturated  with  an  acid,  ulmic  acid 
in  the  form  of  a  gelatinous  black  precipitate.  The  acid  is  slightly 
soluble  in  fresh  water,  but  does  not  dissolve  in  water  containing 
acids  or  salts.  The  composition  of  ulmic  acid,  dried  at  284°,  is  the 
same  as  that  of  ulmin,  but  at  383°  it  loses  2  equivalents  of  water 
without  further  change,  and  takes  the  formula  C^oHj^O^^.  The 
acid  dried  at  284°  is  therefore  a  hydrate  04^11^^0^3+2110.  By 
dissolving  ulmic  acid  in  ammonia,  a  soluble  salt  is  obtained,  of  the 
formula  (NH3,H0),C^Hj40j2;  and  by  pouring  soluble  metallic 
salts  into  a  solution  of  ulmate  of  ammonia,  double  ammoniacal 
ulmates  are  precipitated.  Thus,  the  formula  of  the  precipitate 
yielded  by  nitrate  of  silver  is 

(NH3H0),C„H„0„+Ag0,C„H,,0,,. 

The  water  which  distilled  over  during  the  ebullition  of  the  sugar 
with  sulphuric  acid  contains  a  certain  quantity  of  formic  acid 
C2H03,H0  ;  the  production  of  which,  being  rich  in  oxygen,  explains 
how  sugar,  in  which  oxygen  and  hydrogen  exist  in  quantities  form- 
ing water,  yields,  in  this  new  reaction,  substances  in  which  hydro- 
gen predominates.     If  the  contact  of  air  is  not  avoided  in  this  ex- 


490  ACTION   OF   ACIDS   ON   CELLULOSE. 

periment,  or  better  still,  if  the  boiling  be  eifected  in  glass  vessels, 
the  ulmin  and  ulmic  acid  undergo  new  transformations,  which,  to  be 
perfect,  require  a  prolonged  action  of  the  sulphuric  acid,  which  is 
still  further  concentrated  by  evaporation :  two  black  substances, 
humin,  and  humie  acid,  are  formed,  and  are  separated  by  potassa, 
which  dissolves  the  latter.  The  formula  of  humin  is  C^H^fi^^,  and 
that  of  humic  acid  O^H^fi^^;  and  these  substances  are  therefore 
derived  from  ulmin  and  ulmic  acid  by  simple  oxidation.  The  for- 
mula of  hydrated  humic  acid  is  C^H^fl^^,  showing  it  to  be  isomeric 
with  humin ;  but  as  it  loses  3  equivalents  of  water  by  heat,  its  for- 
mula should  be  written  C^oH^g^^a+SHO.  In  fact,  the  formula  of 
the  humate  of  silver,  dried  at  212°,  is  AgOjC^^^HjgOjg. 

When  the  action  of  acids  is  continued  for  a  long  time,  and  espe- 
cially when  the  humin  and  humic  acid  are  boiled  with  concentrated 
chlorohydric  acid,  formic  acid  is  again  disengaged,  and  a  black 
substance  is  obtained,  the  composition  of  which,  dried  at  293°, 
corresponds  to  G^Ji^fig.  The  same  substance  is  formed  when 
humin  and  humic  acid  are  boiled  with  a  concentrated  solution  of 
caustic  potassa,  and  the  residue  of  evaporation  is  heated  to  572°. 
When  the  action  of  the  caustic  potassa  is  continued,  raising  the 
temperature  more  and  more,  there  are  successively  formed  two  new 
substances,  insoluble  in  potassa,  the  formula  of  the  first  of  which  is 
Cg^HjoOg,  and  that  of  the  second  C^Ji^O^.  By  comparing  the 
formula  of  these  compounds,  it  will  be  observed  that  the  potassa 
immediately  efiects  the  separation  of  new  quantities  of  water. 

ACTION  OF  SULPHURIC  ACID  ON  CELLULOSE. 

§  1308.  Cellulose  dissolves  readily  in"  cold  concentrated  sulphuric 
acid,  being  first  converted  into  dextrin,  and  then  into  glucose.  The 
experiment  is  made  by  wetting  2  parts  of  old  linen,  or  paper,  with 
3  parts  of  concentrated  sulphuric  acid,  digesting  the  mixture  for 
several  hours,  and  treating  the  gummy  matter,  which  remains  per- 
fectly colourless,  with  water.  The  sulphuric  acid  is  then  saturated 
with  carbonate  of  baryta,  and  filtered,  when  the  liquor  contains 
dextrin,  and  a  very  small  quantity  of  a  soluble  salt  of  baryta, 
formed  by  a  peculiar  acid  containing  sulphuric  acid.  If,  on  the 
contrary,  the  mixture  be  boiled  for  several  hours  with  water,  the 
dextrin  is  completely  converted  into  glucose,  and  a  weight  of  this 
sugar  may  be  obtained  greater  than  that  of  the  linen  used  in  the 
experiment ;  which  result  is  explained  by  the  formulae  of  the  two 
substances ;  that  of  cellulose  being  G^JI^qO^q,  while  that  of  glucose 
is  C^aHj^Oi^ ;  showing  that  the  cellulose  combines  with  water  to  form 
glucose. 

Starch,  inulin,  and  the  gums  likewise  dissolve  in  cold  concen- 
trated sulphuric  acid,  and  are  converted  into  products  analogous  to 
those  yielded  by  cellulose. 


OXYSACCHABIC   ACID.  491 

ACTION  OP   NITRIC  ACID  ON  CELLULOSE,  AMYLACEOUS  MATTER,     ^ 
DEXTRIN,  AND  SUGARS. 

§  1309,  The  concentrated  nitric  acid  of  commerce  acts  energe- 
tically, when  hot,  on  all  these  substances,  first  dissolving  them,  and 
then  giving  off  nitrous  vapours  ;  while,  if  the  operation  be  sufficiently 
prolonged,  the  liquid  is  found  to  contain  only  oxalic  mixed  with  an 
excess  of  nitric  acid.  It  has  been  mentioned  (§  259)  that  this  is 
one  way  of  preparing  oxalic  acid.  But  by  using  more  dilute  nitric 
acid,  and  heating  it  in  a  water-bath,  a  new  acid,  which  has  been 
called  oxy saccharic^  and  sometimes  oxalhydrie  acid,  is  first  formed  ; 
the  best  method  of  obtaining  which  consists  in  heating  in  a  water- 
bath  1  part  of  cane-sugar  dissolved  in  a  large  quantity  of  water, 
with  2  parts  of  nitric  acid.  When  the  evolution  of  nitrous  vapours 
ceases,  the  liquor  is  saturated  with  chalk,  and  then  filtered  to  sepa- 
rate the  oxalate  of  lime  and  chalk  in  excess ;  after  which  acetate 
of  lead  is  added,  which  throws  down  a  white  precipitate  of  oxysac- 
charate  of  lead.  The  precipitate  is  suspended  in  water,  and  decom- 
posed by  a  current  of  sulfhydric  acid  gas,  which  precipitates 
sulphide  of  lead,  while  the  oxysaccharic  acid  remains  isolated  in  the 
liquor.  This  is  divided  into  2  equal  parts,  one  of  which  being 
exactly  saturated  by  carbonate  of  potassa,  the  other  half  is  added 
to  it ;  by  which  means  a  binoxysaccharate  of  potassa  is  produced,  a 
salt  which  crystallizes  readily,  and  may  be  purified  by  successive 
crystallizations.  It  is  easy  to  prepare  oxysaccharic  acid  by  means 
of  this  salt,  by  again  precipitating  it  by  acetate  of  lead,  and  decom- 
posing the  salt  of  lead  by  sulfhydric  acid. 

Oxysaccharic  acid  is  very  soluble  in  water,  and  has  never  been 
obtained  in  a  crystalline  form. 

The  binoxysaccharate  of  potassa,  which  dissolves  in  4  parts  of 
boiling  water,  but  is  very  slightly  soluble  in  cold  water,  has  the 
formula  (K0+H0),C,2H30,. 

The  formula  of  oxysaccharate  of  zinc  is  2ZnO,Cj3HgOy,  showing 
the  acid,  therefore,  to  be  bibasic,  (§  1225.) 

Nitric  acid  readily  converts  oxysaccharic  into  oxalic  and  carbonic 
acids. 

§  1310.  Monohydrated  nitric  acid,  when  cold,  exerts  on  starch, 
cellulose,  and  sugar — an  action  very  different  from  that  of  the  same 
acid  when  hot  and  more  dilute  ;  forming  highly  explosive,  insoluble 
substances,  which  are  suddenly  converted  into  a  gaseous  volume 
600  or  800  times  larger  than  themselves.  During  the  last  few 
years,  these  substances  have  attracted  considerable  attention,  as  it 
was  supposed  that  they  could  be  substituted  for  gunpowder. 

When  cotton  is  dipped,  for  12  or  15  minutes,  into  monohydrated 
nitric  acid,  it  does  not  change  its  appearance,  although  it  absorbs  a 
certain  quantity  of  the  acid;  but  if  it  be  washed  and  carefully 
dried,  a  substance  retaining  the  appearance  of  cotton,  but  which 
suddenly  deflagrates  when  touched  with  a  burning  coal,  is  obtained. 


492 

This  substance  has  been  called  gun-cotton^  nitric  cotton,  dmdipyroxyl. 
Its  composition,  from  the  most  correct  analysis,  corresponds  to 
the  formula  Cg^HjyO^yjSNO^ ;  according  to  which,  2  equivalents  of 
cellulose  CjaHj^O^o  have  lost  3  equivalents  of  water  and  gained  5  of 
nitric  acid. 

Pyroxil  is  insoluble  in  water,  alcohol,  and  acetic  acid,  but  dis- 
solves sparingly  in  pure  ether,  while  a  much  larger  proportion 
dissolves  in  ether  to  which  a  few  hundredths  of  alcohol  have  been 
added ;  and  it  also  dissolves  slightly  in  acetic  ether.  When  pro- 
perly prepared,  pyroxil  explodes  at  a  temperature  of  about  338^, 
and  yields  a  mixture  of  oxide  of  carbon,  carbonic  acid,  nitrogen, 
and  vapour  of  water. 

Hemp,  flax,  linen,  paper,  and,  in  short,  all  substances  consisting 
of  cellulose,  yield  analogous  products,  the  inflammability  and  pro- 
jectile force  of  which  are,  however,  not  the  same,  owing  undoubt- 
edly to  the  difference  of  cohesion  of  the  cellulose  in  the  original 
substance.  Starch  yields  a  similar  product,  called  nitric  starch,  or 
fyroxam,  the  chemical  composition  of  which  appears  to  be  the 
same  as  that  of  pyroxyl.  But  pyroxam  is  soon  spoiled  spontane- 
ously, especially  in  a  moist  atmosphere. 

It  has  been  ascertained  that  a  mixture  of  equal  equivalents  of 
monohydrated  nitric  acid  and  concentrated  sulphuric  acid  can  be 
advantageously  substituted  for  pure  monohydrated  nitric  acid.  The 
cotton  is  dipped  into  it,  withdrawn  in  15  or  20  minutes,  and  com- 
pressed with  a  glass  spatula  so  as  to  dry  it  as  much  as  possible ; 
after  which  it  is  washed  several  times,  and  carefully  dried  at  a  tem- 
perature not  exceeding  212°. 

Gun-cotton,  when  used  in  firearms,  communicates  to  the  ball  the 
same  initial  force  as  four  times  the  same  weight  of  powder,  and 
possesses  in  addition  the  advantage  of  not  fouling  the  piece  nearly 
so  much.  It  is  also  more  easily  transported,  and  is  not  injured  by 
moisture;  but  all  these  good  qualities  are  more  than  counter- 
balanced by  great  disadvantages,  which  have  led  to  its  rejection, 
after  numerous  experiments  in  various  countries.  Its  chief  objec- 
tion is  its  liability  to  burst  the  gun,  and  in  all  cases  to  strain  it 
more  than  common  powder.  Its  price  is  also  six  times  greater 
than  that  of  powder ;  and  several  serious  accidents  have  occurred  in 
its  manufacture,  which,  however,  might  possibly  be  avoided  by 
greater  care. 

Comparative  experiments  made  in  mining  with  gun-cotton  and 
blasting-powder  have  proved  the  great  superiority  of  the  former ; 
the  explosive  force  of  gun-cotton  having  been  found  to  be  4  times 
that  of  blasting-powder ;  and  still  greater  effect,  with  more  economy, 
has  been  produced  by  adding  {-^  of  its  weight  of  nitrate  of  potassa 
to  the  pyroxyl. 

§  1311.  A  solution  of  gun-cotton  in  ether  yields  by  evaporation 
a  transparent  substance  insoluble  in  water,  and  adhering  power- 


MUCIC  ACID.  493 

fully  to  any  bodies  to  which  the  etherial  solution  is  applied.  This 
substance,  called  collodion,  is  now  extensively  used  in  surgery ; 
and  in  its  preparation  the  process  just  described  for  the  manufac- 
ture of  pyroxyl  is  slightly  modified ;  the  cotton  being  allowed  to 
remain  for  1  or  2  hours  in  a  mixture  of  3  parts  of  concentrated 
sulphuric  acid  and  2  parts  of  nitrate  of  potassa,  and  then  washed 
and  dried  as  usual ;  after  which  the  product  is  treated  with  ether 
containing  6  or  8  hundredths  of  -alcohol,  which  dissolves  a  portion 
of  it.  The  syrupy  solution,  spread  over  the  skin,  leaves,  after  the 
evaporation  of  the  ether,  an  impervious  pellicle  insoluble  in  water, 
and  sufficiently  adhesive  to  be  advantageously  substituted  for  the 
ordinary  adhesive  plaster  sometimes  called  court-plaster, 

ACTION  OF  NITRIC  ACID  ON  GUMS. 

Mucic  Acid  CeH^O^HO. 

§  1312.  Gums  treated  with  hot  nitric  acid  of  commerce  (§  1287) 
yield,  in  addition  to  oxalic  and  carbonic  acids,  another,  the  mucic, 
which  is  very  slightly  soluble  in  cold  water ;  and  we  have  said 
before  that  the  production  of  this  acid  established  a  ready  distinc- 
tion between  gums,  amylaceous  matter,  dextrin,  and  the  mucilagi- 
nous and  gelatinous  principles  of  vegetables.  A  peculiar  kind  of 
sugar,  called  sugar  of  milk,  is  found  in  the  milk  of  mammiferous 
animals,  differing  essentially  from  the  various  kinds  of  sugar  hitherto 
described,  and  also  yielding  mucic  acid  with  nitric  acid.  It  is  gene- 
rally employed  in  the  preparation  of  the  acid,  by  boiling  1  part  of 
powdered  sugar  of  milk  with  6  parts  of  ordinary  nitric  acid,  and 
allowing  the  liquid  to  cool  as  soon  as  the  nitrous  vapours  cease 
passing  over,  when  the  mucic  acid  is  deposited  in  the  form  of  small 
granular  crystals.  It  is  washed  in  cold  and  then  dissolved  in  boil- 
ing water,  from  which  the  liquor  deposits  pure  mucic  acid  on  cool- 
ing. Mucic  acid  dissolves  in  QQ  parts  of  boiling  water,  is  almost 
insoluble  in  cold  water,  and  reddens  tincture  of  litmus.  If  a  solu- 
tion of  it  be  rapidly  evaporated,  the  substance  undergoes  an  iso- 
meric modification  and  becomes  soluble  in  alcohol,  which  does  not 
dissolve  ordinary  mucic  acid ;  and  the  alcoholic  solution  deposits, 
by  evaporation,  flattened  crystals  which  dissolve  in  17  parts  of 
boiling  water.  But  this  modification  of  mucic  acid  is  not  very  fixed, 
being  rapidly  converted  into  ordinary  mucic  acid  when  its  solutions 
are  allowed  to  cool.  The  two  modifications  of  mucic  acid  yield  dif- 
ferent salts ;  and  those  of  the  second  modification,  which  are  the 
more  soluble,  are  converted,  when  cold,  into  salts  of  the  first  modi- 
fication. 

The  alkaline  mucates  are  but  slightly  soluble  in  cold  water,  and 
the  other  salts  are  insoluble.     The  formula  of  mucate  of  silver  is 


494  DECAY  OF  VEGETABLE  MATTER. 

AgOjCgH^O,.;  and  the  formula  of  crystallized  mucicacid  is  CgHjOg, 
which  should  perhaps  rather  be  written  CgH^O^jHO. 

Mucic  acid,  heated  in  a  glass  retort  furnished  with  a  receiver,  is 
decomposed  and  yields,  together  with  very  complicated  empyreu- 
matic  products  and  a  residue  of  carbon,  a  new  acid,  called  pyro- 
mucic^  which  is  partly  deposited  in  the  form  of  crystals  in  the  neck 
of  the  retort.  By  dissolving  these  crystals  in  the  liquor  collected 
in  the  receiver,  evaporating  it  to  dryness,  and  subjecting  the  resi- 
due to  resublimation,  purer  pyromucic  acid  is  obtained ;  and  lastly, 
the  acid  is  redissolved  in  water  and  purified  by  crystallization. 
Pyromucic  acid,  which  is  colourless,  melts  at  about  266°,  volatiliz- 
ing at  a  higher  degree,  and  dissolves  in  26  parts  of  cold  and  4  of 
boiling  water.  The  alkaline  pyromucates  are  very  soluble  in  water, 
while  those  of  the  alkaline  earths  are  very  slightly  so. 

The  formula  of  pyromucate  of  silver  is  AgOjC^^HgO^,  and  that 
of  sublimed  pyromucic  acid  is  CjoHgO^+HO. 


PRODUCTS  OF  THE  SPONTANEOUS  DECOMPOSITION  OF  CELLULOSE 
AND  OF  THE  OTHER  ESSENTIAL  PRINCIPLES  OF  VEGETABLES. 

§  1313.  Vegetables  decompose  spontaneously  when  exposed  to 
moisture  and  the  oxygen  of  the  atmospheric  air,  being  converted 
into  a  brown  substance  called  humus,  or  mould,  the  nature  of  which 
is  very  imperfectly  known.  Peat  in  an  advanced  stage  of  decom- 
position, as  well  as  the  decomposed  ligneous  substances  found  in  the 
cavities  of  certain  trees,  contain  the  same  substances.  Four  prin- 
cipal substances  have  been  procured  from  it,  which  appear  to  be 
identical  with  those  obtained  by  causing  acids  to  act  on  sugar  at 
the  temperature  of  ebullition,  and  which  we  have  designated  by  the 
names  of  humin,  humic  acid,  ulmin,  and  ulmic  acid ;  although 
they  sometimes,  indeed,  present  states  of  hydration  difiering  from 
those  of  the  analogous  products  prepared  with  sugar. 

The  formula  of  an  ulmic  acid  obtained  from  a  peat  from  Frise 
was  C4oHjg0^4+2HO,  that  is,  it  contained  2  equivs.  of  water  more 
than  the  ulmic  acid  of  sugar ;  and  the  composition  of  its  ammonia- 
cal  salt  was  (NH3,HO),C^H,gO,,. 

A  black  peat  from  Harlem  (Holland)  yielded  a  humate  of  ammo- 
nia (NH5,HO),C4oHj^Oi3+3HO;  which  retained  its  water  at  the 
temperature  of  284°,  which  is  not  the  case  in  the  analogous  salt 
prepared  with  the  humic  acid  resulting  from  the  decomposition  of 
sugar. 

MINERAL  FUEL. 

§  1814.  Enormous  quantities  of  combustible  substances,  of  im- 
mense importance  in  metallurgy  and  the  various  arts,  are  found  in 


COAL   FORMATIONS.  495 

the  bosom  of  the  earth.  They  are  evidently  produced  by  the  de- 
composition of  vegetables  which  grew  in  the  vicinity,  or  the  debris 
of  vegetables  carried  down  by  rivers.  Peat  mosses  exhibit,  though 
on  a  smaller  scale,  an  example  of  this  formation ;  as  they  consist 
of  innumerable  herbaceous  vegetables,  spontaneously  decomposed 
by  the  action  of  water  and  atmospheric  air ;  and  their  various  stages 
of  alteration  may  be  followed,  from  the  perfectly  herbaceous  turf  to 
the  earthy  turf  presenting  but  few  or  no  recognisable  remains. 

The  vegetable  structure  is  frequently  perfectly  preserved  in  the 
mineral  combustibles  of  the  tertiary  formation,  where  pieces  of 
wood,  called  lignite^  are  found  still  retaining  their  original  form, 
but  having  become  friable,  and  yielding  a  brown  powder  by  pul- 
verization. 

In  the  mineral  fuel  of  older  formations,  the  vegetable  structure 
has  generally  disappeared,  and  it  forms  black,  brilliant,  compact 
masses,  of  a  schistose  texture,  yielding  a  black  or  more  or  less 
brown  powder ;  it  is  called  pit-coal,  or  sea-coal,  and  is  rare  in  the 
secondary,  but  very  abundant  in  the  transition  formation ;  in  the 
upper  stratum  of  which  they  are  so  frequent  as  to  characterize 
them  by  the  name  of  coal  formation. 

In  the  upper  strata  of  the  transition  rocks  the  mineral  fuel, 
Avhich  is  sometimes  called  anthracite,  is  generally  very  compact, 
rich  in  carbon,  difficult  to  ignite,  and  yielding  but  little  volatile  mat- 
ter by  calcination.  Anthracite  is  sometimes,  though  rarely,  found 
in  the  superior  strata,  and  even  in  the  secondary  rocks. 

Pit-coal  of  the  coal  formation  yields  on  calcination  a  great  quan- 
tity of  volatile  substances  and  inflammable  gases,  and  experiences, 
prior  to  decomposition,  an  incipient  fusion,  while  the  coal  remaining, 
or  the  coke,  presents  the  appearance  of  a  swollen  or  bloated  mass.  Al- 
though the  structure  of  plants  can  no  longer  be  recognised  in  certain 
combustible  minerals,  their  vegetable  origin  is  undoubted,  for  in  the 
layers  of  schist  or  sandstone  which  bound  the  layers  of  coal,  impres- 
sions of  plants  are  frequently  found,  which  are  so  distinct  and  clear 
as  to  enable  the  botanists  to  detect  the  family  to  which  they  belong, 
and  thus,  partly,  to  restore  the  flora  of  antediluvial  epochs. 

In  the  tertiary  rocks  a  mineral  fuel  is  also  found,  which  is  soft,  or 
easily  fusible,  forming  irregular  masses,  or  a  kind  of  strata,  and  pre- 
senting a  bearing  analogous  to  that  of  the  lignites,  while  at  other 
times  they  permeate  layers  of  schist  or  sandstone  belonging  to  va- 
rious geological  formations,  and  then  seem  to  arise  from  the  decom- 
position, by  heat,  of  other  combustible  minerals  contained  in  the 
earth.  Some  of  these  substances,  which  are  called  bitumen,  con- 
tain a  large  amount  of  nitrogen,  and  are  fetid,  yielding,  on  distilla- 
tion, considerable  quantities  of  carbonate  of  ammonia.  They  appear 
to  have  been  generated  by  the  putrefaction  of  animal  matter,  chiefly 
by  that  of  fishes,  the  impressions  of  which  are  frequently  found  in 
the  neighbouring  rocks. 


496  DECAY  OF  VEGETABLE  MATTER. 

§  1315.  Coals  may  be  divided  into  five  classes : 

1.  The  anthracites. 

2.  Fat  and  strong^  or  hard  pit-coal. 

3.  Fat  blacksmith's  or  bituminous  coal. 

4.  Fat  coal  burning  with  a  long  flame. 

5.  Dry  coal  burning  with  a  long  flame. 

1.  Calcination  scarcely  changes  the  appearance  of  anthracites,  as 
their  fragments  still  retain  their  sharp  edges,  and  do  not  adhere  to 
each  other.  They  have  a  vitreous  lustre,  and  their  surface  is  some- 
times iridescent,  while  their  powder  is  black  or  grayish-black.  They 
burn  with  difficulty,  but  generate  a  large  amount  of  heat  when  their 
combustion  is  properly  effected.  In  blast-furnaces  anthracites  re- 
quire a  great  blast,  and  those  only  can  be  used  which  do  not  soon  fall 
to  powder,  as  otherwise  the  furnace  would  be  speedily  choked.  We 
have  seen  (§  1072)  that  anthracite  is  used  in  Wales  for  heating  re- 
verberatory  furnaces ;  and  it  is  now  proper  to  remark,  that  the  flame 
produced  by  the  combustible  under  these  circumstances  is  not  owing 
to  the  combustion  of  the  volatile  substances  given  off  by  the  anthra- 
cite, but  rather  to  the  combustion  of  the  carbonic  oxide  formed  by 
the  passage  of  air  through  a  thick  layer  of  fuel. 

2.  Fat  and  strong,  or  hard  pit-coals,  yields  a  coke  with  metallic 
lustre,  but  less  bloated  and  more  dense  than  that  of  blacksmiths' 
coals.  They  are  more  esteemed  in  metallurgic  operations  requiring 
a  lively  and  steady  fire,  and  yield  the  best  coke  for  blast-furnaces. 
Their  powder  is  brownish-black. 

3.  Fat  bituminous,  or  blacksmith's  coals,  yield  a  very  bloated  or 
swollen  coke,  with  metallic  lustre,  and  are  more  highly  valued  for 
forging  purposes,  because  they  produce  a  very  strong  heat,  and  allow 
the  formation  of  small  cavities,  in  which  the  pieces  to  be  forged  can 
be  heated.  Blacksmith's  coal  is  of  a  beautiful  black  colour,  and 
exhibits  a  characteristic  fatty  lustre :  its  powder  is  brown.  It  is 
generally  brittle,  and  breaks  into  cubical  fragments,  which  adhere 
to  each  other  in  the  fire. 

4.  Fat  coals  burning  with  a  long  flame  generally  yield  a  swollen, 
metalloid  coke,  less  bloated,  however,  than  that  of  blacksmith's 
coal.  These  coals  are  much  esteemed  in  a  reverberatory  furnace, 
particularly  when  a  sudden  blast  is  required,  as  in  puddling,  and 
are  also  well  adapted  to  domestic  purposes,  and  are  preferred  for 
the  manufacture  of  illuminating  gas.  They  yield  a  good  coke,  but 
in  small  quantity,  and  their  powder  is  brown. 

5.  Dry  pit-coal  burning  with  a  long  flame  yields  a  solid,  me- 
talloidal  coke,  the  various  fragments  of  which  scarcely  adhere  to  each 
other  by  carbonization.  This  coal  is  also  applicable  to  steam-boilers, 
and  burns  with  a  long  flame,  which,  however,  soon  fails,  and  does 
not  produce  the  same  amount  of  heat  as  the  coals  of  the  preceding 
class. 


ANALYSIS   OF   MINERAL   FUEL.  497 

§  1316.  The  elementary  analysis  of  combustible  minerals,  which 
easily  explains  their  various  properties,  and  indicates  the  uses  to 
which  each  is  most  applicable,  is  effected  like  that  of  organic  sub- 
stances, (§  1210  et  seq.;)  but  as  coal  is  generally  difficult  to  burn,  it 
is  necessary,  at  the  close  of  the  experiment  by  which  the  quantity 
of  water  and  carbonic  acid  it  contains  is  determined,  to  pass  a  cur- 
rent of  oxygen  gas  through  the  tube,  (§  1211,)  which  burns  the  last 
particles  of  carbon.  The  organic  analysis  of  coal  yields  the  hydro- 
gen, carbon,  and  nitrogen  which  they  contain  ;  but  it  is  also  neces- 
sary to  determine  the  proportion  of  earthy  matter  which  exists  in 
very  various  degrees  in  them,  and  which  remains  in  the  ashes  after 
combustion. 

For  this  purpose  two  grammes  of  the  coal  are  ignited  in  a  thin 
platinum  capsule,  heated  by  an  alcoholic-lamp,  and  the  ashes  re- 
rafkining  are  weighed.  This  method  of  incineration  is  difficult,  and 
requires  considerable  time,  only  in  those  anthracites  which  do  not 
burn  readily,  and  it  is  then  more  easily  effected  if  the  coarsely  pow- 
dered anthracite  be  placed  in  a  small  platinum  vessel,  heated  in  a 
current  of  oxygen  in  a  porcelain  tube. 

It  is  essential  carefully  to  examine  the  nature  of  the  ashes. 
Sea-coal  of  the  coal  formation  frequently  leaves  argillaceous  ashes, 
in  which  case  there  is  a  trifling  error  in  the  supposed  composition 
of  the  fuel,  because  the  small  quantity  of  water  always  contained  in 
clay,  and  which  it  loses  at  a  red-heat,  is  regarded  as  existing  in  the 
state  of  hydrogen ;  and  this  error,  which  is  of  no  importance  if  the 
quantity  of  ashes  is  small,  may  be  considerable  in  the  opposite  case. 
The  ashes  often  contain,  likewise,  peroxide  of  iron,  which  metal  ge- 
nerally exists  in  coal  in  the  state  of  pyrites,  and  the  analysis  is 
thus  inaccurate  for  two  reasons:  the  proportion- of  ashes  is  valued 
at  too  low  a  rate,  because,  instead  of  the  iron  pyrites,  sesquioxide 
of  iron  is  weighed,  the  weight  of  which,  for  the  same  quantity  of 
iron,  is  less ;  and  again,  in  combustion  by  oxide  of  copper,  the 
substance  may  yield  sulphurous  acid,  which  interferes  with  the  deter- 
mination of  hydrogen  and  carbon.  The  latter  cause  of  error  is 
avoided  by  placing  in  the  combustion-tube,  in  front  of  the  oxide  of 
copper,  a  column  of  one  or  two  decimetres  of  oxide  of  lead,  which 
completely  retains  the  sulphurous  acid,  (§  1216.)  The  quantity  of 
pyrites  in  the  coal  may  be  ascertained  by  determining,  on  the  one 
hand,  the  quantity  of  sesquioxide  of  iron  which  exists  in  the  ashes, 
and,  on  the  other,  the  quantity  of  sulphuric  acid  yielded  by  a  known 
weight  of  coal,  powdered  very  finely,  and  acted  on  by  fuming  nitric 
acid,  or  ordinary  nitric  acid,  to  which  small  quantities  of  chlorate  of 
potassa  are  gradually  added.  It  is  evident  that  these  determina- 
tions are  necessary  only  when  the  combustible  produces  a  large  quan- 
tity of  ashes,  and  when  the  latter  are  very  ochrous. 

Coal  belonging  to  the  secondary  and  tertiary  formations  often 

Vol.  IL— 32 


498  DECAY  OF  VEGETABLE  MATTER. 

yields  calcareous  ashes,  in  which  case  it  becomes  necessary,  before 
weighing  them,  to  sprinkle  them  with  a  solution  of  carbonate  of  am- 
monia, which  is  subsequently  evaporated  at  a  gentle  temperature. 
But  the  determination  of  the  carbon  is  generally  inaccurate,  because 
the  carbonate  of  lime  of  the  ashes  gives  off,  by  contact  with  the  ox- 
ide of  copper  in  the  combustion-tube,  a  portion  of  its  carbonic  acid ; 
and  the  oxide  of  copper  must  then  be  replaced  by  chromate  of  lead, 
intimately  and  largely  mixed,  with  the  coal  reduced  to  impalpable 
powder,  (§  1216,)  after  which  the  carbonic  acid  produced  by  the  car- 
bonates of  the  ashes,  which  has  been  determined  by  direct  weighing 
of  these  carbonates,  is  subtracted  from  the  carbonic  acid  formed 
by  combustion. 

Coal  also  retains  one  or  two  per  cent,  of  hygrometric  water,  which 
must  be  previously  driven  off  by  drying  it  in  a  stove  at  270°  or  280°. 

§  131T .  It  is  necessary,  in  order  to  form  a  correct  judgment  of 
the  nature  of  a  combustible,  to  determine  the  weight  of  coke  it 
yields  by  burning  ;  and  it  is  indispensable  that  this  operation  should 
always  be  conducted  under  the  same  circumstances,  as  the  quantity 
and  nature  of  the  coke  depend  on  the  manner  of  calcination.  The 
best  method  consists  in  placing  3  gm.  of  the  coal  in  a  thin  pla- 
tinum crucible,  accurately  covered  by  its  lid,  and  rapidly  heating 
it  to  a  red-heat.  The  crucible  is  kept  at  a  red-heat  for  eight 
minutes,  and  after  cooling  without  being  uncovered,  the  coke  is 
weighed,  and  carefully  examined.* 

§  1318.  The  calorific  power  of  fuel  is  calculated  from  its  chemi- 
cal composition ;  admitting  that  this  power  is  equal  to  the  sum  of 
that  of  the  carbon  it  contains,  and  that  of  the  hydrogen  obtained 
by  subtracting  from  the  total  quantity  of  hydrogen  that  which 
would  form  water  with  the  oxygen  contained  in  the  fuel.  This  hy- 
pothesis is  not  strictly  true,  but  it  may  be  admitted  when  the  quan- 
tities of  heat  afforded  by  various  kinds  of  fuel  are  only  to  be  com- 
pared by  approximation,  f 

This  comparison  is  generally  made  in  another  way,  based  on  the 
supposition  that  the  calorific  powers  of  combustibles  are  in  propor- 
tion to  their  reducing  powers ;  that  is,  to  the  weight  of  the  same  oxide 
which  they  can  reduce  to  the  metallic  state.  An  intimate  mixture 
of  1  gramme  of  finely  powdered  combustible  and  40  gm.  of  litharge 
being  introduced  into  an  earthen  crucible,  20  gm.  of  litharge  are 
added,  and  the  crucible  is  covered  with  its  lid  and  rapidly  heated 
to  a  red-heat.  It  is  allowed  to  cool,  and,  after  being  broken,  the 
lump  of  lead  is  weighed,  which  rapidly  separates  from  the  scoria  of 
the  litharge ;  and  it  is  assumed  that  the  calorific  powers  of  combus- 

*  Rapid  coking  is  very  wasteful  of  coke,  and  yields  a  larger  amount  of  tar  and 
gaseous  products. — J.  G.  B, 

f  M.  Bull's  experiments  on  fuel,  the  best  ever  made,  have  shown  the  fallacy 
of  the  assumption  named  in  the  text. — J.  C.  B. 


MINERAL   FUEL.  499 

tibles  are  in  proportion  to  the  weight  of  lead  yielded  by  this  experi- 
ment. This  supposition  is  not  absolutely  exact,  because  combusti- 
bles yield,  before  attaining  the  temperature  at  which  they  act  on 
the  litharge,  a  small  quantity  of  volatile  substances  possessing  a  re- 
ducing power — which  substances  are  more  abundant  in  combustibles 
of  recent  formation  than  in  those  containing  a  larger  proportion 
of  oxygen. 

§  1319.  The  following  table  exhibits  the  composition  of  a  large 
number  of  kinds  of  mineral  fuel,  taken  from  various  geological  for- 
mations, and  from  the  kinds  best  marked  and  most  extensively  ap- 
plied in  the  arts.  The  fragments  containing  least  ashes  have  also 
been  chosen,  in  order  to  cast  no  uncertainty  on  the  composition  of 
the  combustible  itself. 

The  table  contains,  1st,  the  actual  composition  of  the  coal,  as 
afforded  by  direct  analysis;  and,  2dly,  the  composition  calculated 
by  abstracting  the  ashes  contained : — 


500 


MINERAL   FUEL. 


Species  of 
Combustible. 


I.  Anthracites. 


II.    Fat    and 
hard  pit-coal. 


IIL  Fat  black- 
smith's coal. 


rV.  Fat  pit- 
coal  burning 
with  a  long 
flame. 


V.  Drypit-coan 
burning  with  > 
a  long  flame,  j 


Locality. 


Pennsylvania. 

Wales 

Mayenne 

Rolduo 


Alais  (Roche- 
Belle) 


Rive-de-Gier. 
(P.  Henri). 


Rive-de-Gier. 
1. 

Rive-de-Gier. 
2. 


Newcastle. 


FlenuofMons 
1. 

Idem  2 


Rive-de-Gier. 
(cemetery)  1. 

Idem  2 


Rive-de-Gier. 
Couzon  1.... 


Idem  2. 


Lavaysse 

Lancashire.... 

Epinac 

Commentry... 


Blanzy. 


Nature  of  the  Coke,  and  other  remarks. 


{Is  found  in  an  argillaceous  transition 
schist;  fracture  vitreous;  coke 
pulverulent 

{In  the  lower  portion  of  the  coal  for- 
mation ;  fracture  vitreous  and  con- 
choidal;  coke  pulverulent 

{In  argillaceous  transition  schist; 
fracture  conchoidal  and  vitreous; 
coke  not  adherent 

{Lower  part  of  the  coal  formation; 
fracture  vitreous,  but  texture  lami- 
nated; coke  slightly  adherent 

{Coal  sandstone;  fracture  unequal; 
coke  metalloid ;  slightly  swollen  or 
bloated  

f  Coal  sandstone ;    fracture  schistose ; 
I      coke  metalloid  and  swollen 

{Coal  formation;  of  a  beautifully 
black,  greasy  lustre ;  very  swollen 
metalloid  coke 

{Coal  formation;  of  a  beautiful  black ; 
fracture  more  schistose ;  coke  rathfer 
less  swollen 

{Coal  formation  ;  of  a  beautiful  black ; 
fracture  schistose  and  prismatic: 
coke  swollen 

f  Coal    formation ;    rhomboidal    frag- 

(      ments;  coke  swollen 

I  Coat  formation ;  less  marked  rhom- 
1      boidal  cleavage ;  coke  swollen 

{Coal  formation ;  lustre  feeble,  texture 
schistose;  coke  swollen,  but  less 
brilliant 

The  same  as  No.  1 

{Coal  formation ;  lustre  more  marked, 
texture  very  schistose  ;  coke  swol- 
len, but  less  brilliant 

{Coal  formation ;  lustre  very  feeble ; 
fracture  unequal,  and  not  schistose ; 
coke  less  swollen 

{Coal  formation ;  lustre  brilliant ;  frac- 
ture conchoidal ;  coke  swollen  and 
light 

{Coal  formation;  English  canne^-coai,- 
without  lustre ;  fracture  conchoidal; 
coke  fritted  and  brilliant 

{Coal  formation ;  lustre  brilliant,  tex- 
ture schistose ;  adherent  metalloid 
coke,  but  slightly  swollen 

{Coal  formation;  resembling  cannel- 
coal;  fracture  conchoidal;  metal- 
loid fritted  coke 

{Coal  formation ;  fracture  laminated ; 
lustre  brilliant;  coke  slightly  ad- 
herent, but  not  swollen 


MINERAL   FUEL. 


501 


Density. 

Coke 
yielded 
by   calci- 
nation. 

ZLEUENTART  COMPOSITION. 

COMPOSITION,  THE  ASHES  BEING 
HEMOVED. 

Carbon. 

Hydrogen. 

Oxygen 

and 
Nitrogen. 

Ashes. 

Carbon. 

Hydrogen. 

Oxygen 
Nitrogen. 

1.462 

89.5 

89.21 

"2.4a 

3.69 

4.67 

93.59 

2.55 

3.86 

1.348 

91.3 

91.29 

3.33 

4.80 

1.58 

92.76 

3.38 

3.86 

1.367 

90.9 

90.72 

3.92 

4.42 

0.94 

91.58 

3.96 

4.46 

1.343 

89.1 

90.20 

4.18 

3.37 

2.25 

92.28 

4.28 

3.44 

1.322 

77.7 

88.05 

4.85 

5.69 

1.41 

89.31 

4.92 

5.77 

1.315 

76.3 

86.65 

4.99 

5.49 

2.96 

89.29 

5.05 

5.66 

1.298 

68.5 

86.25 

5.14 

6.83 

1.78 

87.82 

6.f 

J3 

6.96 

1.302 

69.8 

86.59 

4.86 

7.11 

1.44 

87.85 

4.9S 

7.22 

1.280 

u 

86.75 

5.24 

6.61 

1.40 

87.97 

5.31 

6.72 

1.276 

69.8 

83.51 

5.29 

9.10 

2.10 

85.30 

5.40 

9.30 

1.292 

(t 

82.72 

5.42 

8.18 

3.68 

85.88 

6.63 

8.49 

1.288 
1.294 

70.9 
69.1 

80.92 
83.67 

5.27 
5.61 

10.24 

7.73 

3.57 
2.99 

83.91 

86.25 

5.46 

5.77 

10.63 
7.98 

1.298 

64.6 

81.45 

5.59 

10.24 

2.72 

83.73 

6.75 

10.52 

1.311 

65.6 

80.59 

4.99 

9.10 

5.32 

85.12 

5.27 

9.61 

1.284 

57.9 

81.00 

6.27 

8.60 

6.13 

85.38 

5.6 

S 

9.06 

1.317 

57.9 

82.60 

5.66 

9.19 

2.55 

84.63 

6.86 

9.62 

1.353 

62.5 

80.01 

5.10 

12.36 

2.53 

82.08 

5.23 

12.69 

1.319 

63.4 

81.59 

5.29 

12.88 

0.24 

81.79 

6.30 

12.91 

1.362 

57.0 

75.43 

5.23 

17.06 

2.28 

77.19 

6.35 

17.46 

502 


MINERAL   FUEL. 


Species  of 
Combustible. 

Locality. 

Nature  of  the  Coke,  and  other  remarks. 

O 

§ 

o 
o 

OQ 

Inferior  stratum. 

Anthracites 

Pit-coaJ 

Lamure 

Macot.. 

r Jurassic  formation j    grayish-black; 
^      lustre  vitreous;  fracture  conchoi- 

(     dal;  coke  pulverulent 

f  Jurassic  formation;    grayish-black; 
1      lustre  vitreous  ;  coke  pulverulent. 
(Jurassic    formation;    aspect    of   fat 
\      coals ;  coke  metalloid  and  swollen, 
r  Marls  of  the  lower  oolite  ;  aspect  of 
•<      coals  burning  with  a  long  flame; 
1      coke  metalloid  and  fritted 

Obernkirchen 
Ceral 

tt 

Noroy 

'Variegated  marls;  of  a  dull  black; 
fracture  unequal;  coke  not  adhe- 

Superior 
stratum. 

Jet 

Saint-Girons.. 
Belestat 

r  Green    sandstone;    very    brilliant; 
I      fracture  conchoidal ;  adherent  me- 

The  same  as  that  from  Saint  Girons. 

L  Perfect  lig- 
nites  ■ 

Dax 

Of  a  beautiful  black;    fracture  un- 
equal ;  free  from  ligneous  texture ; 
coke  not  adherent 

'  Schistose ;  pure  and  brilliant  black ; 
free  from  ligneous  texture;  coke 

TERTIARY  ROCKS. 

Bouches-du- 
Rhone 

Mt.  Meissner. 

Lower  Alps... 

Brilliant;  fracture  conchoidal;  coke  . 

Black;  lustre  greasy;  coke  slightly 

11.    Imperfect 
lignites 

Greece 

r  Laminated  ;  of  a  dull  black ;  indices 
of  vegetable  organization ;  coke  not 
adherent 

Cologne 

'  Umber-coloured;  friable;  streak  red- 
dish-brown ;  texture  ligneous ;  coke 
not  adherent 

Fossil  wood ;    woody  texture ;   very 
hard 

IIL     Lignites  C 
passing  into  < 
bitumen ( 

Ellebogen 

Cuba 

Compact,  homogeneous;  fracture  con-^ 

choidal ;  very  light  metalloid  coke 

[Velvet-black  colour;  lustre   greasy; 

1      coke  swollen  and  very  light 

IV.  Asphaltum.. 

Mexico 

'  Black ;  very  brilliant ;  strong  smell ; 
melts  below  212°;    coke  exceed- 
ingly swollen 

Hi 

Turfs  or  Peats  - 

/ 

Vulcaire 

r  In  a  very  advanced  stage  of  altera- 
■j      tion,  though  still  exhibiting  some 
1      remains  of  vesretables... 

Champ-du- 
Feu 

r  In  a  less  advanced  stage  of  altera- 
<      tion,  though  still  containing  some 

"Wood 

Averagre  composition 

MINERAL  FUEL. 


503 


Density. 

Coke 
yielded 
by  calci- 
nation. 

ELEMENTABT  COMPOSITIOW. 

COMPOSITION,  THE  ASHES  BEINQ 
REMOVED. 

Carbon. 

Hydrogen. 

Oxygen 

and 
Nitrogen. 

Ashes. 

Carbon. 

Hydrogen. 

Oxygen 

Nitrogen. 

1.362 

89.5 

88.54 

1.67 

5.22 

4.57 

92.78 

1.75 

6.47 

1.919 

88.9 

70.51 

0.92 

2.10 

26.47 

95.90 

1.25 

2.85 

1.279 

77.8 

88.27 

4.83 

6.90 

1.00 

89.16 

4.88 

6.96 

1.294 

53.3 

74.36 

4.74 

10.05 

11.86 

83.40 

6.32 

11.28 

1.410 

51.2 

62.41 

4.35 

14.04 

19.20 

77.25 

6.38 

17.57 

1.316 
1.305 

42.5 
42.0 

71.94 
74.38 

5.45 
5.79 

18.53 
18.94 

4.08 
0.89 

75.02 
75.06 

6.69 
5.84 

19.29 
19.10 

1.272 

49.1 

69.52 

5.59 

19.90 

4.99 

73.18 

6.88 

21.14 

1.254 

41.1 

63.01 

4.58 

18.98 

13.43 

72.78 

5.29 

21.93 

1.351 

48.5 

70.73 

4.85 

22.65 

1.77 

72.00 

4.93 

23.07 

1.276 

49.5 

69.05 

6.20 

22.74 

3.01 

71.20 

6.36 

23.44 

1.185 

38.9 

60.36 

5.00 

25.62 

9.02 

66.36 

6.49 

28.15 

1.100 

36.1 

63.42 

4.98 

27.11 

6.49 

66.04 

6.27 

28.69 

1.167 

(t 

55.27 

5.70 

36.84 

2.19 

56.50 

5.83 

37.67 

1.157 

27.4 

72.78 

7.46 

14.80 

4.96 

76.58 

7.86 

15.57 

1.197 

39.0 

74.82 

7.25 

13.99 

3.94 

77.88 

7.55 

14.57 

1.063 

9.0 

78.10 

9.30 

9.80 

2.80 

80.34 

9.57 

10.09 

u 

56.25 

57.29 

5.63 
5.93 

32.54 
32.17 

5.58 
4.61 

59.67 
60.06 

5.96 
6.21 

34.47 
33.73 

tt 

tl 

57.00 

6.11 

31.56 

5.33 

60.21 

6.45 

33.34 

1 

t( 

49.60 

5.80 

42.56 

2.04 

60.62 

6.94 

43.44 

504  DECAY  OF  VEGETABLE  MATTER. 

§  1320.  In  order  to  see  how  the  composition  of  mineral  com. 
"bustibles  varies  with  their  qualities  in  the  arts  and  geological  age, 
the  numbers  contained  in  the  last  three  columns  of  the  table  must 
be  compared;  that  is,  those  which  exhibit  the  composition  of  these 
combustibles  after  the  ashes  are  removed.  On  assuming  as  a 
standard  of  comparison  the  coals  of  the  third  class,  and  ascending 
from  this  to  those  of  the  second,  it  will  be  found  that  the  quantity 
of  hydrogen  is  nearly  the  same,  but  that  the  oxygen  has  remarkably 
decreased  and  been  replaced  by  carbon.  On  passing  from  the 
second  class  to  the  first,  it  will  be  observed  that  both  the  hydrogen 
and  oxygen  decrease,  while  the  carbon  increases  in  the  same  ratio. 

Starting  always  from  the  blacksmith's  coal,  we  descend  toward 
the  fourth  class,  and  remark  that,  generally,  the  hydrogen  exists  in 
greater  quantity;  and  that  the  carbon  decreases  remarkably  and 
is  replaced  by  oxygen.  Lastly,  in  the  fifth  class,  the  oxygen  has 
still  increased,  and  taken  the  place  of  a  corresponding  quantity  of 
carbon. 

Fat  pit-coal  may  become  dry  in  two  ways :  either  by  passing  into 
anthracite,  the  hydrogen  and  oxygen  both  decreasing,  and  the  carbon 
increasing  in  the  same  ratio,  or  by  approaching  the  more  modern 
combustibles,  the  lignites^  the  carbon  decreasing  and  being  replaced 
by  oxygen;  in  which  latter  case  the  ratio  between  the  oxygen  and 
hydrogen  increases. 

By  now  comparing  the  combustibles  of  the  secondary  with  those 
of  the  coal  formation,  it  will  be  seen  that,  in  the  inferior  stratum 
of  the  latter  formation,  the  same  variety  can  be  distinguished. 
Thus,  the  anthracites  of  Lamure  and  Macot,  which  are  found  in 
the  lower  part  of  the  Jurassic  rocks,  present  the  same  composition 
as  those  in  the  transition  rocks ;  while  the  coal  from  Obernkirchen, 
which  also  exists  in  the  Jurassic  formation,  has  the  same  properties 
and  composition  as  those  of  the  carboniferous  formation.  Lastly, 
the  coal  from  Cdral,  which  also  occurs  in  the  Jurassic  formation, 
belongs,  on  account  of  its  composition  and  applications  in  the  arts, 
to  the  class  of  fat  coal  burning  with  a  long  flame. 

The  coal  found  in  the  upper  stratum  of  secondary  rocks  re- 
sembles, on  the  contrary,  the  combustibles  of  the  tertiary  rocks  or 
the  lignites,  which  differ  from  the  coal  of  the  older  rocks  by  con- 
taining less  carbon  and  more  oxygen ;  and,  as  their  formation 
approaches  a  modern  period,  their  composition  resembles  more 
closely  that  of  wood.  The  charcoal  they  yield  by  calcination  be- 
comes more  and  more  dry :  thus,  the  jet  of  chalk  still  yields  a  fritted 
metalloid  coke,  while  the  lignites  of  the  tertiary  rocks  produce  a 
non-metalloid  charcoal,  the  fragments  of  which  do  not  adhere  to 
each  other,  and  resemble  in  appearance  wood  charcoal. 

The  bitumens,  which  are  evidently  products  of  distillation  of 
older  combustibles,  or  produced  by  the  spontaneous  decomposition 


ALCOHOLIC   FERMENTATION.  505 

of  animal  substances,  differ  essentially  from  coal  properly  so  called, 
by  containing  much  larger  quantities  of  hydrogen. 

ALCOHOLIC  FERMENTATION 

§  1321.  The  majority  of  vegetables  containing  amylaceous  matter 
contain,  at  the  same  time,  substances  which  can,  under  favourable 
circumstances,  convert  this  matter  into  sugar.  These  substances 
are  sometimes  developed  only  at  certain  stages  of  vegetation ;  as, 
e.  g.  the  grains  of  the  cerelia  contain  at  the  moment  of  germination 
a  peculiar  substance,  diastase,  (§  1305,)  which  chiefly  resides  at  the 
point  of  insertion  of  the  germ  in  the  grain,  and  which,  under  fa- 
vourable conditions,  rapidly  converts  starch  into  a  soluble  sub- 
stance, dextrin,  and  then  into  sugar,  if  its  action  be  continued  for 
a  sufficient  length  of  time.  In  these  successive  transformations  the 
chemical  composition  of  the  amylaceous  matter  is  unchanged,  while 
it  has  become  soluble,  and  may  be  carried  into  the  circulation  of  the 
sap,  where  it  aids  in  the  development  of  the  vegetable,  by  forming 
the  cellulose  which  is  to  constitute  the  skeleton  of  the  new  plant. 

Ripe  fruits  which  contain  a  large  quantity  of  sugar,  like- 
wise contain  a  peculiar  substance,  called  ferment,  which,  under 
certain  circumstances,  possesses  the  property  of  decomposing  the 
sugary  matter  into  alcohol  and  carbonic  acid ;  a  certain  tempera- 
ture and  the  contact  of  oxygen  or  atmospheric  air  being  required 
for  the  exercise  of  the  action.  If  ripe  grapes  be  expressed  under 
mercury,  and  the  juice  collected  in  a  bell-glass  completely  filled 
with  mercury,  it  will  remain  unchanged  for  several  days ;  but  if  a 
few  bubbles  of  oxygen  or  atmospheric  air  be  introduced  into  the 
bell-glass,  a  considerable  volume  of  gas  is  disengaged,  the  evolution 
of  which  ceases  generally  in  2  or  3  days.  If  the  juice  be  then  ex- 
amined, a  volatile  liquid,  called  alcohol,  will  be  found  to  have  taken 
the  place  of  all  the  sugar  ;  but  if  the  sugary  substance  of  the  fruit 
is  not  decomposed  in  the  uninjured  fruit,  it  is  because  the  active 
principle,  or  ferment,  or  the  substances  which  produce  it,  did  not 
come  in  contact  with  oxygen,  a  condition  indispensable  for  the  pro- 
duction of  fermentation. 

Ferment  is  also  produced  when  animal  or  vegetable  matter  is 
allowed  to  decompose  spontaneously,  as  in  the  manufacture  of  beer, 
when  it  is  called  yeast  of  beer,  or  simply  yeast,  which  substance  soon 
effects  the  fermentation  of  the  aqueous  solution  of  the  sugars  and 
their  complete  conversion  into  alcohol  and  carbonic  acid.  Muscular 
flesh,  urine,  gelatin,  white  of  eggs,  cheese,  gluten,  legumin,  extracts 
of  meat  and  blood,  left  to  themselves  for  some  time,  exposed  to  air 
and  moisture,  and  thus  undergoing  the  process  known  as  putrefac- 
tion, cause  sugars  to  ferment,  and  convert  them  into  alcohol  and 
carbonic  acid. 

All  the  sugars  above  described  undergo  this  decomposition  under 
the  influence  of  ferment,  and  it  is  a  distinctive  character  of  this 


506  ACTION  OF  FERMENTS. 

class  of  organic  products,  although  they  do  not  all  experience  it  in 
the.  same  space  of  time ;  the  sugar  of  acid  fruits  turning  to  the  leftj 
the  solid  sugar  of  dry  fruits  and  glucose  being  very  rapidly  de- 
stroyed by  fermentation,  while  cane-sugar  requires  a  longer  time. 
It  is  even  easy  to  perceive,  by  the  inversion  of  the  rotatory  powers, 
that  cane-sugar  undergoes  fermentation  only  after  being  converted 
into  fruit-sugar.  Fresh  ferment  always  contains  a  considerable 
quantity  of  acid,  which  first  changes  the  cane-sugar  into  fruit 
sugar;  but  as  vegetable  acids  require  considerable  time  to  effect 
this  transformation,  its  fermentation  is  very  slow.  Yeast,  freed 
from  these  acids  by  washing,  for  a  long  time  exerts  no  action  on 
cane-sugar,  and  fermentation  commences  only  when  fresh  quantities 
of  acid  are  formed  by  the  spontaneous  change  in  the  yeast  from  ex- 
posure to  air  and  water.  If,  on  the  contrary,  the  acid  liquid  arising 
from  washing  the  yeast  be  added  to  the  solution  of  sugar,  the  cane- 
sugar  is  gradually  transformed  into  fruit-sugar,  which  immediately 
ferments  when  brought  into  contact  with  the  washed  yeast. 
One  hundred  parts  of  fruit-sugar  yield  by  fermentation 

48.88  of  carbonic  acid 
and  51.12  of  alcohol ; 

so  that  the  chemical  elements  of  the  yeast  appear  to  have  no  agency 
in  the  reaction,  which  is  expressed  by  the  following  equation : 
C.A,0„=4C0,+2C.H,0, 

Sugar.  Alcohol. 

§  1322.  That  the  decomposition  of  sugar  by  fermentation  is  effected 
only  by  the  immediate  contact  of  yeast,  is  easily  shown  by  the  follow- 
ing experiment: — Having  adapted,  by  means  of  a  cork,  to  the  mouth 
«  Fi  of  a  bottle  A,  (fig.  666,)  containing  a  solution  of  sugar, 

^^JL  a  large  tube  ab  open  at  both  ends,  the  lower  one  of  which 
^mr^  j^  is  covered  by  a  sheet  of  bibulous  paper,  a  small  quantity 
rni  of  yeast  of  beer  slightly  diluted  with  water  is  introduced 
^^  into  the  tube.  As  the  solution  of  sugar  penetrates  the 
^1  tube  ab  through  the  paper,  fermentation  ensues  very 
*  Im  actively,  and  carbonic  acid  is  copiously  disengaged, 
^^^^  while  no  similar  reaction  takes  place  in  the  liquor  in  the 
Fig.  666.  bottle,  which  remains  unchanged  for  any  length  of  time. 
During  the  decomposition  of  sugar  by  fermentation,  the  ferment 
itself  is  destroyed,  so  that  a  small  quantity  of  the  active  principle 
cannot  decompose  an  indefinite  quantity  of  sugar ;  and  if  the  pro- 
portion of  yeast  be  too  small,  its  decomposition  is  effected  before 
that  of  the  sugar,  a  portion  of  which  then  remains  unchanged  in 
the  liquor.  If,  on  the  contrary,  the  yeast  predominates,  the  de- 
composition of  the  sugar  is  effected  before  that  of  the  yeast,  and 
the  latter  continues  to  change  spontaneously ;  and  if  an  additional 
quantity  of  the  solution  of  sugar  be  introduced,  it  produces  fermenta- 
tion until  it  is  entirely  destroyed.     The  best  proportions  to  induce 


ALCOHOLIC  FERMENTATION.  507 

rapid  fermentation  are  1  part  of  cane-sugar,  3  or  4  of  water,  and 
J  of  fresh  yeast ;  and  if  the  proportion  of  sugar  be  increased,  the 
fermentation  becomes  less  active,  and  ceases  entirely  if  a  saturated 
solution  of  sugar  be  used.  In  all  cases  sugar  does  not  destroy 
more  than  2  per  cent,  of  its  weight  of  ferment. 

The  weak  acids,  in  small  quantities,  increase  fermentation,  while 
alkalies,  on  the  contrary,  arrest  or  completely  modify  the  process. 

§  1323.  Ferment  is  a  species  of  microscopic  vegetable,  which  is 
spontaneously  developed  in  the  organs  of  plants,  and  in  a  large 
number  of  nitrogenous  substances  when  left  to  putrefy ;  and  which 
is  also -formed  by  exposing  to  the  ordinary  temperature  a  solution 
of  sugar  mixed  with  albuminous  substances  of  vegetable  or  animal 
origin.  After  some  time  the  liquor  becomes  cloudy,  and  small 
ovoidal  bodies  are  deposited,  gradually  increasing  in  size  until  they 
attain  a  diameter  of  the  jio  of  a  millimetre.  Two  species  of  fer- 
ments, differing  in  their  manner  of  development  and  mode  of  action 
on  solutions  of  sugar,  may  be  observed.  The  first,  called  upper 
yeasty  is  developed  in  a  mixture  of  sugar  and  water  and  albuminous 
substances,  when  the  temperature  is  comprised  between  64.5°  and 
77° ;  while  the  second,  or  lower  yeasty  is  only  found  at  temperatures 
between  32°  and  46.4°.  In  order  to  study  the  shape  and  develop- 
ment of  the  globules  under  the  microscope,  a  very  small  quantity 
of  yeast  is  diluted  in  an  infusion  of  grain,  sprouted  barley  for 
example,  and  a  drop  of  the  liquid  is  placed  between  two  pieces  of 
thin  glass,  the  edges  of  which  are  luted  to  prevent  the  evaporation 
of  the  water.  These  plates  are  placed  under  the  microscope,  taking 
care  to  bring  an  isolated  globule  of  yeast  under  the  centre  cross- 
threads  of  the  micrometer,  in  order  to  study  its  development.  Figs. 
667  to  674  represent  the  arrangement  of  the  new  globules  of  fer- 
ment which  form  successively  around  an  original  globule  1,  the 
temperature  being  about  66.2°.  During  the  first  two  hours  the 
globule  1  (fig.  667)  exhibits  nothing  peculiar ;  while,  after  this 
period,  there  forms  at  a  point  of  its  surface  a  rupture  which  gradu- 
ally increases  for  six  hours,  until  it  has  attained  the  dimensions  of 
the  original  globule,  (fig.  668.)  The  second  globule  soon  generates 
a  third,  which  arises  on  the  sides  of  the  second  (figs.  669  and  670) 
in  the  same  way  as  this  grew  on  the  first,  and  so  on.  In  an  ex- 
periment lasting  three  days,  30  globules  (fig.  674)  had  formed 
around  the  original  globule  1 ;  and  on  the  fourth  day  another 
formed,  which  was  the  last,  the  albuminous  matter  necessary  for 
their  formation  having  probably  been  exhausted.  Six  successive 
generations,  which  were  thus  observed,  are  indicated  in  the  figures 
by  ciphers,  according  to  the  order  of  their  origin.  The  various 
globules  adhered  to  each  other,  but  there  appeared  to  be  no  inter- 
communication. 

It  will  hence  be  perceived  that,  on  adding  an  albuminous  sub- 
stance to  a  mixture  of  sugar  and  ferment,  the  sugar  is  not  alone 


508 


ACTION   OF  FERMENTS. 


affected  by  the  ferment,  as  the  albuminous  matter  itself  undergoes 
several  metamorphoses  and  is  converted  into  yeast ;  which  fact  ex- 
plains the  reason  why,  in  breweries,  at  the  close  of  the  operation, 


o 


Fig.  667. 


^ 


Fig.  668. 


Fig.  669. 


Fig.  671. 


Fig.  673. 


Fig.  674. 


a  quantity  of  yeast  is  withdrawn  seven  or  eight  times  greater  than 
that  which  had  been  originally  used.  The  yeast  is  carefully  col- 
lected, and  subsequently  used  to  effect  other  fermentations,  par- 
ticularly in  the  making  of  bread. 

It  is  easy  to  observe  that  each  globule  is  composed  of  a  solid 
envelope  containing  a  liquid ;  and  it  therefore  forms  a  sort  of  cell, 
which  is  lined  with  a  layer  of  mucilaginous  substance.  On  ob- 
serving for  several  days  the  systems  of  globules  which  have  acquired 
their  perfect  development,  it  will  be  seen  that  smaller  granules, 
whose  rapid  motion  proves  that  they  float  in  a  liquid,  are  formed 
in  each  globule  ;  and  after  a  sufficient  length  of  time  the  whole  of 
the  contained  liquid  is  converted  into  granules. 
.X  The  globules  the  development  of  which  we  have  followed  belong 


ALCOHOLIC  FERMENTATION.  509 

to  the  upper  yeast ;  and  it  is  easy  to  see  that  they  are  formed  by 
shoots  upon  each  other.  The  lower  yeast  is  always  composed  of 
isolated  globules  scattered  through  the  liquid ;  their  formation 
obeying  the  same  laws  as  those  of  the  upper  yeast,  while  the  tem- 
perature must  not  exceed  44.6°  or  46.4°.  Each  globule  appears 
at  first  like  an  isolated  point  in  the  liquid,  and  gradually  increases 
until  it  attains  a  diameter  of  about  ^  of  a  millimetre.  Some  ob- 
servers think  that  the  old  globules  of  lower  yeast  burst  and  suspend 
in  the  liquor  the  granules  they  contain,  each  of  which  would  then 
be  transformed  into  a  globule ;  in  which  case  the  mode  of  genera- 
tion of  the  lower  would  differ  totally  from  that  of  the  upper  yeast. 
If  the  temperature  be  raised  to  68°  or  77°,  the  isolated  globules 
of  lower  yeast  are  immediately  developed  by  shoots,  and  then  pro- 
duce upper  yeast. 

§  1324.  The  action  of  the  two  kinds  of  yeast  on  solutions  of 
sugar  is  also  very  different ;  upper  yeast  producing  a  much  more 
active  fermentation,  with  a  copious  evolution  of  carbonic  acid, 
while  the  yeast  is  violently  agitated  in  the  liquid,  and  ascends  to 
its  surface ;  while,  on  the  other  hand,  lower  yeast  acts  much  more 
slowly,  and  frequently  requires  two  or  three  months  to  effect  the 
complete  transformation  of  sugar  into  alcohol  and  carbonic  acid,  the 
ferment  being  disturbed  by  no  rapid  movement,  but  on  the  contrary 
gently  deposited  at  the  bottom  of  the  liquid.  Lower  yeast  is  used 
in  the  manufacture  of  certain  kinds  of  beer,  particularly  that 
called  Bavarian. 

It  has  been  impossible  to  follow  with  the  microscope  the  trans- 
formations of  yeast  during  the  fermentation  of  sugar,  on  account 
of  the  disengagement  of  carbonic  acid  ;  and  it  has  been  merely  as- 
certained that  the  yeast  increases  by  about  J  of  its  weight.  Its 
chemical  composition  is  also  changed ;  and  while  fresh  yeast  has 
been  found  to  contain 

Carbon 47.0 

Hydrogen Q.Q 

Nitrogen 10.0 

Oxygen,  about 35.0 

and,  in  addition,  small  quantities  of  sulphur,  phosphorus,  and  some 
mineral  bases,  such  as  potassa  and  lime  ;  the  same  yeast,  after  fer- 
mentation was  composed  of 

Carbon 47.6 

Hydrogen 7.2 

Nitrogen 5.0 

Thus,  the  carbon  remained  nearly  the  same,  while  the  hydrogen 
sensibly  increased,  and  the  nitrogen  decreased  by  one-half. 

On  bringing  an  aqueous  solution  of  iodine  into  contact  with 
globules  of  ferment,  the  outer  envelope  is  not  coloured,  while  the 


510  ACTION   OF   FERMENTS. 

liquid  inside  becomes  of  a  brown  colour,  which  may  be  proved  by 
crushing  the  globules  between  plates  of  glass,  when  the  envelopes 
exhibit  the  characters  of  cellulose.  When  a  certain  quantity  of 
yeast  is  allowed  to  decompose  completely,  in  contact  with  a  solu- 
tion of  sugar,  and  the  residue  is  bruised  in  a  mortar,  and  perfectly 
exhausted  by  water,  alcohol,  and  ether,  a  white  substance  remains, 
which  yields  glucose  with  sulphuric  acid,  and  does  not  dissolve  in 
alkaline  liquids,  which,  on  the  contrary,  immediately  dissolve  the 
albuminous  substances  in  yeast.* 

§  1325.  Ferment,  dried  in  vacuo  or  at  a  low  temperature,  yields 
a  hard,  corneous,  semi-transparent,  and  reddish-gray  mass  ;  the  pro- 
perty of  which,  of  causing  the  fermentation  of  saccharine  liquors,  is 
only  suspended,  and  is  again  called  forth  by  digesting  the  substance 
for  some  time  in  water.  If  it  be  boiled  for  a  few  moments,  it 
loses  this  property;  but  may  recover  it  by  contact  with  the  air, 
when  it  has  not  been  exposed  for  too  long  a  period  to  a  temperature 
of  212°.  Alcohol,  sea-salt,  and  a  great  excess  of  sugar,  oxide  of 
mercury,  corrosive  sublimate,  pyroligneous  acid,  sulphurous  acid, 
nitrate  of  silver,  the  essential  oils,  etc.  etc.  destroy  the  fermenting 
power  of  yeast ;  while  certain  substances,  which  are  very  violent 
poisons  to  animals,  such  as  arsenious  acid  and  tartar  emetic,  do  not 
produce  this  effect;  and  neither  do  these  substances  prevent  the 
fermentation  of  certain  microscopic  plants,  for  solutions  of  tartar 
emetic,  if  exposed  to  the  air,  become  covered  with  confervse. 

The  action  by  which  ferment  converts  sugar  into  alcohol  and 
carbonic  acid  is  yet  unexplained.  Some  chemists  insist  that  vital 
force  causes  the  development  and  successive  metamorphoses  of  the 
globules  of  ferment ;  while  others  think  that  ferment  only  acts  by 
its  presence,  and  that  its  action  should  be  compared  to  that  by 
which  certain  mineral  substances  effect  the  decomposition  of  feeble 
compounds  without  any  change  in  their  elementary  composition. 
Thus,  binoxide  of  manganese  will  decompose  binoxide  of  hydrogen 
into  oxygen  and  water,  without  being  itself  in  the  least  changed ; 
and  so  again,  chlorate  of  potassa,  which  is  decomposed  only  at  a 
temperature  of  930°  or  1020°  when  heated  alone,  experiences  this  de- 
composition at  a  much  lower  temperature  when  it  is  intimately  mixed 
with  oxide  of  copper  or  binoxide  of  manganese,  oxides  which  remain 
unchanged  in  the  residue.  Lastly,  according  to  some  authors,  the 
movements  of  the  particles  of  ferment  during  their  successive  meta- 
morphoses are  the  principal  cause  of  the  decomposition  of  sugar ; 
as  these  movements,  by  being  communicated  to  the  saccharine  par- 


*  In  an  investigation  of  the  products  of  the  spontaneous  decomposition,  or  fer- 
mentation, of  yeast  of  beer  alone,  I  found  the  liquid  contained  in  the  small  cells 
to  be  completely  decomposed  into  butyric  acid  with  traces  of  valerianic,  and  into 
a  substance  the  behaviour  of  which  corresponded  in  all  respects  to  leucin,  but 
the  analysis  of  which  was  unfortunately  prevented  by  accident. —  TF.  L.  F. 


ALCOHOL.  511 

tides,  destroy  their  inertia,  and  cause  the  elementary  molecules  to 
be  grouped  so  as  to  form  more  fixed  compounds.  We  shall  be 
satisfied  with  stating  what  is  known  concerning  alcoholic  fermenta- 
tion, and  shall  venture  no  explanation  of  this  mysterious  phenomenon, 
which  is  as  yet  too  imperfectly  understood  to  allow  the  establish- 
ment of  any  theory  upon  certain  data. 

Alcohol  C^HgOg. 

§  1326.  It  has  been  mentioned  that  a  solution  of  sugar,  when 
left  for  some  time  in  contact  with  yeast  of  beer,  soon  ferments,  and 
is  converted  into  alcohol  and  carbonic  acid ;  but  the  same  decompo- 
sition takes  place  spontaneously  in  the  saccharine  juice  of  many 
fruits,  such  as  grapes,  cherries,  currants,  apples,  pears,  etc. ;  and 
also  ensues,  when  assisted  by  yeast,  in  the  saccharine  liquors  pro- 
duced by  amylaceous  substances  in  the  presence  of  diastase.  The 
alcohol  remains  in  the  liquor,  and  may  be  separated  from  it  by 
distillation,  because  it  is  more  volatile  than  water.  In  fact,  on  dis- 
tilling in  an  alembic,  wine,  beer,  cider,  or  other  alcoholic  liquors, 
the  first  portions  of  liquid  which  pass  over  are  much  richer  in  alco- 
hol than  the  residue ;  and  if  the  distillation  be  arrested  at  the 
proper  moment,  the  residue  contains  scarcely  any  alcohol.  For 
this  purpose,  alcoholic  liquors  are  used,  the  production  of  which 
exceeds  their  consumption,  or  the  inferior  quality  of  which  renders 
them  unfit  for  market. 

If  the  distilled  portions  be  redistilled,  the  first  liquors  are  still 
richer  in  alcohol,  and  thus  alcoholic  liquors  are  obtained  bearing 
different  names,  according  to  their  strength;  and  while  liquors 
containing  50  to  ^b  per  cent,  of  alcohol  are  called  brandies^  those 
containing  more  are  called  spirits.  By  a  proper  process  of  distilla- 
tion, liquors  containing  from  85  to  90  per  cent,  of  alcohol  may  be 
obtained,  which  then  nearly  consist  of 

leq.  of  alcohol  C^HgO, 46 83.T 

1  eq.  of  water 9 16.3 

55 ioOO 

The  last  portions  of  water  cannot  be  removed  by  distillation,  but 
they  are  separated  by  combining  them  with  substances  which  have 
a  great  affinity  for  water,  and  which  do  not  unite  permanently 
with  alcohol. 

The  best  method  of  obtaining  anhydrous  alcohol  consists  in  pour- 
ing alcohol  of  85  or  90  per  cent,  into  a  large  bottle  containing  quick- 
lime prepared  by  the  process  mentioned  §  555,  shaking  the  bottle 
several  times,  and  allowing  it  to  rest  for  24  hours  ;  after  which  the 
liquid  is  distilled  in  a  water-bath,  arranged  as  in  fig.  149,  until  no 
more  liquid  passes  over.  The  alcohol  thus  obtained  being  not 
entirely  freed  from  water,  the  operation  must  be  renewed ;  but  this 
process  will  often  not  yield  completely  anhydrous  alcohol;    and 


At  59° 0.8021 

68  0.7978 

77  0.7933 


512  FERMENTATION. 

the  highly  concentrated  alcohol  must  be  dissolved  in  a  certain  quan- 
tity of  melted  caustic  potassa,  and  distilled  over  a  fire,  or  in  a  bath 
of  chloride  of  calcium,  until  f  of  the  liquor  have  passed  over.  The 
distilled  liquid,  which  is  then  anhydrous  or  absolute  alcohol,  has  a 
peculiar  odour,  owing  probably  to  the  presence  of  a  small  quantity 
of  volatile  oil,  formed  by  the  reaction  of  the  oxygen  of  the  air  on 
the  alcohol  in  the  presence  of  alkaline  substances.  The  alcoholic 
liquor  which  remains  in  the  distilling  apparatus  is  coloured  brow^n  by 
a  small  quantity  of  resinous  matter,  also  produced  by  the  reaction. 
§  1327.  Absolute  alcohol  is  a  colourless  liquid,  more  fluid  than 
water,  of  a  burning  taste  and  agreeable  odour.  It  does  not  solidify, 
even  at  the  lowest  temperature  which  can  be  produced  ;  and  it  boils 
at  the  temperature  of  173.1°  under  a  pressure  of  760  millimetres, 
or  29.92  inches.  The  density  of  its  vapour,  compared  with  air,  is 
1.5890 ;  and  its  specific  gravity  in  the  fiuid  state  is, 

At  32° 0.8151 

41  0.8108 

50  0.8065 

Alcohol  is  composed  of 

4  eq.  of  carbon 24 52.65 

6  eq.  of  hydrogen 6 12.90 

2  eq.  of  oxygen 16 34.45 

46         100.00 

1  volume  of  vapour  of  alcohol  contains 

1  vol.  of  vapour  of  carbon 0.8290 

1    "  "  hydrogen 0.2074 

J   "  "  oxygen 0.5526 

1.5890 

Its  equivalent  C^HgOa  is  therefore  represented  by  4  volumes  of 
vapour,  (§  1237.) 

A  weak  solution  of  alcohol,  left  in  a  bladder  exposed  to  the  air, 
allows  more  water  than  alcohol  to  pass,  and  in  time  becomes 
stronger. 

Absolute  alcohol  attracts  the  moisture  of  the  air.  The  temper- 
ature rises  and  contraction  ensues  when  it  is  mixed  with  water; 
the  maximum  of  contraction  being  produced  by  mixing 

53.7  volumes  of  alcohol, 

49.8  "  water, 

103.5 
which  are  reduced  to  100  volumes ;  which  proportions  correspond 
to  1  equivalent  of  alcohol  and  6  equivalents  of  water.     Very  cold 
absolute  alcohol,  mixed  with  snow,  lowers  the  temperature  to  34.6°; 
all  which  facts  show  a  powerful  affinity  between  alcohol  and  water : 


ALCOHOLOMETRY.  513 

the  two  liquids,  however,  dissolve  each  other,  in  all  proportions. 
Alcohol  burns  in  the  air  with  a  feebly  brilliant  flame,  and  in  the 
open  air  its  combustion  is  perfect. 

Alcohol  is  frequently  used,  either  absolute,  or  mixed  with  greater 
or  less  proportions  of  water,  in  the  laboratory  as  a  solvent. 
Generally  speaking,  it  dissolves  gases  more  largely  than  water ;  and 
a  great  number  of  very  soluble  and  deliquescent  compounds  dissolve 
in  even  absolute  alcohol,  as,  for  example,  caustic  potassa  and  soda, 
the  chlorides  of  calcium,  strontium,  nitrates  of  lime,  magnesia,  etc. 
etc. ;  and  it  frequently  dissolves  certain  compounds  which  are  not 
very  soluble  in  water  more  freely  than  the  latter  liquid,  as,  for 
example,  corrosive  sublimate,  and  the  corresponding  bromide  and 
iodide  of  mercury.  Lastly,  it  dissolves  a  large  number  of  organic 
substances  insoluble  in  water.  Alcohol  is  frequently  used  in  che- 
mical analyses,  in  order  to  separate  substances  soluble  in  water  but 
very  unequally  soluble  in  alcohol ;  the  differences  of  solubility  being 
sometimes  increased  by  adding  ether  to  the  alcohol. 

Alcohol  also  combines  with  several  salts,  which  are  soluble  in  it, 
playing  a  part  analogous  to  that  of  water  of  crystallization,  and 
forming  compounds,  called  alcoates.  When  dry  chloride  of  calcium 
is  brought  into  contact  with  alcohol,  the  temperature  rises  consider- 
ably, in  consequence  of  the  formation  of  an  alcoate. 

When  substances  are  dissolved  in  alcohol,  their  reactions  are 
frequently  very  different  from  those  of  their  solutions  in  water.  It 
has  been  mentioned  (§  378)  that  acetic  acid  will  readily  expel 
carbonic  acid  from  carbonate  of  potassa  dissolved  in  water ;  but,  on 
the  other  hand,  carbonic  acid  will  displace  the  acetic  acid  of  acetate 
of  potassa  dissolved  in  alcohol;  the  insolubility  of  carbonate  of 
potassa  in  alcohol  thus  becoming  a  new  condition,  which  changes  the 
order  of  affinities. 

§  1328.  By  adding  larger  and  larger  proportions  of  water  to 
alcohol,  its  specific  gravity  increases  progressively ;  and  processes 
for  determining  the  richness  in  alcohol  of  these  mixtures  have  been 
based  on  the  variation  of  density.  An  areometer  was  formerly 
used,  called  Cartiers  hydrometer  for  spirits,  which  marked  0°  in 
pure  water  and  44°  in  absolute  alcohol,  the  space  between  these 
points  being  divided  into  44  equal  parts ;  but  this  instrument  has 
been  superseded  by  G-ay  Lussacs  alcoholometer,  of  which  the  gra- 
duation marks  the  richness  immediately  in  hundredths.  The  zero 
of  the  instrument  corresponds  to  pure  water,  while  absolute  alcohol 
marks  100;  and  several  intermediate  points  have  been  fixed  by 
plunging  it  into  liquors  the  composition  of  which  was  known.  The 
centesimal  alcoholometer  only  gives  the  exact  quantity  of  alcohol 
when  the  liquid  is  at  a  temperature  of  59°,  at  which  the  graduation 
was  made ;  and  as  alcohol  expands  considerably  by  heat,  corrections 
must  be  made  for  all  other  temperatures ;  which  have  been  carefully 

Vol.  IL--33 


514  FERMENTATION. 

calculated  and  set  down  in  tables  for  a  certain  extent  of  the  ther- 
mometric  scale. 

The  alcoholometer  can  show  the  richness  in  alcohol  only  of  those 
liquids  which  contain  merely  water  and  alcohol ;  for  if  they  con- 
tained sugar  or  saline  substances,  the  result  would  be  inaccurate, 
because  these  substances  would  increase  the  density  of  the  liquor. 
This  process,  therefore,  cannot  indicate  immediately  the  richness  of 
alcoholic  drinks,  which  always  contain  sugar  and  saline  substances ; 
and  for  this  purpose  the  following  method  is  used : — After  intro- 
ducing 300  cub.  cent,  of  the  liquor  to  be  tested  into  a  small  alembic 
of  tinned  copper,  it  is  distilled  by  means  of  an  alcohol-lamp,  and 
the  liquid  which  condenses  in  the  worm  is  collected  in  a  test-tube, 
graduated  to  cubic  centimetres.  The  distillation  is  arrested  as  soon 
as  100  cub.  cent,  have  collected,  when  the  liquor  is  reduced  to  the 
temperature  of  59°,  and  the  quantity  of  alcohol  it  contains  deter- 
mined by  the  alcoholometer ;  after  which  J  of  the  quantity  found 
represents  the  richness  in  alcohol  of  the  liquor  subjected  to  the  test. 

If  the  liquor  were  very  poor  in  alcohol,  only  50  cub,  cent,  would  be 
distilled,  in  order  to  obtain  a  distilled  liquor  somewhat  rich  in  alco- 
hol, for  the  test  then  affords  a  greater  degree  of  accuracy,  and  the 
percentage  of  alcohol  in  the  liquor  tested  is,  in  this  case,  ^  of  that 
obtained  on  the  product  distilled.  If,  on  the  contrary,  the  liquor 
were  very  rich  in  alcohol,  it  would  be  proper  to  distil  only  J  or  f 
of  it,  and  take  the  j^  or  f  of  the  standard  found. 

The  richness  of  an  alcoholic  liquor  may  also  be  determined  by  as- 
certaining the  temperature  marked  by  a  thermometer,  the  bulb  of 
which  is  dipped  into  the  liquor  at  the  moment  it  boils.  A  table, 
which  shows  the  temperature  of  ebullition  corresponding  to  the 
various  mixtures  of  alcohol  and  water,  must  then  be  made,  and  de- 
duced from  direct  experiments  made  in  the  same  apparatus  and  on 
known  mixtures  of  alcohol  and  water.  This  process  shows  the 
richness  of  alcoholic  liquors  used  as  beverages  pretty  exactly,  be- 
cause the  quantities  of  sugar  and  salt  they  contain  affect  their 
temperature  of  ebullition  but  slightly. 

Lastly,  the  calculation  may  be  based  on  the  great  differences  of 
expansibility  between  alcohol  and  water,  by  using  a  kind  of  ther- 
mometer having  the  form  of  a  pipette,  the  lower  tube  terminating 
the  bulb  of  which  is  very  short,  and  its  orifice  may  be  closed  by  a 
stopper  fitting  exactly  by  means  of  a  spring.  The  liquor  to  be 
tested  is  brought  exactly  to  the  temperature  of  77°,  and  the  ther- 
mometric  apparatus,  having  the  lower  orifice  open,  is  plunged  into 
it.  The  fluid  is  made  to  rise  by  means  of  sucking  above  the  zero  in 
the  upper  graduated  stem ;  and  it  is  then  allowed  to  recede  slowly 
until  it  exactly  reaches  the  division  0.  The  stopper  being  then  fitted, 
and  the  apparatus  immediately  introduced  into  a  vessel  containing 
water  at  122°,  the  division  at  which  the  level  of  the  liquid  remains 
stationary  indicates  the  richness  in  alcohol,  because  the  instrument 


SULPHOVINIC   ACID.  515 

has  been  graduated  by  direct  experiments  made  on  mixtures  of  al- 
cohol and  water,  the  composition  of  which  was  exactly  known. 
This  process  is  applicable  to  alcoholic  liquors  containing  sugar  or 
salts,  because  they  influence  but  slightly  the  expansibility  of  the 
liquid. 

Concentrated  alcohol  acts  as  a  poison  on  the  animal  economy, 
and  will  produce  death  when  taken  in  large  quantities ;  but  when 
more  dilute,  its  eff"ects  are  merely  intoxication.  Injected  into  the 
veins,  it  produces  almost  sudden  death,  by  coagulating  the  albumen 
of  the  blood. 

PRODUCTS  OF  THE  ACTION  OF  SULPHURIC  ACID  ON  ALCOHOL. 

§  1329.  When  brought  into  contact  with  sulphuric  acid  in  various 
proportions  and  at  diff"erent  temperatures,  alcohol  yields  several 
very  important  products,  which  are  now  to  be  described. 

SULPHOVINIC  ACID  C,H.0,2S0,-|-H0. 

§  1330.  By  pouring  concentrated  sulphuric  acid  into  absolute 
alcohol,  the  two  liquids  dissolve  with  an  elevation  of  temperature, 
while  a  peculiar  acid,  called  sidphovinic,  is  formed,  the  best  pro- 
portion for  producing  which  is  1  part  of  alcohol  to  2  parts  of  sul- 
phuric acid.  A  considerable  quantity  of  sulphovinic  acid  is  also 
formed  when  alcohol  of  85  per  cent,  is  substituted  for  absolute  al- 
cohol ;  but  if  the  alcohol  is  more  dilute,  the  proportion  of  sulpho- 
vinic acid  is  very  small :  the  temperature  must  be  prevented,  during 
the  reaction,  from  rising  above  158°,  for  which  reason  the  alcohol 
should  be  added  very  gradually.  The  liquid  is  then  diluted  with 
water  and  saturated  with  carbonate  of  baryta,  with  which  the  excess 
of  sulphuric  acid  forms  the  insoluble  sulphate,  while  the  sulphovinic 
acid  yields  a  soluble  salt.  The  liquid  being  evaporated  at  a  gentle 
heat,  or  still  better,  in  vacuo,  a  salt  crystallized  in  beautiful  colour- 
less laminae  is  obtained.  The  formula  of  crystallized  sulphovinate 
of  baryta  is 

BaO,(C,H30,2S03)+2HO; 

but  it  readily  parts  with  these  two  equivalents  of  water,  in  a  dry  va- 
cuum, at  a  temperature  between  104°  and  122°. 

The  sulphovinic  acid  may  be  easily  extracted  from  sulphovinate 
of  baryta,  by  pouring  sulphuric  acid,  drop  by  drop,  into  a  solution 
of  the  salt,  until  a  precipitate  is  no  longer  formed ;  when  an  acid 
liquid  is  obtained,  which,  being  evaporated  in  a  cool  place,  under 
the  receiver  of  an  air-pump,  finally  leaves  sulphovinic  acid  in  its 
highest  state  of  concentration,  as  a  syrupy  liquid  of  the  formula 
HO,(C4H50,2S03).  It  decomposes  very  easily,  even  at  the  ordi- 
nary temperature,  the  decomposition  becoming  very  rapid  if  it  is 
heated,  when  free  sulphuric  acid  is  found  in  the  liquid. 

Two  equivalents  of  anhydrous  sulphuric  acid  combine  in  this  re- 


516  TRANSFORMATIONS   OF  ALCOHOL. 

action  with  1  equivalent  of  alcohol  C^HgOa  and  form  sulphovinic  acid 
Cfifi^,2S0^ ;  but  the  formula  of  the  acid  must  be  written 
H0,(C4H50,2S03),  as  the  equivalent  of  water  may  be  replaced  by 
1  equivalent  of  base.  Anhydrous  sulphovinates  may  be  regarded 
as  double  sulphates  of  the  base  and  the  substance  C^H^O,  or  etJier, 
which  shall  soon  be  treated  of,  or  an  isomeric  of  this  body. 

All  the  sulphovinates  being  soluble,  they  are  easily  made,  by 
double  decomposition,  by  pouring  into  a  solution  of  sulphovinate  of 
baryta  a  soluble  sulphate  of  the  base,  until  a  precipitate  ceases  to 
form.     Generally  speaking,  they  crystallize  readily. 

Crystallized  sulphovinates  of  potassa  and  ammonia  are  anhydrous, 
and  their  formulae  are 

K0,(C,H,0,2S0,),      (NH3HO),(CAO,2SO,) ; 

that  of  crystallized  sulphovinate  of  lime  is  CaO,(C4H50,2S03) 
+H0  ;  and  it  loses  its  water  in  vacuo.  Crystallized  sulphovinate 
of  copper  is  represented  by  CuO,(C4H50,2S03)+4HO,  and  that  of 
silver  by  AgO,(C,H,0,2S03)+2HO. 

Solutions  of  the  sulphovinates  are  easily  decomposed  by  boiling ; 
and  the  dry  salts  of  the  acid  yields,  when  heated,  an  oleaginous 
product,  which  will  subsequently  be  met  with  under  the  name  of 
heavi/  oil  of  wine. 

ETHER  C4H,0. 

§  1381.  By  heating  to  185°  a  mixture  of  2  parts  of  alcohol  and 
3  parts  of  concentrated  sulphuric  acid,  a  very  volatile  liquid,  called 
ether,  of  which  the  formula  is  C^H.O,  is  formed.  The  formula  of 
alcohol  being  C^HgO^,  we  are  naturally  led  to  admit  that  the  alco- 
hol parts  with  1  equivalent  of  water  to  the  sulphuric  acid,  and  is 
converted  into  ether  C^H^O ;  but  on  examining  the  reaction  more 
closely,  it  will  not  be  found  quite  so  simple.  In  fact,  the  ether  does 
not  pass  over  alone  in  distillation,  as  water  distils  at  the  same 
time,  and  in  such  quantity  that  it  would  exactly  reproduce  alcohol 
with  ether  formed ;  for  which  reason  it  cannot  be  admitted  that  al- 
cohol is  transformed  into  ether  by  the  affinity  of  sulphuric  acid  for 
water. 

In  order  to  analyze  all  the  circumstances  of  the  production  of 
ether,  the  operation  must  be  arranged  as  follows  : — Place  in  a  flask 
A  (fig.  675)  100  parts  of  concentrated  sulphuric  acid,  containing 
consequently  18.5  of  water,  and  add  20  parts  of  water  and  50  of 
absolute  alcohol ;  then  close  the  mouth  of  the  flask  with  a  cork 
pierced  with  three  holes,  through  one  of  which  passes  a  thermome- 
ter t,  the  bulb  of  which  enters  the  fluid  mixture,  while  the  second 
is  traversed  by  a  tube  ab  descending  to  the  bottom  of  the  flask  and 
terminating  in  a  funnel  a ;  and  lastly,  through  the  third  hole  passes 
a  curved  tube  cde,  the  end  c  of  which  is  drawn  out  so  that  the  liquid 
drops  which  condense  in  it  may  fall  more  easily  into  the  balloon. 


ETHER. 


517 


The  tub^  cde  is  fitted  to  an  ordinary  cooling  apparatus  BC,  resem- 
bling that  used  in  distilling,  the  end  fg  of  the  cooled  tube  being 
bent  in  order  that  it  may  descend  to  the  bottom  of  the  bottle  D. 


Fig.  675. 

The  flask  is  heated  with  an  alcohol-lamp  until  the  thermometer 
marks  284°,  while  a  small  Ocular  piece  of  paper  pasted  on  the 
balloon  indicates  the  original  level  of  the  liquid.  After  carefully 
opening  the  stopcock  r,  in  order  to  allow  the  flow  of  a  continuous 
current  of  absolute  alcohol  contained  in  the  bottle  E,  the  current  is 
so  regulated  that  the  thermometer  t  shall  always  mark  284°  ;  and 
if  the  temperature  should  rise  above  this  point,  more  alcohol  is 
poured  in ;  while  if,  on  the  contrary,  the  temperature  falls,  the 
stream  of  alcohol  is  diminished. 

A  mixture  of  ether  and  water  which  collects  in  the  bottle  D  then 
distils  constantly,  and  care  must  be  taken  to  keep  very  cold  water 
in  the  refrigerator  BC.  For  greater  certainty,  the  tube  fg  is 
slightly  dipped  into  the  bottle  D,  when  a  stratum  of  liquid  has  col- 
lected there ;  and  as  the  level  of  the  latter  rises,  the  bottle  is  gra- 
dually lowered.  By  operating  in  this  manner,  ether  may  be  formed, 
with  the  same  quantity  of  sulphuric  acid,  from  an  almost  indefinite 
quantity  of  alcohol.  The  bottle  D  receives  a  mixture  of  water  and 
ether,  the  weight  of  which  is  exactly  equal  to  that  of  the  alcohol 
used,  if  the  flask  has  been  carefully  maintained  at  the  temperature 
of  284°,  and  the  ether  and  water  exist  in  this  mixture  precisely  iu 
the  proportions  constituting  alcohol. 

The  sulphuric  acid,  under  the  circumstances  in  which  the  opera- 


518  TRANSFORMATIONS   OF  ALCOHOL. 

tion  has  been  performed,  has  merely  effected  the  separation  of  the 
alcohol  into  ether  and  water,  without  attacking  either  of  these  pro- 
ducts ;  and  the  affinity  of  sulphuric  acid  for  water  did  not  therefore 
cause  the  reaction.  Alcohol  may  moreover  be  distilled  with  a  large 
excess  of  caustic  potassa,  or  its  vapours  be  passed  over  potassa  heated 
to  any  temperature,  without  ether  being  formed,  and  yet  potassa 
has  a  greater  affinity  for  water  than  sulphuric  acid. 

As  by  the  direct  mixture  of  alcohol  with  sulphuric  acid  sulpho- 
vinic  acid  is  formed,  it  might  be  supposed  that  this  acid  plays  a 
part  in  the  phenomenon :  it  might,  for  example,  be  assumed  that 
when  the  alcohol  comes  into  contact  with  the  sulphuric  acid,  the 
temperature  is  depressed  by  the  arrival  of  cold  alcohol  sufficiently 
to  allow  sulphovinic  acid  to  form,  and  that  this  acid,  expanding 
afterward  in  the  heated  mixture,  is  decomposed  into  ether  and  sul- 
phuric acid.  But  it  must  be  remembered  that,  by  placing  in  the 
flask  A  (fig.  675)  sulphuric  acid  diluted  with  water  sufficient  to  make 
it  boil  naturally  at  293°  under  the  ordinary  pressure  of  the  atmo- 
sphere, and  by  passing  into  the  acid  vapours  of  alcohol  heated  to 
212°  or  over,  there  distils  constantly  a  mixture  of  ether  and  water, 
with  a  small  quantity  of  alcohol ;  which  arises  from  the  circumstance 
that  a  portion  of  the  alcoholic  vapours  escape  the  action  of  the  sul- 
phuric acid.  It  is  difficult  to  admit  that  sulphovinic  acid  is  formed 
in  this  case,  for  it  would  be  necessary  to  grant  that  the  acid  was 
formed  and  decomposed  under  the  same  circumstances. 

The  transformation  of  alcohol  into  ether  by  sulphuric  acid  is 
therefore  as  yet  an  unexplained  ph^omenon,  unless  we  admit  that 
sulphuric  actd  here  e'xerts  an  actisfcof  presence,  or  catalytic  ac- 
tion ;  whicb  is  putting  a  word  in  the  ffcice  of  a  fact. 

A  highly  concentrated  solution  of  phosphoric  acid  also  converts 
alcohol  when  hot  into  ether  and  water,  but  the  water  is  retained  by 
the  phosphoric  acid;  and  when  it  is  sufficiently  hydrated,  it  no 
longer  acts  on  the  alcohol.  Several  chlorides  and  fluorides,  for  ex- 
ample the  chloride  of  boron,  effect  the  same  transformation,  as  well 
as  several  metallic  chlorides.  The  anhydrous  chloride  of  zinc  dis- 
solves largely  in  alcohol ;  and  if  the  liquor  be  distilled,  alcohol  first 
passes  over ;  but  the  temperature  now  rising  above  392°,  a  large 
quantity  of  ether,  which  distils  over  with  the  alcohol,  is  formed  ;  and 
if  the  heat  be  continued,  two  carburetted  hydrogens  pass  over  with 
the  ether ;  the  formula  of  one,  which  boils  below  212°,  being  CgHg, 
and  the  density  of  its  vapour  3.96,  while  the  formula  of  the  second, 
which  boils  at  about  572°,  and  is  of  a  syrupy  consistence,  is  C^Hy. 
It  should  be  remarked  that  CJlg+GJly==4tCJifi^—SIlO  ;  thus,  4 
equiv.  of  alcohol  would  yield  1  equiv.  of  each  of  these  substances, 
by  losing  8  equiv.  of  water. 

Ether  is  manufactured  on  a  large  scale  by  a  continuous  process 

,  analogous  to  that  just  described ;  the  distillation  being  arrested 

when  the  sulphuric  acid  has  transformed  into  ether  a  weight  of 


ETHER.      .  '  519 

alcohol  30  or  40  times  greater  than  its  own ;  for  if  it  were  con- 
tinued for  a  longer  time,  the  ether  would  be  impure  and  contain  a 
considerable  quantity  of  oil  of  wine.  The  ether  collected  in  the 
receiver  is  shaken  with  a  small  quantity  of  water,  which  dissolves 
the  greater  portion  of  the  alcohol  it  contains,  after  which  it  is 
mixed  with  milk  of  lime,  and  distilled  after  some  time  in  a  water- 
bath.  The  lime  retains  the  acid  products  which  the  ether  may 
contain,  while  the  ether  distilled  still  retains  water  and  alcohol ;  to 
free'  it  entirely  from  which  it  must  be  digested  with  a  large  quan- 
tity of  powdered  chloride  of  calcium  and  distilled  by  means  of  a 
water-bath. 

When  the  alcohol  which  is  to  be  converted  into  ether  contains  a 
large  proportion  of  water,  or  when  the  sulphuric  acid  is  very  aque- 
ous, ether  is  not  generated,  but  water  and  alcohol  pass  over.  If 
the  alcohol  is  in  excess,  it  passes  over  isolated  until  the  residue 
contains  alcohol  and  sulphuric  acid  in  the  proportions  which  form 
ether,  and  then  the  ordinary  transformation  into  ether  and  water 
commences. 

By  rectifying  considerable  quantities  of  crude  ether  over  lime,  a 
yellow  oleaginous  liquid  remains  in  the  distilling  vessel,  which, 
being  distilled  several  times  over  lime  and  then  over  potassium, 
becomes  fluid  and  completely  colourless.  Its  density  is-0.897,  and 
it  boils  at  545°.  This  carburetted  hydrogen  is  probably  furnished 
by  the  impure  alcohol  used  in  the  preparation  of  ether. 

§  1332.  Ether  is  a  colourless,  very  fluid  liquid,  of  an  agreeable 
and  pungent  odour,  and  an  acid  and  burning  taste.  Its  density  at 
32°  is  0.736,  and  it  boils  at  95.9°  under  the  pressure  of  29.92 
inches,  the  density  of  its  vapour^  being  2.586.  Its  composition  is 
expressed  by 

4  eq.  of  carbon 24  65.31 

5  "      hydrogen 5  13.33 

1  "      oxygen ^  21.36 

37  100.00 

One  vol.  of  vapour  of  ether  contains 

2  vol.  of  vapour  of  carbon 1.6876 

5      "      hydrogen 0.3465 

J      "      oxygen 0.5528 

2.5869 

and  its  equivalent  C^H^O  is  therefore  represented  by  2  volumes 
of  vapour. 

Ether  is  very  inflammable,  and  burns  with  a  flame  possessing  a 
certain  degree  of  brilliancy,  and  depositing  lamp-black  on  cold 
substances  introduced  into  it.  Being  extremely  volatile,  it  evapo- 
rates rapidly  in  the  air,  producing  detonating  mixtures  which  have 
occasioned  serious  accidents. 


520 


TRANSFORMATIONS   OF  ALCOHOL. 


Ether  is  soon  changed  by  the  oxygen  of  the  air,  which  converts 
it  into  acetic  acid ;  and  in  order  to  preserve  it  in  a  state  of  purity, 
it  should  be  kept  in  well-stoppered  bottles,  completely  filled,  or. 
better  still,  in  tubes  hermetically  closed.  The  alteration  is  more 
rapid  under  the  influence  of  alkaline  bases.  Ether  dissolves  in  9 
parts  of  water ;  and  if  a  larger  quantity  of  ether  be  added,  the  por- 
tion which  does  not  dissolve  floats  on  the  water.  Ether  also  dis- 
solves a  small  quantity  of  water,  while  alcohol  and  ether  dissolve 
each  other  in  all  proportions. 

Ether  dissolves  about  ^  of  sulphur  and  ^^  of  phosphorus,  which 
substances  separate  in  the  form  of  crystals  after  evaporation.  Chlo- 
rine and  bromine  act  powerfully  on  ether,  and  yield  peculiar  pro- 
ducts, which  shall  soon  be  described ;  while  iodine  at  first  simply 
dissolves  in  it,  but  is  changed  in  a  short  time. 

Ether  exerts  an  energetic  action  on  the  animal  economy :  its 
vapour  being  rapidly  absorbed  by  the  respiratory  organs,  soon 
causes  a  kind  of  intoxication,  accompanied  by  insensibility,  which 
curious  efi'ect  has  been  latterly  applied  as  an  anaesthetic  agent  in 
surgical  operations. 


BICARBURETTED  HYDROGEN,  OR  OLEFIANT  GAS,  C«H,. 

§  1333.  When  an  excess  of  concentrated  sulphuric  acid  acts  upon 
alcohol  at  a  temperature  of  320°  or  over,  only  a  small  quantity  of 
ether  results,  while  a  gaseous  carburetted  hydrogen  of  the  formula 
C^H^  is  formed.  On  comparing  the  formula  of  this  body  with  that 
of  alcohol,  it  would  be  natural  to  explain  the  decomposition  by  as- 
suming that  sulphuric  acid  determines  the  formation  of  2  equiv.  of 
water,  which  combine  with  it,  and  that  it  sets  free  bicarburetted 
hydrogen  C^H^. 

C,H,0,==C,H,-f2H0. 

But  the  following  experiment  seems  to  contradict  this  explanation, 
Having  placed  in  the  flask  A  (fig.  676)  concentrated  sulphuric  acid, 

to  which  a 
quantity  of 
water  has 
been  added, 
such  that 
the  mixture 
shall  boil  at 
about  320°, 
(for  which 
purpose  100 
p  a  r  ts  of 
m  0  n  0  h  y- 
drated  sul- 
Fig.  676.  phuric  acid 


OLEFIANT   GAS.  621 

and  30  of  water  must  be  used,)  the  acid  is  heated  to  boiling.  The 
flask  B  contains  absolute  alcohol,  which  is  heated  to  ebullition,  and 
the  vapours  of  alcohol  traverse  the  flask  A,  the  temperature  of 
which  is  kept  constantly  at  about  329°,  by  allowing  more  or  less 
alcohol  to  enter,  and  by  increasing  or  diminishing  the  flame  of  the 
lamp  which  heats  the  flask.  Olefiant  gas  is  disengaged  in  the  form 
of  small  bubbles  from  the  acid  mixture,  and  carries  over  vapours  of 
water  and  alcohol,  which  condense  in  the  bottle  C,  while  the  gas 
may  be  collected  in  a  gasometer,  or  in  bottle  D  over  a  pneumatic 
trough.  The  alcohol  carried  over  is  that  which  has  escaped  the 
action  of  the  sulphuric  acid,  and  the  water  which  distils  is  exactly 
equal  to  that  which  would  form  alcohol  with  the  bicarburetted  hy- 
drogen; while  the  acid  liquor  in  the  flask  A  retains  the  same  com- 
position, and  can  convert  an  almost  indefinite  quantity  of  alcohol 
into  bicarburetted  hydrogen  and  water;  very  little  ether  being 
formed.  The  experiment  shows  that  the  decomposition  of  alcohol 
into  bicarburetted  hydrogen  and  water,  by  contact  with  sulphuric 
acid,  is  not  owing  to  the  afiinity  of  the  acid  for  water,  since  water 
and  olefiant  gas  are  both  disengaged  at  the  same  time. 

Bicarburetted  hydrogen  is  generally  prepared  in  the  laboratory 
by  heating  a  mixture  of  1  part  of  alcohol  at  0.85  and  6  parts  of 
concentrated  sulphuric  acid  in  a  retort,  (fig.  285,)  which  should  be 
only  be  J  filled;  the  gas  evolved  being  made  to  pass  first  through 
a  bottle  containing  concentrated  sulphuric  acid,  which  retains  the 
vapours  of  alcohol  and  ether,  and  then  through  a  second  bottle  con- 
taining a  solution  of  caustic  potassa,  to  absorb  the  sulphurous  acid 
and  carbonic  acid  which  are  copiously  evolved  toward  the  close  of 
the  operation;  the  cause  of  which  evolution  is  the  reaction  which 
ensues  between  the  concentrated  sulphuric  acid  and  the  carbona- 
ceous substances  remaining  in  the  retort.  The  disengagement  of 
gas,  which  is  pretty  regular  at  the  commencement  of  the  operation, 
soon  becomes  tumultuous  and  violent,  when  the  acid  mixture  turns 
black,  becomes  viscous,  and  swells  to  such  a  degree  that  if  the  re- 
tort be  not  very  large  it  will  fill  the  neck.  At  the  end  of  the  ex- 
periment there  remains  in  the  retort  a  solid  black  substance,  which 
gives  oif  to  water  sulphuric  acid,  and  sulphovinic  acid,  or  an  iso- 
meric of  it ;  while  the  composition  of  the  black  insoluble  residue  is 
very  complex,  and  corresponds  to  the  formula  CgoHg^OaoSg. 

§  1334.  Bicarburetted  hydrogen  is  a  colourless  g^s  which  does  not 
liquefy  at  the  lowest  temperatures :  its  density  is  0.978,  and  it  burns 
with  a  very  brilliant  flame,  which  deposits  a  large  quantity  of  lamp- 
black on  cold  substances  immersed  in  it.  When  passed  through  a 
procelain  tube  heated  to  redness,  charcoal  is  deposited  on  the  sides 
of  the  tube,  and  it  is  transformed  into  protocarburetted  hydrogen ; 
but  if  the  temperature  is  more  elevated,  all  the  carbon  is  deposited, 
and  hydrogen  only  disengaged.     The  formula  of  bicarburetted  hy- 


522  TRANSFORMATIONS   OF  ALCOHOL. 

drogen  is  C^H^,  (266,)  and  its  equivalent  is  represented  by  4  vo- 
lumes of  gas. 

§  1335.  Bicarburetted  hydrogen  combines  with  anhydrous  sul- 
phuric acid,  forming  a  white  compound,  fusible  at  about  176°,  and 
of  the  formula  €4114,4803,  which  has  been  improperly  called  sul- 
phate of  carhyle.  In  order  to  prepare  it,  olefiant  gas,  totally  free 
from  ether,  and  vapours  of  anhydrous  sulphuric  acid,  are  passed 
simultaneously  into  a  U-tube,  when  the  combination  takes  place  with 
great  elevation  of  temperature,  while  the  substance,  which  is  at 
first  liquid,  solidifies  into  a  radiated  crystalline  mass  on  the  sides  of 
the  tube.  In  order  to  purify  it,  it  is  left  for  several  days  in  vacuo, 
over  a  cup  containing  caustic  potassa,  which  absorbs  the  vapours  of 
the  anhydrous  sulphuric  acid. 

The  same  product  is  formed  by  placing  an  open  tube  containing 
absolute  alcohol  in  a  bottle  containing  anhydrous  sulphuric  acid, 
and  allowing  the  bottle,  after  being  well  corked,  to  rest  for  several 
days.  The  vapours  of  alcohol  and  sulphuric  acid  combine  and  sul- 
phate of  carbyle  is  formed,  but  the  latter  is  injured  by  hydrated 
sulphuric  acid,  from  which  it  is  freed  with  difficulty.  The  reaction 
in  this  case  is  expressed  by  the  following  equation : 

CA0,+6S03=C4H4,4S03+2(S03,H0). 

Sulphate  of  carhyle  absorbs  moisture  from  the  air;  and  if  the 
absorption  take  place  slowly,  and  without  any  elevation  of  tempera- 
ture, a  peculiar  acid,  called  ethionic,  is  obtained,  of  which  the  for- 
mula is  041150,4803.  This  acid  forms,  with  baryta,  a  salt  soluble 
in  water  but  insoluble  in  alcohol;  and  it  yields  crystallizable  salts 
with  the  majority  of  bases. 

By  boiling  the  solution  of  ethionic  acid  for  a  few  moments,  or  by 
dissolving  the  sulphate  of  carbyle  in  hot  water,  a  new  acid,  called 
isethionic,  is  obtained,  presenting  the  same  composition  €41150,2803 
as  sulphovinic  acid,  while  the  liquid  contains  free  sulphuric  acid.  Is- 
ethionic  acid  differs  from  sulphovinic  acid  by  being  much  more  fixed, 
as  its  solution  may  be  boiled  indefinitely  without  undergoing  any 
change.  Isethionates  are  also  much  more  stable  than  sulphovinates, 
for  they  bear  without  decomposition  temperatures  of  400°  or  550°. 

Action  of  Chlorine,  Bromine,  and  Iodine  on  Bicarburetted 
Hydrogen. 

§  1336.  By  causing  chlorine  in  greater  or  less  quantity  to  act 
upon  bicarburetted  hydrogen,  and  under  the  influence  of  a  more  or 
less  intense  degree  of  light,  various  products  result,  which  shall  be 
mentioned:  if  both  gases,  moist,  and  in  nearly  equal  volumes,  be 
introduced  into  a  large  flask  exposed  to  the  diff'use  light  of  day, 
they  combine  with  evolution  of  heat,  and  an  oleaginous  liquid  trickles 
down  the  sides  of  the  flask.  If  the  gases  were  dry,  reaction  would 
ensue  under  the  influence  of  direct  solar  light. 


DUTCH    LIQUID. 


523 


When  any  considerable  quantity  of  this  product  is  to  be  prepared, 
the  apparatus  must  be  arranged  as  represented  in  fig.  677.  A  is  a 
large  retort,  in  which  is  prepared  the  olefiant  gas  which  traverses 
the  washing  bottle  B  containing  concentrated  sulphuric  acid,  which 
retains  the  vapours  of  alcohol  and  ether,  and  then  the  bottle  C  con- 


Fig.  677. 

taining  a  solution  of  potassa  to  absorb  the  sulphurous  and  carbonic 
acids:  whence  it  passes  into  a  flask  D  having  3  tubulures,  which 
also  receives  the  chlorine  disengaged  from  the  flask  G,  having 
been  made  to  traverse  the  water  in  the  bottle  F.  The  ends  of  the 
tubes  which  convey  the  two  gases  into  the  flask  D  are  placed  op- 
posite to  each  other,  so  that  the  gases  may  mix  immediately ;  while 
the  liquid  formed  falls  through  the  lower  part  of  the  flask  into  a 
well-cooled  bottle  E;  the  excess  of  gas  escaping  by  the  same 
tubulure.  The  liquid  obtained  is  shaken  several  times  with  water, 
and  then  distilled  again  and  again,  alternately  with  sulphuric  acid 
and  potassa,  which  destroy  a  small  quantity  of  the  foreign  sub- 
stances produced  by  the  reaction  of  chlorine  on  the  vapour  of  ether 
which  accompanies  olefiant  gas  when  the  evolution  of  the  gas  is  too 
rapid.  If  the  operation  be  continued  for  a  long  time,  by  exhausting 
the  action  of  the  sulphuric  acid  on  the  alcohol,  it  frequently  hap- 
pens toward  the  close  that  the  potassa  of  the  bottle  C  passes  into 
the  state  of  bisulphite  of  potassa,  and  the  sulphurous  acid  is  no 
longer  absorbed;  in  which  case  a  certain  quantity  of  chlorosul- 
phuric  acid  (§  132)  is  obtained  intimately  mixed  with  the  principal 
product.  The  liquid  condensed  in  the  bottle  E,  which  then  pos- 
sesses a  sulphurous,  acid,  and  extremely  penetrating  odour,  becomes 
heated  when  it  is  shaken  with  water,  and  yields  a  large  quantity  of  sul- 
phuric and  chlorohydric  acids,  arising  from  the  decomposition  of  the 
chlorosulphuric  acid.  It  is  important  to  remark  that  chlorine  and 
sulphurous  acid,  alone,  do  not  combine  in  the  presence  of  the  most 
intense  solar  rays,  while  in  the  presence  of  bicarburetted  hydrogen 


524  TRANSFORMATIONS   OF  ALCOHOL. 

the  combination  takes  place  in  diffuse  light.  The  chlorine  and 
bicarburetted  hydrogen,  which,  when  dry,  exert  no  action  on  each 
other  in  diffuse  light,  combine,  on  the  contrary,  very  readily,  when 
sulphurous  acid  exists  in  the  mixture ;  the  latter  then  forming 
chlorosulphuric  acid  with  a  portion  of  the  chlorine.  The  formation 
of  one  of  these  compounds  assists,  therefore,  the  production  of  the 
other. 

The  product  resulting  from  the  combination  of  1  vol.  of  chlorine 
with  1  vol.  of  defiant  gas,  which  has  long  been  known  under  the 
name  of  Dutch  liquid^  because  it  was  discovered  by  an  association 
of  chemists  in  Holland,  is  a  colourless  liquid,  of  an  agreeable  odour. 
Its  density  is  1.280  at  32°,  and  it  boils  at  184.1°.  The  density 
of  its  vapour  being  3.45,  its  composition  is  represented  by  the  for- 
mula C4H4CI2,  which  corresponds  to  four  volumes  of  vapour,  but  it 
is  generally  written  C4H3C1,HC1,  from  the  manner  in  which  the 
substance  behaves  with  an  alcoholic  solution  of  potassa. 

§  1337.  Dutch  liquid  is  not  decomposed  by  an  aqueous  solution 
of  potassa,  and  may  be  distilled  with  it  without  any  apparent 
change ;  while  if  it  be  dissolved  in  an  alcoholic  solution  of  potassa, 
it  is  immediately  decomposed,  and  a  large  quantity  of  chloride  of 
potassium  is  deposited,  while  the  alcohol  contains  in  solution  a  new 
and  very  volatile  substance.  In  order  to  separate  it,  the  liquid  must 
be  distilled  in  a  water-bath  slightly  heated,  and  the  gas  disengaged 
must  be  passed  first  through  an  apparatus  containing  concentrated 
sulphuric  acid,  which  retains  the  vapours  of  the  alcohol,  and  then 
into  a  receiver  reduced  to  a  low  temperature  by  a  mixture  of  ice  and 
chloride  of  calcium.  A  very  volatile  liquid  condenses  in  the  re- 
ceiver, boiling  below  32°,  having  a  sharp  and  slightly  alliaceous 
smell,  and  of  which  the  composition  corresponds  to  the  formula 
C4H3CI,  represented  by  4  vol.  of  vapour.  The  composition  of  this 
substance  is  exactly  the  same  as  that  of  bicarburetted  hydrogen,  ex- 
cept that  1  equiv.  of  hydrogen  is  replaced  by  1  equiv.  of  chlorine. 
Dutch  liquid  may  itself  be  considered  as  a  combination  of  the  substance 
C4H3CI  and  chlorohydric  acid.  When  the  chlorine  reacts  on  the  bicar- 
buretted hydrogen,  1  equivalent  of  chlorine  abstracts  1  equivalent  of 
hydrogen  to  form  1  equivalent  of  chlorohydric  acid,  while  the  place 
thus  made  empty  in  the  molecule  of  defiant  gas  is  immediately  filled 
by  1  equivalent  of  chlorine,  forming  1  equivalent  of  monochlori- 
nated  bicarburetted  hydrogen,  which  remains  in  combination  with 
the  equivalent  of  chlorohydric  acid  formed. 

§  1338.  The  action  of  chlorine  on  bicarburetted  hydrogen  is  not 
confined  to  the  abstraction  of  but  one  equivalent  of  hydrogen  and 
its  replacement  by  1  equiv.  of  chlorine  ;  and  the  other  three  equiva- 
lents of  hydrogen  may  successively  be  replaced  by  a  corresponding 
number  of  equivalents  of  chlorine,  thus  furnishing  the  series  of  pro- 
ducts ; 


DUTCH   LIQUID.  525 

C^H^      and  their  compounds  with  chlorohydric  acid. 
C.HgCl  "  "  C,H3C1,HC1. 

C,H,C1,  "  "  C,H,C1„HC1. 

C,HCl3  «     '  "  C,HCl3,HCl. 

C,C1,  «  "  C,C1„HC1. 

On  passing  dry  chlorine  through  Dutch  liquid,  the  latter  will  be 
found  to  dissolve  it  largely,  and  if  the  bottle  be  then  placed  in  the 
sun,  a  powerful  reaction  ensues,  a  large  quantity  of  chlorohydric  acid 
being  disengaged,  while  the  liquid  is  completely  discoloured ;  and  by 
repeatedly  saturating  it  with  chlorine,  and  exposing  it  to  the  rays  of 
the  sun,  at  properly  regulated  intervals,  Dutch  liquid  may  be  con- 
verted into  a  less  volatile  product,  which  boils  at  239°,  and  of  which 
the  density  in  the  liquid  state  is  1.422,  while  that  of  its  vapour  is 
4.60.  The  formula  of  this  substance  being  C4H3CI3,  it  will  be  re- 
cognised as  Dutch  liquid,  in  which  1  equiv.  of  hydrogen  is  replaced 
by  1  equiv.  of  chlorine.  The  same  product  is  formed  when  chlorine  is 
caused  carefully  to  act  upon  monochlorinated  bicarburetted  hydro- 
gen C4H3CI,  but  it  is  more  easily  obtained  by  passing  the  latter 
substance  in  the  state  of  gas  through  the  perchloride  of  antimony 
SbgOj,  which  dissolves  it  freely.  When  the  perchloride  of  antimony- 
is  saturated,  it  is  distilled,  and  a  colourless  liquid,  consisting  of 
C4H3CI3,  or  monochloruretted  Dutch  liquid,  is  collected.  The  for- 
mula of  this  substance  may  be  written  C4H3Cl2,HCl  for  the  same 
reasons  which  have  been  stated  for  Dutch  liquid.  In  fact,  on  dis- 
solving monochlorinated  Dutch  liquid  in  an  alcoholic  solution  of 
potassa,  a  precipitate  of  chloride  of  potassium  is  formed,  and  a  liquid 
of  which  the  formula  is  (jjlju\  separates  by  distillation.  The 
density  of  this  liquid,  which  may  be  considered  as  hichlorinated  hi- 
carburetted  hydrogen,  is  1.250,  and  it.  boils  between  95°  and  104°. 
The  density  of  its  vapour  3.35,  and  the  equivalent  C^HaCla  there- 
fore correspond  to  4  vol.  of  vapour  like  that  of  defiant  gas. 

By  operating  on  monochlorinated  Dutch  liquid  C^H3Cl2,HCl,  in 
the  same  manner  as  has  been  explained  for  the  original  liquid 
C4H3C1,HC1,  the  chlorine  again  abstracts  hydrogen  in  the  state  of 
chlorohydric  acid,  while  a  substance  results  which  may  be  con- 
sidered as  hichlorinated  Dutch  liquid,  and  of  which  the  formula  is 
C^HgCl^.  The  density  of  this  substance  is  1.576:  it  boils  at  275°, 
the  density  of  its  vapour  being  5.79,  so  that  the  equivalent  QJlfi\ 
is  again  represented  by  4  vol.  of  vapour. 

We  shall  write  the  formula  of  this  product  CHClgjHCl,  because, 
in  contact  with  an  alcoholic  solution  of  potassa,  it  is  decomposed 
into  chlorohydric  acid,  which  combines  with  the  potassa,  and  into  a 
new  substance  C4HCI3,  which  is  trichlorinated  bicarburetted  hy- 
drogen. 

Bichlorinated  Dutch  liquid,  subjected  again  to  the  action  of  chlorine 
in  the  manner  above  indicated,  is  converted  into  trichlorinated  Dutch 


526  TRANSFORMATIONS   OF  ALCOHOL. 

liquid  C4HCI5,  which  hoils  at  307°,  and  the  density  of  which  at 
32°  is  1.663,  while  that  of  its  vapour  is  7.08,  and  the  equivalent 
C^HClg  is  therefore  still  represented  by  4  vol.  of  vapour.  The  for- 
mula C4HCI5  may  be  written  C^Cl^jHCl,  because  this  substance, 
in  contact  with  an  alcoholic  solution  of  potassa,  is  decomposed  and 
yields  the  product  C^Cl^,  which  should  be  considered  as  quadrichlo- 
rinated  or  perchlorinated  hicarhuretted  hydrogen,  all  the  hydrogen 
of  the  defiant  gas  being  here  replaced  by  an  equivalent  quantity 
of  chlorine,  while  the  new  substance  is  a  simple  chloride  of  carbon, 
but  its  composition  is  still  the  same  as  that  of  bicarburetted  hydro- 
gen, since  its  formula  corresponds  to  4  vol.  of  vapour. 

The  density  of  chloride  of  carbon  C^Cl^  is  1.61 :  it  boils  at  251.6°. 

Finally,  by  treating  trichlorinated  Dutch  liquid  C^HCl^  with 
an  excess  of  chlorine,  in  the  sun,  it  loses  the  last  equivalent  of  hy- 
drogen, which  is  replaced  by  1  equiv.  of  chlorine,  when  a  chloride 
of  carbon  C^Clg,  which  may  be  considered  as  quadriehlorinated  or 
perchlorinated  Dutch  liquid,  is  formed.  This  chloride  of  carbon, 
sometimes  called  sesquichloride  of  carbon  on  account  of  its  compo- 
sition, is  solid  and  crystalline,  having  a  peculiar  aromatic  smell,  and 
is  readily  purified  by  dissolving  it  in  boiling  alcohol,  when  the  liquid 
deposits  the  chloride  of  carbon,  on  cooling,  in  the  form  of  small 
white  crystals,  which  melt  at  320°,  while  the  substance  boils  at  356°. 
The  density  of  its  vapour  being  8.16,  the  equivalent  C^Clg  is  there- 
fore represented  by  4  vol.  of  vapour. 

The  chloride  of  carbon  C^Cl^,  of  the  series  of  bicarburetted  hy- 
drogen, combines  readily  with  chlorine,  and  is  converted  into  solid 
chloride  of  carbon  C^Clg,  of  the  series  of  Dutch  liquid  ;  while,  reci- 
procally, the  chloride  of  carbon  C^Clg  is  readily  transformed  into 
chloride  of  carbon  C^Cl^.  By  passing  the  vapour  of  the  chloride 
of  carbon  C^Clg  through  a  tube  heated  to  redness,  it  is  converted  into 
chloride  of  carbon  C^Cl^  and  chlorine ;  but  it  is  difficult  by  this  me- 
thod to  obtain  the  chloride  C^Cl^  pure,  on  account  of  the  facility 
with  which  it  combines  with  chlorine  when  it  passes  with  the  latter 
gas  into  the  receiver  in  which  it  is  condensed.  This  transforma- 
tion is  more  readily  effected  by  dissolving  the  chloride  of  carbon  in 
an  alcoholic  solution  of  sulf hydrate  of  sulphide  of  potassium,  when 
a  very  energetic  reaction  ensues  if  it  be  slightly  heated,  while  a  large 
quantity  of  sulfhydric  acid  is  disengaged.  The  chloride  of  carbon 
should  be  added  by  small  quantities  at  a  time,  and  too  great  an 
excess  of  sulf  hydrate  of  sulphide  of  potassium  must  be  avoided. 
When  the  solution  of  gas  ceases,  the  alcoholic  liquor  collected  in  the 
receiver  is  distilled  and  diluted  with  water,  when  the  chloride  of 
carbon  C^Cl^  is  deposited  in  the  form  of  a  colourless  liquid. 

§  1339.  There  exist,  therefore,  two  series  of  products  derived  from 
two  original  substances,  bicarburetted  hydrogen  C^H^  and  Dutch 
liquid  C^H^Clg,  by  the  successive  substitution  of  equivalent  quantities 
of  chlorine  for  hydrogen,  while  Dutch  liquid  itself  may  be  considered 


DUTCH   LIQUID.  527 

AS  being  derived,  by  the  same  mode  of  generation,  from  a  carbu- 
retted  hydrogen  C^Hg  as  yet  unknown. 

In  proportion  as  the  chlorine  thus  replaces  the  hydrogen,  the 
density  of  the  substance  increases,  and  its  boiling  point  rises; 
which  relations  are  easily  seen  in  the  following  tables : 

Series  of  Bicarhuretted  Hydrogen, 

Bicarburetted  hydrogen  C^H^,       gas  does  not  liquefy  at  any  tem- 
perature. 

Monochlorinated  bicar- 
buretted hydrogen...  C^HgCl,  boils  at  about  14°. 

Bichlorinated    bicarbu- 
retted hydrogen QJlJu\,  boils  at  95°,  density  1.250. 

Trichlorinated  bicarbu- 
retted hydrogen C.HClg,      "  "  "  " 

Quadrichlorinated      bi- 
carburetted hydrogen  C,C1„         "    251.6°,       "       1.619. 

Series  of  Butch  Liquid, 
Carburetted    hydrogen  , 

(unknown) C^Hg. 

Dutch  liquid C^H.Cla  boils  at  180.5°,  density  1.256. 

Monochlorinated  Dutch 

liquid C,H3Cl3      "         239°,       "      1.422. 

Bichlorinated        Dutch 

liquid C,H,C1,      "         275°,      «      11576. 

Trichlorinated      Dutch 

liquid C.HCl,       "      307.4°,      «      1.619. 

Quadrichlorinated 

Dutchliquid C.Clg  "  356°. 

In  all  these  products,  the  equivalent  is  represented  by  4  volumes  of 
vapour,  and  it  may  be  admitted  that  the  substances  of  the  same  series 
present  the  same  molecular  grouping^  and  only  differ  from  each  other 
in  the  chemical  nature  of  one  of  their  elements,  hydrogen,  which  is 
more  or  less  completely  replaced  by  equivalent  quantities  of  chlorine. 

§  1340.  Bromine  also  combines  with  bicarburetted  hydrogen,  and 
yields  a  substance  C^H^Br^  which  corresponds  exactly  to  Dutch 
liquid.  It  is  prepared  by  dropping  bromine  into  a  current  of  bicar- 
bui'etted  hydrogen;  when  the  bromine  is  almost  instantaneously 
discoloured  and  converted  into  an  etherial  liquid,  the  odour  of  which 
resembles  that  of  Dutch  liquid.  In  order  to  purify  it,  it  is  washed 
with  a  small  quantity  of  water,  and  then  distilled  several  times, 
alternately,  over  concentrated  sulphuric  acid  and  baryta.  The 
density  of  the  liquid  is  2.16  at  69.8°  ;  it  boils  at  271.4°,  and  so- 
lidifies at  55.4°  into  a  white  crystalline  mass  resembling  camphor. 
Its  equivalent  is  represented  by  4  volumes. 

The  product  C^H^Brg  undergoes,  by  distillation  with  an  aboholic 


528  TRANSFOKMATIONS   OF   ALCOHOL. 

solution  of  potassa,  a  decomposition  analogous  to  that  experienced 
by  Dutch  liquid ;  bromide  of  potassium  and  a  gas  C^HgBr,  which 
condenses  readily  in  a  mixture  of  ice  and  sea-salt,  being  formed.  It 
is  monohrominated  bicarburetted  hydrogen^  and  its  density  is  about 
1.52,  while  the  density  of  its  vapour  is  3.64,  and  its  equivalent  is 
represented  by  4  volumes  of  vapour. 

Bromine  attacks  monohrominated  bicarburetted  hydrogen,  and 
converts  it  into  a  liquid  C^HgBrg  which  corresponds  to  monochlo- 
rinated  Dutch  liquid.  The  action  of  bromine  does  not  appear  to 
extend  any  further,  even  by  long  exposure  to  the  rays  of  the  sun. 

§  1341.  If  bicarburetted  hydrogen  be  passed  to  the  bottom  of  a 
matrass  containing  iodine  and  heated  to  120°  or  140°,  the  iodine 
soon  fuses,  and  yellowish  needles,  which  become  completely  white 
by  the  prolonged  action  of  the  olefiant  gas,  condense  in  the  neck 
of  the  matrass ;  by  treating  which  with  alkaline  or  ammoniacal 
water,  a  crystalline  substance  C^H^Ig  is  obtained  corresponding 
to  Dutch  liquid.  This  substance  becomes  slightly  yellow  by  dry- 
ing, but  recovers  its  whiteness  when  exposed  to  a  current  of  bicar- 
buretted hydrogen.  It  has  an  ether-like,  sharp,  and  penetrating 
odour,  causing  a  flow  of  tears  ;  and '  light  decomposes  it  spontane- 
ously. It  melts  at  167°,  but  is  destroyed  at  a  temperature  slightly 
above  that  point.  Potassa  dissolved  in  alcohol  decomposes  it,  and 
produces  moniodinated  bicarburetted  hydrogen  C^Hgl,  which  is  a 
volatile  liquid ;  while  the  greater  part  of  the  product  is  still  further 
decomposed  and  yields  a  gaseous  carburetted  hydrogen. 

By  decomposing  Dutch  liquid  by  alcoholic  solutions  of  mono- 
sulphide  of  potassium,  solid  products  result,  in  which  the  sulphur 
replaces  the  chlorine  of  the  original  substances ;  but  these  products 
have  been  but  little  studied,  and  as  yet  only  the  compound  C^H^S^, 
which  corresponds  to  Dutch  liquid,  is  known  with  certainty. 

Oil  of  Wine,* 

§  1342.  During  the  preparation  of  ether  or  bicarburetted  hydro- 
gen by  the  reaction  of  concentrated  sulphuric  acid  on  alcohol,  a 
certain  quantity  of  a  very  heavy  oily  substance,  called  heavy  oil  of 
wine,  which  dissolves  in  ether,  but  separates  from  it  when  it  is 
diluted  with  a  sufficient  quantity  of  water,  is  constantly  formed. 
The  best  method  of  preparing  it  consists  in  heating  1  part  of  abso- 
lute alcohol  and  2J  parts  of  concentrated  sulphuric  acid,  and  first 
collecting  the  products  in  a  bottle  kept  at  the  temperature  of  95° 
or  104°,  in  which  very  little  ether,  but  the  greater  portion  of  the 
heavy  oil  of  wine  condenses ;  and  then  in  a  second  cold  receiver, 
if  the  ether  is  to  be  preserved.  The  same  substance  is  obtained  by 
decomposing  by  heat  well-dried  sulphovinates.  It  is  washed  several 
times  with  cold  water,  in  order  to  remove  the  alcohol,  ether,  the 
sulphurous  and  sulphuric  acids  which  impurify  it,  and  then  exposed 
for  several  days  in  vacuo  over  concentrated  sulphuric  acid,  in  order 


ETHERS.  529 

to  absorb  the  water.  It  is,  however,  difficult  to  obtain  a  uniform 
composition  of  the  substance,  and  chemists  are  not  agreed  as  to  its 
nature.  From  analyses  most  worthy  of  confidence,  its  formula 
would  be  CgH90,2S03,  although  it  may  possibly  be  true  sulphuriG 
ether  CJlfi,&0^,  belonging  to  the  series  of  compound  ethers  of 
which  we  are  about  to  treat,  and  mixed  with  a  small  quantity  of 
foreign  substances,  principally  carburetted  hydrogen,  which  may, 
in  fact,  be  separated  from  it.  It  is  sufficient  to  digest  heavy  oil  of 
wine  for  some  time  with  hot  water,  or  better  still,  with  an  alkaline 
liquid,  in  order  to  decompose  it  into  sulphovinic  acid  and  a  light  oil 
having  the  same  elementary  composition  as  bicarburetted  hydrogen, 
but  the  boiling  point  of  which  is  as  high  as  536^.  It  is  not  yet 
decided  whether  this  latter  substance  is  a  product  of  the  decompo- 
sition of  heavy  oil  of  wine,  or  if  it  be  merely  mixed  with  it.  This 
oily  carburetted  hydrogen,  allowed  to  rest  for  some  time,  deposits 
crystals  which  are  purified  by  pressing  them  between  tissue-paper, 
and  the  composition  of  which  is  the  same  as  that  of  liquid  carbu- 
retted hydrogen :  they  melt  at  230°,  and  distil  at  320°. 

COMPOUND  ETHERS  AND  VINIC  ACIDS. 

§  1343.  The  action  of  acids  on  alcohol  calls  into  existence  nume- 
rous compounds,  formed  by  the  combination  of  1  equiv.  of  ether 
C^H^O  with  1  or  2  equiv.  of  acid.  Compounds  containing  2  equiv. 
of  acid  are  powerful  acids,  which  accurately  saturate  the  bases,  and 
form  a  great  number  of  crystallizable  salts,  and  they  are  commonly 
called  vinic  acids ;  sulphovinic  acid,  the  preparation  and  properties 
of  which  we  have  described,  (§  1330,)  belonging  to  this  class.  The 
compounds  containing  only  1  equiv.  of  acid  are  neutral  with  re- 
agents, and  are  called  compound  ethers. 

Certain  acids,  such  as  oxalic  and  carbonic,  form  both  compounds, 
while  others,  as  phosphoric,  form  only  the  acid  compound,  vinic  acid ; . 
and,  lastly,  others,  as  nitric  and  acetic,  yield  the  neutral  compound 
alone.  The  majority  of  compound  ethers  may  be  distilled  without 
alteration,  but  are  decomposed  by  being  boiled  with  an  alkaline  so- 
lution ;  the  acid  of  the  compound  ether  generally  combining  with  the 
alkali,  while  the  ether  C^H^O  set  free  combines  with  1  equiv.  of  water 
to  form  alcohol.  Nearly  all  the  known  acids  are  capable  of  forming 
with  alcohol  compound  ethers  or  vinic  acids ;  and  we  shall  now  de- 
scribe such  of  these  compounds*  as  are  formed  by  mineral  acids  and 
some  organic  acids  already  described,  and  shall  refer  the  study  of 
the  others  to  those  chapters  in  which  the  properties  of  the  acid  en- 
tering into  their  composition  is  to  be  described. 

We  shall  not  again  touch  on  sulphovinic  acid,  which  has  been 
sufficiently  described,  (§1330;)  and  the  neutral  compound,  sul- 
phuric ether  C^H. 0,863,  ^^^  hitherto  not  been  obtained.* 

*  It  was  recently  formed  by  Dr.  C.  WetherilL — J.  C.  B 
Vol.  XL— 34 


530  TRANSFORMATIONS    OF   ALCOHOL. 

Phosphovinic  Acid  (C^H50+2H0),P05. 

§  1344.  Phosphovinic  acid  is  obtained  by  heating  for  some  time, 
at  a  temperature  of  176°,  equal  part^  of  absolute  alcohol  and  a 
syrupy  solution  of  phosphoric  acid ;  after  which  the  liquid  is  allowed 
to  rest  until  the  following  day,  when  it  is  diluted  with  water  and 
saturated  with  carbonate  of  baryta,  when  the  free  phosphoric  acid 
forms  an  insoluble  phosphate  with  baryta,  while  the  phosphovinate 
produced  with  this  base  is  soluble.  The  solution,  when  evaporated, 
deposits,  on  cooling,  crystals  of  phosphovinate  of  baryta,  which  is 
much  less  soluble  than  the  sulphovinate  :  at  104°,  its  greatest  point 
of  solubility,  100  parts  of  water  dissolve  only  9.3.  It  is  also  much 
more  fixed  than  the  sulphovinate,  for  it  may  be  heated  up  to  570° 
without  change.  By  dropping  sulphuric  acid  into  a  solution  of  phos- 
phovinate of  baryta,  the  baryta  is  precipitated  and  a  solution  of 
phosphovinic  acid  obtained,  which  may  be  boiled  without  alteration, 
and  which,  when  evaporated  to  the  consistence  of  syrup  in  the 
vacuum  of  an  air-pump,  deposits  crystals,  if  the  temperature  be  low. 
The  majority  of  the  phosphovinates  being  soluble  in  water,  are 
easily  prepared  by  double  decomposition,  by  pouring  the  sulphate 
of  the  base  into  a  solution  of  phosphovinate  of  baryta. 

Crystallized  phosphovinate  of  baryta  contains  12  equiv.  of  water 
of  crystallization,  which  may  be  driven  off  by  heat  without  altera- 
tion. The  formula  of  the  dried  salt  is  (2BaO  +  C4H30),P05;  jand 
it  presents,  therefore,  the  composition  of  the  tribasic  phosphates,  by 
admitting  that  ether  C^H^O  replaces  1  equiv.  of  base.  The  compo- 
sitions of  the  other  phosphovinates  are  analogous. 

No  neutral  compound  of  ether  with  phosphoric  acid  is  known. 

Nitric  Ether  Q^YLfi.l^O,. 

§  1345.  Nitric  acid  forms  with  ether  only  a  neutral  compound, 
nitric  ether ;  no  vinic  acid  having  hitherto  been  discovered. 

On  mixing  alcohol  with  nitric  acid  and  heating  it  gently,  a  violent 
reaction  ensues,  and  a  large  quantity  of  nitrous  gas  is  disengaged, 
while,  together  with  other  products,  there  results  an  ether  which  is 
not  nitric  ether  Q^fi^^O^,  but  nitrous  ether  (jfi^O^^O^.  Nitric 
ether  may,  however,  be  produced  by  the  direct  action  of  nitric  acid 
on  alcohol,  if  the  forming  of  nitrous  acid  be  avoided,  because  this 
acid,  on  account  of  its  more  powerfill  oxidizing  agency,  yields  very 
complicated  products.  It  is  effected  by  gently  heating  in  a  retort 
150  gm.  of  a  mixture  of  equal  parts  of  alcohol  at  0.85°  and  very  pure 
concentrated  nitric  acid,  of  the  density  of  1.4,  to  which  is  added  1  gm. 
of  urea,  an  organic  substance  which  shall  be  described  among  the 
products  of  the  animal  economy.  The  first  product  of  distillation 
is  composed  chiefly  of  alcohol  diluted  with  water,  but  the  nitric 
ether  itself  very  soon  distils  over,  and,  toward  the  close  of  the 
operation,  this  liquor  forms  a  denser  layer  at  the  bottom  of  the 


ETHERS.  531 

receiver.  The  operation  is  arrested  when  about  J  of  the  liquid  still 
remains  in  the  retort ;  and  in  order  to  separate  that  which  is  dis- 
solved in  the  supernatant  alcoholic  liquor,  water  is  added  to  it  and 
it  is  shaken ;  after  which  'the  ether  is  decanted,  washed  with  an 
alkaline  solution,  then  with  water,  and,  lastly,  it  is  distilled  over 
chloride  of  calcium. 

The  object  of  the  small  quantity  of  urea  added  to  the  mixture  is 
to  prevent  the  formation  of  nitrous  acid,  or  rather  to  effect  the 
destruction  of  this  acid  as  fast  as  it  is  formed.  The  urea  combines 
with  the  nitric  acid  and  constitutes  nitrate  of  urea,  which  compound 
is  readily  destroyed  by  contact  with  nitrous  acid,  the  two  substances 
being  converted  into  nitrogen,  water,  and  carbonic  acid.  Nitric 
ether  has  a  pleasant  and  sweet  smell,  and  a  saccharine  taste :  its 
density  is  1.112,  and  it  boils  at  185°,  decomposing  at  a  tempera- 
ture slightly  above  its  boiling  point,  and  forming  explosive  vapour 
when  heated  abov^e  212°.  An  aqueous  solution  of  potassa  does  not 
decompose  nitric  ether,  but  an  alcoholic  solution  of  potassa  de- 
stroys it,  even  w^hen  cold,  alcohol  and  nitrate  of  potassa  being 
formed. 

Nitrous  Ether  C^H.OjNOg. 

§  1346.  It  has  ^st  been  said  that  nitrous  ether  is  one  of  the  products 
of  the  action  of  ordinary  nitric  acid  on  alcohol,  but  the  reaction  is 
extremely  tumultuous,  and  if  large  quantities  of  the  mixture  are  ope- 
rated on,  especially  when  in  a  small-necked  retort,  an  explosion  may 
ensue.  The  best  method  of  preparing  it  consists  in  pouring  carefully 
into  a  bottle,  by  means  of  a  funnel  terminating  in  a  narrow  tube 
descending  to  the  bottom  of  the  bottle,  first,  one  part  in  volume  of 
alcohol  of  0.85,  then  one  part  of  nitric  acid  with  4  equiv.  of  water. 
The  bottle,  loosely  corked  in  order  to  allow  the  gases  to  escape,  is 
left  for  2  or  3  days  in  as  cold  a  place  as  possible,  when  the  upper 
layer,  which  contains  a  large -quantity  of  nitrous  ether,  is  decanted, 
and  then  agitated  with  a  w^eak  solution  of  caustic  potassa,  and 
digested  with  chloride  of  calcium. 

Pure  nitrous  ether  is  colourless,  and  its  odour  resembles  that  of 
pippiii  apples,  while  its  density  is  0.886,  and  it  boils  at  about  69.8°. 

Sulphurous  Ether  QJlfi^^O^. 

§  1347.  This  compound  ether  is  not  formed  by  the  direct  action 
of  sulphurous  acid  on  alcohol,  or  on  a  mixture  of  alcohol  and  sul- 
phuric acid,  but  is  obtained  by  pouring  alcohol  on  protochloride  of 
sulphur,  when  the  mixture  becomes  heated,  while  chlorohydric  acid 
is  disengaged  and  sulphur  deposited.  By  distillation,  alcohol  first 
passes  over,  and  then,  when  the  temperature  approaches  338°  a 
colourless  liquid,  having  the  smell  of  mint,  and  the  density  1.085, 
and  which  is  sulphurous  ether  C4H3O.SO2.  It  decomposes  slowly 
in  a  moist  atmosphere. 


532  TRANSFORMATIONS   OF  ALCOHOL. 

Boracic  Ether  C^H30,2B03. 

§  1348.  On  mixing  equal  weights  of  fused  and  finely  powdered 
boracic  acid,  and  absolute  alcohol,  a  considerable  quantity  of  heat 
is  evolved ;  and  if  the  mixture  be  distilled  in  a  retort  furnished 
with  a  thermometer,  alcohol  first  passes  over,  while  the  tempera- 
ture gradually  rises  and  soon  exceeds  212°.  The  distillation  is 
arrested  when  the  temperature  reaches  230°  ;  and  the  mass,  w^hen 
cooled,  is  dissolved  in  ether,  the  etherial  solution  is  evaporated, 
and  the  viscous  residue  heated  to  392°  in  an  oil-bath ;  when  the 
substance  remaining  is  boracic  ether.  It  is  a  transparent  glass, 
somewhat  soft  at  the  ordinary  temperature,  and  which,  at  the  tem- 
perature of  104°  or  120°,  maybe  drawn  out  into  thread.  It  smells 
feebly  of  ether,  and  at  392°  it  yields  white  vapours,  while  a  tem- 
perature of  570°  decomposes  it,  disengaging  very  pure  bicarburetted 
hydrogen.  Tepid  water  also  decomposes  it,  forming  alcohol  and 
boracic  acid.  Alcohol  and  ether  dissolve  boracic  ether  and  form 
solutions  which  set  into  gelatinous  masses  on  the  addition  of  water. 
When  an  alcoholic  solution  of  boracic  ether  is  distilled,  a  consider- 
able quantity  of  it  is  carried  over  by  the  alcoholic  vapours,  which 
then  burn  with  a  beautiful  green  flame,  owing  to  the  presence  of 
boracic  acid. 

Silicic  Ethers  3C,H30,Si03  and  3C^H30,2Si03. 

§  1349.  When  absolute  alcohol  is  carefully  poured  into  chloride 
of  silicium,  a  very  energetic  reaction  ensues,  and  a  large  quantity 
of  chlorohydric  acid  gas  is  generated.  Alcohol  is  gradually  added 
until  a  new  addition  produces  no  evolution  of  gas ;  and  on  then 
distilling  the  mixture,  chlorohydric  ether  is  first  disengaged,  and 
the  temperature  in  the  retort  soon  rises  to  320°,  while  the  greater 
portion  of  the  substance  distils  between  320°  and  338°,  which  is 
separately  collected.  When  the  temperature  exceeds  338°  the 
receiver  is  changed,  and  distillation  is  carried  to  dryness.  The 
product  distilled  between  between  320°  and  338°  is  again  rectified, 
and  then  is  almost  entirely  composed  of  a  liquid  boiling  between 
323.5°  and  325.5,  and  of  which  the  formula  is  30^1130,8103.  It  is 
a  silicic  ether,  difiering  in  composition  from  the  compound  ethers 
hitherto  described,  in  containing  3  equiv.  of  ether  C^H^O  for  1 
equiv.  of  silicic  acid.  Silicic  ether  is  a  colourless  liquid,  of  an 
ether-like  and  penetrating  smell,  of  a  taste  like  pepper,  and  of  the 
density  0.942.  Water  does  not  dissolve  it,  but  decomposes  it  after 
a  time,  and  silicic  acid  is  separated.  When  silicic  ether  is  left  for 
a  very  long  time  in  a  badly-stoppered  bottle,  decomposition  is  gra- 
dually efiected  at  the  expense  of  atmospheric  moisture,  the  silicic 
ether  becoming  more  and  more  viscous,  while  it  still  preserves  its 
transparency,  while  there  remains  at  last  a  perfectly  transparent, 
vitreous  mass,  of  great  hardness,  consisting  of  hydrated  silicic  acid. 


ETHERS.  583 

By  again  rectifying  the  products  of  the  action  of  alcohol  on 
chloride  of  silicium  which  have  distilled  above  392°,  and  collecting 
separately  the  product  which  distilled  above  572°,  a  new  ether  of 
the  formula  3C4H.O,2Si03  is  obtained.  The  formula  of  the  two 
silicic  ethers  differ  greatly  from  those  of  other  compound  ethers. 
It  has  been  seen  (§  244)  that  chemists  are  not  agreed  upon  the 
equivalent  of  silicium  and  the  formula  of  silicic  acid,  and  that  some 
think  that  the  formula  should  be  written  SiO ;  in  which  case  the 
two  silicic  ethers  would  assume  the  formula  C^H^OjSiO  and 
CJifi,2SiO,  the  former  being  analogous  to  that  of  ordinary  com- 
pound ethers,  and  the  latter  to  that  of  vinic  acids. 

Carbonic  Ether  QJlfi^QO^  and  Carbovinic  Acid  0^1150,2008. 

§  1350.  Oarbonic  ether  is  not  obtained  by  the  direct  action  of 
carbonic  acid  on  alcohol,  but  has  been  produced  by  distilling  oxalic 
ether  with  potassium.  The  oxalic  ether  is  introduced  into  a  tubu- 
lated retort  and  heated,  potassium  or  sodium  being  gradually  added 
until  gas,  consisting  of  carbonic  oxide,  is  no  longer  evolved.  The 
colour  of  the  substance  remaining  in  the  retort  is  of  a  deep  red ; 
and  when  it  is  again  distilled  with  a  quantity  of  water,  the  carbonic 
ether  forms  the  upper  layer  of  the  distilled  liquid,  which  is  decanted 
and  redistilled  over  chloride  of  calcium. 

Carbonic  ether  is  a  colourless,  very  fluid  liquid,  of  an  aromatic 
smell  and  acrid  taste,  and  its  density  is  0.975,  while  it  boils  at 
258.8°,  yielding  a  vapour  of  the  density  4.1 ;  and  its  equivalent 
0^1150,003  is  represented  by  2  volumes  of  vapour.  Potassa  dis- 
solved in  alcohol  changes  it  but  slightly  when  cold ;  while,  when 
hot,  carbonate  of  potassa  is  formed,  and  alcohol  is  separated. 

Oarbonic  ether  is  decomposed  by  a  solution  of  ammonia,  and 
yields  alcohol,  and  a  white  crystalline  substance  soluble  in  water 
and  alcohol,  to  which  the  name  of  urethan  has  been  given.  The 
formula  of  urethan  is  0^1130,(0303,^113) ;  and  it  may  be  regarded 
as  a  compound  ether,  formed  by  a  peculiar  acid  0303,NH3,  which 
has  been  called  carbamic  acid  ;  in  which  case  urethan  would  be  car- 
bamic  ether.     We  have,  in  fact, 

2(C.H,0,CO,)+NH,=C.H,0,(NH^C,03)+CAO,. 

If  a  concentrated  solution  of  caustic  potassa  in  anhydrous  alcohol 
be  saturated  with  carbonic  acid  gas,  the  liquor  at  last  sets  into  a 
mass,  in  consequence  of  a  copious  deposit  of  carbonate,  bicarbonate, 
and  carbovinate  of  potassa.  Ether,  which  completes  the  precipita- 
tion of  the  carbovinate  of  potassa,  is  poured  into  the  flask,  and  after 
having  decanted  the  liquor,  th-e  deposit  is  shaken  with  absolute 
alcohol,  which  dissolves  only  the  carbovinate.  The  alcoholic  solu- 
tion is  filtered  and  dropped  into  very  anhydrous  ether,  which  again 
precipitates  the  carbovinate  of  potassa.  The  formula  of  the  salt, 
dried  in  vacuo,  is  KO,(04H.O,2003) ;  and  it  forms  white,  pearly 


534  TRANSFORMATIONS   OF  ALCOHOL. 

spangles,  greasy  to  the  touch.     Water  decoraposes  it  instantly  into 
alcohol  and  bicarbonate  of  potassa. 

Oxychlorocarhonic  Ether  QJlfiCjJd^Ql. 

§  1351.  On  pouring  absolute  alcohol  into  a  matrass  filled  with  chlo- 
rocarbonic  gas,  COCl  (§  258,)  the  temperature  rises,  and  the  liquid 
separates  into  two  layers,  the  lower  of  which  is  formed  of  oxychlo- 
rocarbonic  ether.  It  is  purified  by  digesting  it  over  litharge  or 
chloride  of  calcium,  and  then  distilling  it. 

This  ether  is  liquid,  colourless,  having  a  penetrating  odour,  which 
excites  to  tears ;  and  its  density  is  1.133,  while  it  boils  at  201.2°, 
and  burns  with  a  green  flame.  Boiling  water  decomposes  it ;  and 
it  may  be  considered  as  a  compound  of  carbonic  ether  0^1150,002  and 
chlorocarbonic  gas  COCl.  Ammonia  decomposes  it,  chlorohydrate 
and  carbonate  of  ammonia,  and  carbonic  ether,  being  formed. 

Oxalic  JEther  0^1150,0303,  and  Oxalovinic  Acid  0^H50,2C303. 

§  1352.  The  best  method  of  preparing  oxalic  ether  consists  in 
mixing  in  a  tubulated  retort  1  part  of  oxalic  acid  dried  at  212°,  the 
formula  of  which  is  then  Ca03,H0,  with  6  parts  of  absolute  alcohol. 
A  thermometer,  the  bulb  of  which  reaches  nearly  to  the  bottom  of 
the  retort,  is  fitted  to  its  tubulure,  and  the  distillation  is  continued 
until  the  thermometer  marks  284°,  when  distilled  alcohol  is  intro- 
duced and  the  distillation  repeated,  ceasing  only  when  the  thermo- 
meter marks  320°.  The  liquid  remaining  in  the  retort  is  then 
poured  into  water,  when  oxalic  ether  separates  as  a  heavy  liquid, 
which,  after  being  washed  several  times  with  water,  is  again  distilled 
over  litharge,  which  seizes  upon  the  free  oxalic  acid.  The  product, 
after  being  left  for  some  time  in  contact  with  fused  chloride  of  cal- 
cium, is  pure  oxalic  ether.  It  is  colourless,  and  of  an  aromatic 
odour ;  and  its  density  is  1.093,  while  it  is  very  slightly  soluble  in 
water,  but  perfectly  so  in  alcohol.  The  density  of  its  vapour  is 
5.078:  it  boils  at  363.2°,  and  its  equivalent  Qfifi,Qfi^  corre- 
sponds to  2  volumes  of  vapour. 

Oxalic  ether  is  decomposed  by  contact  with  a  solution  of  potassa, 
into  alcohol  and  oxalic  acid,  which  decomposition  is  also  effected, 
after  a  long  time,  by  pure  water  ;  and  when  left  in  a  badly-stoppered 
bottle,  in  contact  with  moist  air,  it  deposits  crystals  of  hydrated 
oxalic  acid.  Ammonia  exerts  a  remarkable  action  upon  it,  forming 
two  new  products,  oxamid  and  oxamic  ether. 

On  dropping  oxalic  ether  into  a  solution  of  ammoniacal  gas  in 
absolute  alcohol,  a  peculiar  substance,  first*  called  oxamethan,  is 
formed,  which  is  now  regarded  as  ,a  compound  ether,  formed  by  a 
peculiar  acid,  called  oxamic,  Cfi^l^H^yCfi^.  On  evaporating  the 
liquid,  the  substance  separates  in  the  form  of  lamellated  crystals, 
of  a  greasy  aspect,  melting  at  about  212°,  and  distilling  without 
change  at  248°.     It  dissolves  readily  in  water  and  in  alcohol,  its 


ETHERS.  535 

aqueous  solution  being  decomposed,  by  boiling,  into  binoxalate  of 
ammonia  and  alcohol.  The  formula  of  oxamic  ether  is  C^H^O, 
(C203NH3,C20g) ;  and  the  reaction  from  which  it  arises  is  expressed 
by  the  following  equation  : 

2(CXO,CA)+NH3=C.H,0,(C,0,NH„C,03)+C,H,0,. 

It  has  already  been  shown  that  the  oxamid  C3O3NH3  is  formed 
during  the  distillation  of  oxalate  of  ammonia.  This  substance  is 
more  easily  prepared  by  decomposing  oxalic  ether  by  an  aqueous 
solution  oiP  ammonia.  Oxamid  is  a  white  crystalline  substance, 
having  no  action  on  coloured  tests ;  and  cold  water  does  not  sensi- 
bly dissolve  it,  while  hot  water  dissolves  a  small  quantity  of  it, 
which  is  again  deposited  on  the  cooling  of  the  liquid.  Dilute  acids 
and  alkalies,  when  cold,  do  not  affect  oxamid ;  but  at  the  boiling 
point,  oxamid  again  takes  up  two  equivalents  of  water,  and  yields 
ammonia  NH3,IlO  and  oxalic  acid  CgOg. 

On  adding  to  oxalic  ether  dissolved  in  absolute  alcohol  a  quan- 
tity of  potassa  also  dissolved  in  anhydrous  alcohol,  in  such  quantity 
that  it  shall  saturate  one-half  of  the  oxalic  acid  existing  in  the  ether, 
a  salt  almost  insoluble  in  absolute  alcohol  is  precipitated  in  the 
form  of  small  crystalline  lamellae,  consisting  of  oxalovinate  of 
2Jotassa,  which  dissolves  without  alteration  in  water,  but  subse- 
quently crystallizes  with  difficulty.  If  too  great  a  quantity  of 
potassa  be  added,  oxalate  of  potassa  and  alcohol  only  are  obtained. 
The  formula  of  the  salt  is  K0,(C4H.0,2C203) ;  and  when  it  is  pre- 
cipitated mixed  with  a  certain  quantity  of  oxalate  of  potassa,  it  may 
be  separated  from  it  by  treating  the  precipitate  with  slightly  diluted 
alcohol,  which  dissolves  only  the  oxalovinate  of  potassa.  By  adding 
sulphuric  acid  to  this  solution,  the  potassa  is  precipitated  in  the 
state  of  sulphate,  and,  if  the  liquid  be  then  saturated  with  caustic 
baryta,  a  solution  of  oxalovinate  of  baryta  is  obtained.  The  aqueous 
solution  of  oxalovinic  acid  is  readily  decomposicd  by  evaporation, 
and  crystals  of  hydrated  oxalic  acid  are  obtained. 

Mucic  Ether  C,H,0,CaH30,. 

§  1353.  Mucic  acid  does  not  form  a  compound  ether  by  its  direct 
action  on  alcohol,  but  a  mucic  ether  is  obtained  by  dissolving,  with 
the  aid  of  heat,  1  part  of  mucic  acid  in  4  of  sulphuric,  and  then 
adding  to  the  liquid,  when  cooled,  4  parts  of  alcohol.  After  some 
time  a  copious  deposit  of  acicular  crystals  is  formed,  which  are 
purified  by  solution  in  boiling  alcohol,  from  which  they  again  sepa- 
rate on  cooling.  The  crystals  are  mucic  ether  C^H^OjCgHgOy, 
which  melts  at  about  284°,  and  is  decomposed  at  338°  without  dis- 
tilling. It  dissolves  in  boihng  water,  from  which  it  again  separates 
almost  entirely  on  cooling ;  and  boiling  alcohol  also  dissolves  it, 
while  after  cooling  it  retains  but  very  feeble  traces  of  it. 


536  TRANSFORMATIONS   OF  ALCOHOL. 

Compounds  of  Ether  C^H^O  with  the  Metallic  Chlorides, 

§  1354.  Simple  ether  forms  or jstallizable  compounds  with  several 
metallic  chlorides,  particularly  with  the  bichlorides  of  tin  and  titanium. 
By  introducing  into  a  very  dry  bottle,  containing  bichloride  of  tin 
or  titanium,  an  open  tube  containing  ether,  and  allowing  the  bottle 
to  rest,  crystals  remarkable  for  their  sharpness,  and  of  which  the 
formula  is  2C^H,0,SnCl„  SC^H^OjTiCl,,  are  formed  on  its  sides. 
The  crystals  dissolve  without  change  in  ether  and  absolute  alcohol, 
but  are  decomposed  by  contact  with  water,  the  ether  being  set 
free. 

Compound  of  Ether  with  Sulphide  of  Carbon^  Sulphoearhovinie 
Acid  or  Xanthic  Acid  0^11^0,2083. 

§  1355,  These  compounds  are  obtained  by  dropping  into  a  solu- 
tion of  potassa  in  absolute  alcohol  sulphide  of  carbon  until  the  liquid 
has  lost  its  alkaline  reaction,  when  a  peculiar  salt  of  potassa  is 
formed,  the  greater  portion  of  which  separates  in  the  form  of  orange- 
coloured  crystals.  The  composition  of  the  salt  corresponds  to  the 
formula  KO^iQ^lfi^^Q^^,  and  it  may  therefore  be  regarded  as  a 
vinic  acid  in  which  the  ether  O^H^O  is  combined  with  sulphocar- 
bonic  acid  CSgi  it  is  also  called  xanthic  acid. 

The  acid  is  separated  by  pouring  sulphuric  or  chlorohydric  acid 
into  a  solution  of  xanthate  of  potassa,  when  the  liquid  becomes 
milky,  while  a  colourless  oil  separates  from  it,  which  is  several 
times  washed  with  water.  This  is  xanthic  acid,  which  is  not  very 
fixed  when  isolated.  The  alkaline  xanthates  are  soluble  in  water, 
while  the  other  metallic  xanthates  are  insoluble  and  are  precipitated 
in  the  form  of  yellow  powders.  Xanthates  yield,  by  distillation, 
several  new  products,  which,  however,  have  not  been  hitherto  suffi- 
ciently investigated. 

SIMPLE  ETHERS. 

§  1356.  The  equivalent  of  oxygen  in  ether  O^H.O  may  be  re- 
placed by  respectively  1  equivalent  of  chlorine,  bromine,  iodine, 
sulphur,  selenium,  tellurium,  and  cyanogen  ;  and  volatile  substances 
may  be  thus  obtained,  some  of  which  can  form  compound  ethers  and 
vinic  acids.  We  shall  call  this  class  of  ethers  simple  ethers;  and 
ordinary  ether  O^H^O  necessarily  belongs  to  it. 

Chlorohydric  Ether  O^H^Ol. 
§  1357.  This  substance  is  directly  formed  by  the  reaction  of 
chlorohydric  acid  on  alcohol.  Absolute  alcohol,  made  very  cold  by 
being  surrounded  with  ice,  is  completely  saturated  with  chlorohydric 
acid  gas,  and  the  liquid  is  then  distilled,  the  gas  evolved  being  con- 
veyed through  a  washing-bottle  containing  water  and  kept  at  a  tem- 
perature of  77°  or  86°,  and  thence  into  a  receiver  cooled  by  a  re- 


ETHERS.  537 

frigerating  mixture.  Chlorohjdric  ether  being  gaseous  at  a  tem- 
perature above  55.4°,  traverses  the  water  in  the  washing-bottle, 
which  retains  the  excess  of  chlorohydric  acid  or  alcohol ;  and  con- 
denses in  the  receiver.  In  order  to  remove  all  traces  of  alcohol 
and  water,  the  chlorohydric  ether  is  distilled  with  concentrated  sul- 
phuric acid.  The  reaction  from  which  it  arises  is  expressed  by  the 
following  equation : 

C,HeO,H-HCl=C,H3Cl4-2HO. 

Chlorohydric  ether  may  also  be  prepared  by  heating  in  a  flask 
a  mixture  of  alcohol  at  0.85  and  concentrated  chlorohydric  acid 
of  commerce  ;  the  gas  being  first  passed  through  a  washing-bottle 
containing  water,  and  then  through  a  second  containing  concentrated 
sulphuric  acid ;  both  bottles  being  kept  at  a  temperature  of  68°  or 
77°.  It  may  also  be  procured  by  introducing  into  the  flask  12 
parts  of  sea-salt,  and  then  adding  a  mixture  of  1  part  of  sulphuric 
acid  and  5  parts  of  alcohol.  If  the  temperature  of  the  laboratory 
exceed  59°,  the  ether  may  be  collected  in  the  gaseous  state  in  bell- 
glasses  over  mercury. 

Chlorohydric  ether,  at  a  low  temperature,  is  a  colourless  liquid, 
of  a  sharp,  slightly  alliaceous  smell ;  and  its  density  at  32°  is 
0.291,  while  it  boils  at  54.5°  under  the  ordinary  pressure  of  the 
atmosphere.  It  should  be  preserved  in  a  vessel  the  neck  of  which 
is  hermetically  sealed.  It  dissolves  in  50  parts  of  water  at  32°, 
and  mixes  with  alcohol  in  every  proportion.  The  density  of  its 
vapour  is  2.235,  and  its  equivalent  C^H^Cl  corresponds  to  4  volumes 
of  vapour.  Aqueous  alkaline  solutions  decompose  it  slowly  into 
alcohol  and  chlorohydric  acid,  the  decomposition  being  immediate 
if  the  alkali  is  dissolved  in  alcohol. 

Chlorohydric  ether  combines  with  several  metallic  chlorides,  and 
its  compounds  may  be  regarded  as  compound  ethers  of  the  simple 
ether.  It  is  largely  soluble  in  perchloride  of  tin,  and  a  definite 
compound  in  the  form  of  acicular  crystals  separates  from  it.  Per- 
chloride of  antimony  also  forms  a  crystalline  compound,  but  very 
soon  reaction  ensues  with  the  formation  of  protochloride  of  anti- 
mony. Chlorohydric  ether  also  combines  with  sesquichloride  of 
iron ;  but  all  these  compounds  are  destroyed  by  water,  and  the 
chlorohydric  ether  again  becomes  free. 

Chlorohydric  ether  is  freely  absorbed  by  anhydrous  sulphuric 
acid ;  a  liquid,  fuming  in  the  air,  and  readily  decomposed  by  heat, 
being  formed. 

Bromohydric  Ether  C^H^Br. 

§  1358.  This  ether  is  prepared  by  placing  in  a  tubulated  retort, 
furnished  with  its  receiver,  1  part  of  phosphorus  and  40  parts  of 
alcohol  at  0.85,  and  then  adding,  drop  by  drop,  through  the  tubu- 
lure,  7  or  8  parts  of  bromine.     By  the  reaction  of  the  bromine  on 


538  TKANSFORMATIONS   OF  ALCOHOL. 

the  phosphorus,  in  presence  of  the  water  contained  in  the  alcohol, 
phosphorus  and  bromohydric  acid  are  formed,  which  latter  converts 
the  alcohol  into  bromohydric  ether  C4He03+HBr=C4H,Br+2H0. 
When  the  reaction  is  terminated  the  retort  is  heated,  still  keeping 
the  receiver  very  cold ;  and  the  bromohydric  ether  is  washed  with 
a  very  weak  solution  of  potassa,  and  then  distilled  over  chloride  of 
calcium,  when  it  appears  as  a  colourless  liquid,  having  a  density  of 
1.473,  at  32°,  and  boiling  at  105.8°. 

lodohydric  Ether  C^Hgl. 
§  1359.  It  is  prepared  by  heating  in  a  retort  5  parts  of  iodide 
of  phosphorus  with  2  parts  of  alcohol  at  0.85,  shaking  with  alkaline 
water  the  liquid  collected  in  the  receiver,  and  then  distilling  over 
chloride  of  calcium.  lodohydric  ether  is  a  colourless  liquid,  having 
a  density  of  1.97  at  32°,  and  boiling  at  158°.  Light  soon  turns  it 
brown,  announcing  the  commencement  of  decomposition.  Its  for- 
mula C4H5I  corresponds  to  4  volumes  of  vapour.  • 

Oyanohydric  Ether  QJlfij, 

§  1360.  This  ether  is  obtained  by  distilling  a  concentrated  solu- 
tion of  sulphovinate  of  baryta  with  cyanide  of  potassium,  washing 
the  distilled  product  with  water  slightly  alkaline,  and  distilling  over 
chloride  of  calcium.  Oyanohydric  ether  is  a  colourless  liquid  having 
a  strongly  alliaceous  smell,  and  highly  poisonous :  its  density  is 
0.787,  and  it  boils  at  179.6°.  Alkalies  dissolved  in  water  decom- 
pose it  slowly,  while  oxide  of  mercury  effects  a  much  more  rapid 
decomposition,  resulting  in  cyanide  of  mercury,  oyanohydric  acid, 
and  alcohol. 

Sulfhydric  Ether  C^H^S  and  its  Com'pound  Ethers, 

§  1361.  Sulfhydric  ether  is  prepared  by  passing  chlorohydric 
ether  through  an  alcoholic  solution  of  monosulphide  of  pot^assium, 
after  which  the  liquid  is  allowed  to  rest,  for  24  hours,  in  a  well- 
corked  bottle,  and  then  distilled ;  when  alcohol,  sulfhydric  ether, 
and  chlorohydric  ether  condense  in  the  receiver.  This  mixture  is 
shaken  several  times  with  water,  which  dissolves  the  alcohol  and 
chlorohydric  ether,  and  the  supernatant  fluid,  being  then  separated 
by  means  of  a  pipette,  is  distilled  over  chloride  of  calcium.  The 
first  portions  which  pass  over  in  distillation  should  be  rejected,  be- 
cause they  may  contain  chlorohydric  ether. 

Sulfhydric  ether  is  a  colourless,  very  volatile  liquid,  of  a  pene- 
trating alliaceous  smell,  to  which  it  is  dangerous  to  be  long  ex- 
posed; and  its  density  is  0.825,  while  it  boils  at  163.4°.  It  is 
slightly  soluble  in  water,  but  in  all  proportions  in  alcohol.  The 
density  of  its  vapour  is  3.138  ;  and  the  equivalent  C^H^S  therefore 
corresponds  to  2  vols,  of  vapour  like  ordinary  ether  C4H5O.  ^ 

§  1362.  If  chlorohydric  ether  be  passed  through  an  alcoholic 


ETHERS.  539 

Bolution  of  sulfhydrate  of  sulphide  of  potassium  KS,HS,  and  be 
distilled,  a  much  more  volatile  liquid  is  obtained,  the  composition 
of  which  is  represented  by  C^HgSg ;  and  which  is  therefore  alcohol 
C^HgOg  with  2  equiv.  of  sulphur  substituted  for  2  equiv.  of  oxygen. 
It  may  be  called  sulfhydric  alcohol,  and  its  formula  may  also  be 
written  C^H^SjHS,  regarding  it  as  a  compound  ether  of  sulfhydric 
ether  C^H^S.  It  has  been  called  mercaptan,  on  account  of  its  pro- 
perty of  combining  with  oxide  of  mercury,  (mercurium  captans.) 

This  compound  is  also  obtained  by  distilling  in  a  water-bath  a 
mixture  of  a  solution  of  sulfhydrate  of  sulphide  of  potassium  and  a 
concentrated  solution  of  sulphovinate  of  lime.  The  receiver  should, 
in  all  cases,  be  cooled,  because  the  product  is  very  volatile : 

KS,HSH-CaO,(C,H30,2S03)=C,H,S,HS+KO,S034-CaO,S03. 

The  substance  is  freed  from  a  small  quantity  of  sulfhydric  acid 
by  distilling  it  over  red  oxide  of  mercury. 

Sulfhydric  alcohol  is  a  colourless  liquid,  of  very  disagreeable  and 
penetrating  alliaceous  smell :  its  density  is  0.84  ;  it  solidifies  at 
about  —7.6°,  and  boils  at  -f96.8°  ;  the  density  of  its  vapour  being 
2.14,  so  that  its  equivalent  C^H^SjHS  is  represented  by  4  volumes, 
like  that  of  alcohol. 

Sulfhydric  alcohol  forms,  with  the  metallic  oxides,  compounds  in 
which  the  hydrogen  of  the  sulfhydric  acid  is  replaced  by  1  equiv. 
of  metal,  and  these  compounds  have  been  called  mercaptides.  The 
most  interesting,  on  account  of  the  facility  with  which  it  is  pro- 
duced, is  the  mercaptide  of  mercury,  which  may  be  called  sulpho- 
mercuric  alcohol.  In  order  to  prepare  it,  an  alcoholic  solution  of 
sulfhydric  alcohol  is  gradually  poured  upon  red  oxide  of  mercury, 
when  they  combine  with  elevation  of  temperature,  while  a  white 
substance  is  formed.  It  is  dissolved  in  boiling  alcohol,  and,  on 
cooling,  separatees  into  white,  pearl-like  spangles,  of  which  the  for- 
mula is  C4H5S,HgS.  This  substance  melts  at  about  185°,  and  de- 
composes above  248°.  Treated  with  sulfhydric  acid  it  yields  sul- 
phide of  mercury  and  sulfhydric  alcohol. 

If  sulfhydric  alcohol  be  poured  into  an  alcoholic  solution  of 
acetate  of  lead,  a  yellow  crystalline  precipitate  of  sulphoplumhic 
alcohol  C4H5S,PbS  is  formed. 

When  sulfhydric  alcohol  is  heated  with  potassium,  hydrogen  is 
disengaged,  and  a  sulphopotassic  alcohol  CJlfi,KS  is  formed ; 

C,H3S,HS+K=C,H3S,KS+H. 

A  solution  of  the  product  in  alcohol  yields,  on  evaporation,  a  white 
granular  substance ;  and  the  salt,  when  treated  with  acids,  yields  a  salt 
of  potassa  and  sulfhydric  alcohol.  When  mixed  with  an  alcoholic 
solution  of  chloride  of  mercury,  sulphomercuric  alccthol  is  formed.* 
By  distilling  a   concentrated  solution  of  2  parts  of  pentasul- 

*  These  bodies  may  be  viewed  as  sulf  hydrates  conjugate  with  2C3H3. — J.  C.  B. 


540  TEANSFORMATIONS   OF   ALCOHOL. 

phide  of  potassium  KS^  with  3  parts  of  sulpliovinate  of  lime,  water 
and  a  peculiar  etherial  liquid  pass  over,  by  washing  which  with 
water,  and  distilling  it  over  chloride  of  calcium,  a  liquid  results 
of  a  very  disagreea^ble  alliaceous  odour,  boiling  at  303.8°,  and  of 
which  the  formula  is  C^H^Sg. 

On  heating  an  excess  of  sulfhydric  alcohol  with  dilute  nitric 
acid  the  liquor  becomes  red,  from  the  production  of  a  certain 
quantity  of  deutoxide  of  nitrogen  which  dissolves  in  it,  but  it  loses 
its  colour  when  heated,  and  after  some  time  an  oleaginous  liquid 
separates  from  it.  Nitric  acid  is  gradually  added,  until  the  sulf- 
hydric alcohol  is  -entirely  decomposed;  after  which  the  liquid  is 
diluted  with  water,  and,  after  having  washed  the  oleaginous  sub- 
stance several  times,  it  is  distilled.  This  new  substance  is  without 
colour,  of  an  extremely  disagreeable  odour,  of  the  density  1.24; 
and  it  boils  at  about  266°,  but  not  without  alteration.  Its  com- 
position is  represented  by  the  formula  0^1158,803 ;  and  it  would 
therefore  be  a  compound  ether,  formed  by  the  combination  of  sulf- 
hydric ether  with  sulphurous  acid. 

When  the  action  of  dilute  nitric  acid  on  sulfhydric  alcohol  is 
prolonged  until  the  oxidizing  action  ceases,  an  acid  compound  is 
obtained,  which  forms  crystallizable  salts  with  bases ;  and  from  the 
analyses  which  have  been  made,  the  formula  of  the  salt  of  baryta 
would  be  BaO,(C^H38,OJ+HO. 

§  1363.  If  chlorohydric  ether  be  passed  through  an  alcoholic 
solution  of  sulphocarbonate  of  sulphide  of  potassium  K8,C33,  ^ 
sulphoearbonic  ether  0^1158,082  which  corresponds  to  carbonic 
ether  C^H50,003  is  formed.  After  having  allowed  the  substances 
to  act  for  some  time,  the  liquor  is  heated  to  drive  off  the  excess  of 
chlorohydric  ether,  and  it  is  treated  with  water ;  when  a  liquid  of 
an  alliaceous  smell,  heavier  than  water,  separates  from  it,  which 
new  substance  is  sulphoearbonic  ether  0^1158,082. 

A  sulphocyanohydric  ether  04H58,02NS  is  obtained  by  distil- 
ling a  mixture  of  equal  parts  of  sulphovinate  of  lime  and  sulpho- 
cyanide  of  potassium,  both  in  concentrated  solution.  The  product, 
purified  by  washing,  and  then  by  distillation,  is  a  colourless,  very 
limpid  liquid,  of  the  density  1.020,  boiling  at  294.8°.  Its  equiva- 
lent is  represented  by  4  volumes  of  vapour. 

Selenohydric  Ether  O^HgSe. 

§  1364.  It  is  obtained  by  distilling  selenide  of  potassium  with 
sulphovinate  of  potassa ;  but  its  properties  are  little  known. 

Tellurohydrie  Ether  O^H.Te. 

§  1365.  By  projecting  telluride  of  potassium  into  a  hot  solution 
of  sulphovinate  of  baryta,  and  then  distilling,  a  liquid  is  obtained 
of  a  reddish-yellow  colour,  heavier  than  water,  very  poisonous,  and 


ALDEHYDE.  541 

which  boils  above  212°.  It  is  tellurohydric  ether;  and  oxidizes 
slowly  in  the  air,  depositing  tellurous  acid. 

PRODUCTS   OF   THE   OXIDATION   OF   ALCOHOL   AND  ETHER. 

§  1366.  When  alcohol  and  ether  are  subjected  to  a  very  powerful 
oxidizing  action,  they  are  completely  consumed,  and  converted  into 
water  and  carbonic  acid ;  while,  when  the  oxidizing  action  is  less 
powerful,  they  are  converted  into  acetic  acid  €511303,110,  in  which 
case  they  lose  2  equiv.  of  hydrogen,  which  form  water  with  2  equiv. 
of  oxygen  given  off  by  the  oxidizing  substance,  while  the  2  equiv. 
of  hydrogen  are  replaced  by  2  equiv.  of  oxygen,  also  given  off  by 
the  oxidizing  reagent.     We  thus  have 

C.H^O  -}-40=C,H303,H0+H0, 
or  C,H,0,HO+40=C,H303,HO+2HO. 

When  the  oxidizing  action  is  still  more  feeble,  it  is  limited  to  the 
abstraction  of  a  single  equiv.  of  hydrogen,  and  to  its  replacement 
by  1  equiv.  of  oxygen,  which  furnishes  aldehyde  C^H^Og,  according 
to  the  formulae 

C,H30+20=C,H,0,+HO, 
and  C,H,0,H0+20=C,H,0,+2H0. 

Aldehyde  C^H^O^. 

§  1367.  Aldehyde  is  formed  under  a  number  of  circumstances,  in 
which  alcohol,  ether,  and  the  compound  ethers  are  subjected  to 
oxidizing  agencies ;  while  the  best  method  of  preparing  it  consists  in 
distilling  in  a  retort,  at  a  gentle  heat,  a  mixture  of  6  parts  of  con- 
centrated sulphuric  acid,  4  parts  of  water,  4  parts  of  alcohol  at 
0.80,  and  6  parts  of  finely  powdered  peroxide  of  manganese.  The 
retort  should  only  be  one-third  filled,  because  the  mixture  swells 
considerably  during  the  operation ;  and  a  cooling  apparatus,  through 
which  very  oold  water  passes,  and  a  receiver  surrounded  by  a  re- 
frigerating mixture  are  fitted  to  the  retort.  When  the  reaction 
appears  to  be  terminated  in  the  retort,  the  liquid  which  condensed 
in  the  receiver  is  withdrawn  and  distilled  at  two  different  times 
over  an  equal  weight  of  chloride  of  calcium.  The  liquid  obtained 
is  composed  of  aldehyde,  a  small  quantity  of  alcohol  and  water,  and 
acetic  and  formic  ether.  In  order  to  obtain  the  aldehyde,  it  is 
poured  into  ether  saturated  with  ammoniacal  gas;  when  white 
crystals,  consisting  of  a  combination  of  aldehyde  and  ammonia 
NHjjC^H^Oa  are  separated.  The  crystals  are  dissolved  in  their 
own  weight  of  water,  and  the  solution  is  introduced  into  a  retort 
furnished  with  a  receiver  cooled  by  a  refrigerating  mixture,  while 
sulphuric  acid  diluted  with  its  volume  of  water  is  poured  through 
the  tubulure.  On  distilling  it  over  a  water-bath,  a  liquid  is  ob- 
tained which,  when  distilled  over  melted  chloride  of  calcium,  yields 
pure  aldehyde. 


542  TRANSFORMATIONS   OF   ALCOHOL. 

Aldehyde  is  a  colourless,  very  limpid  liquid,  of  a  suffocating 
odour,  and  its  density  is  0.790  at  64.4°,  while  it  boils  at  71.3°,  the 
density  of  its  vapour  being  1.479,  and  its  equivalent  C^H^O^  there- 
fore corresponding  to  2  vol.  of  vapour.  It  dissolves,  in  all  propor- 
tions, in  water,  alcohol,  and  ether,  burns  with  a  white  flame,  and 
exerts  no  action  on  vegetable  colours.  Aldehyde  readily  absorbs 
oxygen  from  the  air,  particularly  in  the  presence  of  water,  and  is 
converted  into  acetic  acid,  which  transformation  is  effected  by  all 
oxidizing  agents :  thus  oxide  of  silver  is  reduced  by  a  solution  of 
aldehyde,  the  metallic. silver  adhering  to  the  sides  of  the  vessel  and 
covering  them  with  a  glittering  coating  ;  and  nitrate  of  silver  pro- 
duces the  same  effect  if  a  small  quantity  of  ammonia  be  added. 
Alkalies  decompose  aldehyde,  forming,  together  with  other  products, 
a  brown  resinous  matter,  which  reaction  is  often  indicated  as  being 
characteristic  of  aldehyde. 

Pure  and  anhydrous  aldehyde,  preserved  for  some  time  in  a  tube 
hermetically  closed,  undergoes  isomeric  modifications,  differing  ac- 
cording to  the  temperature.  At  32°  it  is  converted  into  a  crystal- 
line, colourless,  and  transparent  substance,  which  melts  at  35.6°, 
and  boils  at  201.2°.  The  density  of  its  vapour  being  three  times 
greater  than  that  of  aldehyde,  its  formula  may  be  assumed  to  be 
Cj^HjgOg.  It  has  been  called  elaldeliyde.  If,  on  the  contrary,  the 
external  temperature  range  from  59°  to  68°,  elongated  prismatic 
crystals,  which  finally  fill  the  tube,  are  developed  in  the  aldehyde, 
and  which  volatilize  at  248°  without  melting.  This  second  isome- 
ric modification  of  aldehyde  has  been-  called  metaldehyde^  and  the 
density  of  its  vapour  is  unknown. 

Aldehyde  is  also  formed  whenever  alcohol  is  burned  imperfectly 
in  contact  with  the  air ;  for  example,  when  that  liquid  is  dropped 
upon  metallic  plates  heated  to  482°,  or  when  a  wick  soaked  in 
alcohol  is  lighted,  and  extinguished  as  soon  as  the  greater  portion 
of  the  alcohol  has  evaporated ;  when  the  wick  is  carbonized,  and  the 
small  quantity  of  vapour  of  alcohol  which  comes  in  contact  with  the 
ignited  portions  is  imperfectly  burned,  and  yields  aldehyde,  which  is 
known  by  its  suffocating  smell.  A  large  quantity  of  aldehyde  is 
also  produced  in  the  experiment  of  Davy's  flameless  lamp,.(§  1169.) 

When  chlorine  is  passed  through  diluted  and  cold  alcohol,  chloro- 
hydric  acid  and  aldehyde  only  are  formed,  the  chlorine  then  exert- 
ing an  oxidizing  agency  on  the  alcohol,  by  decomposing  the  water 
and  combining  with  its  hydrogen :  C^H50,H0+2C1+H0=2HC1+ 

Acetie  Acid  Qfifi^^'RO. 

§  1368.  Alcohol,  when  pure,  or  merely  diluted  with  water,  does 
not  combine  with  the  oxygen  of  the  air,  while  the  combination  is 
readily  effected  in  the  presence  of  certain  substances  the  chemical 
elements  of  which  do  not  interfere,  as,  for  example,  very  finely  di- 


ACETIC   ACID.  543 

dded  platinum,  which  metal  may  cause  the  oxidation  of  a  large 
(|uantity  of  alcohol  at  the  expense  of  tHe  oxygen  of  the  air.  In 
order  to  perform  the  experiment,  a  capsule  a  (fig.  678)  containing 
platinum-black  is  placed  on  a  plate,  and  the 
capsule  is  covered  with  a  large  bell-glass  hav- 
ing an  opening  o  at  the  top,  and  which  rests  on 
three  small  wooden  wedges,  to  allow  the  air  to 
enter  from  beneath;  and  finally,  a  funnel  h 
having  a  long  and  delicate  neck  c  is  introduced 
into  the  opening.  By  pouring  alcohol  into  the 
5  funnel,  the  liquid  drops  on  the  platinum  con- 
tained in  the  capsule,  and  while  a  slight  eleva- 
tion of  temperature  ensues,  vapours  which  con- 
dense and  trickle  down  the  sides  of  the  glass  are  developed  therein. 
The  liquid  thus  formed  on  the  bottom  of  the  plate  is  nearly  pure 
acetic  acid  ;  but  there  is  produced  at  the  same  time,  1st,  a  certain 
quantity  of  aldehyde,  easily  recognised  by  its  smell ;  2dly,  a  peculiar 
substance  called  acetal ;  and  3dly,  a  small  quantity  of  acetic  ether, 
arising  from  the  reaction  of  the  acetic  acid  on  the  undecomposed 
alcohol. 

If  the  acid  liquor  be  saturated  with  chalk  and  distilled,  there  is 
obtained  in  the  receiver,  water  holding  in  solution  aldehyde,  acetic 
ether,  and  acetal.  If  this  new  liquid  be  digested  with  its  own  weight 
of  chloride  of  calcium,  the  latter  combines  with  the  water  and  acetic 
acid,  and  etherial  liquid  separates,  which  is  again  distilled,  the  first 
portions  which  pass  over  being  rejected,  because  they  contain  a  large 
amount  of  aldehyde,  while  the  last  portions  are  pure  acetal.  Acetal 
is  a  colourless  liquid,  boiling  at  167°,  of  a  density  of  0.844,  and  so- 
luble in  water  and  alcohol.  Its  composition  corresponds  to  the  for- 
mula CJ4H4O4,  and  it  may  be  regarded  as  being  formed  by  the  union 
in  a  single  group  of  three  molecules  of  ether,  one  of  them,  having 
been  modified,  under  the  oxidizing  influence,  by  the  substitution  of  1 
equiv.  of  oxygen  in  the  place  of  1  equiv.  of  hydrogen,  3C4H50  +  20= 
C„H„0,+HO. 

§  1369.  The  oxidation  of  alcohol  at  the  expense  of  the  oxygen 
of  the  air  is  also  eifected  by  organic  ferments,  and  in  general  by 
all  albuminous  substances,  upon  which  mysterious  action  is  based 
the  conversion  of  spirituous  liquors  into  vinegar,  that  is  to  say,  into 
acetic  acid.  Wines  of  certain  vintages,  rich  in  albuminous  matter, 
soon  turn  sour  in  the  air,  and  become  vinegar;  which  change  new 
wines  undergo  much  more  rapidly  than  the  old,  because  the  latter 
are  freed  from  albuminous  substances,  which  coagulate  and  fall  to 
the  bottom  of  the  barrel ;  and  therefore,  in  order  to  make  them  fer- 
ment, they  must  be  diluted  with  a  small  quantity  of  water  and  be 
exposed  to  the  air.  What  has  just  been  said  of  wines  is  equally  ap- 
plicable to  other  alcoholic  liquors,  and  even  to  solutions  of  sugar 
mixed  with  yeast  and  exposed  to  the  air.    During  the  acid  ferment- 


544  TRANSFORMATIONS   OP  ALCOHOL. 

ation  of  alcoholic  liquors,  a  mucilaginous  substance,  which  greatly 
assists  this  fermentation,  is  separated,  and  which,  consisting  chiefly 
of  albuminous  matter,  is  called  the  mother  of  vinegar. 

In  order  that  acetification  may  progress  rapidly,  the  alcoholic 
liquor  must  be  sufficiently  diluted  with  water,  and  present  a  large 
surface  to  the  oxidizing  action  of  the  air.  These  conditions  are  ful- 
filled on  a  large  scale  by  using  an  alcoholic  liquor  containing  1  part 
of  alcohol  to  8  or  9  parts  of  water,  and  adding  about  -^-^  of  ferment- 
able liquor,  such  as  beet-juice,  potato-juice,  or  small  beer,  when  the 
liquor  thus  prepared  is  dropped  into  barrels  (fig.  679)  filled  with 
beech  shavings.  The  lower  part  of  the  barrel  is  pierced  with  seve- 
ral holes  a^  and  the  upper  part  with  other  holes  5,  5,  while  a  false 

bottom  cde  forms  a  vat,  into  which 
the  alcoholic  liquor  is  poured.  The 
false  bottom  has  a  great  number  of 
holes,  through  which  pass  pieces  of 
twine,  having  a  knob  on  the  end  to 
prevent  them  from  slipping  through. 
The  alcoholic  liquor  flows  along  the 
twine,  and  dropping  on  the  shavings, 
spreads  into  a  thin  layer,  and  pre- 
sents a  large  surface  to  the  oxidiz- 
ing action  of  the  air,  oxidation  being 
effected  by  means  of  the  ferment  con- 
tained in  the  liquor  and  the  albumi- 
nous substances  in  the  wood,  while 
the  temperature  rises  and  produces  a  current  of  air  which  enters  at 
the  lower  holes  a  and  escapes  through  the  upper  ones  h.  Oxidation 
is  so  rapid  that  when  the  liquid  reaches  the  bottom  of  the  barrel, 
it  frequently  no  longer  contains  any  alcohol,  but  if,  after  one  pas- 
sage, the  alcohol  is  not  completely  converted  into  acetic  acid,  it  is 
passed  through  a  second  time.  The  presence  of  acetic  acid  itself 
assists  the  acetic  fermentation,  for  which  reason  the  fresh  shavings 
to  be  used  are  previously  left  for  some  time  in  concentrated  vine- 
gar. The  temperature  of  the  barrel  also  exerts  great  influence,  and, 
if  it  be  too  cool,  heated  alcoholic  liquor  must  be  added  to  bring  the 
temperature  to  between  86°  and  97°. 

The  acid  liquors  thus  obtained,  which  constitute  common  table- 
\dnegar,  are  dilute  solutions  of  acetic  acid,  containing  in  addition 
the  non-fermentable  principles  which  exist  in  alcoholic  liquors. 
Pure  acetic  acid  is  obtained  from  this  liquid  by  distillation,  a  very 
weak  acid  first  passing  over,  while  the  following  portions  contain 
more  acid,  and  the  latter  are  richer,  but  are  generally  deteriorated 
by  the  products  of  the  decomposition  of  foreign  substances.  The 
richer  liquors  are  saturated  with  carbonate  of  soda,  and  crystallized 
acetate  of  soda  is  separated  by  evaporation,  and  then  decomposed 


ACETIC  ACID.  545 

by  sulphuric  acid,  more  or  less  dilute,  according  to  the  desired 
strength  of  the  acetic  acid. 

§  1370.  Acetic  acid  is  now  largely  obtained  from  the  acid  liquors 
obtained  by  the  distillation  of  wood,  which  yields  very  complicated 
products:  carbonic  acid  gas,  oxide  of  carbon,  protocarburetted  hy- 
drogen, water  containing  acetic  acid  in  solution,  a  volatile  liquid 
called  spirit  of  wood,  some  other  soluble  substances,  and,  lastly, 
a  black,  pitchy  portion.  The  solution  of  impure  acetic  acid  is  called 
in  the  2^x1^  pyroligneous  acid;  and  in  order  to  separate  acetic  acid 
from  it,  it  is  first  saturated  with  chalk,  which  furnishes  a  solution 
of  acetate  of  lime  decomposable  by  sulphate  of  soda,  acetate  of 
soda  and  sulphate  of  lime  being  formed,  which  latter,  being  but 
slightly  soluble,  is  nearly  wholly  deposited.  The  solution  is  eva- 
porated to  dryness,  and  the  residue  heated  to  400  or  480°,  a 
temperature  which  does  not  afi'ect  the  acetate,  but  decomposes  the 
empyreumatic  substances  with  which  it  is  mixed.  Three  parts  of 
roasted  acetate  of  soda  being  then  treated  in  a  distilling  vessel  with 
9.7  of  sulphuric  acid,  the  first  third  of  the  liquid  which  distils  over, 
consisting  of  a  weaker  acetic  acid,  is  set  aside,  while  the  other  two- 
thirds,  which  are  composed  of  very  concentrated  acid,  always  con- 
tain a  small  quantity  of  sulphuric  acid,  in  order  to  free  the  product 
from  which  it  is  distilled  over  anhydrous  acetate  of  soda.  The  acetic 
acid  thus  obtained,  having  not  yet  reached  its  greatest  degree  of 
concentration,  is  exposed  to  a  low  temperature  by  surrounding  with 
ice,  or  better  still  by  a  refrigerating  mixture,  the  vessels  contain- 
ing it;  when  the  acid,  at  its  maximum  of  concentration  C^H^OjjHO, 
sets  in  a  crystalline  mass,  and  the  more  watery  acid  is  decanted. 
The  crystallized  acid  is  remelted  and  again  cooled,  when  only  one- 
half  of  the  product  is  congealed,  and  the  liquid  portion  being  de- 
canted ofi*,  the  solid  acid  may  be  considered  as  having  attained  its 
maximum  of  concentration. 

§  1371.  Acetic  acid,  monohydrated,  or  at  its  maximum  of  concen- 
tration C^HgOgjHO,  is  solid  at  low  temperatures,  but  melts  at  60.8°. 
The  acid  liquid  may  be  cooled  often  to  32°  and  below,  .without  crys- 
tallizing, and  the  bottle  may  even  be  shaken  without  causing  crys- 
tallization ;  but  if  a  small  glass  point  be  introduced,  a  crystal  is 
immediately  formed  at  the  end  of  the  point,  and  the  whole  mass 
gradually  crystallizes;  the  temperature  rapidly  rising  to  60.8°,  and 
remaining  stationary  until  the  solidification  is  complete.  The 
density  of  monohydrated  liquid  acetic  acid  is  1.063  at  64.4°,  and 
its  smell  is  sharp  and  penetrating,  while  its  taste  is  highly  acid ; 
but  in  this  state  of  concentration  it  exerts  a  vesicating  action  and 
raises  blisters  on  the  skin.  It  boils  at  248°,  the  density  of  its 
vapour  being  2.09 ;  but  it  is  necessary  to  measure  the  density  at  a 
very  high  temperature,  because  the  vapour  of  acetic  acid  diff'ers 
considerably  from  the  laws  of  permanent  gases  at  temperatures 
which  exceed  but  slightly  its  boiling  point,  (1234.)     Thcv  equivalent 

Vol.  IL— 35 


546  TRANSFORMATIONS   OF  ALCOHOL. 

C^H303,HO  is  represented  by  4  volumes  of  vapour,  like  that  of 
alcohol. 

Acetic  acid  mixes  with  water  in  all  proportions ;  and  for  the  first 
quantities  of  water  added,  the  acid  liquor  acquires  a  density  greater 
than  that  of  the  monohydrated  acid ;  the  maximum  of  density  which 
corresponds  to  the  acid  C^HgOg+SHO  being  1.079.  By  adding 
larger  quantities  of  water  the  density  diminishes,  and  the  hydrometer 
can,  therefore,  not  be  used  to  ascertain  the  strength  of  acetic  liquids. 

Chlorine  acts  powerfully  on  acetic  acid,  forming,  when  the  latter 
is  in  the  monohydrated  state  C^HgOgjHO  a  new  acid  C4C]303,HO, 
called  chloracetic  acid,  in  which  the  hydrogen  of  the  anhydrous  acid 
is  replaced  by  an  equivalent  quantity  of  chlorine ;  while,  if  the  acid 
is  further  diluted  with  water,  the  chlorine  exerts  an  oxidizing  action 
by  decomposing  the  water,  and  the  acetic  acid  is  converted  into 
oxalic  and  then  into  carbonic  acid. 

Ordinary  nitric  acid  acts  but  feebly  on  acetic  acid,  even  when 
assisted  by  heat. 

§  1372.  Acetic  acid  forms,  with  bases,  a  numerous  series  of  salts, 
several  of  which  are  applied  in  the  arts.  They  are  generally  solu- 
ble in  water,  and  some  dissolve  in  alcohol ;  and  the  acid  forms  fre- 
quently several  salts  with  the  same  base. 

All  the  acetates  are  decomposed  by  heat,  but  the  decomposition 
takes  place  at  very  different  temperatures,  and  its  products  vary 
according  to  the  nature  of  the  base.  The  acetates  formed  by  the 
easily  reducible  metallic  oxides,  such  as  the  oxides  of  silver  and 
mercury,  leave  a  metallic  residue,  and  evolve  a  portion  of  their 
acetic  acid  unchanged,  while  another  portion  of  the  acid  is  com- 
pletely consumed  by  the  oxygen  given  off  by  the  metallic  oxide,  and 
yields  water  and  carbonic  acid.  The  acetates  formed  by  the  more 
powerful  bases,  as  the  alkaline  acetates,  leave  as  a  residue  an  alka- 
line carbonate,  the  acetic  acid  being  converted  into  a  neutral  vola- 
tile liquid  C3H3O,  called  acetone,  or  pyroacetic  spirit;  which  reaction 
is  expressed  by  the  following  equation : 

•      NaO,C,H303=NaO,CO,+C3H30. 

Acetates  formed  by  bases  of  medium  strength,  as  oxide  of  lead, 
undergo  a  complicated  decomposition:  unchanged  acetic  acid  and 
acetone  are  both  disengaged  at  once,  while  the  carbonic  acid  arising 
from  the  portion  of  decomposed  acetic  acid  is  disengaged  or  remains 
combined  with  the  base,  according  to  the  temperature. 

Lastly,  when  the  metallic  oxide  of  moderate  strength  is  easily 
reduced,  as  oxide  of  copper,  a  portion  of  the  acetic  acid  is  consumed 
by  the  oxygen  of  the  oxide,  and  yields  carbonic  acid,  while  the 
residue  of  the  distillation  is  composed  of  metal,  or  suboxide. 

Acetic  acid  forms  two  crystallizable  salts  with  potassa :  the  neutral 
acetate  K0,C^H303  and  the  hinacetate  K0,C^H303+H0,C,H303; 
the  former  of  which  is  obtained  by  saturating  acetic  acid  by  car- 


ACETIC   ACID.  547 

bonate  of  potassa  and  evaporating  the  liquor.  The  salt  crystallizes 
with  difficulty  and  is  soluble  in  water  and  alcohol ;  and,  if  it  be  dis- 
solved in  an  excess  of  acetic  acid  and  evaporated,  crystals  of  the 
binacetate  are  obtained,  which  is  deliquescent,  melts  at  298.4°,  and 
at  392°  yields  monohydrated  acetic  acid,  furnishing  the  means  of 
preparing  very  pure  acid. 

Acetate  of  soda  NaO,C4H303+6HO.'  It  has  been  seen  that  this 
salt  is  prepared  on  a  large  scale  in  the  manufacture  of  wood-vinegar. 
It  crystallizes  in  large  colourless  and  transparent  prisms,  which  are 
often  remarkable  for  the  great  sharpness  of  their  faces.  It  has  a 
cool  and  saltish  taste,  and  dissolves  in  3  parts  of  cold  water  and  5 
of  alcohol.  When  heated,  it  first  dissolves  in  its  water  of  crystalliza- 
tion, but  soon  parts  with  it ;  while,  if  further  heated,  it  undergoes 
igneous  fusion  without  decomposition,  which  begins  to  ensue  only 
at  a  degree  of  heat  approaching  a  dull  red. 

Acetate  of  ammonia  (NH3,H0),C4H303,  which  is  obtained  by  the 
direct  combination  of  ammonia  with  acetic  acid,  is  very  soluble  in 
water  and  alcohol,  and  is  used  in  medicine.  When  boiled,  it  loses 
a  portion  of  its  ammonia  and  is  converted  into  binacetate. 

Acetate  of  baryta  BaOjC^HaOg-f  3H0  forms  brilliantly  white 
prismatic  crystals,  which  readily  part  with  2  equiv.  of  water  at  a 
slightly  elevated  temperature. 

Acetate  of  lime  produces  only  confused  crystallizations,  resem- 
bling cauliflowers. 

Acetate  of  alumina  is  prepared  by  pouring  a  solution  of  sulphate 
of  alumina  into  a  solution  of  acetate  of  baryta  or  lead,  until  no 
precipitate  is  thrown  down;  and  the  solution,  which  then  contains 
acetate  of  alumina,  is  used  in  dyeing.  In  order  to  separate  the 
salt  from  it,  the  liquor  must  be  evaporated  in  vacuo,  because,  when 
heated,  acetic  acid  is  disengaged;  when  the  acetate  of  alumina  re- 
mains in  the  form  of  a  gummy  mass,  without  any  appearance  of 
crystallization. 

The  properties  of  the  acetates  of  lead  and  copper,  which  are  of 
important  application  in  the  arts,  have  already  been  sufficiently  de- 
tailed when  treating  of  those  metals. 

When  concentrated  acetic  acid  is  poured  into  a  boiling  solution 
of  subnitrate  of  mercury  Hg20,N0„  anhydrous  white  crystalline 
lamellae  of  subacetate  of  mercury  Hg30,C4H30j  are  deposited  on 
cooling.  Red  oxide  of  mercury  dissolves  readily  in  -acetic  acid,  and 
the  liquid  yields  by  slow  evaporation  beautiful  colourless  crystals  of 
protoacetate  of  mercury  HgO,C4H303,  which  dissolves  without  change 
in  cold  water,  but  on  boiling  deposits  perfectly  pure  red  oxide  of 
mercury. 

Acetate  of  silver  AgO,C4H303  is  obtained  by  dissolving  carbonate 
of  silver  in  acetic  acid;  and  as  it  is  but  little  soluble  in  cold  water, 
it  may  also  be  prepared  by  double  decomposition,  by  pouring  nitrate 


548  TRANSFORMATIONS   OF   ALCOHOL. 

of  silver  into  a  solution  of  acetate  of  soda.     If  the  liquors  are  con- 
centrated, the  acetate  of  silver  is  deposited  on  cooling. 

Acetic  Ether,  Qfifi.QfLfi^. 

§  1373.  Acetic  ether  is  formed  by  the  direct  reaction  of  acetic  acid 
on  alcohol,  but  the  combination  is  effected  with  difficulty,  because  it 
is  necessary  to  use  anhydrous  alcohol  and  acetic  acid  at  its  maximum 
of  concentration,  and  pour  back  again  into  the  retort  the  liquor 
which  has  passed  over  in  distillation ;  and  the  formation  of  acetic 
ether  is  much  more  rapid  if  10  or  15  per  cent,  of  sulphuric  acid  be 
added.  The  best  method  of  preparing  this  ether  consists  in  pouring 
a  mixture  of  7  parts  of  concentrated  sulphuric  acid  with  8  of  ab- 
solute alcohol,  or  10  parts  of  anhydrous  acetate  of  soda,  or  20  parts 
of  acetate  of  lead,  into  a  retort,  and  distilling  as  long  as  any  etherial 
liquor  passes  over,  the  product  being  collected  in  a  well-cooled  re- 
ceiver. The  liquor  is  poured  upon  dried  pulverized  carbonate  of 
soda,  which  abstracts  the  greater  portion  of  water  from  the  acetic 
ether,  and  combines  with  the  free  acetic  acid  which  passes  over  in 
distillation.  The  supernatant  liquid  stratum  is  decanted,  and  dis- 
tilled over  chloride  of  calcium,  which  takes  up  the  alcohol ;  but  the 
complete  purification  of  acetic  ether  is  very  difficult,  because  it  com- 
bines with  chloride  of  calcium,  and  forms  a  crystalline  compound, 
which  is  destroyed  only  by  the  addition  of  water. 

Acetic  ether  is  a  colourless,  very  mobile  liquid,  of  an  agreeable 
ether-like  smell,  and  of  the  density  0.907  at  32°.  It  boils  at  165.2°, 
and  the  density  of  its  vapour  is  2.920,  its  equivalent  0^1130,0411503 
being  therefore  represented  by  4  volumes  of  vapour.  It  mixes  in 
all  proportions  with  alcohol  and  ether,  and  dissolves  in  7  parts  of 
water.     It  is  used  in  medicine. 

Sulphacetic  Acid  0^11404,2808. 

§  1374.  By  bringing  into  contact  anhydrous  sulphuric  acid  and 
monohydrated  acetic  acid  04HsO,H03,  the  two  acids  combine  and 
form  a  compound  acid.  The  liquid  is  diluted  with  water  and  satu- 
rated with  carbonate  of  baryta,  when  the  free  sulphuric  acid  forms 
insoluble  sulphate  of  baryta,  while  the  sulphacetic  acid  yields  a 
soluble  sulphacetate  of  baryta.  The  liquor,  when  evaporated, 
affords  crystals  of  the  formula  2BaO,(04H404,2S03)+HO,  and  which 
part  with  their  water  without  decomposition.  If  the  baryta  be  pre- 
cipitated from  sulphacetate  of  baryta,  by  sulphuric  acid  poured  in 
by  drops,  or  if  a  solution  of  sulphacetate  of  lead  be  decomposed  by 
sulf  hydric  acid,  an  acid  liquid  results,  which  on  evaporation  yields 
deliquescent  crystals,  melting  at  143.6°,  and  solidifying  in  a  crys- 
talline mass  on  cooling.  At  a  more  elevated  temperature  the 
sulphacetic  acid  is  decomposed. 

Crystallized  sulphacetic  acid,  placed,  in  vacuo,  over  anhydrous 
phosphoric  acid,  gives  off  one  equivalent  of  water,  and  then  assumes 


ACETONE.  549 

the    formula    C4H^04,2S03+2HO ;    the    2    equivalents  of   water 
which  it  retains  being  basic. 

Acetone  Cfifi. 

§  1375.  It  has  been  said  (§  1372)  that  the  alkaline  acetates  yield 
acetone  when  they  are  decomposed  by  heat ;  but  the  best  method 
of  preparing  it  consists  in  heating  a  mixture  of  2  kilog.  of 
acetate  of  lead  with  1  kilog.  of  finely  powdered  quicklime,  in  an 
earthen  retort,  or  in  the  iron  bottles  used  for  the  transportation 
of  mercury ;  the  temperature  being  gradually  raised  to  a  dull  red- 
heat.  The  liquor  condensed  in  the  receiver  is  rectified  over  chloride 
of  calcium,  and  then  allowed  to  rest  for  several  days  on  melted 
chloride  of  calcium ;  after  which  it  is  distilled,  the  first  }  only  of 
the  product  being  collected,  while  the  other  fourth  contains,  besides 
a  still  large  quantity  of  acetone,  a  considerable  quantity  of  a  peculiar 
substance,  boiling  at  248°,  and  which  has  been  called  dumasin. 

Acetone  is  a  very  mobile,  colourless  liquid,  of  a  peculiar  odour ; 
and  its  density  is  0.792,  while  it  boils  at  132.1°,  the  density  of  its 
vapour  being  2.022 ;  so  that  its  equivalent  C3H3O  is  represented 
by  2  volumes  of  vapour.  The  formula  of  acetone  may  be  written 
CgHgOg  or  CgH^OjHO,  in  which  case  its  equivalent  is  represented 
by  4  volumes  of  vapour  like  that  of  alcohol.  It  burns  with  a  bril- 
liant flame ;  and  is  soluble  in  all  proportions  in  water,  alcohol,  and 
ether,  while  chloride  of  calcium  and  caustic  potassa  readily  abstract 
its  water. 

§  1376.  On  mixing  acetone  with  twice  its  weight  of  concentrated 
sulphuric  acid,  heat  is  evolved,  and  the  mixture  turns  brown,  while 
the  smell  of  sulphurous  acid  is  perceived  at  the  same  time ;  and  if 
the  liquor  be  then  diluted  with  water  and  saturated  with  carbonate 
of  baryta,  insoluble  sulphate  of  baryta  is  separated,  and  a  soluble 
salt  of  baryta,  which  crystallizes  in  pearly  lamellae,  is  obtained. 
The  formula  of  the  salt  is 

2BaO,(C«H30,2S03)+HO; 
its  equivalent  of  water  -being  removed  by  drying. 

If  the  acid  liquor  be  saturated  with  carbonate  of  lime,  a  salt  of 
lime  is  obtained ; 

2CaO,(CeH30,2SO,)+HO. 

If  a  smaller  quantity  of  sulphuric  acid  be  used,  for  example,  by 
treating  two  volumes  of  acetone  with  1  volume  of  sulphuric  acid,  a 
soluble  salt  of  baryta  is  still  obtained  by  saturating  with  carbonate 
of  baryta,  but  which  contains  only  one-half  of  the  sulphuric  acid  of 
the  preceding  acid,  and  only  1  equivalent  of  base.  The  formula  of 
this  salt  is  BaO(CeH50,S03)+HO. 

§  1377.  By  distilling  2  volumes  of  acetone  and  1  volume  of  sul- 


650  TRANSFORMATIONS   OF   ALCOHOL. 

phuric  acid,  two  new  products  result,  mesitylen  CgH^  and  mesitic 
ether  Q^YLfi. 

The  mesitylen  floats  on  the  surface  of  the  distilled  liquid,  from 
which  it  is  separated  with  a  pipette,  and  shaken  several  times  with 
pure  water,  and  then  distilled  over  chloride  of  calcium.  Mesitylen 
is  an  oleaginous,  colourless  liquid,  of  an  alliaceous  odour,  lighter  than 
water,  and  boiling  at  276.8°. 

§  1378.  Impure  mesitic  ether  is  obtained  by  treating  acetone  with 
sulphuric  acid ;  while  it  is  obtained  in  a  very  pure  state  by  decom- 
posing the  chlorohydric  ether  CgH^Cl  of  acetone  by  an  alcoholic 
solution  of  potassa.  To  effect  this,  the  ether  is  dissolved  in  alcohol, 
and,  after  having  heated  it,  an  alcoholic  solution  of  potassa  is  added 
until  an  alkaline  reaction  is  produced ;  when,  on  diluting  the  liquor 
with  water,  an  etherized  liquid  separates,  forming  the  upper  stratum, 
which  is  drawn  off  by  a  pipette,  washed  several  times  with  water, 
and  distilled  over  chloride  of  calcium.  It  is  a  colourless  liquid, 
boiling  at  248°,  insoluble  in  water,  but  soluble  in  alcohol,  and  its 
formula  is  CgH^O. 

§  1379.  On  passing  chlorohydric  acid  gas  through  acetone,  it 
dissolves  largely  in  it,  and  a  brown  oleaginous  liquid  results,  which 
is  to  be  digested  for  some  time  over  litharge  to  remove  the  free 
chlorohydric  acid ;  after  which  it  is  washed  several  times  with  water, 
and  dried  by  means  of  chloride  of  calcium.  This  liquid  is  the 
chlorohydric  ether  of  acetone  CgH^Cl,  but  it  is  difficult  to  obtain  it 
pure  by  this  method,  and  it  is  more  easily  effected  by  pouring  into 
1  part  of  acetone,  cooled  by  ice,  2  parts  of  perchloride  of  phosphorus 
PCI5,  added  by  small  quantities  at  a  time.  It  is  then  treated  with 
water,  which  causes  the  separation  of  the  chlorohydric  ether  in  the 
form  of  a  yellow  oleaginous  liquid.  It  cannot  be  distilled,  because 
it  is  destroyed  by  heat ;  and  the  alkaline  liquids  decompose  it,  even 
water  effecting  decomposition  after  some  time. 

Concentrated  nitric  acid  acts  powerfully  on  acetone,  forming 
several  products,  the  nature  of  which  is,  however,  not  yet  sufficiently 
understood. 

§  1380.  From  the  nature  of  its  compounds,  acetone  will  be  seen  to 
resemble  alcohol,  if  its  formula  be  written  CgHgO^.  But  the  acid 
C8H30,2S03,  which  may  be  assimilated  with  sulphovinic  acid,  differs 
from  it  by  saturating  2  equivalents  of  base,  while  sulphovinic  acid 
saturates  only  one.  Sulphovinic  acid,  chlorohydric  ether,  and  the 
compound  ethers  of  alcohol  reproduce  alcohol  when  boiled  with 
alkaline  liquids ;  while  the  corresponding  products  of  acetone  do  not 
yield  acetone  under  the  same  circumstances.  When  the  vapour  of 
alcohol  is  passed  over  hydrated  potassa  heated  to  about  500°, 
acetate  of  potassa  is  obtained ;  but  under  the  same  circumstances 
acetone  does  not  yield  an  acid  corresponding  to  acetic  acid.  Lastly, 
no  compound  ether  has  hitherto  been  obtained  with  acetone. 


CACODYL.  551 

Cacodyl  Series. 
§  1381.  By  distilling,  in  a  retort  furnished  with  a  receiver,  a 
mixture  of  equal  parts  of  anhydrous  acetate  of  potassa  and  arsenious 
acid,  a  liquid  product  is  obtained,  called  at  first  Cadet's  liquid^  then 
alcarsiriy  and  lastly  oxide  of  caeodyl ;  and  which  ignites  when 
exposed  to  the  air,  and  possesses  many  other  remarkable  properties. 
The  composition  of  this  substance,  supposed  to  be  pure,  corresponds 
to  the  formula  C^HgAsO.  It  behaves  in  its  chemical  reactions  like 
the  oxide  of  a  radical  C^HgAs,  playing  a  part  analogous  to  that 
of  cyanogen,  and  has  been  called  cacodyl.  This  radical  enters 
into  a  great  number  of  other  compounds,  as  shall  presently  be 
described.* 

In  consequence  of  the  facility  with  which  this  substance  changes 
when  exposed  to  the  air,  and  its  poisonous  action  on  the  animal 
economy,  great  caution  must  be  used  in  preparing  it ;  and  the 
retort  should  be  hermetically  fitted  to  the  receiver,  which  must  be 
furnished  with  a  tube  to  conduct  the  vapours  out  of  the  laboratory. 
At  the  close  of  the  operation  the  receiver  contains  3  strata  of  liquid ; 
the  middle  one,  which  is  brown  and  of  an  oleaginous  consistence, 
consists  of  impure  oxide  of  cacodyl,  and  is  decanted  by  means  of  a 
siphon  filled  with  water,  and  conveyed  to  the  bottom  of  a  bottle 
filled  with  boiled  water.  It  is  shaken  several  times  with  the  water, 
which  is  then  poured  off  and  replaced  by  alcohol,  which  dissolves 
the  oxide  of  cacodyl.  By  pouring  the  alcoholic  solution  into  boiled 
water,  the  oxide  of  cacodyl  is  again  precipitated  in  the  form  of  a 
liquid  layer  at  the  bottom  of  the  bottle ;  and  the  supernatant  water 
being  rapidly  removed,  the  access  of  air  is  prevented  by  a  rapid 
current  of  hydrogen  which  is  passed  into  the  bottle.  The  latter  is 
then  closed,  after  having  introduced  into  it  chloride  of  calcium  in- 
tended to  absorb  the  water  and  alcohol ;  and  the  liquid  is  first 
decanted  in  a  tubulated  retort  traversed  by  a  current  of  hydrogen, 
and  to  which  a  receiver  is  fitted ;  and  is  then  distilled,  still  keeping 
up  the  current  of  hydrogen,  when  pure  oxide  of  cacodyl  is  obtained 
as  a  colourless,  very  fluid  liquid.  It  has  a  strong  and  very  disa- 
greeable smell,  is  very  poisonous,  and  its  density  is  1.46.  It  soli- 
difies at  —9.4°,  and  boils  at  about  302°,  the  density  of  its  vapour 
being  7.8,  and  1  volume  of  the  gaseous  substance  therefore  consist- 
ing of 

2  vol.  of  vapour  of  carbon 0.552 

6    "        hydrogen 0.662 

J    "        vapour  of  arsenic 5.185 

I    "        oxygen. : 1.688 

7.977 
and  its  equivalent  C^HgAsO  is  represented  by  2  volumes  of  vapour. 

*  The  discovery  of  cacodyl,  and  the  masterly  investigatiou  of  all  the  compounds 
of  this  radical,  is  wholly  due  to  Robert  Bunsen. —  W.  L.  F. 


652  TRANSFORMATIONS   OF  ALCOHOL. 

The  chemical  reaction  which  produces  it  is  represented  by  the 
following  equation ; 

2(KO,C,H303)4-As03=^2(KO,CO,)+2CO,+C,H3AsO. 

Oxide  of  cacodyl  is  insoluble  in  water,  but  it  dissolves  largely  in 
alcohol  and  ether.  It  dissolves  phosphorus  and  sulphur  without 
any  change,  while  chlorine,  bromine,  and  iodine  decompose  it 
rapidly.  It  combines  with  anhydrous  sulphuric  acid  and  forms  a 
crystalline,  deliquescent  compound,  which  dissolves  in  water,  yield- 
ing an  acid  liquid. 

By  pourmg  a  dilute  solution  of  corrosive  sublimate  into  an  alco- 
holic solution  of  oxide  of  cacodyl  a  white  precipitate  is  formed, 
which  is  a  simple  combination  of  oxide  of  cacodyl  with  chloride  of 
mercury,  according  to  the  formula  C4HgAsO,2HgCl,  and  which 
dissolves  in  boiling  water,  and  again  separates  from  it  in  crystals 
on  cooling.     Bromide  of  mercury  forms  an  analogous  compound. 

Oxide  of  cacodyl  dissolves  in  several  acids,  with  which  it  appears 
to  play  the  part  of  a  weak  base.  By  adding  nitrate  of  silver  to  a 
solution  of  oxide  of  cacodyl  in  nitric  acid  a  white  crystalline  precipi- 
tate is  formed,  of  which  the  formula  is  3C4HgAsO,(AgO,N05). 

§  1382.  Exposed  to  the  air,  oxide  of  cacodyl  becomes  heated  and 
incandescent,  its  combustion  being  complete,  while  thick  vapours  of 
arsenious  acid  are  formed.  But  if  cacodyl  covered  with  a  stratum 
of  water  be  exposed  to  the  air,  the  oxygen  is  slowly  absorbed,  and 
arsenious  acid,  a  peculiar  etherial  substance,  and  a  more  oxy- 
genated product  of  cacodyl,  cacodylic  acid,  are  formed.  By  adding 
a  sufficient  quantity  of  water  the  cacodylic  acid  is  dissolved ;  and 
by  evaporating  the  solution  and  treating  with  boiling  alcohol,  the 
alcoholic  liquor  deposits,  on  cooling,  cacodylic  acid  in  colourless 
cystals.  This  substance,  which  is  inodorous  and  nearly  tasteless, 
does  not  change  in  the  air,  and  is  poisonous,  but  less  so  than  arse- 
nious acid.  It  is  decomposed  at  446°  without  distilling ;  its  formula 
is  C^HgAsO^+HO;  and  it  combines  with  bases  without  yielding 
crystallizable  salts.  Protochloride  of  tin  and  phosphorous  acid 
abstract  its  oxygen  and  restore  it  to  the  state  of  oxide  of  cacodyl. 

§  1383.  By  distilling  with  highly  concentrated  chlorohydric  acid 
the  compound  of  oxide  of  cacodyl  with  chloride  of  mercury,  a  chl<h 
ride  of  cacodyl  C^HgAsCl  is  obtained,  which  should  be  brought  into 
contact  with  chloride  of  calcium  and  quicklime,  and  then  redistilled. 
Chloride  of  cacodyl  is  a  colourless  liquid,  heavier  than  water,  of  a 
sharp  smell,  and  insoluble  in  water  and  ether,  but  soluble  in  all  pro- 
portions in  alcohol.  It  resists  a  temperature  of  —49°  without  be- 
coming solid,  and  boils  at  a  little  above  212°,  its  vapour  becoming 
incandescent  in  contact  with  the  air.  Nitrate  of  silver  wholly 
abstracts  its  chlorine  and  reproduces  oxide  of  cacodyl.  When 
oxide  of  cacodyl  is  treated  with  gaseous  chlorohydric  acid,  chloride 
of  cacodyl  is  also  formed,  but  a  portion  is  precipitated  in  combina- 


CACODYL.  553 

tion  with  the  water  formed.  The  density  of  the  vapour  of  chloride 
of  cacodyl  is  4.86 ;  and  its  equivalent  corresponds,  therefore,  to  4 
volumes  of  vapour. 

A  bromide  and  iodide  of  cacodyl  may  be  obtained  by  similar 
processes. 

Chloride  of  cacodyl  is  partially  decomposed  by  contact  with 
water,  a  combination  of  3  equiv.  of  oxide  of  cacodyl  with  3  equiv. 
of  chloride  of  cacodyl  being  formed,  which  is  volatile,  and  boils  at 
228.2°,  the  density  of  its  vapour  being  5.35,  so  that  it  is  formed 
of  3  vol.  of  vapour  of  chloride  of  cacodyl  and  1  vol.  of  oxide  of 
cacodyl  without  condensation.  The  bromide  and  iodide  of  cacodyl 
yield  similar  compounds. 

By  adding  perchloride  of  platinum  to  an  alcoholic  solution  of 
chloride  of  cacodyl,  a  brick-red  precipitate  is  obtained,  which  is, 
probably,  a  simple  combination  of  the  two  substances  ;  while,  if  the 
liquid  be  boiled,  the  precipitate  is  redissolved,  and  yields  a  liquor 
ifrom  which  neither  the  platinum  nor  the  chloride  of  cacodyl  can  be 
precipitated  by  reagents  which  commonly  produce  that  effect.  This 
new  compound  is  a  true  base  which  forms  crystallizable  compounds 
with  several  acids. 

§  1384.  A  sulphide  of  cacodyl  C^H^AsS  is  obtained  by  distilling 
chloride  of  cacodyl  with  sulfhydrate  of  sulphide  of  barium,  when 
sulfhydric  acid  is  disengaged,  while  water  and  the  sulphide  of 
cacodyl  pass  over  in  distillation,  the  latter  of  which  is  purified 
by  digesting  it  over  chloride  of  calcium  and  carbonate  of  lead,  and 
then  distilling  it  in  a  current  of  hydrogen.  Sulphide  of  cacodyl  is 
a  colourless  liquid,  which  does  not  fume  in  the  air,  is  insoluble  in 
water,  but  readily  soluble  in  alcohol  and  ether.  It  combines  di- 
rectly with  sulphur  and  forms  a  more  sulphuretted  compound, 
which  may  be  obtained  crystallized  by  dissolving  it  in  ether.  It 
rapidly  absorbs  the  oxygen  of  the  air,  and  then  forms  several  com- 
pounds, among  which  cacodylic  acid  is  observed.  Chlorohydric 
acid  decomposes  sulphide  of  cacodyl,  disengaging  sulfhydric  acid, 
while  chloride  of  cacodyl  is  formed ;  sulphuric  and  phosphoric  acids 
also  decompose  it,  a  sulphate  and  phosphate  of  oxide  of  cacodyl 
being  formed. 

The  density  of  the  vapour  of  sulphide  of  cacodyl  is  8.39,  and  its 
formula  therefore  corresponds  to  2  volumes  of  vapour. 

§  1385.  Cyanide  of  cacodyl  C^HgAsCy  is  obtained  by  distilling 
oxide  of  cacodyl  with  cyanide  of  mercury,  when  oxide  of  mercury 
remains  in  the  retort,  while  the  cyanide  of  cacodyl  distils  over  and 
forms,  at  the  bottom  of  the  water  in  the  receiver,  an  oily  stratum, 
which,  on  cooling,  assumes  a  crystalline  appearance.  The  crystals 
are  pressed  between  several  folds  of  tissue-paper,  and  distilled  over 
baryta.  Cyanide  of  cacodyl  melts  at  90.5°,  boils  at  284°,  and  is 
but  slightly  soluble  in  water,  but  largely  so  in  alcohol  and  ether. 

It  is  an  excessively  poisonous  substance,  the  vapour  of  which  it 


554  TRANSFORMATIONS   OF   ALCOHOL. 

is  very  dangerous  to  inhale,  and  it  oxidizes  rapidly  in  the  air.  The 
density  of  its  vapour  is  4.55,  and  its  equivalent  is  represented  by 
4  volumes  of  vapour. 

§  1386.  By  heating,  protected  from  the  air,  cleanly  scraped  zinc 
with  chloride  of  cacodyl,  the  metal  is  attacked  without  any  evolu- 
tion of  hydrogen,  and  a  white  crystalline  mass  is  obtained,  on 
treating  which  with  water  to  dissolve  the  chloride  of  zinc,  an  olea- 
ginous liquid,  heavier  than  water,  separates,  which  is  digested  for 
some  time  vith  highly  polished  zinc,  and  then  distilled  after  having 
been  allowed  to  remain  for  some  time  over  chloride  of  calcium  and 
quicklime.  This  substance,  which  is  eaeodyl,  the  radical  of  all  the 
compounds  just  described,  consists  of  a  colourless,  highly  refracting 
liquid,  still  more  inflammable  than  the  oxide  of  cacodyl,  which  it 
closely  resembles :  it  solidifies  at  212°,  and  boils  at  about  338°. 
Exposed  to  a  feeble  current  of  air,  it  forms  a  thick  cloud,  and  is 
first  converted  into  oxide  of  cacodyl,  and  then  into  cacodylic  acid. 
Sulphur,  chlorine,  and  bromine  combine  directly  with  it,  and  form 
sulphide,  chloride,  and  bromide  of  cacodyl. 

The  density  of  its  vapour  is  7.28,  and  its  equivalent  C^HgAs  cor- 
responds to  2  volumes  of  vapour. 

The  products  of  cacodyl  present  a  double  interest,  first  as  organic 
substances  of  which  arsenic  is  the  chief  constituent,  and  secondly, 
because  they  belong  to  the  small  number  of  organic  substances  in 
which  the  existence  of  a  compound  radical  has  been  proved,  which, 
when  isolated,  reproduces,  by  direct  combination,  all  the  substances 
of  the  series. 

PRODUCTS  OF  THE  ACTION  OF  CHLORINE  ON  SUBSTANCES  OF  THE 
ALCOHOLIC  SERIES. 

Action  of  Chlorine  on  Chlorohydric  Ether. 

§  1387.  In  a  badly  lighted  situation,  chlorine  exerts  no  action  on 
chlorohydric  ether ;  while  in  a  bright  light,  or  still  better,  in  the 
direct  rays  of  the  sun,  reaction  ensues  with  development  of  heat, 
chlorohydric  acid  being  disengaged,  while  an  etherial  liquid  con- 
denses. When  any  considerable  quantity  of  this  liquid  is  to  be 
prepared,  the  apparatus  is  arranged  as  represented  in  fig.  680.  Into 
the  flask  A  is  introduced  alcohol  saturated  with  chlorohydric  acid 
gas,  or  merely  a  mixture  of  equal  volumes  of  alcohol  and  highly 
fuming  chlorohydric  acid  of  commerce.  The  gas  is  passed  through 
a  first  washing-bottle  B  containing  water,  then  through  a  second 
bottle  C  with  concentrated  sulphuric  acid,  and  lastly  through  a 
third  bottle  D  again  containing  water.  Into  another  flask  I  is  in- 
troduced peroxide  of  manganese  and  chlorohydric  acid  to  generate 
the  chlorine,  which  is  washed  in  the  water  in  the  bottle  ll.  The 
two  gases  are  conveyed,  by  two  tubes,  the  orifices  of  which  are  op- 
posite to  each  other,  into  the  flask  E,  having  three  tubulures,  the 


ACTION  OF  CHLORINE  ON  ETHERS. 


555 


lower  of  which  passes  into  the  bottle  F  intended  to  collect  the  least 
volatile  portion  of  the  product,  while  the  most  volatile  portion  col- 
lects in  the  bottle  G,  which  should  be  well  cooled.     The  flask  E  in 


Fig.  680. 

which  the  two  gases  unite  should  be  exposed  to  the  sun,  at  least  in 
the  commencement  of  the  operation ;  for  when  the  reaction  is  once 
established,  it  continues  in  the  shade,  and  does  not  cease  with  the 
setting  of  the  sun.  Care  must  be  taken  to  keep  the  chlorohydric 
ether  in  excess  as  regards  the  chlorine,  as  otherwise  the  latter  would 
exert  a  subsequent  action  on  the  first  product  and  produce  a  second 
one  more  chlorinated.  It  is  moreover  difficult  to  avoid,  in  an  ope- 
ration which  lasts  for  a  long  time,  the  formation  of  a  small  quantity 
of  this  product,  unless  the  operation  be  continued  in  the  shade ; 
but,  as  it  is  less  volatile,  nearly  the  whole  of  it  remains  in  the  first 
receiving-bottle.  The  liquid  is  washed  several  times  with  water, 
and  then  distilled  in  a  water-bath,  over  quicklime,  in  order  to  en- 
tirely deprive  it  of  water  and  chlorohydric  acid.  The  first  drops 
which  pass  over  in  distillation  should  be  rejected,  because  they  often 
contain  a  small  quantity  of  unaltered  chlorohydric  ether,  which  re- 
mains in  solution ;  and  the  last  fourth  is  also  set  aside  because  it 
may  contain  a  small  proportion  of  more  highly  chlorinated  pro- 
ducts. 

The  formula  of  the  liquid  thus  obtained  is  C^H^Clg ;  and  it  is 
monocJilorinated  chlorohydric  ether,  presenting  the  same  composition 
as  Dutch  liquid,  the  taste  and  smell  of  which  it  exactly  resembles. 
The  density  of  its  vapour  is  also  exactly  the  same,  3.42 ;  while  its 
boiling  point  is  very  different,  for  monochlorinated  chlorohydric 
ether  boils  at  147.2°,  while  Dutch  liquid  boils  at  180.5°.  These 
two  substances  also  differ  entirely  in  their  chemical  reactions :  thus, 
an  alcoholic  solution  of  potassa  immediately  decomposes  Dutch 
liquid  when  cold,  chloride  of  potassium  being  formed  and  monochlo- 
rinated bicarburetted  hydrogen  C4H3CI  disengaged.     Nothing  simi- 


556  ^HANSFORMATIONS  OF  ALCOHOL. 

lar  occurs  in  monoclilorinated  chlorohy dric  ether ;  and  if  this  sub- 
stance be  distilled  with  an  alcoholic  solution  of  potassa,  a  very 
small  fraction  only  of  it  is  changed,  without  producing  monochlori- 
nated  bicarburetted  hydrogen.  Dutch  liquid  is  acted  on  immedi- 
ately, when  cold,  by  potassium,  hydrogen  beiijg  disengaged,  while 
chloride  of  potassium  and  monochlorinated  bicarburetted  hydrogen 
are  formed ;  but  in  monochlorinated  chlorohydric  ether,  on  the  con- 
trary, the  potassium  preserves  its  metallic  brilliancy.  Dutch  liquid 
differs  therefore  from  its  isomeric,  monochlorinated  chlorohydric 
ether,  in  the  fact  that  1  equivalent  of  hydrogen  and  1  equivalent 
of  chlorine  exist  in  the  compound  in  quite  different  conditions.  In 
the  reactions  just  described,  these  two  elements  behave  as  if  they 
existed,  in  Dutch  liquid,  in  the  state  of  chlorohydric  acid;  for 
which  reason  some  chemists  have  assigned  to  Dutch  liquid  the  for- 
mula C^HgCljHCl,  and  to  monochlorinated  chlorohydric  ether  the 
formula  C^H^Cla,  which  perfectly  represents  the  difference  of  the 
chemical  reactions. 

§  1388.  By  causing  chlorine  to  act  gradually  and  with  the 
assistance  of  solar  light  on  monochlorinated  chlorohydric  ether, 
with  the  precautions  described  in  the  preparation  of  the  various 
degrees  of  chlorination  of  Dutch  liquid,  the  following  products  are 
obtained : 

Bichlorinated  chlorbhydric  ether C^HgClj,  isomeric  with 

monochlorinated  Dutch  liquid ; 
Terchlorinated  chlorohydric  ether C^HgCl^,  isomeric  with 

bichlorinated  Dutch  liquid ; 
Quadrichlorinated  chlorohydric  ether C^HCl,,  isomeric  with 

terchlorinated  Dutch  liquid ; 
Perchlorinated  chlorohydric  ether C^Clg,    identical   with 

perchlorinated  Dutch  liquid,  or  sesquichloride  of  carbon. 

The  final  product  of  the  action  of  chlorine  on  chlorohydric  ether 
is  therefore  the  same  as  that  afforded  by  Dutch  liquid :  it  is  crys- 
tallyzed  sesquichloride  of  carbon,  the  properties  of  which  have  been 
described,  (§  1338.)  The  three  products  C^H^Clg,  C^HgCl^  and 
C4HCI5  derived  from  chlorohydric  ether,  differ  entirely  in  their  phy- 
sical properties  from  the  isomeric  products  obtained  from  Dutch 
liquid ;  and,  in  fact, 

Bichlorinated  chlorohydric  ether C^HjCl,  boils  at...  167.0^ 

Monochlorinated  Dutch  liquid "  "  239.0° 

Terchlorinated  chlorohydric  ether...   CJlfi\     "  215.6° 

Bichlorinated  Dutch  liquid "  "  275.0° 

Quadrichlorinated  chlorohydric  ether  C^HCl,      "  294.8° 

Terchlorinated  Dutch  liquid "  "  307.4° 

The  last  product,  the  sesquichloride  of  carbon,  which  is  common 
to  both  series,  boils  at  356°. 


ACTION  OF  CHLORINE  ON  ETHERS.    *        557 

The  difference  between  the  boiling  points  of  isomeric  chlorinated 
products  of  chlorohjdric  ether  and  Dutch  liquid  becomes  smaller 
and  smaller,  as  the  quantity  of  chlorine  substituted  for  the  hydro- 
gen increases ;  and  lastly,  it  is  reduced  to  nothing  in  the  perchlo- 
rinated  products,  which  are  identical :  thus 

The  difference  of  ebullition  between  monochlorinated  chloro- 

hydric  ether  and  Dutch  liquid  is 71.0° 

Between  bichlorinated  chlorohydric  ether,  and  monochlori- 
nated Dutch  liquid,  it  is 72.0° 

Between  terchlorinated  chlorohydric  ether  and  bichlorided 

Dutch  liquid,  it  is 59.4° 

Between  quadrichlorinated  chlorohydric  ether  and  terchlori- 
nated Dutch  liquid,  it  is 12.6° 

Lastly,  between  identical  perchlorinated  products,  it  is  ne- 
cessarily      0.0° 

§  1389.  Bichlorinated  and  terchlorinated  chlorohydric  ethers  differ 
very  distinctly  in  their  chemical  reactions  from  their  isomerics, 
monochlorinated  and  bichlorinated  Dutch  liquid.  In  fact,  the  pro- 
ducts derived  from  Dutch  liquid  yield,  with  an  alcholic  solution  of  • 
potassa,  the  former,  bichlorinated  bicarburetted  hydrogen  C^HgClg, 
the  latter,  terchlorinated  bicarburetted  hydrogen  C^HClj ;  while  the 
isomeric  products  derived  from  chlorohydric  ether  afford  no  similar 
results :  they  resist  the  action  of  potassa,  and,  after  a  long  time,  sub- 
stitutions of  oxygen  for  chlorine  alone  are  formed.  The  differences 
exhibited  in  this  chemical  reaction  by  the  two  isomeric  series  is 
therefore  perfectly  explained  by  writing  the  products  derived  from 
Dutch  liquid  C,H,Cl2,HCl  and  C,HCl3,HCl. 

Quadrichlorinated  chlorohydric  ether  and  its  isomeric  terchlori- 
nated Dutch  liquid  exhibit  also  remarkable  differences  in  their 
chemical  reactions ;  the  latter  substance  being  readily  acted  on  by 
the  alcoholic  solution  of  potassa,  and  yielding  perchlorinated  bicar- 
buretted hydrogen  C4CI4  or  chloride  of  carbon ;  while  quadrichlori- 
nated chlorohydric  ether  is  much  more  easily  acted  on  by  the 
alcoholic  solution  of  potassa  than  the  products  which  preceded  it, 
but  the  reaction  is  far  from  btnng  as  simple  as  that  exerted  on  its 
isomeric. 

§  1390.  Chlorohydric  ether  may  be  regarded  as  being  derived 
from  a  carburetted  hydrogen  C^Hg,  which  has  hitherto  not  been 
obtained,  and  which,  in  its  constitution,  would  differ  from  carburet- 
ted hydrogen,  which  we  assumed  (§1339)  as  the  starting  point  of  the 
series  of  Dutch  liquid,  and  we  should  then  have  the  following  series : 

Carburetted  hydrogen  unknown C^Hg,  density  "  boils  at  " 

Chlorohydric  ether C^H.Cl    "     0.840    "     54.5° 

Monochlorinated  chlorohydric  ether.  C.H^Cl^  "     1.174    "  147.2° 
Bichlorinated  "  "      CfiC\    "    1.372    "  167.0° 


558  TRANSFORMATIONS   OF  ALCOHOL. 

Terchlorinated  chlorohjdric 

ether C,H,C1,  density  1.530  boils  at  215.6^ 

Quadrichlorinatedchlo.  ether..  C4HCI5        "     1.644         "      294.8° 
Perchlorinated  "         "      C^Clg  "         "  "      356.0° 

Products  of  the  Action  of  Chlorine  on  Ether  C^H^O. 

§  1391.  Ether  is  very  violently  acted  on  by  chlorine,  the  temper- 
ature rising  considerably,  while  the  substance  turns  black  and 
ignites,  if  the  chlorine  be  in  too  great  quantity,  and  if  the  apparatus 
is  exposed  to  the  sun.  By  operating  in  a  darkened  room,  and  ex- 
hausting the  action  of  the  chlorine  by  elevating  even  slightly  the 
temperature  toward  the  close  of  the  operation,  a  product  is  obtained 
which  may  be  regarded  as  hichlorinated  ether^  for  its  formula  is 
C4H3CI2O.  It  is  a  colourless,  oleaginous  liquid,  of  a  smell  resem- 
bling fennel;  and  its  density  is  2.5,  while  it  decomposes  at  about 
284°  without  boiling.  Heated  with  an  alcoholic  solution  of  potassa, 
chloride  of  potassium  and  acetate  of  potassa  are  formed,  from  the 
following  equation : 

C,H30C1,+3K0=2KC1+K0,C,H303, 

the  2  equiv.  of  chlorine  are  therefore  replaced  by  2  equiv.  of  oxygen. 
By  heating  hichlorinated  ether  in  a  current  of  sulf hydric  acid 
gas,  chlorohydric  acid  is  disengaged,  and,  if  it  be  sufficiently  heated, 
an  oleaginous  liquid,  the  greater  portion  of  which  solidifies  on  cool- 
ing, passes  over  in  distillation.  This  substance  is  removed,  pressed 
between  several  folds  of  tissue-paper,  and  dissolved  in  boiling  alco- 
hol. On  cooling,  crystals  of  the  two  substances  are  separated, 
which  are  again  crystallized,  until  only  the  prismatic  forms  of  a  single 
species  are  obtained.  The  composition  of  the  substance  then  cor- 
responds to  the  formula  C4H3S2O,  and  is  derived  from  the  primitive 
substance  C4H3CI2O,  hichlorinated  ether,  by  2  equiv.  of  sulphur 
being  substituted  for  2  equiv.  of  chlorine ;  and  it  is  therefore  ether 
C4H5O  of  which  2  equiv.  of  hydrogen  have  been  replaced  by  2 
equiv.  of  sulphur,  or  bisulphuretted  ether.  It  is  insoluble  in  water, 
and  decomposed  at  about  248°,  without  distilling.  An  alcoholic 
solution  of  potassa  decomposes  it,  forming  sulphide  of  potassium 
and  acetate  of  potassa : 

C,H3S,04-3KO=2KS+KO,C,H30,. 

Alcoholic  liquors  which  have  been  used  in  the  purification  of 
bisulphuretted  ether  deposit,  after  evaporation,  yellow  aciculge  of 
the  formula  C4H3CISO,  which  consist  of  hichlorinated  ether,  in 
which  a  single  equivalent  of  chlorine  has  been  replaced  by  1  equiv. 
of  sulphur. 

§  1392.  By  arresting  the  action  of  chlorine  on  ether  at  a  suitable 
moment,  the  liquid  contains  a  large  quantity  of  monochlorinated 
ether  C^H^CIO,  which  is  particularly  formed  when  chlorine  and 


ACTION  OF  CHLORINE  ON  ETHER.  559 

vapour  of  ether  in  excess  are  introduced  into  a  flask  exposed  to  dif- 
fused light,  and  the  liquid  obtained  is  distilled,  dividing  the  pro- 
ducts into  fractions,  when  the  first  portions  which  pass  over  in  dis- 
tillation contain  a  large  amount  of  ether  and  chlorohydric  ether, 
while  the  monochlorinated  ether  C^H^CIO  does  not  distil  before 
about  356°.  This  product  is  often  formed  in  large  quantities  in  the 
preparation  of  Dutch  liquid  when  the  bicarburetted  hydrogen  be- 
comes loaded  with  vapours  of  ether. 

The  preparation  of  pure  chlorinated  ethers  is  often  very  difficult, 
and  would  be  almost  impossible  if  carried  on  in  the  sun.  A  large 
quantity  of  chlorohydric  ether  is  necessarily  formed  in  this  prepara- 
tion, from  the  reaction  which  the  chlorohydric  acid,  arising  from  the 
combination  of  the  chlorine  with  the  hydrogen  abstracted  from  the 
ether,  exerts  on  the  unaltered  ether  C^H^O ;  and  if  the  operation  be 
carried  on  in  a  darkened  place,  the  chlorohydric  ether  is  disengaged 
almost  entirely,  without  being  ultimately  attacked  by  the  chlorine ; 
which  would  not  be  the  case  in  the  light  of  the  sun,  because  the 
chlorohydric  ether  would  then  be  attacked  by  the  chlorine,  and 
yield  chlorinated  chlorohydric  ethers,  much  less  volatile,  and  which 
would  remain  dissolved  in  the  chlorinated  ethers. 

§  1393.  The  action  of  chlorine  on  ether  does  not  stop  at  bichlori- 
nated  ether  C^HjClgO,  but  continues,  if  the  experiment  be  made  in 
the  sun,  furnishing  liquids  richer  and  richer  in  chlorine,  and  corre- 
spondingly poor  in  hydrogen.  By  exhausting  the  action  of  the 
chlorine,  by  pouring  the  highly  chlorinated  liquid  into  large  bottles 
filled  with  dry  chlorine,  and  exposed  to  intense  solar  light,  there  are 
found  white  crystals,  remarkable  for  their  beautiful  forms  and  their 
size,  consisting  of  perchlorinated  ether  C^Cl^O,  in  which  all  the 
hydrogen  of  ether  C^H^O  has  been  replaced  by  chlorine.  Perchlo- 
rinated ether  melts  at  156.2°,  and,  when  heated  to  572°,  it  does  not 
boil,  but  is  decomposed  into  sesquichloride  of  carbon  C^Clg,  and  a 
liquid  product  of  the  formula  C^Cl^Oj,  consisting  of  chlorinated 
aldehyd.  The  decomposition  is  represented  by  the  following  equation : 

2C,C1,0=C,C1,+C,C1A. 
When  perchlorinated  ether  is  heated  with  an  alcoholic  solution  of 
monosulphide  of  potassium,  chloride  of  potassium  and  a  new  com- 
pound of  the  formula  C4CI3O  are  found,  which  substance  evidently 
belongs  to  the  series  of  bicarburetted  hydrogen  C^H^;  3  equiv.  of 
chlorine  having  replaced  3  of  hydrogen,  and  1  equiv.  of  oxygen  oc- 
cupying the  place  of  the  last  equiv.  of  hydrogen.  Treated  with 
chlorine,  in  the  sun,  the  substance  C^ClgO  reproduces  perchlorinated 
ether  C^Cl^O.  The  two  substances  C^CljO  and  C4CI3O  present, 
therefore,  relations  precisely  similar  to  those  existing  between  the 
two  chlorides  of  carbon  C^Clg  and  Gfi\,  the  first  of  which  belongs 
to  the  series  of  chlorohydric  ether,  and  the  second  to  that  of  bicar- 
buretted hydrogen. 


660  TRANSFORMATIONS   OF  ALCOHOL. 

It  is  essential,  in  order  to  obtain  pure  perchlorinated  ether,  to 
expose  to  the  action  of  chlorine  in  excess,  influenced  by  the  solar 
rajs,  only  ether  already  completely  chlorinated  in  the  shade  and 
freed  from  ether  and  chlorohydric  ether ;  as  otherwise  large  quan- 
tities of  chloride  of  carbon  C^Clg,  which  would  remain  mixed  with 
the  chlorided  ether,  would  be  inevitably  formed. 

"It  is  equally  necessary  to  operate  upon  anhydrous  ether,  and  with 
perfectly  dried  chlorine,  for,  if  water  be  present,  it  is  entirely  de- 
composed by  the  chlorine,  and  its  nascent  oxygen  exerts  an  oxidizing 
action  on  the  ether,  (§1366,)  forming  aldehyd  C^H^O^,  and  conse- 
quently causing  the  products  of  the  action  of  chlorine  on  aldehyd  to 
be  mixed  with  those  of  the  action  of  chlorine  on  ether  C^H^O. 

Action  of  Chlorine  on  Sulfhydric  Ether^  C^H^S. 

§  1394.  Sulfhydric  ether  is  powerfully  acted  on  by  chlorine,  with 
disengagement  of  chlorohydric  acid,  and  it  even  ignites  when  pro- 
jected into  a  bottle  filled  with  gaseous  chlorine.  After  attacking 
the  sulfhydric  ether  by  chlorine,  in  a  darkened  place,  and  intro- 
ducing the  chlorine  slowly,  in  order  to  avoid  too  great  an  elevation 
of  temperature,  the  apparatus  is  exposed  to  the  sun  as  soon  as  the 
action  ceases,  and  chlorine  passed  through  until  chlorohydric  acid 
is  no  longer  disengaged.  The  liquid  is  exposed  in  vacuo  near  a  cup 
filled  with  a  concentrated  solution  of  caustic  potassa,  which  absorbs 
the  chlorine  and  chlorohydric  acid  it  contains;  and  there  remains  a 
yellow  liquid,  of  an  extremely  disagreeable  and  persistent  smell,  of 
the  density  1.673,  and  which  decomposes  at  about  320°.  Its  for- 
mula is  C^HCl  S,  and  it  constitutes  quadrichlorinated  sulfhydric 
ether :  intermediate  products  probably  exist,  but  they  have  not  yet 
been  discovered. 

^Action  of  Chlorine  on  Alcohol  C^Ufi^. 

§  1395.  Chlorine  acts  very  powerfully  on  alcohol,  and  yields  very 
various  products,  according  to  the  strength  of  the  alcohol.  We 
shall  suppose  the  most  simple  case,  that  in  which  the  alcohol  is 
anhydrous,  and  admit  that  the  chlorine  is  perfectly  dry.  Alcohol 
absorbs  a  large  quantity  of  chlorine,  without  any  disengagement  of 
chlorohydrj^c  acid,  if  its  temperature  be  kept  sufficiently  low ;  and 
if,  after  a  certain  length  of  time,  water  be  poured  on  the  product, 
an  oleaginous  liquid  is  separated  from  it,  which  falls  to  the  bottom 
of  the  vessel,  and  is  a  mixture  of  several  chlorinated  substances : 
this  substance  is  called  chloralcoholic  oil,  but  the  substances  com- 
posing it  are  unknown.  If  the  action  of  chlorine  on  alcohol  be 
indefinitely  continued,  an  oily  liquid  soon  separates,  which  gradually 
increases,  and  finally  constitutes  the  whole  mass.  This  liquid, 
which  is  also  very  complex,  is  gently  heated,  in  order  to  disengage 
the  very  volatile  products,  such  as  chlorohydric  ether  and  its  highly 
chlorinated  products,  w^hich,  if  they  remained  in  the  mixture,  would 


^  OHLORAL.  561 

be  subsequently  transformed  into  chloride  of  carbon  C^Clg.  The 
action  of  the  chlorine  is  continued,  the  temperature  elevated,  and 
it  is  terminated  by  the  assistance  of  the  solar  rays.  The  liquid 
obtained  should  be  mixed  with  3  or  4  times  its  volume  of  sulphuric 
acid,  and  the  bottle  is  shaken  several  times,  after  which  its  contents 
are  distilled  over  sulphuric  acid.  The  product  of  this  distillation 
is  again  distilled  in  a  tubulated  retort  furnished  with  a  thermo- 
meter, and  the  first  products,  containing  a  large  amount  of  chlo- 
rohydric  acid,  are  rejected,  the  product  distilling  at  201.2°  being 
separately  collected,  which  forms  a  colourless  liquid,  of  a  suffocat- 
ing odour,  and  exciting  to  tears.  Its  density  is  1.502,  and  its  com- 
position corresponds  to  the  formula  C^HClgOg :  it  is  called  chloral^ 
but  is  only  ter chlorinated  aldehyd.  Its  equivalent  corresponds  to 
4  volumes  of  vapour. 

The  formation  of  chloral  by  the  action  of  chlorine  on  alcohol,  is 
explained  in  the  following  manner : — The  formula  of  anhydrous 
alcohol  is  C^HgOg,  while,  in  the  majority  of  its  reactions,  it  behaves 
like  a  compound  of  ether  C^H.O  and  water  HO  ;  and  the  action  of 
chlorine  on  alcohol  yields  the  same  products  as  if  it  acted  on  a 
mixture  of  1  equivalent  of  ether  and  1  equivalent  of  water  :  it  first 
exerts  an  oxidizing  action,  by  decomposing  the  equivalent  of  water, 
and  the  product  of  this  action  is  aldehyd  C^H^Og,  which  is  in  fact 
obtained  in  large  quantity  during  the  first  periods  of  the  action  of 
chlorine  on  alcohol,  and  may  be  separated  by  distillation.  But  if 
the  action  of  the  chlorine  continues,  as  there  is  no  more  water,  the 
previous  oxidizing  action  is  replaced  by  a  chlorinating  action,  by 
which  the  substance  loses  hydrogen  and  gains  equivalent  quantities 
of  chlorine  ;  the  reaction  ceasing,  even  in  the  most  intense  solar 
heat  of  our  climate,  at  the  moment  when  the  substance  still  retains 
1  equivalent  of  hydrogen,  and  is  converted  into  chloral  C^HClaOa. 
The  reaction  is  expressed  by  the  following  equation : 

C,H30,H0+8Cl=C,HCl30,+5HCl. 

Chloral  should  therefore  be  considered  as  terchlorinated  aldehyd. 
It  has  hitherto  been  in  vain  attempted  to  remove  directly  by  chlorine 
the  equivalent  of  hydrogen  which  remains  in  terchlorinated  aldehyd, 
so  as  to  produce  quadrichlorinated  or  fer chlorinated  aldehyd 
C^Cl^Og,  although  this  substance  has  been  indirectly  obtained,  it 
being  one  of  the  products  of  the  decomposition  of  perchlorinated 
ether  C,C1,0,  by  heat,  (§  1393.) 

Chloral  dissolves  largely  in  water  without  decomposing,  and  if 
the  solution  be  evaporated  in  vacuo  over  concentrated  sulphuric 
acid,  crystals  are  formed  consisting  of  a  combination  of  chloral 
with  water,  hydrated  chloral  QJlGlfi^^HO^  which  exhibits  the 
molecular  grouping  of  alcohol  C4H50,H0.  Chloral  has  so  great  an 
affinity  for  water  that  it  attracts  the  moisture  of  the  air,  and  is  con- 
verted into  crystals  of  hydrated  chloral.     The  crystals  may  be 

Vol.  IL— 36 


562  TKANSFORMATIONS   OF  ALCOHOL. 

sublimed  without  decomposing,  while  they  give  off  their  water  when 
they  are  distilled  with  concentrated  sulphuric  acid,  and  allow  anhy- 
drous chloral  to  pass  over  in  distillation. 

Chloral  is  decomposed  by  an  aqueous  solution  of  potassa,  two  pro- 
ducts belonging  to  the  series  of  protocarburetted  hydrogen  CgH^  being 
formed,  namely,  formic  acid  CJlfi.^  and  chloroform  CgHClg;  and 
the  reaction  is  expressed  by  the  following  equation : 

C,HCl30„HO+KO=KO,C,H03+C,HCl3. 
The  molecular  grouping  of  alcohol  is  therefore  doubled  in  this  case, 
and  produces  two  groups,  exhibiting  the  grouping  of  protocarburet- 
ted hydrogen. 

When  anhydrous  chloral  is  left  for  some  time  in  a  tube  hermeti- 
cally closed  it  becomes  cloudy,  and  a  white  substance,  which  in- 
creases until  it  has  taken  the  place  of  the  whole  of  the  liquid,  is  de- 
posited on  the  sides  of  the  tube.  This  is  an  isomeric  modification 
of  chloral,  which  no  longer  presents  any  of  the  characteristic  proper- 
ties of  the  latter  substance :  thus  it  is  inodorous,  resembles  porcelain 
in  appearance,  and  no  longer  dissolves  in  water,  whence  it  has  been 
called  insoluble  chloral.  It  reproduces,  when  heated,  ordinary 
>^       chloral,  which  distils  over.     If  the  tube  in  which  the 

y^^^c^.    chloral   is    contained   be   shaped   as   represented   in 

^^  v^  fig.  681,  the  part  a,  in  which  the  chloral  is  solidified, 

*  may  be  heated,  and  the  liquid  chloral  obtained  in  the 

^^*       *       part  b;    and  since  the  liquid  chloral  soon  solidifies 

again,  the  experiment  may  be  indefinitely  repeated  in  the  same  tube. 

It  is  important  to  remark  that  liquid  chloral  C^HClgOg  does  not 
correspond  exactly  to  aldehyd,  for  its  equivalent  is  represented  by 
4  volumes  of  vapour,  while  that  of  aldehyd  C^H^Og  is  represented 
by  2  volumes.  It  must  therefore  be  admitted  that  in  the  conversion 
of  aldehyd  into  terchlorinated  aldehyd  or  chloral,  each  molecule  of 
aldehyd  has  afforded  2  molecules  of  chloral,  or  rather  that  the  mole- 
cules, by  being  charged  with  chlorine,  have  separated  so  as  to  fill  a 
double  space.  If  the  first  hypothesis  is  correct,  insoluble  chloral 
may  possibly  present  the  molecular  grouping  of  aldehyd ;  while 
insoluble  chloral  may  possibly  also  correspond  to  one  of  the  isomeric 
modifications  of  aldehyd  described  §  1367 — to  elaldehyd  or  metal- 
dehyd. 

If  the  alcohol  contained  water,  or  if  the  chlorine  were  not  per- 
fectly dry,  the  reaction  might  be  still  more  complicated.  Supposing 
the  alcohol  to  contain  an  equivalent  of  water,  the  first  stage  of 
oxidation  due  to  the  decomposition  of  the  water  would  not  stop  at 
the  formation  of  aldehyd  C^H^Oa,  but  would  convert  this  substance 
into  acetic  aid  C^HgOj. 

C,H,0,H0+H0+2C1=C,H303+2HC1; 

and  at  a  later  period  during  the  stage  of  chlorination,  products  of 
the  action  of  jchlorine  on  acetic  acid  would  be  formed. 


CHLOEACETIC   ACID.  ^  563 

But  again,  acetic  acid,  by  dissolving  in  unaltered  alcohol,  might 
produce,  particularly  under  the  influence  of  the  chlorohydric  acid, 
which  is  copiously  formed,  acetic  ether,  which  at  a  later  period 
would  form,  by  the  action  of  chlorine,  chlorinated  acetic  ether.  It 
will  hence  be  seen  how  complicated  these  products  may  become,  and 
it  would  be  often  impossible  to  disentangle  the  reactions,  unless 
guided  by  theory. 

Lastly,  if  the  alcohol  were  very  hydrated,  the  oxidizing  stage 
would  continue  until  the  alcohol  was  wholly  converted  into  water 
and  carbonic  acid. 

Products  of  the  Action  of  Chlorine  on  Aldehyde  C^H^Og. 

§1396.  From  what  has  been  just  said  concerning  the  action  of 
chlorine  .on  alcohol,  there  remains  but  little  to  add  touching  the 
action  of  chlorine  on  aldehyde.  By  causing  chlorine  to  act  on  alde- 
hyde C^H^Og,  a  large  quantity  of  chloral  C^HClgOg  is  obtained,  which 
is  mixed  with  other  less  volatile  products,  which  have  not  yet  been 
examined.  They  are  probably  the  chlorinated  aldehydes  C4H3CIO3 
and  C^HjjClgOg,  which  a  more  prolonged  action  of  the  chlorine 
would  have  converted  into  chloral. 

Products  of  the  Action  of  Chlorine  on  Acetic  Acid,  C4H303,HO. 

§  139T.  Chlorine  acts,  powerfully  on  monohydrated  acetic  acid, 
and  at  last,  when  assisted  by  the  rays  of  the  sun,  deprives  it  wholly 
of  its  oxygen,  which  is  replaced  by  an  equivalent  quantity  of  chlo- 
rine; a  crystallized  product  C^ClgOgjHO,  or  chlor acetic  acid,  which  is 
powerfully  acid,  and  possesses  the  same  capacity  of  saturation  as 
acetic  acid,  being  formed.  Intermediate  chlorinated  compounds 
probably  exist,  but  they  have  not  yet  been  examined.  In  order  to 
prepare  chloracetic  acid,  ground-stoppered  bottles,  holding  5  or  6 
litres,  are  filled  with  very  dry  chlorine,  and  into  each  is  poured  4  or 
5  grammes  of  monohydrated  acetic  acid,  after  which  the  bottles  are 
exposed  to  the  sun;  when  their  sides  soon  become  covered  with 
crystals,  which  consist  of  a  mixture  of  oxalic  and  chloracetic  acid, 
while  the  gas  in  the  bottle  is  formed  of  chlorohydric  acid  and 
chlorocarbonic  gas,  resulting  from  a  more  advanced  decomposition, 
which  takes  place,  perhaps,  in  consequence  of  the  small  quantity  of 
water  from  which  it  is  difficult  to  free  the  chlorine  and  the  sides  of 
the  flask.  The  crystals  being  dissolved  in  water,  and  the  solution 
evaporated  in  vacuo  over  concentrated  sulphuric  acid,  the  oxalic  acid 
crystallizes  first,  when  the  mother  liquid  is  decanted,  completely 
evaporated,  and  the  residue  distilled  with  anhydrous  phosphoric  acid. 
The  oxalic  acid  which  might  remain  is  decomposed  into  oxide  of 
carbon  and  carbonic  acid,  and  the  chloracetic  acid  distils  over,  but 
the  first  product  should  not  be  collected,  because  it  may  contain  a 
small  proportion  of  acetic  acid. 


564  TRANSFORMATIONS   OF   ALCOHOL. 

Chloracetic   acid   crystallizes   in   rhombohedral   lamellae    or   in 
colourless  aciculse,  deliquescent  in  the  air;  and  it  melts  at  113° 
and  boils  at  about  392°.    It  combines  with  bases  and  forms  a  large 
number  of  soluble  and  crystallizable  salts. 
The  formula  of  chloracetate  of  potassa  is  K0,C4Cl303+2H0. 

"       of  chloracetate  of  ammonia,  (NH3,H0),C4Cls03  4-4HO. 
"       of  chloracetate  of  silver,        AgO,C4Cl303. 
The  chloracetates  heated  with  an  excess  of  potassa  yield  chloro- 
form and  an  alkaline  carbonate ;  and  if  the  action  be  prolonged,  the 
chloroform  is  itself  converted  into  formic  acid.     We  have,  in  fact, 
KO,C,Cl3034-KO,HO=C,HCl3+2(KO,CO„) 
KO,C,Cl303+5KO=KO,C2H03+2(KO,CO,)+3KCl. 
When  chloracetic  acid  is  treated  with  an  amalgam  formed  of  1 
part  of  potassium  and  150  parts  of  mercury,  it  is  converted  into 
ordinary  acetic  acid,  and  hydrogen  is  substituted  for  the  chlorine : 

C4Cl303,HO+7K+2HO=KO,C,H303+3KCl+3KO. 

§  1398.  Chloracetic  acid  forms  a  compound  ether,  chloracetic  ether 
C4H.O,C4Cl303,  and  a  perchlorinated  chloracetic  ether  C4CI5O, 
C4CI3O3.  Chloracetic  ether  is  prepared  by  distilling  chloracetic 
acid,  or  a  chloracetate,  with  a  mixture  of  alcohol  and  sulphuric  acid, 
and  diluting  the  distilled  product  with  water,  when  the  ether  sepa- 
rates in  the  form  of  oil.  By  exposing  it  to  the  sun  in  bottles  filled 
with  dry  chlorine,  it  is  converted  into  an  oleaginous  product,  per- 
chlorinated chloracetic  ether,  which  boils  at  473°. 

Action  of  Chlorine  on  Compound  Ethers. 

§  1399.  Chlorine  acts  on  the  compound  ethers  and  removes  their 
hydrogen ;  the  hydrogen  removed  being,  in  all  cases,  replaced  by  an 
equivalent  quantity  of  chlorine. 

The  first  action  of  chlorine  on  acetic  ether  Q^fi^QJlfi^  consists 
in  removing  2  equiv.  of  hydrogen  from  simple  ether  C^H.O,  and 
replacing  them  by  2  equiv.  of  chlorine;  which  furnishes  a  hichlori- 
nated  acetic  ether  of  the  formula  C4H3Cl30,C4H303.  It  is  decom- 
posed by  an  alcoholic  solution  of  potassa,  and  yields  of  acetate  of 
potassa  and  chloride  of  potassium 

C,H3Cl,0,C,H303+4KO=2(KO,C,H303)+2KCl. 
If,  on  the  contrary,  the  action  of  the  chlorine  be  exhausted  by 
intense  solar  radiation,   perchlorinated   chloracetic   ether  results, 
C,Cl30,C,Cl,0,. 

By  passing  chlorine,  under  the  influence  of  the  solar  rays,  into 
oxalic  ether  CJi fififi^  until  chlorohydric  acid  is  no  longer  disen- 
gaged, the  ether  is  converted  into  a  crystalline  mass,  which  may  be 
purified  by  pressing  it  between  tissue-paper.  This  is  perchlorinated 
oxalic  ether  Cfi\fi,Cfi^,  which  melts  at  291.2°,  and  is  decomposed 
at  a  higher  temperature. 


SUBSTITUTION.  565 

Carbonic  ether  C^H.OjCOa  subjected  to  the  action  of  chlorine  in 
diffused  light  yields  chlorinated  ether  C^HgClaOjCOg;  and  if  the 
action  of  the  chlorine  be  continued  under  the  influence  of  the  direct 
rays  of  the  sun,  perchlorinated  carbonic  either  CJJlfiyCO^  is  ob- 
tained. 


§  1400.  By  comparing  together  the  numerous  compounds  derived 
from  alcohol,  it  will  be  observed  that  the  greater  part  of  them  are 
formed  by  means  of  the  molecule  of  ether  C^H^O,  or  that  of  alcohol 
CJifi,I{0,  in  which  the  hydrogen  or  oxygen  is  replaced  by  equi- 
valent quantities  of  other  elements :  oxygen,  sulphur,  chlorine,  etc. 
When  the  hydrogen  is  replaced  by  equivalent  quantities  of  chlorine, 
the  equivalent  of  the  derived  substance  is,  in  general,  represented 
by  the  same  number  of  volumes  of  vapour  as  the  substance  from 
which  it  is  derived,  as  in  the  chlorinated  products  derived  from 
chlorohydric  ether.  The  same  is  true  when  oxygen  is  replaced  by 
sulphur,  as  in  ether  C^H^O  and  sulf  hydric  ether  C^H^S.  In  these 
difierent  ^cases  the  gaseous  volume  of  the  element  substituted  is  the 
same  as  that  of  which  it  takes  the  place.  But  when  oxygen,  the 
equivalent  of  which  is  1  vol.,  is  replaced  by  chlorine,  of  which  the 
equivalent  is  2  vol.,  the  equivalent  in  volume  of  the  substance  de- 
.  rived  is  often  different  from  that  of  the  original  substance :  thus,  the 
equivalent  of  ether  C^H^O  is  2  vol.,  while  that  of  chlorohydric 
ether  is  4  vol.  Many  exceptions  to  these  rules  nevertheless  occur: 
thus,  aldehyde  is  derived  from  ether  by  the  replacement  of  1  equiv. 
of  hydrogen  (2  vol.)  by  1  equiv.  of  oxygen,  (1  vol.,)  and  yet  aldehyde 
C4H4O3  is  represented  by  2  vol.  of  vapour,  like  ether  C^H.O ;  while 
by  replacing  3  equiv.  of  hydrogen  (6  vol.)  by  3  equiv.  of  chlorine 
(6  vol.)  in  the  molecule  of  aldehyde,  chloral  or  terchlorinated  alde- 
hyde is  obtained,  of  which  the  equivalent  C4HCI3O3  is  represented 
by  4  vol.,  while  that  of  aldehyde  is  represented  by  2  vol. 

When  chlorine  is  substituted  for  hydrogen,  the  chemical  proper- 
ties of  the  compound,  as  regards  its  acid,  basic,  or  neutral  reactions, 
do  not,  in  general,  appear  to  be  changed ;  the  most  striking  example 
of  which  is  given  by  chloracetic  acid,  which  is  an  acid  as  powerful 
as  acetic,  and  possesses  exactly  the  6ame  capacity  of  .saturation. 
The  compound  chlorinated  ethers  present  additional  examples,  and 
others  shall  subsequently  be  described  which  are  not  less  remarkable. 
But  when  hydrogen  is  replaced  by  oxygen,  the  basic,  acid,  or  neu- 
tral properties  of  the  substances  change  wonderfully.  Thus  ether 
C4H5O,  which  has  a  manifest  affinity  for  acids,  loses  this  property 
when  it  is  converted  into  aldehyde  C^H^Og,  and  becomes  a  powerful 
acid  when  changed  into  acetic  acid  CJlfiy 

In  order  to  appreciate  more  readily  the  relations  of  composition 
of  the  substances  belonging  to  the  alcoholic  or  vinic  series,  we  have 
collected  them  in  the  following  table : 


666 


TRANSrOEMATIONS    OF   ALCOHOL. 


2  vol.  of  vapour. 
2 


4  vol.  of  vapour. 


TABLE  OF  THE  COMPOUNDS  DERIVED  FROM  ETHER,  C^H^O,  OR 
FROM  ALCOHOL,  C4H60,H0,  BY  MEANS  OF  SUBSTITUTION. 

Carburetted  hydrogen  unknown  C4HS,  which  may  be  regarded  as  the  starting 
point  of  the  whole  series. 

SIMPLE  ETHERS. 

Ether C^H.O 

Sulfhydric  ether C^H.S 

Hydroselenic   '* C4HjSe 

Hydrotelluric  "  C«HJe 

Chlorohydric   "  C.H.Cl 

Bromohydric    " C4HjBr 

lodohydric       "  C4HJ 

Cyanohydric    "  C4H,Cy 

Sulphocyanhydric  ether C4HsSCy 

COMPOUND  ETHERS. 
Alcohols. 

Ordinary  alcohol C.H.OjHO 

Sulfhydric     "     C4H,S,HS 

Sulphopotassic  alcohol C4HjS,KS 

Sulphoplumbic       "      C4H,S,PbS 

Sulphomercurio     " C4H,S,Hg,S. 

Compound  Ethers  properly  so  called. 

General  formula  (A  representing  the  acid) C4H,0,A        2  or  4  voL 

Boracic  ether C4H,0,2B0, 

1st  Silicic  ether 3C4H,0,SiO, 

2d  Silicic  ether 3C4H,0,2SiO,. 

Vinic  acids. 
General  formula  of  vinic  acids  formed  by  the 

monobasic  acids  A (C4HJO4- H0),2A 

Formula  of  vinic  acids  produced  by  the  tribasic 

acids,  such  as  P0.,3H0 (C4H.O  +  2HO),POs. 

PRODUCTS  SUCCESSIVELY  DERIVED  FROM  ETHER  C4H,0. 
Ist.  By  oxidation. 

Ether C4H,0  2  vol. 

Acetal (2C4H,0,C4H40a) 

Aldehyde C4H40a  2    " 

Anhydrous  acetic  acid C4H3O,  unknown, 

remains  in  combination  with  the  water  formed,  and  yields 

Hydrated  acetic  acid C4H30„H0        4  vol. 

but  corresponding  to  alcohol C4H,0,H0. 

2dly.  By  the  action  of  Chlorine. 

Ether C4H,     0 

Monochlorinated  ether C4H4CI  0 

Bichlorinated  ether C4HaCl,0 


Perchlorinated  ether C4CI,   0. 


TRANSFORMATIONS    OF   ALCOHOL.  567 

Zdly.  By  the  successive  action  of  Chlorine  and  Sulphur. 

Monochlorinated  and  monosulphuretted  ether C4H8CISO 

Bisulphuretted  ether C4H3S4O. 

PRODUCTS  DERIVED  FROM  SULFHYDRIC  ETHER  C^H.S. 
By  the  action  of  Chlorine. 
Sulfhydric  ether C^HjS 

Quadrichlorinated  sulfhydric  ether C4HC1«S. 

PRODUCTS  DERIVED  FROM  CHLOROHYDRIC  ETHER,  C4H,CL 
By  the  action  of  Chlorine.       / 

Chlorohydric  ether C.H.Cl  4  vol. 

Monochlorinated  chlorohydric  ether C4H4Cla  4    " 

Bichlorinated  *'  "    C4H3CI,  4    " 

Terchlorinated  "  "    C4H<,Cl4  4    " 

Quadrichlorinated        "  *' C4H  CI,  4    " 

Perchlorinated  "  "   C4     CI.  4    « 

PRODUCTS  DERIVED  FROM  ALDEHYDE  C4H40a. 
1st.  By  the  action  of  Oxygen. 

Aldehyde C4H,0a 

Acetic  acid C4H,0, 

which  remains  in  combination  with  the  water  formed. 

2dly.  Bji  the  action  of  Chlorine. 
Aldehyde C^^Jd^     2  voL 

Terchlorinated  aldehyde  or  chloral C4HCla09  4  " 

Perchlorinadte  aldehyde C4CI4O,. 

PRODUCTS  DERIVED  FROM  ALCOHOL  C4H,0,H0. 
1st.  By  the  action  of  Oxygen. 

Alcohol C4H,0,H0  4  vol. 

Aldehyde C4H4O,         2  " 

parts  with  its  equivalent  of  water,  and  belongs  to  the  series  of  ether. 

2dly.  By  the  action  of  Chlorine. 

Alcohol C4H,0,H0   4  vol. 

Aldehyde  (Ist  stage  of  oxidation) C4H40a         2    " 

Chloral  (2d  stage  of  chlorination) C4HCl,0a     2    *« 

Aqueous  ether  C4H,0-|-H0  yields  the  same  products. 

PRODUCTS  DERIVED  FROM  AQUEOUS  ALCOHOL,  C.H.CHO+HO. 

By  the  action  of  Chlorine. 

By  an  oxidizing  action,  acetic  acid C4H,0„H0. 

Aqueous  ether  C4H,04-2H0  yields  the  same  product. 

PRODUCTS  DERIVED  FROM  ACETIC  ACID  C4H,0„H0. 
By  the  action  of  Chlorine. 
Acetic  acid C4H,0„H0  4  voL 

Chloracetic  acid C4C1,0„H0  4   " 


568  TRANSFORMATIONS   OF  ALCOHOL. 

PRODUCTS  DERIVED  FROM  COMPOUND  ETHERS. 
By  the  action  of  Chlorine. 

On  Carbonic  ether C^H.OjCO, 

Bichlorinated  carbonic  ether C^HaClaO.COa 

Perchlorinated  carbonic  ether C4Cls0,C0a 

On  Oxalic  ether C^H.O.C^O, 

Perchlorinated  oxalic  ether C^CljOjCaO, 

On  Acetic  ether; C4H,0,C4H80, 

Bichlorinated  acetic  ether C4H3C]aO,C4H,0, 

Chloracetic  ether C4HjO,C4Cl303 

Perchlorinated  chloracetic  ether 0*01,0, C4CI3O,. 

§  1401.  Some  chemists  regard  ether  as  a  hydrate  of  hicarburetted 
hydrogen,  and  give  it  the  formula  0^11^,110  ;  in  which  case  alcohol 
becomes  a  bihydrate  of  hicarburetted  hydrogen,  and  all  the  products 
of  the  vinic  series  are  considered  as  derived  from  the  same  radical, 
hicarburetted  hydrogen  C^H^.  In  this  point  of  view,  chlorohydric 
ether  is  a  chlorohydrate  of  hicarburetted  hydrogen  C4H^,HC1,  and 
should  be  the  first  of  the  series  of  Dutch  liquid  C4H3C1,HC1  (§  1338) ; 
and  the  action  of  chlorine  upon  chlorohydric  ether  should  therefore 
yield  products  identical  with  those  composing  this  series.  Now  we 
have  seen  that  the  products  derived  from  chlorohydric  ether  exhibit, 
in  fact,  the  same  composition  as  those  deriyed  from  Dutch  liquid, 
but  that  they  differ  essentially  in  their  properties ;  and  it  is  there- 
fore evident  that  ether  cannot  be  regarded  as  a  hydrate  of  olefiant 
gas. 

Other  chenpists  consider  ether  C^H^.O  as  an  oxide  of  carburetted 
hydrogen  C^H^,  to  which  they  have  given  the  name  of  etliyl^  and 
have  supposed  it  to  be  the  radical  of  the  ethers.  All  attempts  to 
obtain  this  hypothetical  root  in  an  isolated  form,  have  hitherto 
failed ;  and  its  supposition  being  entirely  gratuitous,  does  not  assist 
the  explanation  of  chemical  reactions. 


* 


*  The  theory  adopted  by  the  author,  in  which  the  unknown  carburetted  hydro- 
gen C^Hg  is  assumed  as  the  starting  point  of  the  ether  or  alcohol  series,  is  entirely 
French,  and  is  in  other  countries  regarded  in  a  similar  manner  as  the  author 
regards  the  theory  which  assumes  the  hydrocarbon  ethyl,  C4H,,  as  the  radical  of 
which  ether  is  the  oxide  ;  but  since  the  masterly  investigations  of  Prof.  Frankland, 
who  actually  succeeded  in  isolating  ethyl,  probability  inclines  very  much  to  the 
side  of  the  ethyl  theory,  which  requires  description  in  a  work  like  the  present. 

Before  treating  particularly  of  ethyl  one  general  feature  of  the  theory,  which 
equally  applies  to  a  number  of  other  substances,  must  be  described :  the  theory 
of  the  pairing  or  conjugation  of  organic  compounds.  An  organic  body  is  said  to 
be  paired  with  another  when  the  latter,  termed  the  pairling  or  conjugate,  enters 
into  combination  with  the  former  without  the  former  losing  its  essential  pro- 
perties ;  examples  of  which  also  occur  in  inorganic  chemistry,  when  e.  g.  oxide 
of  platinum  combines  with  ammonia  to  form  a  new  oxide,  the  compound  oxide  of 
platinum  and  ammonia,  described  (^1178,)  the  salts  of  which  present  the  same 
general  character  with  those  of  oxide  of  platinum.  The  formula  of  the  compound 
oxide  is  PtO,N3H6,  or  PtO,2NH3,  and  it  may  be  regarded  as  the  oxide  of  a  new 
base,  consisting  of  PtNaHe  or  Pt,2NH3,  1  equiv.  of.  platinum  being  paired  with 


LACTIC   AND   BUTYRIC   FERMENTATION.  569 


LACTIC  AND  BUTYRIC  FERMENTATION. 

§  1402.  Under  certain  conditions,  and  when  assisted  by  ferments, 
sugars  and  their  congeners  experience  decompositions  very  different 
from  those  which  take  place  in  alcoholic  fermentation ;  and  they 
then  give  rise  to  peculiar  acids,  called  lactic  and  butyric^  and  to 
other  substances,  the  nature  of  which  is  but  little  known.  The 
concomitant  circumstances,  or  those  which  produce  lactic  and 
butyric  fermentations,  are  still  less  known  than  those  of  the  alcoholic 
fermentation. 

The  various  kinds  of  sugar,  dextrin,  sugar  of  milk,  yield  a  large 

2  equiv.  of  ammonia;  in  which  case  the  formula  of  the  oxide  in  order  to  express 
the  phenomenon  oi  pairing,  would  be  written  Pt(N3H,)0  or  Pt(2NH8)0. 

In  organic  chemistry  the  pairing  of  combinations  is  of  frequent  occurrence ; 
and  one  of  the  most  beautiful  instances  of  it  is  the  pairing  of  hydrogen  with  one 
or  more  equivalents  of  bicarburetted  hydrogen  or  olefiant  gas.  Hydrogen  may, 
for  the  moment,  be  regarded  as  a  radical,  or  a  metal,  of  which  water  is  the  oxide, 
sulf  hydric  acid  the  sulphide,  chlorohydric  acid  the  chloride,  etc. ;  and  now,  by 
pairing  it  with  1  equiv.  of  olefiant  gas,  (assumed  to  be  CgHg)  there  results  the  com- 
pound ll(Cali<i)  or  CaHs;  which,  if  the  theory  be  correct,  ought  to  form  compounds 
with  oxygen,  sulphur,  chlorine,  etc.  corresponding  to  the  compounds  of  those  ele- 
ments with  hydrogen.  This  is  actually  found  to  be  the  case,  as  will  be  seen  in  the 
description  of  the  substance  CaHj,  or  methyl,  the  radical  of  its  oxide  mether,  of 
which  methylic  alcohol,  or  wood-spirit,  is  the  hydrate,  (^  1406.) 

Hydrogen  paired  with  2  equivalents  of  olefiant  gas,  forms  the  compound  ^.[QnYit), 
or  C^Hj,  which  is  the  formula  of  ethyl,  and  forms  an  oxide  Y{{G^Rt)0,  or  ether, 
corresponding  to  water,  of  which  alcohol  is  the  hydrate.  Ethyl,  C«Hj,  is  an  or- 
ganic radical,  corresponding  to  a  metal  in  inorganic  chemistry,  because  it  has 
its  oxide  C4H5O,  its  chloride  C4H,C1,  its  sulphide  C4HJS,  and  similar  compounds 
with  other  metalloids,  and  because  its  oxide,  ether,  forms  salts  with  acids  corre- 
sponding to  those  of  a  metallic  base  RO.  Chloride  of  ethyl,  which  the  author 
calls  chlorohydric  ether,  undergoes  mutual  decomposition  with  hydrate  of  po- 
tassa,  forming  chloride  of  potassium  and  hydrated  oxide  of  ethyl,  or  alcohol; 
which  behaviour  is  peculiar  to  the  metals.  If  the  radical  be  really  hydrogen 
paired  with  2  equivalents  of  olefiant  gas,  then  will  the  behaviour  of  ethyl  be  in  all 
respects  analogous  to  that  of  hydrogen;  and  its  chloride,  sulphide,  etc.,  will  have 
the  properties  of  acids  corresponding  to  chlorohydric,  sulf  hydric,  etc.  ;  which  is, 
in  fact,  the  case,  as  chloride  of  ethyl  forms  double  chlorides  with  many  metallic 
chlorides,  the  formulae  of  which  may  be  written  RC1,H(C4H4)C1;  and  the  mercap- 
tids,  the  general  formula  of  which  is  RS,H(C4H4)S,  are  instances  of  double  sul- 
phides. Nor  does  the  analogy  of  hydrogen  with  its  paired  compounds  stop  here ; 
for  as  hydrogen  forms  compounds  with  arsenic,  antimony,  and  phosphorus,  so  it 
is  probable  that  methyl  R{G^\{^)  and  ethyl  H(C4H4)  will  form  similar  substances ; 
and  Frankland  has  actually  succeeded  in  forming  several  of  them.  Cacodyl, 
which  has  been  described  (§  1381)  is  arseniuretted  methyl,  corresponding  to  arse- 
niuretted  hydrogen,  and  even  possessing  its  properties ;  a  phosphuretted  methyl 
has  been  obtained,  similar  to  phosphuretted  hydrogen ;  and  combinations  of  both 
ethyl  and  methyl  with  zinc,  according  to  the  formulae  H(C4H4)Zn  and  H(C2Ha)Zn, 
are  already  discovered;  the  corresponding  compound  of  hydrogen,  however,  being 
yet  unknown,  which  would  take  the  formula  HZn. 

If  hydrogen  be  paired  with  more  than  2  equivalents  of  olefiant  gas,  other  ra- 
dicals are  formed,  which  shall  be  duly  mentioned  in  their  proper  places ;  they  are 
butyryl,  valyl,  amyl,  and  several  others,  corresponding  to  the  formula  H(CbH8), 
H(C«H,),  H(C.oH.o),  etc._ 

Hydrogen,  and  all  radicals  formed  by  its  pairing  with  olefiant  gas,  will  again 
form  a  paired  compound  with  oxalic  acid  CaO,,  constituting  a  series  of  acids, 


570  LACTIC   AND   BUTYRIC   FERMENTATION. 

amount  of  lactic  acid  when  they  are  mixed  with  a  solution  of  di- 
astase, which  has  been  exposed  to  the  air  for  some  time.  Sprouted 
barley,  which  has  been  well  soaked  in  water,  is  left  in  the  air  for 
two  or  three  days,  and  then  bruised,  and,  after  having  diluted  it 
with  water  it  is  subjected  for  several  days  to  a  temperature  of  77° 

which  will  be  described  in  the  text.  It  will  suffice  at  present  to  give  a  tabular 
view  of  the  series,  since  only  one  of  these  acids,  the  acetic,  has  been  already  de- 
scribed in  the  present  work. 

Hydrogen..  H  paired  with  C^Oaforms  formic  acid...   CJIO3     or      H  (CaOj) 

Methyl CaH,  '*  "  CgO,  *'  acetic  acid C.HsO,    or  CaHgCCaOs) 

Ethyl C^H,  "  "  C2O3  "  metacetonic  acid  C^R.O^    or  CJIs^C^Ob) 

Butyryl....  CeH,  "  "  QO,  "  butyric  acid....  CsB.O^   or  CeH,(Ca03) 

Valyl CgH,  «  "  C^O,  "  valeric  acid....  CjoH^O,  or  C8H3(Ca03) 

Amyl CoHu  "  "  0,0,  "  caj>roic  acid...  C,Ji,,0,ov  C,oii^t{C^O,) 

I  I                                                 i                    I 

1  I                                                 i                    I 

I  I  II 

II  II 
Margaryl..  C:„H33     "       "        CA     "     margaric  acid  C:,,E^,0,  or  C,J1;,,{C^0^) 

The  series  is  nearly  complete,  and  it  is  probable  that  the  connecting  links,  up  to 
margaryl,  will  be  discovered  ere  long. 

In  the  foregoing  I  have  endeavoured  to  present  a  general  view  of  the  theory 
adopted  in  Germany  and  England,  in  relation  to  organic  radicals,  and  paired 
compounds,  without  entering  into  details;  and  it  now  remains  only  to  describe 
the  substances  which  have  been  discovered  since  the  original  was  written,  and 
which  will  be  noticed  under  the  chapters  where  the  new  compound  ought  to  find 
its  place. 

Mhyl  C^H,. 

This,  for  a  long  time  hypothetic  radical,  is  obtained  isolated  by  decomposing 
iodohydric  ether,  C4H5I,  more  properly  called  iodide  of  ethyl,  by  means  of  me- 
tallic zinc,  in  an  hermetically  sealed  tube  which  has  been  freed  from  oxygen  by 
exhaustion  with  an  air-pump.  The  tube  contains,  after  being  heated  to  above 
800°,  ethyl  C4HJ.  olefiant  gas  C^H,,  and  methyl  CJi,  formed  by  the  decomposition 
of  a  certain  quantity  of  ethyl,  besides  iodide  of  zinc,  which  with  the  methyl  forms 
methylide  of  zinc  CaHgZn.  The  gaseous  ethyl,  and  the  olefiant  gas  are  brought 
into  a  glass-tube  over  mercury,  and  after  absorbing  the  carburetted  hydrogen  by 
fuming  sulphuric  acid,  the  tube  contains  pure  ethyl,  as  a  colourless  and  inodorous 
gas,  burning  with  a  brilliant  white  flatne,  and  condensing  at  9.4°  to  a  very  mobile 
fluid.  The  density  of  the  gas  being  2.000,  its  formula  CJl^  corresponds  to  2 
volumes. 

Stihethyl  SbCx^H,,. 

By  moistening  with  iodohydric  ether,  in  a  small  flask,  a  mixture  of  antimoni- 
uret  of  potassium  with  quartzose  sand,  and  distilling  as  soon  as  iodohydric  ether 
no  longer  evaporates,  the  receiver  is  found  to  contain  stibethyl,  a  compound  of  an- 
timony with  3  equivalents  of  ethyl,  corresponding  to  antimoniuretted  hydrogen 
SbHs,  and  the  formula  of  which  is  SbCi^Hi,  or  rather  Sb,3H(C4H4).  Stibethyl,  is  a 
very  mobile  and  highly  refracting  fluid  of  a  disagreeable  alliaceous  odour,  of  the 
density  1.324,  boiling  at  317.3°,  and  yielding  a  vapour  of  the  density  of  7.440,  so 
that  its  equivalent  corresponds  to  4  volumes.  It  is  soluble  in  alcohol  and  ether, 
and  a  drop  of  the  solution  ignites  in  the  air. 

A  compound  Sb,H(C4H4)  has  also  been  obtained. 

Bismethyl  BiCiaH,j. 
It  is  obtained  with  "bismuth-potassium  similarly  ag  stibethyl  is  formed  with  an- 


LACTIC   AND    BUTYRIC    FERMENTATION.  571 

or  S6°.  The  starch  of  the  barley  is  first  converted  into  glucose  by 
the  diastase,  after  which  lactic  fermentation  is  developed  by  the 
influence  of  the  air,  and  the  liquid  becomes  very  acid  by  the  quan- 
tity of  lactic  acid  formed,  which  is  then  saturated  with  lime,  evapo- 
rated to  the  consistence  of  syrup,  and  treated  with  boiling  alcohol, 
which  dissolves  the  lactate  of  lime. 

Lactic  acid  is  still  more  easily  obtained  by  means  of  milk,  which 
contains  at  the  same  time,  the  fermenting  substance,  sugar  of  milk, 
and  an  albuminoid  matter,  casein,  which  acts  as  a  ferment,  or  gene- 
rates it.  When  it  is  allowed  to  sour  in  the  air,  or  to  turn,  a  coag- 
ulum,  which  is  a  combination  of  lactic  acid  with  casein,  is  formed; 
and  if  bicarbonate  of  soda  be  added  to  neutralize  the  acid,  lactate  of 
soda  is  formed,  while  the  casein,  thus  set  free,  again  acts  as  a  fer- 
ment on  the  sugar  of  milk,  and  converts  an  additional  quantity  of 
it  into  lactic  acid.  A  new  coagulum  of  lactate  of  casein  is  thus 
formed,  which  is  also  decomposed  by  bicarbonate  of  soda ;  and  the 
process  is  continued  until  no  caseous  precipitate  of  lactate  of  casein 
is  formed,  that  is,  until  the  sugar  of  milk  is  wholly  decomposed.  At 
the  close  of  the  operation,' acetic  acid  is  poured  into  the  liquor, 
which  is  then  boiled,  when  the  casein  is  wholly  precipitated  in  the 
form  of  acetate  of  casein.  The  filtered  liquor  is  evaporated  to  dry- 
ness and  the  residue  treated  with  boiling  alcohol,  which  dissolves 
the  lactate  of  soda.  Instead  of  the  sugar  of  milk,  glucose  or  even 
cane-sugar  may  be  added,  but  the  lactic  fermentation  of  the  latter 
kind  of  sugar  is  very  slow,  and  in  order  that  it  may  take  place,  the 
cane-sugar  must,  probably,  be  previously  converted  into  fruit-sugar, 
which  transformation  is  very  slow,  because  it  is  essential  to  lactic 
fermentation  that  the  liquid  should  not  contain  much  acid. 

Other  albuminoid  substances  may  be  substituted  for  casein :  the 
presence  of  fatty  substances  apppears  to  assist  the  formation  of 
lactic  acid,  and  some  chemists  even  suppose  it  to  be  essential. 

The  formula  of  lactic  acid  being  CgH^O^+HO,  2  equivalents  of 
the  acid,  therefore  contain  all  the  elements  of  an  equivalent  of 
fruit-sugar  G^Jl^fi^^;  whence  it  may  be  admitted  that,  in  lactic 
fermentation,  the  molecules  of  sugar  merely  change  their  grouping, 
without  the  intervention  of  any  new  elements  in  the  reaction. 

§  1403.  When  liquors  which  have  undergone  lactic  fermentation, 


timoniuret  of  potassium,  and  behaves  analogous  to  stibethyl,  from  which  it  diiTera 
essentially  by  decomposing  at  a  certain  temperature  with  a  powerful  explosion. 
It  is  a  mobile  fluid  of  the  density  1.82,  and  a  highly  disagreeable  odour;  in  the 
air  it  throws  out  thick  fumes,  inflames  with  a  slight  explosion  and  diffuses  a  deep- 
yellow  smoke  of  oxyd  of  bismuth.     Composition,  Bi,3H(C4H4). 

Zinckethyl  Zn^^H,. 

It  is  formed  in  the  decomposition  of  iodohydric  ether,  or  iodide  of  ethyl  by 
zinc,  and  its  formula  is  Zn,H(C4H«).  In  contact  with  the  air  it  burns  with  a  bril- 
liant flame,  giving  off  dense  fumes  of  oxide  of  zinc. —  W.  L.  F. 


572  LACTIC  AND   BUTYRIC   FERMENTATION. 

are  left  to  themselves  for  a  longer  time,  another  fermentation  is  de- 
veloped, and  a  new  acid,  called  butyric  is  formed. 
Introduce  into  a  large  bottle 

1.  A  solution  of  glucose,  marking  8  or  10°  of  Baum6. 

2.  A  quantity  of  chalk  equal  to  one-half  of  the  sugar  used. 

3.  A  quantity  of  casein  representing,  in  the  dry  state,  8  or  10 
per  cent,  of  the  weight  of  sugar  contained  in  the  solution,  for  which 
purpose  either  cream-cheese,  or  Brie-cheese  is  used;  freshly  pre- 
pared gluten  may  also  be  substituted  for  the  casein. 

The  sugar  is  first  transformed  into  a  viscous  substance  which  has 
hitherto  been  but  little  studied,  and  then  into  lactic  acid,  large 
quantities  of  which  may  by  obtained  by  arresting  the  operation  at 
the  proper  moment ;  while  if  it  be  continued  longer,  the  lactic  acid 
is  finally  converted  into  butyric  acid,  and  a  mixture  of  hydrogen 
and  carbonic  acid  is  disengaged.  The  butyric  fermentation  is  not 
generally  completed  until  2  or  3  months,  after  which  the  liquid  con- 
tains a  mixture  of  butyrate,  lactate,  and  acetate  of  lime. 

The  formula  of  butyric  acid  being  GgHyOgHO,  we  have 

C.AA=C,H,03,HO+4H+4CO,. 

which  equation  accounts  for  the  evolution  of  hydrogen  and  carbonic 
acid  during  the  butyric  fermentation. 

In  order  to  prepare  large  quantities  of  lactic  and  butyric  acid, 
3  killog.  of  sugar  are  dissolved  in  13  killog.  of  boiling  water,  to 
which  15  gm.  of  tartaric  acid  have  been  added,  then  rotten  cheese 
is  added,  diluted  in  sour  milk,  and  1500  gm.  of  powdered  chalk, 
the  whole  is  exposed  to  a  temperature  of  86°  to  95°,  and  the  mass, 
being  shaken  from  time  to  time,  becomes  completely  solid  in  8  or 
10  days.  It  is  then  boiled  for  half  an  hour  with  10  litres  of  water 
containing  10  gm.  of  quick-lime,  and  after  filtering  the  Hquid  and 
evaporating  it  to  the  consistence  of  syrup,  it  is  allowed  to  crystal- 
lize. The  crystals  of  lactate  of  lime  being  redissolved  in  2J  times 
their  weight  of  boiling  water,  100  gm.  of  sulphuric  acid  diluted 
with  its  weight  of  water,  are  added,  in  order  to  precipitate  the  lime 
in  the  state  of  sulphate,  and  isolate  the  lactic  acid ;  after  which  the 
acid  liquor,  when  filtered,  is  boiled  with  carbonate  of  zinc,  which 
forms  sulphate  and  lactate  of  zinc,  a  portion  of  w^hich  latter  salt 
separates  in  crystalline  crusts  during  the  cooling  of  the  liquid,  while 
an  additional  portion  is  removed  by  again  concentrating  it.  The 
lactate  of  zinc,  purified  by  a  second  crystallization,  is  subjected  to 
the  action  of  sulf  hydric  acid  gas,  and  yields  pure  lactic  acid. 

The  compact  mass  which  has  yielded  lactic  acid,  being  again  left 
to  itself,  at  a  temperature  of  98°,  becomes  liquid  and  disengages 
gas ;  and  in  5  or  6  weeks,  the  new  fermentation  is  terminated.  The 
liquid  is  then  diluted  with  its  weight  of  water,  and  a  solution  of  4 
killog.  of  carbonate  of  soda  is  added,  which  precipitates  the  lime  in 
the  state  of  carbonate  and  forms  butyrate  of  soda.     The  liquor, 


LACTIC   ACID.  573 

when  filtered,  Is  evaporated  until  it  occupies  only  a.  volume  of  4  or 
5  litres,  when  3  kilog.  of  sulphuric  acid  diluted  with  its  volume  of 
water  are  added.  The  liquid  then  separates  into  two  layers,  the 
upper  one  of  which,  consisting  of  butyric  acid,  is  removed  and 
brought  into  contact  with  chloride  of  calcium,  and  distilled.  A 
single  operation  may  yield  as  much  as  1  kilog.  of  pure  butyric 
acid. 

Lactic  Acid  CgH^O^jHO. 

§  1404.  Lactic  acid,  concentrated  as  much  as  possible,  in  vacuo, 
over  sulphuric  acid,  is  a  colourless  liquid,  of  a  density  of  1.22,  and 
soluble  in  all  proportions  in  water  and  alcohol.  Its  composition  is 
represented  by  the  formula  CgH505,H0,  the  equivalent  of  water 
being  capable  of  being  replaced  by  1  equiv.  of  base;  and  when 
subjected  to  heat  it  gives  off  its  equivalent  of  water  at  about  266°, 
and  is  changed  into  anhydrous  lactic  acid,  CgH^O^,  which  is  solid, 
fusible,  very  slightly  soluble  in  water,  but  dissolving  readily  in  al- 
cohol and  ether.  In  contact  with  water  or  moist  air,  it  passes 
slowly  into  the  state  of  hydrated  lactic  acid.  Anhydrous  lactic 
acid  combines  with  ammoniacal  gas,  and  yields  a  product  of  which 
the  formula  is  NHgjCgH^O^. 

When  heated  to  482°  lactic  acid  is  further  decomposed;  and 
together  with  other  products,  a  white  crystalline  substance  of  the 
formula  CgH^O^,  is  formed,  which  melts  at  224.6°,  and  sublimes 
without  change  at  about  482°.  It  combines  with  ammoniacal  gas 
and  forms  a  compound  NH3,CqH404  lactamid,  which  dissolves  with- 
out change  in  water  and  alcohol.  The  substance  CgH^O^,  which 
has  been  improperly  called  anhydrous  lactic  acid,  combines  readily 
with  water  and  reproduces  hydrated  lactic  acid.* 

The  lactates  of  potassa,  soda,  and  ammonia,  are  deliquescent, 
and  crystallize  with  difficulty. 

Lactate  of  lime  crystallizes  in  small  radiating  aciculae  of  the  for- 
mula CaO,CgH50.4-5HO,  and  loses  its  5  equiv.  of  water  in  vacuo,  or 
at  a  temperature  of  212°. 

Lactate  of  zinc  ZnO,CeH505+3HO,  dissolves  in  58  parts  of  cold, 
or  6  of  boiling  water,  and  bears  a  temperature  of  410°  without  de- 
composition. 

Protolactate  of  iron  FeO,CgHg05+3HO  is  prepared  by  mixing 
solutions  of  lactate  of  ammonia  and  protochloride  of  iron,  and  pre- 
cipitating by  alcohol,  or  by  decomposing  lactate  of  baryta  by  proto- 
sulphate  of  iron.  After  having  separated  the  sulphate  of  baryta, 
alcohol  is  added  to  precipitate  the  lactate  of  iron  in  the  form  of 
small,  yellow  aciculae.     The  salt  is  used  in  medicine. 

Lactates  of  copper  and  silver  are  obtained  by  boiling  the  carbon- 
ates of  these  metals  with  a  solution  of  lactic  acid,  and  their  formulae 
are  CuO,CeH305+2HO,  and  AgO,C8H,05+2HO. 

*  It  is  usually  called  lactide. — J.  C.  B. 


574  LACTIC   AND   BUTYRIC   FERMENTATIONS. 

Lactic  ether  C^H.OjCgH^O^  is  obtained  by  distilling  2  parts  of 
dried  powdered  lactate  of  lime,  with  a  mixture  of  2  parts  of  anhy- 
drous alcohol,  and  2  parts  of  concentrated  sulphuric  acid,  the  dis- 
tillation being  arrested  at  the  moment  the  liquid  begins  to  turn 
brown.  The  product  is  rectified  over  chloride  of  calcium,  and  a 
colourless  liquid  obtained,  having  a  peculiar  odour,  a  density  of 
0.866,  and  boiling  at  170° :  lactic  ether  dissolves  in  water,  alcohol, 
and  ether,  and  is  decomposed  by  the  alkalies,  yielding  alcohol  and 
lactic  acid. 

Butyric  Acid  CgH^Og.HO. 

§  1405.  Butyric  acid  is  a  colourless  liquid,  of  an  extremely  dis- 
agreeable odour,  and  the  smell  of  rancid  butter  is  owing  to  the  pre- 
sence of  a  small  quantity  of  this  acid.  It  solidifies  at  the  tempera- 
ture of  solid  carbonic  acid,  and  boils  at  327.2°.  It  dissolves  in  all 
proportions  in  water,  alcohol,  and  spirit  of  wood,  and  its  density  is 
0.963,  while  that  of  its  vapour  is  3.09,  its  equivalent  CgH^OgjHO, 
corresponding  to  4  vol.  of  vapour.  Butyric  acid  is  inflammable,  and 
chlorine  acts  on  it,  yielding  two  chlorinated  butyric  acids,  of  which 
the  formulae  are  Q>^,Q\Jd^,^0  and  C,H,Cl3,0s,H0. 

Butyrates  of  potassa,  soda,  and  ammonia,  are  very  soluble  in 
water,  and  crystallize  with  difiiculty. 

Butyrate  of  lime  is  much  less  soluble  hot  than  cold,  and  a  solution  of 
the  salt,  saturated  at  a  low  temperature,  sets  into  a  mass  when  heated. 

The  formula  of  butyrate  of  baryta,  which  is  deposited  from  a  hot 
solution,  is  ^2^Q,Q>^^0^-\-1^0,  while  that  of  crystals  developed  in 
a  cold  solution  is  BaO,C8H703+4HO,  which  latter  salt  melts  in  its 
its  own  water  of  crystallization. 

Butyrate  of  lead  is  precipitated  in  the  form  of  an  insoluble  liquid, 
which  sets  after  some  time. 

Butyric  acid  forms  a  compound  ether,  which  is  easily  prepared 
by  mixing  100  gm.  of  butyric  acid,  100  gm.  of  alcohol,  and  50  gm. 
of  sulphuric  acid,  and  shaking  them  for  some  moments,  when  a  layer 
of  butyric  ether  forms  on  the  surface  of  the  mixture.  It  is  washed 
with  water,  and  purified  by  chloride  of  calcium.  Butyric  ether, 
though  but  slightly  soluble  in  water,  is  very  soluble  in  alcohol,  and 
boils  at  230°,  and  its  formula  is  QJlfifi^^Oy 

Ammonia  reacts  on  butyric  ether,  and  produces  hutyramid  NH, 
CsH,0,. 

C3H,03,H0+NH3=NH„C,H,0,+2H0; 

the  butyric  ether  gradually  disappearing,  and  the  aqueous  solution, 
when  evaporated,  yielding  pearly  crystals  of  butyramid,  which  melts 
at  239°,  and  sublimes  at  a  higher  temperature  without  decomposition. 
Butyrate  of  lime  yields,  when  heated,  an  odorous,  inflammable 
liquid,  boiling  at  about  284°,  and  called  hutyrone.  Its  formuJa  is 
C,HyO,  and  it  arises  from  the  following  reaction : 
Ca0,C3H,03=Ca0,C0,+  C,H,0. 


WOOD  SPIRIT.  575 

By  operating  on  considerable  quantities  of  but jrate  of  lime,  there 
is  formed,  with  the  butyrone,  a  more  volatile  liquid,  boiling  at  203°, 
of  the  formula  CgHgOg,  and  which  has  been  called  hutyral.  Buty- 
ral  CgHgOg  is  to  butyric  acid  C8Hy03,HO  what  aldehyde  QJlfi^  is 
to  acetic  acid  C^HgOjjHO,  which  comparison  is  confirmed  by  the 
chemical  properties  of  butyral,  since  it  oxidizes  in  the  air,  particu- 
larly when  aided  by  platinum  sponge,  and  is  converted  into  butyric 
acid.  It  reduces  oxide  of  silver  like  aldehyde,  the  metallic  silver 
forming  a  coating  on  the  surface  of  the  vessel. 


SPIRIT  OF  WOOD,  OR  METHYLIC  ALCOHOL,  AND  THE  PRODUCTS 
DERIVED  FROM  IT. 

§  1406.  By  subjecting  wood  to  distillation,  there  is  obtained,  in 
addition  to  the  gaseous  products,  an  aqueous  acid  liquor,  which  con- 
tains a  great  number  of  different  substances ;  that  which  imparts  to 
it  its  acidity  being  acetic  acid,  the  method  of  the  extraction  of 
which  has  been  described  (§  1370).  There  also  exists  a  volatile,  in- 
flammable liquid,  called  spirit  of  wood. 

The  proportion*  of  this  liquid  varies  according  to  the  nature  of  the 
wood  and  the  temperature  at  which  the  calcination  is  effected,  and 
it  generally  reaches  1  per  cent,  of  the  whole  quantity  of  fluid.  It  is 
mixed  with  acetone,  aldehyde,  methylacetic  ether,  and  two  volatile 
substances  to  which  the  names  of  mesite  and  xylite  have  been  given, 
and  lastly,  a  pitch-like  matter  is  also  found.  The  liquor  is  saturated 
with  slaked  lime,  which  attacks  the  acids  and  a  portion  of  the  tarry 
substances,  after  which  the  clarified  liquor  is  decanted  and  distilled 
until  the  first  tenth  is  collected  in  the  receiver.  This  first  product, 
which  contains  nearly  the  whole  of  the  spirit  of  wood,  is  again 
distilled,  with  a  small  quantity  of  lime  to  decompose  the  methyl- 
acetic  ether,  and  convert  it  into  spirit  of  wood.  The  first  portions 
distilled  are  alone  collected,  and  by  continuing  these  fractioned  dis- 
tillations, highly  concentrated  spirit  of  wood  is  finally  obtained, 
which,  when  distilled  over  lime,  yields  anhydrous  spirit  of  wood.  This 
is  sufficient  for  all  purposes  of  commerce,  but  in  order  to  separate 
the  pure  principle,  methylic  alcohol^  from  it,  it  is  treated  with  twice 
its  weight  of  melted  and  powdered  chloride  of  calcium,  with  which 
methylic  alcohol  forms  a  crystalline  compound,  reaisting  a  tempera- 
ture of  212°  without  decomposition.  It  is  heated  in  a  water-bath, 
when  the  greater  portion  of  the  foreign  products  distils  over,  and 
the  compound  of  methylic  alcohol  with  chloride  of  calcium  remains. 
By  treating  it  with  water,  it  is  destroyed,  and  the  methylic  alcohol 
is  set  free,  and  separated  by  distillation.  The  product  again  dis- 
tilled over  quick  lime,  yields  pure  and  anhydrous  methylic  alcohol. 

§  1407.  Methylic  alcohol  is  a  colourless  liquid,  of  a  peculiar 


576  METHYLIC   ALCOHOL. 

odour,  resembling  that  of  acetic  ether,  and  its  density  is  0.798, 
while  it  boils  at  151.7°.  Its  ebullition  in  a  glass  vessel  is  accom- 
panied by  violent  agitation,  which  renders  its  distillation  difficult, 
which  is  avoided  by  placing  a  stratum  of  mercury  at  the  bottom  of 
the  vessel.  It  burns  in  the  air 'with  a  flame  resembling  that  of 
alcohol,  and  forms  a  series  of  compounds  so  closely  resembling  those 
of  ordinary  alcohol,  that  it  is  impossible  to  separate  the  study  of 
these  two  substances,  although  their  origin  is  very  different,  on  ac- 
count of  which  analogy  spirit  of  wood  has  been  called  methylic  al- 
cohol (from,  fxiOv,  wine,  and  v-kv^,  wood.)  Its  formula  is  CgH^Og,  and  the 
density  of  its  vapour  being  1.041,  its  equivalent  is  represented  by 
4  vol.  of  vapour  like  that  of  alcohol. 

Methylic  alcohol  readily  dissolves  potassa  and  soda,  and  forms, 
with  anhydrous  baryta,  a  crystallizable  compound  BaO,C2H^08, 
w^hile  the  formula  of  its  crystalline  compound  with  chloride  of  cal- 
cium is  2  (CgH^O,)  2CaCl.  Its  solvent  properties  closely  resemble 
those  of  alcohol,  all  substances  soluble  in  the  latter  liquid  being 
equally  so  in  methylic  alcohol. 

ACTION  OF  SULPHURIC  ACID  ON  METHYLIC  ALCOHOL. 

§  1408.  On  mixing  2  parts  of  concentrated  sulphuric  acid  with  1 
part  of  methylic  alcohol,  a  great  elevation  of  temperature  ensues, 
and  if  the  acid  liquor  be  saturated  with  carbonate  of  baryta,  sulphate 
of  baryta  separates,  and  there  remains  in  solution  a  salt  called  sul- 
phomethylate  of  baryta,  BaO,  (€21130,2803)  which  may  be  obtained 
in  crystals,  by  evaporating  the  liquid  to  the  consistence  of  syrup, 
and  allowing  it  to  rest  in  a  dry  vacuum.  All  the  other  sulphome- 
thylates  are  easily  prepared,  by  double  decomposition,  from  the 
sulphomethylate  of  baryta.  By  carefully  decomposing  a  solution 
of  sulphomethylate  of  baryta  by  dilute  sulphuric  acid,  the  sulpho- 
methylic  acid  is  obtained  isolated,  and  its  solution  exposed  for  a 
long  time  in  a  dry  vacuum,  yields  small  acicular  crystals  of  hydrated^ 
sulphomethylic  acid.  All  the  sulphomethylates  are  very  soluble  in 
water,  and  when  heated  are  decomposed  into  the  metallic  sulphate 
which  remains,  and  a  compound  ether,  metJiylsulphuric  ether  CgH, 
0,S03,  which  shall  presently  be  described. 

§  1409.  By  mixing  1  part  of  methylic  alcohol  with  4  parts  of 
concentrated  sulphuric  acid,  and  distilling  the  mixture,  an  inflam- 
mable gas  of  the  formula  CgHgO  is  disengaged,  consisting  of  methy- 
lic ether,  which  is  to  methylic  alcohol  C2H^03  what  ordinary  ether 
C4H5O  is  to  alcohol  CJifi^.  The  gas  thus  obtained  is,  however, 
always  mixed  with  small  quantities  of  sulphurous  and  carbonic  acids, 
which  are  separated  by  allowing  the  gas  to  remain  for  some  time  in 
contact  with  caustic  potassa. 

Methylic  ether  is  a  colourless  liquid,  of  a  peculiar  etherial  smell, 
and  liquid  only  at  a  temperature  of  —22°  to  —40°  ;  and  its  density 
being  1.61,  its  formula  CaH^O  corresponds  to  2  vol.  of  vapour. 


METHYLIC   ETHER.  577 

Water  dissolves  about  37  times  its  volume  of  it,  and  it  is  still  more 
soluble  in  ordinary  and  methylic  alcohol.  As  we  have  been  led  by 
chemical  reactions  to  write  the  formula  of  alcohol  C^H^OjHO,  so  also 
we  shall  be  induced  to  write  that  of  methylic  alcohol  C2H30,H0.* 

§  1410.  By  distilling  1  part  of  methylic  alcohol  with  8  or  10 
parts  of  concentrated  sulphuric  acid,  very  little  methylic  ether  is 
obtained,  but  an  oleaginous  liquid  distills  over,  which,  when  washed 
several  times  with  water,  and  then  distilled  over  caustic  baryta, 
presents  a  composition  corresponding  to  the  formula  CgHgOjSOg.  It 
is  methyhulphurio  ether,  that  is,  a  compound  ether,  formed  by  the 
combination  of  methylic  ether  with  sulphuric  acid.  The  correspond- 
ing compound  C^H^O^SOg  of  the  alcohol  series  has  recently  been 
obtained. 

This  product  is  also  obtained  by  the  direct  combination  of  methy- 
lic ether  C3H3O  with  anhydrous  sulphuric  acid,  the  combination 
being  accompanied  with  great  evolution  of  heat. 

Methylsulphuric  ether  is  a  colourless  liquid,  of  the  density  1.324, 
and  which  boils  at  370.4°;  the  density  of  its  vapour  being  4.37, 
and  its  equivalent  therefore  represented  by  2  vol.  of  vapour. 
Methylsulphuric  ether  is  slowly  decomposed  by  cold  water,  but  very 
rapidly  by  boiling  water,  the  products  of  decomposition  being 
methylic  alcohol  C2H30,H0,  and  sulphomethylic  acid  031130,2803. 

Dry  ammoniacal  gas,  and  the  aqueous  solutions  of  ammonia,  de- 
compose methylsulphuric  ether,  forming  a  white  crystallizable  sub- 
stance, which  has  been  called  sulphomethylam,  and  also  methylsul- 
phamidic  ether,  regarding  it  as  a  compound  ether,  formed  by  a  pe- 
culiar acid,  methyUulphamidic,  which  has  not  yet  been  isolated;  the 
formula  of  this  substance,  in  fact,  may  be  written 

C,H30,(NH,S0„S0.). 

§  1411.  By  introducing  anhydrous  methylic  alcohol  and  anhy- 
drous sulphuric  acid,  separately,  into  two  open  tubes  entering  a  very 
dry  bottle,  which  is  then  corked,  their  vapours  combine  slowly,  and 
an  acid  is  formed,  yielding,  with  baryta,  a  soluble  salt  having  the 
same  formula  is  the  sulphomethylate  of  baryta,  but  differing  in  its 
properties.     It  is  therefore  an  isomeric  of  sulphomethylic  acid. 

§  1412.  By  causing  sulphuric  acid,  under  the  most  varied  circum- 
stances, to  act  on  methylic  alcohol,  it  has  hitherto  been  impossible  to 
obtain  a  carburetted  hydrogen  C3H3  which  shall  be  to  methylic  ether 
CgHgO,  what  olefiant  gas  C^H^  is  to  ether  C^H^O. 

*  Methylic  ether  is  with  more  propriety  called  mether,  and  regarded  as 
the  oxide  of  a  radical,  CaHg,  or  H(CaH3),  which  has  been  isolated,  and  called 
methyl.  The  following  series  of  compounds,  called  in  the  text  compounds  of 
methylic  ether,  and  methylic  acids,  should  therefore  rather  be  regarded  as  salts 
of  the  oxide  of  methyl,  or  mether;  the  methylic  acids  being  merely  acid  salts. 
The  names  of  methylonitric,  methyloxalic  ether,  etc.,  would  then  change  to  re- 
spectively nitrate  of  mether,  etc. —  W.  L.  F. 
Vol. '11.— 37 


678  METHYLIC   ALCOHOL. 

Ethers  compounded  of  Methylic  Ether  and  Methylic  Acids. 

§  1413.  Compound  methylic  ethers  are  formed  under  the  same 
circumstances  as  compound  alcoholic  ethers,  and  exhibit  the  same 
relations  of  composition.  As  in  the  case  of  alcohol,  two  species  of 
combinations  of  methylic  ether  with  acids  are  known ;  neutral  com- 
pounds, which  are  compound  methylic  ethers  properly  so  called,  and 
acid  compounds,  containing  a  double  proportion  of  acids,  and  which 
we  shall  call  methylic  acids.  Certain  acids  form  both  kinds  of  com- 
pounds, an  example  of  which  has  just  been  shown  m  sulphuric  acid ; 
while  others  produce  only  the  neutral,  and  others  again  only  the 
acid  compound. 

Methylonitric  Ether,  C^Ilfi,1^0^. 

§  1414.  The  preparation  of  this  substance  is  not  so  difficult  as 
that  of  the  nitric  ether  of  the  vinic  series ;  since  nitric  acid  of  com- 
merce may  be  made  to  react  immediately  on  methylic  alcohol,  with- 
out any  fear  of  the  tumultuous  and  complicated  reactions  which  this 
acid  exerts  on  vinic  alcohol.  The  best  method  of  preparing  methylo- 
nitric ether  consists  in  heating  in  a  retort  a  mixture  of  1  part  of 
methylic  alcohol,  1  part  of  nitrate  of  potassa,  and  2  parts  of  con- 
centrated sulphuric  acid,  when  an  etherial  liquid  is  obtained  which 
must  be  rectified  several  times  over  litharge  and  chloride  of  calcium. 

Methylonitric  ether  is  a  colourless  liquid,  of  the  density  1.182, 
and  which  boils  at  154.4° ;  and  the  density  of  its  vapour  being 
2.653,  its  equivalent  CgHgOjNO^  is  represented  by  4  vol.  Methy- 
lonitric ether  detonates  with  extreme  violence  at  a  temperature 
slightly  above  its  boiling  point,  and  must  therefore  be  handled  with 
great  caution. 

A  methylonitrous  ether  CgHgOjNOg  would  probably  be  obtained 
by  distilling  a  mixture  of  concentrated  sulphuric  acid  and  methylic 
alcohol  with  nitrate  of  potassa. 

Methylocarhonic  Acid  C3H30,2C03H0. 

§  1415.  By  passing  a  current  of  carbonic  acid  gas  through  a  so- 
lution of  baryta  in  anhydrous  methylic  alcohol,  a  precipitate  results 
in  the  form  of  pearl-like  spangles,  of  the  formula  BaO(C3H30,2C03), 
which  is  the  carhomethylate  of  baryta.  The  salt  is  insoluble  in 
methylic  alcohol,  but  dissolves  readily  in  water,  being  soon  decom- 
posed into  carbonate  of  baryta,  carbonic  acid  and  methylic  alcohol. 

Methylocarhonic  ether  Cj,H30,C03,  has  not  yet  been  obtained. 

Methyloxalic  Ether  C3H30,C30. 
§  1416.  This  product  is  prepared  by  distilling  a  mixture  of  equal 
parts  of  crystallized  oxalic  acid,  concentrated  sulphuric  acid,  and 
methylic  alcohol,  when  a  liquid  is  obtained  which,  when  allowed  to 
evaporate  spontaneously,  deposits  white  crystals  of  methyloxalic 
acid.  The  crystals  are  dried  between  tissue  paper,  and  distilled 
over  litharge. 


METHYLACETIC    ETHER.  57^ 

Methyloxalic  ether  is  a  solid  substance,  melting  at  123.8°,  and 
boiling  at  321.8°.  It  dissolves  in  water,  alcohol,  ether,  and  methylic 
ether ;  and  water  decomposes  it  slowly  at  the  ordinary  temperature, 
and  rapidly  at  the  boiling  point,  forming  free  oxalic  acid  and  me- 
thylic alcohol.  This  ether  is  decomposed  by  dry  ammoniacal  gas, 
and  converted  into  a  crystalline  substance,  of  which  beautiful  crys- 
tals are  obtained  by  redissolving  it  in  alcohol,  and  which  may  be 
considered  as  a  methyloxamic  etJier,  CaH30,{NH2C303,C303).  If  a 
large  quantity  of  ammonia  in  solution  be  used,  methylic  alcohol  and 
oxamid  NHgCjOg  are  obtained. 

Methylacetic  Ether  02X130,0^11303. 

§  1417.  It  is  obtained  by  distilling  2  parts  of  methylic  alcohol 
with  1  part  of  monohydrated  acetic  acid  and  1  part  of  concentrated 
sulphuric  acid.  The  product  is  poured  over  powdered  anhydrous 
chloride  of  calcium,  and  shaken  frequently,  when,  by  allowing  the 
liquid  to  rest,  two  layers  are  formed,  the  upper  one  of  which,  when 
distilled  over  quicklime  to  retain  the  sulphurous  acid,  and  then 
over  chloride  of  calcium  to  retain  a  small  quantity  of  methylic  alco- 
hol, yields  pure  methylacetic  ether.  It  is  a  colourless  liquid,  hav- 
ing an  odour  resembling  that  of  acetic  ether  of  the  vinic  series,  and 
its  density  is  0.919,  while  it  boils  at  136.4°.  The  density  of  its 
vapour  being  2.57,  its  equivalent  €21130,0411303  is  represented  by 
4  vol.  of  vapour.  It  has  been  shown  (§  1406)  that  crude  spirit  of 
wood  always  contains  a  certain  quantity  of  this  substance.  Boiling 
water,  and  the  alkaline  solutions  particularly,  decompose  it  into 
methylic  alcohol  and  acetic  acid ;  and  it  dissolves  in  2  parts  of 
water,  and  mixes  in  all  proportions  with  vinic  and  methylic  alco- 
hol and  with  ether. 

Methylochlorocarhonic  Ether  C2H30,Cj03Cl. 
§  1418.  This  ether  is  formed  under  circumstances  analogous  to 
those  in  which  the  corresponding  product  of  the  vinic  series  is  pro- 
duced, that  is,  by  pouring  methylic  alcohol  into  a  bottle  filled  with 
chlorocarbonic  gas  0001.  By  treating  it  with  water,  an  oily  liquid 
separates,  which  is  distilled,  after  being  well  washed  with  water, 
first  over  chloride  of  calcium,  and  then  over  oxide  of  lead.  It  is  a 
colourless  liquid,  of  a  sufibcating  odour.  Ammonia  dissolved  in 
water  decomposes  it,  chlorohydrate  of  ammonia  and  a  deliquescent 
crystalline  substance  called  urethylan  being  formed ;  which  lat- 
ter, however,  may  be  considered  as  methyloearhamic  ether,  for  its 
formula  can  be  written  02H30,(NH2,00,OOJ. 

Methylohihoracic  Ether  0aH3O,2BO3  and  Trimethylohoracio  Ether 

302H3O,BO3. 
§  1419.  By  treating  melted  and  finely  powdered  boracic  acid  with 
methylic  alcohol,  a  combination  ensues  with  elevation  of  temperature ; 


580  .  METHYLIC  ALCOHOL. 

and,  after  driving  off  the  excess  of  methylic  alcohol  by  heat,  there 
remains  as  residue  a  soft,  transparent  substance,  which  can  be  drawn 
out  in  threads  at  the  ordinary  temperature,  consisting  of  methylo- 
hiboracie  ether  C2H30,2B03.  Water  decomposes  it  immediately  into 
hydrated  boracic  acid  and  methylic  alcohol. 

By  treating  methylic  alcohol  with  chloride  of  boron,  a  very  vola- 
tile and  colourless  liquid  is  obtained,  having  a  penetrating  smell, 
and  the  formula  is  3C2H30,B03,  while  its  density  is  0.955  at  32°,. 
and  it  boils  at  161.6°.     The  density  of  its  vapour  is  3.60. 

These  two  compounds  burn  with  a  beautiful  green  flame. 

Methylosulphoearhonic  Ether  031130,082,  and  Sulphocarhomethylic 
Acid  02H3O,20S2. 

§  1420.  By  pouring  sulphide  of  carbon  into  caustic  potassa,  dis- 
solved in  anhydrous  amylic  alcohol,  silky  crystals  of  sulphocarho- 
methylate  of  potassa  KO,(02H3O,20S2)  are  formed ;  and  a  great 
number  of  other  sulphocarbomethylates  are  obtained  from  this  salt 
by  double  decomposition. 

If  iodine  be  added  to  a  solution  of  sulphocarbomethylate  of 
potassa  in  methylic  alcohol,  the  temperature  rises,  while  sulf  hydric 
acid  and  oxide  of  carbon  are  disengaged. 

In  addition,  iodide  of  potassium,  crystallized  sulphur,  and  a  brown 
oil,  which,  after  *two  or  three  rectifications,  yields  pure  methylosul- 
phocarhonic  ether,  are  formed.  This  is  an  amber-coloured  liquid, 
having  a  density  of  1.143  at  59°,  and  boiling  at  about  338° ;  and 
the  density  of  its  vapour  being  4.266,  its  equivalent  031130,082  is 
represented  by  2  volumes  of  vapour. 

Methylochlorohydric  Ether  OjHjCI.* 

§  1421.  By  heating  in  a  flask  2  parts  of  sea-salt  with  a  mixture  of 
1  part  of  methylic  alcohol  and  3  parts  of  concentrated  sulphuric 
acid,  a  colourless  gas  is  disengaged,  which  is  to  be  left  for  some 
time  in  contact  with  water,  to  effect'  the  absorption  of  the  mixed 
sulphurous  acid  and  methylic  ether.  This  gas,  which  does  not 
liquefy  at  a  cold  of  —0.4°,  is  methylochlorohydric  ether.  Its  density 
is  1.728,  and  its  equivalent  OgHjOl  corresponds  to  4  volumes  of 
vapour.  It  burns  with  a  flame  edged  with  green ;  and  water  dis- 
solves about  3  times  its  volume  of  it. 

Methyliodohydric  Ether  OjHjI. 

§  1422.  It  is  formed  by  pouring  8  parts  of  iodine  into  12  or  15 
parts  of  methylic  alcohol,  and  gradually  adding  1  part  of  phosphorus, 
and  then  applying  heat  to  distil  the  liquor.  The  liquid  collected  in 
the  receiver  is  shaken  with  water,  the  ether  is  precipitated,  washed 

*  According  to  the  more  probable  theory,  this  substance  would  be  chloride  of 
methyl.— TT.  L.  F 


METHYLIC   ETHELS.  581 

several  times  with  water,  and  then  distilled,  first  over  chloride  of 
calcium,  and  then  over  oxide  of-  lead.  It  is  a  colourless  liquid,  boil- 
ing between  104°  and  122° ;  while  its  density  is  2.237  at  69.8°. 

MetTiylofluohydric  Ether  CgHjFl. 

§  1423.  This  simple  ether,  the  corresponding  one  of  which  in  the 
vinic  series  is  not  yet  known,  is  prepared  by  heating  in  a  retort, 
methylosulphuric  ether  CgHgOjSO,  with  fluoride  of  potassium,  or 
also  with  fluoride  of  calcium  reduced  to  an  impalpable  powder ; 
when  a  colourless  gas  is  disengaged,  of  an  agreeable  etherial  smell, 
burning  with  a  bluish  flame,  and  of  which  the  density  is  1.186 ; 
while  its  equivalent  C^HjFl  corresponds  to  4  volumes.  Water  dis- 
solves 1 J  time  its  volume  of  it. 

Methylocyanohydrie  Ether  CgHgCy. 

§1424.  In  order  to  obtain  this  ether,  it  is  sufficient  to  distil 
methylosulphuric  ether  with  cyanide  of  potassium,  or  finely  pulverized 
cyanide  of  mercury ;  when  it  is  obtained  as  a  liquid,  insoluble  in 
water,  and  very  poisonous. 

Methylosulfhydric  Ether  CgHjS  and  its  Compounds, 

§  1425.  Methylosulfhydric  ether  is  prepared  by  passing  a  current 
of  methylochlrohydric  ether  CjHgCl  through  an  alcoholic  solution  of 
monosulphide  of  potassium,  heating  the  liquid,  and  collecting  the 
distilled  products  in  a  well-cooled  receiver ;  after  which  they  are 
washed  with  water  and  distilled  over  chloride  of  calcium. 

Methylosulfhydric  ether  is  a  very  volatile  liquid,  of  an  extremely 
disagreeable  smell,  and  its  density  is  0.846  at  69.8°,  while  it  boils 
at  105.8°.  The  density  of  its  vapour  is  2.115,  and  its  equivalent 
CgHjS  corresponds  to  2  volumes  of  vapour,  like  methylic  ether 

Methylosulfhydric  ether  is  a  simple  ether,  which  forms  a  great 
number  of  compound  ethers  by  combining  with  electro-negative 
sulphides ;  and  the  principal  of  these  compound  ethers  are : 

§1426.  Methylosulfhydric  Alcohol  C2H3S,HS,  or  methylic  alco- 
hol C2H30,HO,  in  which  the  2  equivalents  of  oxygen  are  replaced 
by  2  equivalents  of  sulphur ;  which  is  obtained  by  passing  a  current 
of  methylochlorohydric  ether  through  an  alcoholic  solution  of  sulf- 
hydrate  of  sulphide  of  potassium,  and  then  distilling  the  mixture. 
It  is  also  prepared  by  distilling  a  mixture  of  sulphomethylate  of 
potassa  K0,(C2H30,2S03)  with  a  solution  of  sulf  hydrate  of  sulphide 
of  potassium ;  the  distilled  product  being  washed  with  water,  and 
rectified  over  chloride  of  calcium.  Methylosulfhydric  alcohol,  also 
called  methylic  mercaptan,  is  a  colourless  liquid,  of  an  extremely 
fetid  odour,  and  very  volatile,  for  it  boils  at  69.8°.  It  is  decom- 
posed by  contact  with  red  oxide  of  mercury,  and  yields'  a  crystal- 
lized product,  in  which  the  sulf  hydric  acid  is  replaced  by  1  equi- 


682  METHYLIC   ALCOHOL. 

valent  of  sulphide  of  mercury  Hg^S ;  analogous  products  being 
obtained  with  several  other  metallic  sulphides. 

§1427.  Sulphocarhomethylosulfhydric  Ether  CgUgSjCSg  is  ob- 
tained by  distilling  a  concentrated  solution  of  sulphomethylate  of 
lime  CaO,(C2H30,2S03)  with  a  solution,  also  concentrated,  of 
sulphocarbonate  of  sulphide  of  potassium  KS,CS2,  and  rectifying 
the  liquid  over  chloride  of  calcium.  It  is  a  yellowish  liquid,  of  a 
density  of  1.159  at  64.4°,  while  it  boils  at  399.2°.  The  density  of 
its  vapour  being  4.650,  its  equivalent  CaHgSjCSa  is  represented  by 
2  volumes  of  vapour:  it  is  methylocarbonic  ether  C2H30,C03, 
hitherto  unknown,  the  oxygen  of  which  is  replaced  by  equivalent 
quantities  of  sulphur. 

§  1428.  By  replacing,  in  the  preparation  of  methylosulf hydric 
ether,  the  alcoholic  solution  of  monosulphide  of  potassium,  by  an 
alcoholic  solution  of  bisulphide  of  potassium,  a  slightly  yellowish 
liquid  is  obtained,  of  an  extremely  disagreeable  and  persistent  alli- 
aceous odour;  while  its  density  is  1.046  at  64.4°,  and  it  boils  at 
240.8°.  The  formula  of  this  substance  being  C3H3S2,  it  may  be 
considered  as  methylosulf  hydric  ether  CjjHgS,  combined  with  1 
equivalent  of  sulphur :  the  density  of  its  vapour  is  3.310,  and  its 
equivalent  corresponds  to  2  volumes  of  vapour. 

Lastly,  by  substituting  pentasulphide  for  the  bisulphide  of  potas- 
sium, there  results  a  product  still  more  sulphuretted,  of  which  the 
formula  is  CgHgSj.  * 

Protocarhuretted  Hydrogen  CgH^,  or  Marsh  Gras, 

§  1429.  Protocarhuretted  hydrogen  evidently  belongs  to  the 
methylic  series,  and  may  be  considered  as  the  starting  point  of  this 
series.  By  causing  chlorine  to  act  on  this  gas,  products  are 
obtained  which  are  identical  with  those  afforded  by  methylochloro- 
hydric  ether  C2H3CI,  and  it  is  not  to  be  doubted,  although  this  is 
not  yet  proved,  that  by  causing  suitable  volumes  of  protocarhuretted 
hydrogen  and  chlorine  to  react  on  each  other,  methylochlorohydric 
ether  itself  will  be  obtained.  Now,  methylochlorohydric  ether, 
treated  with  an  alcoholic  solution  of  potassa,  yields  methylic  alco- 
hol ;  and  it  has  been  mentioned  (§  1390)  that  the  vinic  series  may 
also  be  regarded  as  derived  from  a  carburetted  hydrogen  C^Hg, 
which  is  as  yet  unknown. 

When  vapours  of  monohydrated  acetic  acid  C^HgOgjHO  are  poured 
through  a  glass  tube  containing  platinum-sponge,  and  heated  to 
750°,  the  acetic  acid  is  decomposed  into  carbonic  acid  and  protocar- 
huretted hydrogen, 

C,H303H0=2C0,+aH,. 

A  similar  decomposition  takes  place  by  heating  acetic  acid  in 
contact  with  an  excess  of  alkali ;  but  in  that  case  the  carbonic  acid 
remains  combined  with  the  alkali,  and  the  protocarhuretted  hydrogen 


FORMIC   ACID.  583 

alone  is  disengaged.  The  most  economical  manner  of  preparing 
the  gas  consists  in  heating  4  parts  of  crystallized  acetate  of  soda 
with  10  parts  of  an  alkaline  mixture  composed  of  2  parts  of  caustic 
potassa  and  3  parts  of  quicklime.  In  order  to  make  the  mixture, 
the  2  parts  of  potassa  are  dissolved  in  a  small  quantity  of  water  and 
sprinkled  over  with  the  3  parts  of  pulverized  quicklime ;  and  the 
paste  is  then  heated  to  a  dull-red  to  drive  off  the  excess  of  water. 

Protocarburetted  hydrogen  also  arises  spontaneously  from  marsh 
mud  (§  265)  and  from  layers  of  bituminous  coal. 

It  has  never  been  liquefied  at  any  temperature,  and  its  density  is 
0.559,  while  its  equivalent  CgH^  corresponds  to  4  vol.  of  gas,  and 
it  burns  with  a  bluish  flame,  which  is  much  less  brilliant  than  that 
of  bicarburetted  hydrogen. 

PRODUCTS  OF  THE  OXIDATION  OF  METHYLIC  ALCOHOL. 

Formic  Acid  C^HOgHO. 

§  1430.  Methylic  alcohol  oxidizes,  at  the  expense  of  the  oxygen 
of  the  air,  in  the  presence  of  platinum-sponge,  and,  like  alcohol, 
it  exchanges,  in  this  case,  2  equiv.  of  hydrogen  for  2  equiv.  of  oxy- 
gen,* producing  a  peculiar  acid  CgHOgjHO,  called  formic,  a  large 
portion  of  which  is,  however,  destroyed  by  contact  with  the  platinum- 
sponge,  and,  especially  if  the  temperature  be  elevated,  complete  com- 
bustion and  the  formation  of  carbonic  acid  ensue : 

C2H03,HO+20=2CO,+2HO. 

But  formic  acid  is  obtained  in  a  great  number  of  chemical  reac- 
tions, in  which  certain  organic  substances  are  subjected  to  oxidizing 
agents ;  by  heating,  for  example,  a  mixture  of  peroxide  of  manganese 
and  dilute  sulphuric  acid,  with  alcohol,  sugar,  fecula,  tartaric  acid, 
etc.,  a  portion  of  the  organic  substance  being  completely  converted 
into  water  and  carbonic  acid,  while  the  other  is  imperfectly  oxidized 
and  produces  formic  acid.  When  any  considerable  quantity  of  formic 
acid  is  to  be  prepared,  2  kilog.  of  sugar  are  dissolved  in  10  litres  of 
water,  and  6  kilog.  of  sulphuric  acid  being  gradually  added,  the 
mixture  is  poured  into  the  cucurbit  of  an  alembic,  at  the  bottom  of 
which  have  been  placed  6  kilog.  of  peroxide  of  manganese.  A 
lively  effervescence"  ensues  immediately,  owing  to  the  evolution  of 
carbonic  acid,  and  when  it  lessens,  the  capital  is  adjusted  and  dis- 
tillation effected,  but  it  is  arrested  when  5  or  6  litres  of  liquid  are 
obtained.     This  liquid,  in  which  the  formic  acid  is  concentrated,  is 

*  It  is  more  rational  to  assume,  in  the  case  of  both  acetic  and  formic  acids,  that 
the  alcohol  takes  up  4  equiv.  of  oxygen  and  gives  off  3  equiv.  of  water,  because 
the  substitution  of  oxygen  for  hydrogen  in  combinations  is  scarcely  admissible. 

Vinic  alcohol  Qt\iS)^,  by  taking  up  0^,  becomes  C4H6O6,  and,  by  losing  3H0,  as- 
sumes the  formula  of  acetic  acid  C^HgOs-j-aq- 

In  like  manner,  methylic  alcohol  CaH40a  becomes  CaH^Og  by  gaining  O4,  and  is 
converted  into  formic  acid  CaHO.-faq.  by  giving  off  3H0. —  W.  L.  F. 


584  METHYLIC  ALCOHOL. 

saturated  with  milk  of  lime  and  the  formiate  of  lime  crystallized  by 
evaporation.  The  salt  thus  forms  only  crystalline  crusts ;  and  by 
distilling  it  with  more  or  less  concentrated  sulphuric  acid,  formic 
acid  also  more  or  less  concentrated  is  obtained. 
'  If  formic  acid  is  to  be  obtained  at  its  maximum  of  concentration, 
the  formiate  of  lime  must  be  converted  into  formiate  of  lead,  by 
adding  acetate  of  lead  to  the  solution  of  formiate  of  lime ;  when  the 
formiate  of  lead,  being  but  slightly  soluble  in  cold  water,  is  almost 
wholly  deposited,  and  may  be  purified  by  dissolving  it  in  boiling 
water,  which  deposits  it,  on  cooling,  in  small  prismatic  crystals. 

Formiate  of  lead,  well  dried,  is  introduced  into  a  long  glass  tube, 
heated  by  some  coals,  and  through  which  a  current  of  sulf hydric 
acid  is  passed,  when  sulphide  of  lead  is  formed,  while  mono- 
hydrated  formic  acid  condenses  in  the  receiver.  It  is  a  colourless 
liquid,  of  a  penetrating  and  characteristic  odour,  and  it  solidifies 
at  a  few  degrees  below  32°,  while  it  boils  at  212°.  Its  density  is 
1.235,  and  the  density  of  its  vapour  being  1.556,  its  equivalent 
CaHOgjHO  is  represented  by  4  volumes  of  vapour. 

Monohydrated  formic  acid  is  highly  caustic,  and  produces  blisters 
on  the  skin.  In  combining  with  water,  the  first  portions  of  water 
added  elevate  its  boiling  point;  with  the  addition  of  20.7  of  water, 
that  is  1  equiv.,  it  boils  at  222.8°.  An  excess  of  concentrated  sul- 
phuric acid  decomposes  formic  acid  into  oxide  of  carbon  and  water. 
At  the  boiling  point,  formic  acid  reduces  several  metallic  oxides, 
particularly  the  oxides  of  silver  and  mercury. 

Formiate  of  potassa  and  soda  are  very  soluble  and  deliquescent. 

Formiate  of  baryta  dissolves  in  4  parts  of  water,  and  crystallizes 
readily;  the  formula  of  its  crystals  being  BaOjC^HOg. 

Formiate  of  lime  dissolves  in  10  parts  of  water,  and  is  nearly  as 
soluble  in  hot  as  in  cold  water. 

Formiate  of  lead  requires  36  to  40  parts  of  cold  water  for  solu- 
tion, but  dissolves  more  freely  in  hot  water,  and  its  crystals  are 
anhydrous. 

By  double  decomposition,  a  formiate  of  silver  may  be  obtained 
which  is  destroyed  by  being  boiled  with  water. 

§  1431.  Formic  ether  C4H50,C2H03  of  the  vinic  series  is  obtained 
by  heating  a  mixture  of  7  parts  of  dry  formiate  of  soda,  10  parts 
of  concentrated  sulphuric  acid,  and  9  parts  of  alcohol.  It  is  made 
on  a  larger  scale  and  cheaply,  by  mixing,  in  a  large  retort,  80  parts 
of  starch,  120  of  ordinary  alcohol  at  0.85,  120  parts  of  water,  304 
of  peroxide  of  manganese,  and  240  of  concentrated  sulphuric  acid. 
Heat  is  applied  gently,  and,  when  the  reaction  is  fully  established, 
the  fire  is  removed,  and  the  sides  of  the  retort  cooled  with  moist 
cloths,  when  a  stratum  of  formic  ether  separates,  which  is  removed 
and  treated  with  milk  of  lime  to  free  it  from  acids,  and  subse- 
quently distilled  over  chloride  of  calcium. 

Formic  ether  is  a  colourless  liquid,  of  a  mild  taste,  of  a  density  of 


METHYLAL.  585 

0.912,  and  boiling  at  128.1°,  which  dissolves  in  10  parts  of  water, 
and  mixes  in  all  proportions  with  alcohol.  It  should  be  remarked 
that  formic  ether  0^1150,021103  is  isomeric  with  methylacetic  ether 
031130,0411303.  Formic  ether,  treated  with  chlorine  in  diffused 
light,  forms  a  chlorinated  ether,  of  the  formula  0^1130120,021103, 
and,  by  exhausting  the  action  of  the  chlorine  in  the  sun,  a  per  chlori- 
nated chloroformic  ether  O^Ol^OjOgOlOg  is  obtained. 

Methyloformie  ether  02H30,02H03  is  prepared  in  the  same  man- 
ner as  that  of  the  vinic  series,  except  that  spirit  of  wood  is  substi- 
tuted for  alcohol,  and  it  is  an  etherial,  very  mobile  liquid,  which 
boils  at  about  98.6°. 

Methylal  OgHgO^. 

§  1432.  It  has  not  yet  been  found  possible  to  obtain  aldehyde  of 
the  methylic  series,  the  formula  of  which  would  be  QJlfi^  By 
distilling  a  mixture  of  methylic  acid  and  alcohol  over  peroxide  of 
manganese,  there  results  a  mixture  of  several  volatile  liquids,  in 
which  methyloformie  ether  and  a  peculiar  liquid,  called  methylal, 
predominate.  The  latter  being  dissolved  in  water,  and  potassa 
added,  the  alkali  decomposes  the  methyloformie  ether,  while  the 
methylal  separates  in  the  form  of  a  liquid  layer  floating  on  the  sur- 
face, which  is  purified  by  distillation  over  chloride  of  calcium.  Me- 
thylal boils  at  107.6°,  and  corresponds  to  acetal.  Its  formula  being 
OgH^O^,  it  may  be  regarded  as  resulting  from  the  union  of  3  mole- 
cules of  methylic  ether,  of  which  one  has  taken  1  equiv.  of  oxygen 
in  the  place  of  1  equiv.  of  hydrogen.* 

ACTION  OF  CHLORINE  ON  COMPOUNDS  OF  THE  METHYLIC  SERIES. 

Products  of  the  Action  of  Qhlorine  on  Methylochlorohydric  Ether 
and  on  Protocarhuretted  Hydrogen. 

§  1433.  Chlorine  acts  with  more  difficulty  on  chlorohydric  ether 
of  the  methylic  series  than  on  that  of  the  vinic  series,  the  reaction 
ensuing  only  when  assisted  by  the  direct  rays  of  the  sun ;  and  as 
these  products  are  more  volatile,  greater  care  is  required  in  cooling 
the  receivers.  The  apparatus  described  (§  1387)  and  represented  by 
fig.  680  is  used. 

By  maintaining  the  methylochlorohydric  ether  in  excess,  the 
bottle  0,  (fig.  680),  which  should  be  kept  in  a  refrigerating  mixture, 
receives  a  very  volatile  liquid,  which  should  be  purified  by  distilla- 
tion over  concentrated  sulphuric  acid,  and  then  over  quicklime,  and 
which  is  monochlorinated  methylochlorohydric  ether  O3H3OI3.  The 
odour  of  this  product  resembles  that  of  Dutch  liquid,  and  its  density 

*  Here  again  it  is  unnecessary  to  assume  the  highly  improbable  substitution  of 
oxygen  for  hydrogen,  since  the  reaction  is  very  simply  expiuiued  by  allowing  3 
equiv.  of  methylic  ether  CgHgOg  to  gain  2  equiv.  of  oxygen,  forming  CgHgOj,  and 
then  to  lose  1  equiv.  of  water,  which  gives  methylal  CgilgO*. —  Tf.  L.  F. 


586  METHYLIC  ALCOHOL. 

is  1.344  at  64.4°,  while  it  boils  at  86.9°.  The  density  of  its  vapour 
being  2.94,  its  equivalent  CgHgClg  is  represented  by  4  volumes  of 
vapour,  like  that  of  methylochlorohydric  ether  CgHgCl. 

§  1434.  The  second  product  of  the  action  of  chlorine  on  methylo- 
chlorohydric ether  is  a  liquid  having  a  density  of  1.491  at  62.6°, 
and  boiling  at  141.8°;  the- composition  of  which  is  represented  by 
the  formula  C2HCI3,  corresponding  to  4  vols,  of  vapour.  This  is 
hichlorinated  methyloMorohydric  ether^  more  commonly  known  as 
chloroform,  which  name  has  been  given  to  it  because,  in  contact  with 
an  alcoholic  solution  of  potassa,  it  yields  chloride  of  potassium  and 
formiate  of  potassa, 

C,HCl3+4KO=3KCH-KO,C2H03. 

Chloroform  is  produced  in  several  other  chemical  reactions,  and 
particularly  when  a  solution  of  hypochlorite  of  lime  is  made  to  re- 
act on  alcohol  or  acetone.  This  product  has  been  extensively 
manufactured  since  the  discovery  of  its  power  in  effecting  the 
insensibility  of  patients  during  surgical  operations. 

Chloroform  is  also  obtained  by  decomposing  hydrated  chloral 
C^HClgOjjHO  by  a  solution  of  potassa, 

C,HCl30„HO+KO=C2HCl3+KO,C,H03. 

Lastly,  chloroform  is  produced  when  the  chloracetates  are  heated 
in  the  presence  of  an  excess  of  hydrated  alkali, 

KO,C,Cl3C>3+KO,HO=2(KO,C02)4-C,HCl3. 

It  is  readily  and  economically  prepared,  by  pouring  35  to  40 
litres  of  water  into  the  cucurbit  of  an  alembic,  heating  the  water 
to  106°,  and  adding  first  5  kilog.  of  quicklime,  and  subsequently 
10  kilog.  of  hypochlorite  of  lime  of  commerce ;  and  lastly,  by 
pouring  in  IJ  litre  of  alcohol  at  0.85,  and,  after  having  mixed  it 
well,  and  adjusted  the  capital,  heating  the  liquid  to  boiling.  As 
soon  as  distillation  commences,  the  fire  is  slackened  and  the  pro- 
cess allowed  to  continue  spontaneously,  when  an  aqueous  liquid 
condenses  in  the  receiver,  at  the  bottom  of  which  a  heavier  liquid, 
chloroform,  is  formed.  It  is  separated  and  purified  by  distillation 
over  chloride  of  calcium ;  and  the  process  just  described  yields 
about  600  gm.  of  chloroform. 

§  1435.  Chloroform,  subjected  to  the  action  of  chlorine,  in  the 
light  of  the  sun,  until  chlorohydric  acid  is  no  longer  disengaged, 
loses  its  last  equivalent  of  hydrogen,  while  perchlorinated  methylo- 
chlorohydric ether  C^Cl^,  which  is  a  new  chloride  of  carbon,  is 
formed.  This  compound  is  liquid  at  the  ordinary  temperature,  but 
at  9.4°  solidifies  into  a  pearly  crystalline  mass ;  and  it  boils  at 
172.4°.  Its  density  is  1.599;  the  density  of  its  vapour  being 
5.30,  its  equivalent  is  likewise  represented  by  4  volumes  of  vapour. 

§  1436.  By  exposing  to  the  rays  of  the  sun  a  bottle  containing  a 


CHLOROFORM.  587 

mixture  of  protocarburetted  hydrogen,  and  chlorine  in  excess,  a 
liquid  condenses  on  the  sides,  which  is  a  mixture  of  the  various 
chlorinated  methylochlorohydric  ethers  just  described,  comprising 
principally  chloroform  C^HClg  and  chloride  of  carbon  CgCl^. 
The  first  chlorinated  product,  methylochlorohydric  ether  C2H3Ci, 
would  probably  be  obtained  by  introducing  the  two  gases  in  an  ap- 
paratus resembling  that  of  fig.  680,  maintaining  the  protocarbu- 
retted hydrogen  in  excess,  and  then  passing  the  gases  through  a 
tube  cooled  by  solidified  carbonic  acid,  in  order  to  condense  the 
gaseous  ether.  In  all  cases,  it  is  proved  that,  by  the  action  of 
chlorine  and  protocarburetted  liydrogen  CgH^,  the  same  products  are 
obtained  as  by  the  action  of  chlorine  on  methylochlorohydric  ether 
C3H3CI,  and  it  is  correct  to  regard  this  substance  as  the  starting 
point  of  the  series.     Thus,  we  have 

Protocarburetted  hydrogen C2H4,  a  non-liquefiable  gas. 

Methylochlorohydric  ether C^HjCl,  liquefying  at  a  very 

low  temperature. 
Monochlorinated  methylochlorohydric 

ether C^H^Clj,  boiling  at  86.9°. 

Bichlorinated        methylochlorohydric 

ether,  or  chloroform C3HCI3,  boiling  at  141.8°. 

Perchlorinated      methylochlorohydric 

ether C2CI4,  boiling  at  172.4°. 

§  1437.  But  again,  it  is  possible,  by  operating  on  chloride  of 
carbon  CjCl^,  and  by  proper  chemical  reactions,  to  substitute 
hydrogen  for  the  chlorine,  and  ascend  from  chloride  of  carbon  to 
protocarburetted  hydrogen,  passing  through  all  the  intermediate 
products :  in  order  to  prove  which,  it  is  sufiicient  to  introduce  into 
a  flat-bottomed  flask  a  solution  of  chloride  of  carbon  in  aqueous  al- 
cohol, and  then  to  add  an  amalgam  of  potassium.  On  communi- 
cating the  flask  successively  with  two  U-tubes,  the  first  of  which  is 
kept  at  a  temperature  of  about  86°,  and  the  second  cooled  by  a 
mixture  of  ice  and  salt,  then  with  a  bulb-apparatus  filled  with  water, 
and  lastly  with  a  conducting-tube  which  leads  the  gases  into  a  bell- 
glass  over  the  water-cistern,  and  heating  the  flask,  the  chloride  of 
carbon  is  decomposed,  chloride  of  potassium  and  caustic  potassa 
being  formed ;  and  the  chlorine  abstracted  is  replaced  by  hydrogen 
arising  from  the  decomposition  of  the  water. 

Bichlorinated  methylochlorohydric  ether  C3HCI3  condenses  chiefly 
in  the  first  U-tube,  and  in  the  second  the  monochlorinated  methylo- 
chlorohydric ether  CaHgClg,  while  the  water  in  the  bulb-apparatus 
dissolves  the  methylochlorohydric  ether  CgHjCl,  which  may  be  sepa- 
rated by  saturating  it  with  chloride  of  calcium ;  and  lastly,  proto- 
carburetted hydrogen  is  collected  in  the  bell-glass. 

This  inverse  transformation  has  not  hitherto  succeeded  on  the 
corresponding  series  of  chlorohydric  ether  of  alcohol ;  but  would  be 


588 


METHYLIC   ALCOHOL. 


particularly  interesting,  as  it  would  enable  the  preparation  of  the 
carburetted  hydrogen  C^Hg  which  is  still  wanting  in  the  series. 

Bromoform,  Iodoform,  and  Sulplioform, 

§  1438.  By  treating  alcohol  with  bromine,  a  product  correspond- 
ing to  chloral  is  obtained,  which  is  decomposed  by  alkaline  solu- 
tions, and  yields  bromoform  C^HBrg. 

Iodoform  C3HI3  is  obtained  by  pouring  a  solution  of  caustic  po- 
tassa,  or  carbonate  of  potassa,  into  alcohol  saturated  with  iodine, 
until  the  liquid  is  discoloured ;  when,  by  adding  a  large  quantity  of 
water,  the  iodoform  is  precipitated  in  the  form  of  small  crystalline 
spangles,  which  are  purified  by  redissolving  them  in  alcohol  and 
evaporating  the  liquid. 

By  distilling  1  part  of  iodoform  with  3  parts  of  sulphide  of  mer- 
cury, a  yellow  oleaginous  liquid  is  obtained,  constituting  sulpho- 
form  CJIS,, 

Action  of  Chlorine  on  Methylic  Ether  CjHgO. 

§  1439.  The  action  of  chlorine  on  methylic  ether  is  excessively 
violent,  even  in  diffused  light ;  and  the  experiment,  being  dangerous, 
must  be  carefully  conducted,  in  order  to  prevent  the  apparatus  from 
bursting  to  pieces.     Figure  682  represents  the  apparatus  most  suit- 


Fig.  682. 

able  to  file  production  of  any  considerable  quantity  of  the  product. 
Methylic  ether  is  prepared  by  heating  in  a  flask  A  (fig.  682)  a  mix- 
ture of  1  part  of  wood-spirit  and  4  parts  of  cencentrated  sulphuric 


ACTION   OF   CHLORINE    ON   METHYLIC   ETHER.  589 

acid ;  allowing  the  gas  to  traverse  a  first  washing-bottle  B  contain- 
ing water,  then  a  second  bottle  C  containing  a  solution  of  potassa 
in  order  to  retain  the  sulphurous  and  carbonic  acids,  and  lastly,  a  long 
tube  filled  with  chloride  of  calcium  to  dry  the  gas.  (This  tube  is  not 
represented  in  the  figure.)  The  chlorine  is  prepared  in  the  flask' 
G  by  the  reaction  of  chlorohydric  acid  on  peroxide  of  manganese, 
and  is  washed  in  the  water  of  the  bottle  F,  and  dried  by  passing 
through  concentrated  sulphuric  acid  contained  in  the  bottle  E.  The 
two  gases,  which  are  brought  together  in  the  flask  D,  escape  through 
a  refrigerator  H,  made  very  cold  by  ice,  into  the  atmosphere  by  the 
opening  o.  The  liquids  which  condense  in  the  flask  J)  and  in  the 
refrigerator  H  fall  into  the  bottle  I,  which  should  be  entirely  inde- 
pendent of  the  apparatus,  so  that  if  the  latter  should  burst,  the 
products  already  obtained  will  not  be  lost. 

The  apparatus  should  be  arranged  in  a  well-lighted  place,  but  pro- 
tected from  the  direct  rays  of  the  sun ;  and,  though  the  reaction  is 
sometimes  long  in  being  established,  when  once  commenced,  it  con- 
tinues with  great  energy.  The  operator  should  then  regulate  the 
evolution  of  the  two  gases  with  great  care :  they  should  meet  in 
such  proportion  as  to  destroy  each  other,  immediately,  on  reaching 
the  flask  D ;  for  if  one  of  the  gases  should  flow  too  freely,  as,  for 
example,  if  the  flask  were  to  become  coloured  by  chlorine,  which 
would  require  a  more  rapid  disengagement  of  methylic  ether,  an  ex- 
plosion would  inevitably  ensue.  In  order  to  prevent  thi"S  accident, 
the  current  of  chlorine  must  be  lessened  by  opening  one  of  the 
washing-bottles  E  or  F,  and  the  ether  must  be  allowed  to  flow  very 
slowly  until  the  flask  D  is  deprived  of  colour ;  after  which  the  gases 
would  be  made  to  flow. 

The  bottle  I  is  found  to  contain  a  very  volatile  liquid,  of  a  sufib- 
cating  odour  and  exciting  to  tears,  which  exhales  acid  fumes  by 
being  decomposed  by  the  moisture  of  the  air.  Its  density  at  68° 
is  1.315,  while  it  boils  at  221°,  and  cold  water  decomposes  it, 
though  slowly.  This  liquid  is  monochlorinated  methylic  ether 
C2H3CIO,  the  formula  of  which  corresponds  to  2  volumes  of  vapour, 
like  that  of  methylic  ether  C^Ufi,  from  which  it  is  derived. 

This  product,  subjected  to  the  action  of  chlorine,  exchanges  1 
equivalent  of  hydrogen  for  1  equivalent  of  chlorine,  and  becomes 
hiehlorinated  methylic  ether,  the  density  of  which  is  1.606  at  68°, 
while  it  boils  at  about  266°  ;  its  equivalent  0^11  ClaO  corresponding 
likewise  to  2  volumes  of  vapour. 

Finally,  by  again  exposing  this  new  product  to  the  action  of 
chlorine,  in  the  rays  of  the  sun,  its  last  equivalent  of  hydrogen  is 
replaced  by  1  equivalent  of  chlorine,  forming  perchlorinated  me- 
thylic ether  CgClgO,  which  product  has  not  maintained  a  state  of 
concentration  similar  to  that  of  the  two  preceding,  and  that  of  me- 
thylic ether  C2H3O,  for  its  equivalent  corresponds  to  4  volumes  of 
vapour.     There  has  been  either  a  doubling  of  the  original  mole- 


590  METHYLIC   ALCOHOL. 

cule,  or  a  separation  of  the  molecules,  so  that  the  same  num- 
ber of  molecular  groups  now  occupy  a  double  space ;  which  change 
of  molecular  arrangement  is  manifested  by  an  anomaly  in  the  boil- 
ing point.  It  has  always  hitherto  been  observed  that  when  a  mole- 
cular group  is  modified  merely  by  the  substitution  of  1  equivalent 
of  chlorine  for  1  equivalent  of  hydrogen,  its  boiling  point  rises ; 
which  circumstance  is  not  true  for  terchlorinated  methylic  ether, 
compared  with  bichlorinated  methylic  ether ;  the  boiling  point  of 
the  latter  being  266°,  while  that  of  the  former  is  about  212°. 

Action  of  Qhlorine  on  Methylosulfhydric  Ether. 

§  1440.  Chlorine  readily  acts  on  methylosulfhydric  ether,  which 
gradually  exchanges  its  oxygen  for  equivalent  quantities  of  chlo- 
rine, and  the  final  product  is  percJdorinated  methylosulfhydriG 
ether  C.Cl^S. 

Action  of  Chlorine  on  the  Compound  Methylic  Ethers, 

§  1441.  A  large  number  of  compound  ethers  of  the  methylic  se- 
ries can  exchange  more  or  less  completely  their  hydrogen  for  equi- 
valent quantities  of  chlorine. 

Thus  methyloxalic  ether  €21130,0203  furnishes 

A  bichlorinated  methyloxalic  ether. .......   C2HCI2O,  C2O3, 

And  a  perchlorinated     "  "       0^0130,0203. 

Methylacetic  ether  02X130,0411303  also  yields 

A  bichlorinated  methylacetic  ether 03H0l2O,04H3O3, 

And  a  perchlorinated     "  "     ....  O^OlgOjO^OlgOj. 

It  has  been  shown  that  formic  ether  of  the  vinic  series  O^H^O, 
OjHOg  presents  the  same  elementary  composition  as  methylacetic 
ether  031130,0411303,  although  the  two  substances  difi'er  materially 
in  their  physical  and  chemical  properties ;  and  the  composition  of 
the  perchlorinated  products  of  the  two  ethers  should  therefore  be 
similar :  not  only  are  they  so,  but  they  are  identical,  constitut- 
ing one  and  the  same  substance,  and  no  longer  exhibiting  the  di- 
versity of  their  origin.  We  have  already  mentioned  an  analogous 
case.  Dutch  liquid  04H301,H01  is  isomeric  with  monochlorinated 
chlorohydric  ether  O^H^Olg,  while  the  two  substances  differ  distinctly 
in  their  physical  and  chemical  properties ;  but  when  Ireated  with  chlo- 
rine, they  both  yield  the  same  final  product,  chloride  of  carbon  O^Olg. 

Methyloformic  ether  yields  with  chlorine  two  chlorinated  ethers : 

Bichlorinated  methyloformic  ether 02H0l2O,02HO3, 

And  perchlorinated       "  "      020130,020103. 

This  last  ether  is  liquid,  boils  at  about  856°,  and  is  isomeric  with 
chlorocarbonic  gas  0001;  into  which  it  is  entirely  converted,  by 
passing  its  vapour  into  a  tube  heated  to  a  temperature  above  572°. 


METHYLIC   SERIES.  591 

Action  of  Chlorine  on  Formic  Acid. 
§  1442.  No  chlorinated  formic  acid  is  known,  and  when  mono- 
hydrated  formic  acid  CjHOjHO  is  treated  with  chlorine,  the  equi- 
valent of  water  is  always  decomposed,  chlorohydric  and  carbonic 
acids  being  formed : 

C,H03,H0+2C1=2HC1+2C02. 
But  it  has  been  shown  (§§  1431  and  1441,)  that  the  formic  acid 
which  exists  in  formic  and  methyloformic  ethers  can  exchange  its 
hydrogen  for  chlorine. 


§  1443.  It  will  be  seen  from  the  preceding  observations  that  the 
compounds  of  the  methylic  series  may  be  considered  as  being  pro- 
duced by  the  same  molecule  C^H^,  that  of  protocarburetted  hydro- 
gen, or  marsh  gas,  in  which  one  or  several  equivalents  of  hydrogen 
are  replaced  by  a  corresponding  number  of  other  elements,  such  as 
oxygen,  sulphur,  chlorine,  etc.  etc.  In  order  to  render  this  method 
of  generation  evident,  we  have  collected  into  a  single  table  all  the 
known  products  of  the  methylic  series. 

TABLE  OF  COMPOUNDS  DERIVED  FROM  CARBURETTED  HYDRO- 
GEN C2H4,  OR  FROM  METHYLIC  ETHER  C2H3O. 

Protocarburetted  hydrogen,  or CaH4  2  vols. 

Marsh  Gas,  the  starting  point  of  the  series. 

SIMPLE  ETHERS. 

Methylic  ether CaH.O  2 

Methylosulfhydric  ether 0,11,8  2 

Methylochlorohydric  ether C3H3CI  4 

Methylobromohydric  ether CaH.Br  4 

Methylodohydric  ether C3H3I0  4 

Methylohydrocyanic  ether C^^Qy  4 

Methylosulphohydrocyanic  ether CaHaSCy  4 

COMPOUND  ETHERS. 
Alcohols. 

Methylic  alcohol,  or  wood-spirit CaHgOjHO     4    " 

Methylosulfhydric  alcohol CaH3S,HS       4    " 

Methyloplumbic  "      CHsSjPbS 

Methylomercuric        "      CaH3S,HgaS. 

Compound  Ethers^  properly  so  called. 

General  formula  (A  representing  the  acid) CaHaOjA         2  or  4  vols. 

Methylobiboracic  ether CaH,0,2B0, 

Trimethyloboracio    "     3CaH,0.B0,     4  " 

Methylic  Acids. 
General  formula  of  methylic  acids  formed  by  the 

monobasic  acids  A (CaHg0-|-H0),2A 

Formula  of  the  methylic  acids  produced  by  the 

tribasic  acids,  such  as  P0.,3H0 (C3H,0-}-2H0),P0,. 


592  METHYLIC   SERIES. 

PRODUCTS  DERIVED  SUCCESSIVELY  FROM  METHYLIC  ETHER  CaH.O. 

1st.  By  Oxidation. 

Methylic  ether CaHjO  2  vols. 

Methyal (2C,H30,CaHA)  4    " 

Anhydrous  formic  acid C^HOa  unknown. 

Remains  combined  with  the  water  formed  and  yields 

Hydrated  formic  acid CaHOa,HO      4    " 

But  corresponding  to  methylic  alcohol CaHjOjHO      4    " 

2d.  By  the  Action  of  Chlorine. 

Methylic  ether CaH,    0  2  « 

Monochlorinated  methylic  ether CaHaClO  2  " 

Bichlorinated  "  "     CaHClaO  2  " 

Perchlorinated  "  «*     CaCl,    0  4  " 

PRODUCTS  DERIVED  FROM  METHYLOSULFHYDRIC  ETHER  C^HaS. 
By  the  Action  of  Chlorine. 
Methylosulfhydric  ether CaH,S  2  vols. 

Perchlorinated  methylosulfhydric  ether CaClaS.  • 

PRODUCTS  DERIVED  FROM  PROTOCARBURETTED  HYDROGEN  C,H„  OR 
FROM  METHYLOCHLOROHYDRIC  ETHER  CaHaCl. 

By  the  Action  of  Clorine. 

Protocarburetted  hydrogen CaH4  4  vols. 

Methylochlorohydric  ether CaHgCl  4    " 

Monochlorinated  methylochlorohydric  ether CaH^CL,  4    " 

Bichlorinated        do.,     or  chloroform C3HCI3  4    " 

Perchlorinated       do.,  "  0^014  4    « 

PRODUCTS  DERIVED  FROM  METHYLIC  ALCOHOL  CaH,0,H0. 

1st:  By  the  Action  of  Oxygen. 

Methylic  alcohol CaH,0,HO      4  vols. 

Formic  acid CaH0a,HO     4    " 

Id.  By  the  Action  of  Chlorine. 
Products  unknown 

PRODUCTS  DERIVED  FROM  AQUEOUS  METHYLIC  ALCOHOL 
CaH30,H0+H0. 

By  the  Action  of  Chlorine. 

Formic  acid CaHOajHO. 

An  excess  of  chlorine  converts  the  formic  acid,  by  its  oxidizing  action,  into 

carbonic  acid. 
Aqueous  methylic  ether  CaH,0+2H0  yields  the  same  products. 


METHYLIC   SERIES.  593 

PRODUCTS  DERIVED  FROM  COMPOUND  METHYLIC  ETHERS. 

By  the  Action  of  Chlorine. 

On  Methyloxalic  ether CaH,     0,0,     0,. 

Bichlorinated  methyloxalic  ether CaH  ClaOjCa     0,. 

Perchlorinated         "               "     C,     ClACa     0^, 

On  Methylacetic  ether CaH,     O.C^HgO,. 

Bichlorinated  methylacetic  ether CaH  ClaO,C4H309. 

Perchlorinated         *'                "     C,     Cl30,C4H30,. 

On  Methyloformic  ether CHg      0,CaH  0^^ 

Bichlorinated  methyloformic  ether CaH  Cl30,C3H  O^. 

Perchlorinated         "                   *«     Ca     01,0,0,010^ 

§  1444.  Chemists  have  formed,  for  the  methylic  series,  hypothe- 
ses analogous  to  those  proposed  for  the  vinic  series.  Some  regard 
all  simple  methylic  ethers  as  produced  by  the  combination  of  the 
same  radical  CgHg,  or  methylen^  with  1  equivalent  of  oxygen,  sul- 
phur, chlorine,  etc.  etc.,  in  which  case  methylic  ether  becomes  a 
monohydrate  of  methylen  CaHgjHO,  and  methylic  alcohol  its  bi- 
hydrate  C2H2,2H0.  This  radical  is  entirely  hypothetical,  since  as 
yet  no  carburetted  hydrogen  of  the  formula  C^H^  is  known  which 
yields  by  direct  combination,  either  with  water  or  with  chlorohydric 
acid,  a  simple  ether  of  the  methylic  series ;  a  condition  indispensa- 
ble, neverthless,  to  enable  it  to  be  considered  as  the  radical  of  the 
series.  Moreover,  the  methylic  and  vinic  series  are  so  similar  that 
their  formula  cannot  be  written  in  two  different  ways,  and  we  have 
incontestably  proved  (§  1401)  that  bicarburetted  hydrogen  C^H^ 
could  not  be  considered  as  pre-existing  in  the  state  of  a  radical 
in  vinic  ethers. 

Other  chemists  consider  methylic  ether  C3H3O  as  the  oxide  of  a 
radical  C3H3,  which  they  call  methyl^  and  of  which  methylochloro- 
hydric  ether  is  then  the  chloride ;  but  as  methyl  is  not  any  better 
known  than  is  ethyl  and  methylen,  we  see  no  advantage  in  resorting 
to  hypotheses  of  these  unknown  radicals,  especially  for  the  methylic 
series,  which  may  be  as  easily  derived,  by  means  of  substitution, 
from  a  perfectly  well  known  hydrocarbon,  protocarburetted  hydro- 
gen C3H4.  We  have  shown  it,  in  fact,  (§  1436,)  to  be  very  probable 
that,  by  causing  chlorine,  in  proper  proportions,  to  act  upon  carbu- 
retted hydrogen  CgH^,  methylochlorohydric  ether  C3H3CI  would  be 
obtained :  now,  the  latter  is  decomposed  by  contact  with  alkaline 
solutions,  and  yields  wood-spirit,  whence  the  whole  methylic  series 
may  be  subsequently  derived.' 


* 


*  Referring  the  reader,  on  the  subject  of  the  radicals  of  ether  and  mother,  back 
to  the  note  to  §1401,  (page  568,)  it  now  only  remains  to  describe  the  radical 
methyl,  the  isolation  of  which  renders  the  correctness  of  the  French  theory  ex- 
tremely doubtful. 

Methyl  CaH^ 
Methyl  is  given  off  at  the  positive  pole,  in  decomposing  a  concentrated  solution 
of  acetate  of  potassa  by  a  powerful  galvanic  current,  while  at  the  negative  pole 
Vol.  IL— 38 


594  VEGETABLE   ACIDS. 

OF  CERTAIN  ACIDS  WHICH  EXIST  IN  THE  JUICES  OF 
VEGETABLES. 

§  1445.  We  shall  describe  in  this  chapter  certain  acids  which  are 
found  ready  formed  in  the  juices  of  vegetables,  and  which  have  not 
been  included  in  any  group  of  substances  of  analogous  composition, 
as  chemists  have  succeeded  in  doing  for  acetic,  formic  acid,  etc.  etc. 

OXALIC  ACID  C,03,H0. 

§  1446.  Of  these  acids,  one  of  the  most  important  is  oxalic,  of 
which  the  properties  were  described  (§  259)  when  treating  of  the 
compounds  of  carbon  with  oxygen,  among  which  oxalic  acid  is 
ranked  on  account  of  the  composition  it  presents  in  anhydrous  salts. 
Oxalic  acid  is  found  in  a  large  number  of  vegetables,  which  fre- 
quently, as  in  the  case  of  sorrel,*  owe  their  acid  taste  to  its  presence. 
In  the  Black  Forest  (Southern  Germany)  it  is  obtained  from  certain 
species  of  rumex,  by  pounding  the  plant  in  troughs  and  expressing 
its  juice ;  after  which  the  residue  is  moistened  with  water  and  ex- 
pressed a  second  time.  The  liquid  is  clarified  with  clay,  decanted 
and  evaporated  to  crystallization ;  when  crystals  of  binoxalate  and 
quadroxalate  of  potassa,  (§  451,)  called  in  commerce  salts  of  sorrel, 
are  separated.  In  order  to  extract  the  oxalic  acid,  acetate  of  lead 
is  poured  into  a  solution  of  salt  of  sorrel,  when  oxalate  of  lead  is 
precipitated,  which  is  decomposed  by  sulphuric  acid ;  after  which 
the  liquid,  on  evaporation,  yields  crystals  of  oxalic  acid  CgO^jHO 
-f2H0. 

The  greater  part  of  the  oxalic  acid  now  in  use  in  laboratories  is 
prepared  by  the  reaction  of  nitric  acid  on  sugar,  (§  259.) 

appear  hjdi'ogen  and  carbonic  acid,  resulting  from  the  oxidation  of  the  oxalic 
acid  formed,  at  the  expense  of  an  equivalent  of  water,  whence  the  hydrogen. 
Acetic  acid  is  considered  as  a  pairling  of  oxalic  acid  0^0,  with  methyl  C^ii,,  which 
view  is  sustained  by  the  decomposition  of  the  acid,  ensuing  as  follows : 

KO,C.H,0,4.2HO=KO,HO+C,H,4-C,0,-f-HO,  or 
=K0,H0-|-C,H34-2C0a+H. 

Methyl  is  also  formed  in  the  decomposition  of  iodohydric  ether  by  zinc,  in  pre- 
sence of  water ;  and  in  the  decomposition  of  cyanohydric  ether  (cyanide  of  eth-v  1) 
by  potassium.  It  is  a  colourless  and  inodorous  gas,  almost  insoluble  in  watr^^r, 
soluble  in  alcohol,  and  does  not  liquefy  at  — 0.4°.  Its  specific  gravity  being  1.037, 
its  formula  Calls  corresponds  to  a  condensation  to  2  volumes.  It  should  be  re- 
garded as  H(CaH,),  or  hydrogen  paired  with  elayl,  or  defiant  gas. 

Combinations  of  methyl  with  several  metalloids  and  metals  have  been  discovered, 
but  are  not  yet  fully  investigated  ;  the  only  one  which  is  well  known  being  a  com- 
pound of  arsenic  with  2  equivalents  X)f  methyl,  or  cacodyl^  already  described, 
(^1381.) 

Zincmethyl  ZnC^Ha  or  Zn.I^CjHa)  and 
PhosphurettedmethylV,(^^\i^ovV,\R{Q^^^'\^, 

corresponding  to  phosphuretted  hydrogen  have  been  obtained.  Zincmethyl  resem- 
bles zincethyl ;  and  phosphuretted  methyl  bears  a  close  analogy  to  phosphuretted 
hydrogen. —  W.  L.  F. 

*  Oxalis  acetosella,  whence  the  name. —  W.  L.  F. 


MALIC   ACID.  595 

MALIC  ACID  C8H«0,,2HO. 

"  §  1447.  Malic  acid  is  most  widely  diffused  through  the  organic 
kingdom,  being  found  partly  free  and  partly  combined  with 
potassa,  lime,  magnesia,  and  some  organic  bases,  and  giving  rise  to 
the  acid  taste  observed  in  fruits  before  maturity.  Malic  acid  is 
generally  obtained  from  the  berries  of  the  mountain  ash,  which  are 
collected  before  maturity,  crushed,  and  their  juice  expressed.  The 
juice  is  clarified  by  being  boiled  for  a  few  moments  with  white  of 
egg  and  filtered,  when  acetate  of  lead  is  added,  which  yields  a 
white  crystalline  precipitate  of  malate  of  lead ;  the  salt,  however, 
being  always  mixed  with  a  small  quantity  of  other  organic  sub- 
stances, which  are  precipitated  in  combination  with  the  oxide  of 
lead.  Malate  of  lead  is  nearly  insoluble  in  cold,  but  readily  soluble 
in  boiling  water,  and  is  purified  by  boiling  with  water  the  crude 
malate  of  lead  previously  filtered,  and  rapidly  filtering  the  liquor ; 
when  the  latter  deposits,  on  cooling,  malate  of  lead  in  small  crys- 
talline spangles.  The  mother  liquid  is  again  boiled  with  the  residue 
of  the  first  ebullition,  and  this  is  continued  until  the  hot  liquor  no 
longer  deposits  malate  of  lead  on  cooling.  The  foreign  plumbic 
compounds  remain  in  the  residue. 

Crude  malate  of  lead  is  usually  decomposed  by  sulf  hydric  acid, 
(§  1207,)  and  the  impure  malic  acid  is  thus  isolated  ;  after  which  the 
solution  of  malic  acid  thus  obtained  is  boiled  for  a  few  moments,  in 
order  to  drive  off  the  sulf  hydric  acid,  and  then  divided  into  two  equal 
parts.  One  part,  which  has  been  accurately  saturated  with  ammo- 
nia, is  poured  into  the  second  part,  which  remained  in  the  state  of 
free  malic  acid,  which  furnishes  a  solution  of  bimalate  of  ammonia, 
or  rather  a  neutral  malate  of  ammonia  and  water  (NH3,H04-H0), 
CgH^Og,  which  is  crystallized;  and  as  the  salt  crystallizes  very 
readily,  it  is  purified  by  successive  crystallizations.  If  the  malate 
of  lead  contained  tartrate  and  citrate  of  lead,  as  frequently  happens, 
the  first  crystals  deposited  by  the  solution  of  impure  bimalate  of 
ammonia  would  be  bitartrate  of  ammonia,  which  is  very  slightly 
soluble  ;  after  which  the  bimalate  would  crystallize,  while  the  citrate 
would  remain  in  the  mother  liquid.  In  this  case,  the  bimalate  of 
ammonia  is  again  converted  into  malate  of  lead,  and  the  salt  is 
again  decomposed  by  sulf  hydric  acid. 

The  solution  of  malic  acid  is  evaporated  to  the  consistence  of 
syrup,  and  then  left  in  vacuo,  when  it  deposits  colourless  crystals 
of  hydrated  malic  acid,  CjjIl408,2HO,  which  are  deliquescent,  and 
cannot  be  freed  from  their  water  without  decomposition. 

Malic  acid  is  a  powerful  acid,  forming  a  great  number  of  salts, 
and  producing  in  general,  with  the  same  base,  two  salts,  the  formulae 
of  which,  when  deprived  of  their  water  of  crystallization,  are 

2R0,C,HA, 
(R04-H0),C3H,0„ 

and  it  is  therefore  a  bibasic  acid,  as  we  stated  in  §  1225. 


596  VEGETABLE   ACIDS. 

Alkaline  malates  are  very  soluble  and  deliquescent,  which  is 
equally  true  of  the  malate  of  ammonia  2(NH3,HO),CgH408 ;  while 
the  malate  (NHjjHO-f  H0),CgH408,  on  the  contrary,  crystallizes 
readily.  Malate  of  lime  crystallizes  with  6  equivalents  of  water  of 
crystallization,  and  presents  the  formula  (CaO+HO),C8H408+6HO. 

§  1448.  Crystallized  malic  acid  melts  at  181.4°,  and,  if  kept  for 
some  time  at  a  temperature  of  347°,  is  converted  into  two  new 
acids,  called  maleic  and  paramaleic,  which  are  isomeric,  and  present 
the  formulae  C^H03,H0.  Water  separates  from  them,  without  disen- 
gagement of  gas.  If  the  retort  be  rapidly  heated  to  392°,  the  maleic 
acid  distils  over,  with  very  small  quantities  of  paramaleic  acid,  for, 
at  this  temperature,  but  a  small  quantity  of  the  latter  acid  is 
formed.  Distilled  maleic  acid  solidifies  in  large  crystals  in  the  neck 
of  the  retort  and  the  receiver,  and  is  very  soluble  in  water  and 
alcohol,  its  solution  not  being  clouded  by  limewater,  while  water 
of  baryta  throws  down  a  white  precipitate  in  crystalline  spangles, 
and  acetate  of  lead  produces  a  similar  precipitate.  The  maleatepi 
of  potassa  and  soda  crystallize  readily.  The  general  formula  of  tho 
dried  maleates  is  ROjC^HO,,  showing  maleic  acid  to  be  monobasic 
Maleic  acid  has  been  found  in  several  vegetables,  particularly  in  th<i 
horsetail,  {equisetum  fluviatile\  whence  it  has  also  been  called  equi- 
setic  acid. 

If  maleic  acid  be  heated  to  only  302°,  and  be  kept  for  some  time 
at  this  temperature,  the  second  acid,  or  paramaleic,  is  abundantly 
formed  instead  of  the  first.  It  is  much  less  fusible  than  maleic  acid, 
for  it  melts  at  only  about  390°,  and  sublimes  at  a  higher  tempera- 
ture ;  and  it  is  moreover  easily  distinguished  from  it  by  being  very 
slightly  soluble  in  water,  200  parts  of  water  dissolving  about  1  part 
of  it.  Paramaleic  acid  produces  with  oxide  of  silver,  a  salt  remark- 
able for  its  insolubility,  and  yields,  with  potassa,  soda,  and  ammonia, 
easily  crystallizable  salts.  It  may  be  boiled  with  nitric  acid  without 
undergoing  any  change.  The  general  formula  of  the  paramaleates 
is  RO,C4H03,  and  that  of  crystallized  paramaleic  acid  is  C^HOjHO. 

Maleic  acid  is  converted  into  paramaleic  acid  when  it  is  kept  for 
a  long  time  at  a  temperature  exceeding  302°,  while  the  maleates 
themselves,  heated  to  480°  or  570°,  are  converted  into  paramaleates. 

Paramaleic  acid  is  also  found  in  vegetables,  and  having  been 
obtained  from  fumitory,  (^fumaria  officinalis,)  has  hence  been  called 
fumaric  acid.     It  has  also  been  found  in  Iceland  moss. 

CITRIC  ACID  Ci,H,0„,3HO-|-2HO. 
§  1449.  Citric  acid,  which  exists  in  the  juice  of  a  large  number 
of  acid  fruits,  particularly  in  lemons,  gooseberries,  and  currants,  is 
generally  extracted  from  lemons,  by  allowing  their  juice  to  ferment 
spontaneously  for  some  time,  when  mucilaginous  substances  sepa- 
rate from  it ;  after  which  the  liquid  is  saturated  with  finely  pow- 
dered chalk,  gradually  added,  so  as  not  to  be  in  excess,  and  it  is 
boiled.     Citrate  of  lime,  being  insoluble,  is  precipitated,  and  is  de- 


CITRIC   ACID.  597 

composed  by  a  slight  excess  of  sulphuric  acid ;  and  the  sulphate  of 
lime  being  then  separated  by  filtering,  the  acid  liquid  is  care- 
fully evaporated,  until  a  crystalline  crust  begins  to  form  on  its  sur- 
face, when  it  is  left  to  itself.  Citric  acid  crystallizes  in  large 
crystals,  the  presence  of  a  slight  excess  of  sulphuric  acid  assisting 
the  crystallization.  The  acid  is  very  soluble  in  water,  for  it  dis- 
solves in  J  of  its  weight  of  cold,  and  f  of  its  weight  of  boiling 
water.     After  a  time,  its  aqueous  solutions  become  mouldy. 

The  formula  of  citric  acid  crystallized  at  the  ordinary  tempera- 
ture is  CjjHjOjjSHO,  while  that  of  the  acid  dried  at  212°  is 
G^Jlfi^i,^B.O,  the  3  equivalents  of  water  which  remain  being  basic, 
and  replaceable  by  equivalent  quantities  of  bases.  The  formula  of 
citrate  of  silver  is  SAgO,C ^^Hfi^^,  and  a  methylocitric  ether  is 
known  of  the  formula  Z{Q^nfi\G^^Rfi^^. 

The  alkaline  citrates  are  soluble,  while  those  of  the  alkaline 
earths  and  other  metallic  oxides  are  generally  insoluble,  but  dis- 
solve in  an  excess  of  citric  acid. 

About  1  per  cent,  of  crystallized  citric  acid  may  be  obtained 
from  the  juice  of  common  currants,  by  fermenting  it  with  beer- 
yeast,  when  the  saccharine  matter  is  converted  into  alcohol,  which 
is  separated  by  distillation ;  and  the  residue,  being  saturated  with 
chalk,  yields  citrate  of  lime. 

§  1450."  Citric  acid  is  decomposed  by  heat,  carbonic  acid  being 
first  disengaged,  with  oxide  of  carbon  and  acetone ;  while  at  a 
higher  temperature,  an  oleaginous  substance  is  formed  which  dis- 
tils. If  the  operation  be  arrested  at  the  moment  of  the  appear- 
ance of  the  oleaginous  substance,  the  residue  contains  only  a  very 
small  quantity  of  unaltered  citric  acid,  and  consists  almost  entirely 
of  a  peculiar  acid,  called  aconitie,  because  it  was  first  found  in  a 
vegetable,  the  aconitum  napellus.  The  composition  of  this  acid 
C^H03,H0  is  the  same  as  that  of  maleic  acid,  and  its  properties 
are  very  analogous,  while  it  appears  to  difier  from  it  in  some  of  its 
reactions,  and  seems  therefore  to  be  a  second  isomeric  modification 
of  this  acid. 

Aconitic  acid  melts  at  about  284°,  and  distils  at  320° ;  but  the 
product  which  passes  over  is  no  longer  aconitic  acid,  oleaginous 
drops,  which  crystallize  on  cooling,  being  formed.  The  same  pro- 
duct is  necessarily  obtained  by  the  direct  distillation  of  citric  acid. 
It  dissolves  in  water,  and  yields  an  acid  liquid  depositing  crystals  on 
evaporation,  which  are  purified  by  being  redissolved  in  alcohol  or  ether. 
They  are  formed  by  a  new  acid,  which  has  been  called  pyroaco- 
nitic  and  itaconic  acid,  the  formula  of  which,  in  the  crystallized 
state,  is  0,11203,110,  while  that  of  itaconate  of  silver  is  AgO,C5H303. 

If  itaconic  acid  be  again  distilled,  it  is  soon  found  to  change,  for 
the  oily  drops  which  condense  no  longer  crystallize  by  cooling, 
being  formed  by  a  new  acid,  called  eitraconic.  The  same  acid  may 
be  obtained  by  means  of  the  crude  product  yielded  by  the  imme- 


598  VEGETABLE  ACIDS. 

diate  distillation  of  citric  acid,  for  which  purpose  it  suiBces  to  distil 
it  a  second  time  in  a  retort  heated  in  an  oil-bath,  and  to  collect 
separately  the  products  which  distil  at  a  temperature  beyond  392°. 
A  very  fluid,  colourless  liquid  is  thus  obtained,  boiling  at  413°,  and 
of  which  the  density  is  1.247.  Its  formula  being  C5H2O3,  its  com- 
position is  consequently  the  same  as  that  of  anhydrous  itaconic  acid. 
Exposed  to  a  moist  atmosphere,  it  slowly  absorbs  the  vapour  of 
water,  and  is  converted  into  a  crystalline  compound  which  melts  at 
about  176°,  the  formula  of  which  is  the  same  as  that  of  crystallized 
itaconic  acid,  and  their  composition  is  also  the  same,  while  itaconic 
acid  melts  only  at  about  320°,  and  the  crystallized  acid  formed  by 
the  combination  of  anhydrous  citraconic  acid  with  water  melts  at 
178°.  The  two  products  are  therefore  merely  isomeric.  Hydrated 
citraconic  acid  yields,  by  distillation,  anhydrous  citraconic  acid. 

TARTARIC  ACID  C,H40xo,2HO. 

§1451.  Tartaric  is  one  of  the  most  important  of  the  organic 
acids,  and  exists  in  a  great  number  of  fruits,  such  as  grapes,  pine- 
apples, mulberries,  and  other  vegetables.  On  a  large  scale  it  is 
always  made  from  grape-juice,  in  which  it  exists  in  the  state  of  bi- 
tartrate  of  potassa  and  neutral  tartrate  of  lime,  the  two  salts  being 
in  solution ;  for  the  first  is  eminently  soluble,  and  the  second, 
although  insoluble  in  water,  dissolves  in  an  acid  liquid.  When 
grape-juice  is  fermented  in  order  to  be  made  into  wine,  the  bitar- 
trate  of  potassa  and  tartrate  of  lime  are  slowly  precipitated,  being 
insoluble  in  the  alcoholic  water,  and  they  form  a  crust  which  adheres 
to  the  sides  of  the  barrel.  This  crust,  called  tartar,  is  red  or  white 
according  to  the  colour  of  the  wine  which  produces  it,  and  is  mixed 
with  many  foreign  substances.  In  order  to  purify  this  crude  tartar, 
or  argol,  it  is  powdered,  and  boiled  for  several  hours  with  enough' 
water  to  dissolve  it,  after  which  the  liquid  is  then  allowed  to  cool ; 
when,  in  the  course  of  a  few  days,  crystals  form,  which  adhere  to  the 
sides  of  the  vessel,  while  the  residue  is  composed  chiefly  of  foreign 
substances.  The  crystals,  being  separated,  are  redissolved  in  boil- 
ing water,  while  clay  and  animal  black  are  added,  and  the  boiling 
liquid  is  filtered.  The  latter  yields,  on  cooling,  very  pure  crystals 
of  bitartrate  of  potassa,  which  is  the  cream  of  tartar  of  commerce. 

In  order  to  extract  tartaric  acid  from  cream  of  tartar,  it  is  dis- 
solved in  about  10  times  its  weight  of  boiling  water,  and  finely 
powdered  chalk  is  gradually  added,  until  efi'ervescence  ceases,  when 
the  lime  has  formed,  with  one-half  of  the  tartaric  acid,  an  insoluble 
tartrate  of  lime,  while  the  other  half  of  the  tartaric  acid  remains 
in  the  liquid  in  the  state  of  neutral  tartrate  of  potassa.  A  solution 
of  chloride  of  calcium  is  then  added,  until  no  more  precipitate  is 
thrown  down,  when  the  remainder  of  the  tartaric  acid  is  thus  sepa- 
rated in  the  state  of  tartrate  of  lime.  The  two  portions  of  tartrate 
of  lime  are  united  and  decomposed  by  sulphuric  acid  diluted  with 


TARTARIC    ACID.  599 

8  or  4  times  its  weight  of  water,  52  parts  of  concentrated  sulphuric 
acid  being  usually  taken  for  100  parts  of  cream  of  tartar,  which  is 
a  little  more  than  is  absolutely  necessary  to  decompose  the  tartrate 
of  lime.  The  sulphate  of  lime  being  separated  by  filtering,  the 
acid  liquid,  evaporated  to  the  consistence  of  syi^up,  is  then  left  to 
itself,  in  a  slightly  warm  situation  to  prevent  it  from  becoming  too 
viscous ;  when  it  yields  beautiful  crystals,  which  are  purified  by  a 
second  crystallization.     The  acid  is  largely  used  in  dyeing. 

Tartaric  acid,  dissolved  in  water,  exerts  rotation  to  the  right, 
with  a  specific  energy  the  greater  as  the  proportion  of  water  is 
larger  and  the  temperature  higher.  It  then  divides  the  planes  of 
polarization  of  the  various  simple  rays  according  to  the  laws  pecu- 
liar to  it,  and  in  which  it  difiers  from  all  known  substances.  These 
laws  are  modified,  without  losing  their  peculiarity,  when  it  is  dis- 
solved in  alcohol  or  wood-spirit,  but  disappear  completely  when  it 
is  brought  into  the  presence  of  alkaline  bases  or  boracic  acid,  when 
the  phenomena  reassume  the  appearance  common  to  the  generality 
of  substances  possessing  a  rotatory  power. 

Tartaric  acid  is  obtained  in  large  and  generally  well-defined 
crystals,  of  the  density  1.75.  Boiling  water  dissolves  about  twice 
its  weight  of  it,  and  cold  water  a  little  more  than  its  own  weight, 
while  alcohol  dissolves  it  more  sparingly.  The  composition  of  crys- 
tallized tartaric  acid  corresponds  to  the  formula  CgHgO^g,  which  is 
commonly  written  C8H^Ojo,2HO.  The  two  equivalents  of  water 
cannot  be  driven  ofi"  by  heat  without  injury  to  the  acid,  and  in  the 
anhydrous  tartrates  they  are  replaced  by  2  equivalents  of  the  base* 
The  same  base  generally  forms  two  salts  with  tartaric  acid ;  the 
formula  of  the  first,  called  neutral  tartrate,  being  2^0,Qfifi^^, 
while  that  of  the  second,  or  bitartrate,  is  (RO  +  HO),C8H40io. 

These  denominations  are  very  erroneous,  since  the  salts,  from 
their  constitution,  are  both  neutral,  and  because,  in  both  cases,  the 
acid  is  saturated  by  2  equivalents  of  base ;  with  the  difference  that 
in  the  second  case,  one  of  the  equivalents  of  base,  water,  does  not 
saturate  the  acid  as  regards  its  reaction  on  vegetable  colours. 

From  its  composition,  tartaric  acid  may  be  regarded  as  formed  of 
1  equiv.  of  acetic  acid  and  2  equiv.  of  oxalic  acid,  and  we  have,  in 
fact, 

C3H,0i„2H0=C,H303,H0+2(C,03,H0). 
It  is  actually  decomposed  in  this  manner,  when  heated  with  alka- 
lies in  excess,  at  a  temperature  of  302°. 

It  is  a  powerful  acid,  and  dissolves  several  metals  with  disengage- 
ment of  hydrogen,  particularly  zinc  and  iron.  It  is  decomposed  by 
several  easily  reducible  metallic  oxides :  thus,  at  the  boiling  point, 
peroxide  of  lead  decomposes  it  into  carbonic  acid,  water,  and  formic 
acid;  the  liquid,  on  cooling,  depositing  very  pure  crystals  of  formiate 
of  lead. 

The  soluble  neutral  tartrates  generally  become  less  soluble  by 


600  VEGETABLE   ACIDS. 

th^  addition  of  an  excess  of  acid,  while  the  insoluble  neutral  tartrates 
dissolve,  on  the  contrary,  in  an  excess  of  acid.     * 

§  1452.  Potassa  forms  2  tartrates :  the  neutral^  or  rather  hi- 
potassic  tartrate  2KO,C8H40jo+2HO,  which  dissolves  in  its  own 
weight  of  water,  and  loses  by  heat  its  equivalents  of  water  of  crys- 
tallization, and  the  hitartratey  or  rather  the  monopotassic  tartrate 
{KO-j-ilO),CJifi^Q,  which  is  cream  of  tartar.  This  salt  requires 
for  its  solution  18  parts  of  boiling  and  more  than  200  of  cold  water, 
and  it  is  nearly  insoluble  in  alcohol  at  0.85.  Its  crystals,  which 
are  hard  and  opaque,  are  decomposed  by  heat,  and  yield  a  mixture 
of  carbonate  of  potassa  and  charcoal,  or  black  flux,  (§438.) 

Bitartrate  of  potassa  forms  a  compound  with  boracic  acid,  called 
soluble  cream  of  tartar,  which  is  generally  prepared  by  dissolving 
in  boiling  water  47J  parts  of  cream  of  tartar  and  15J  parts  of  crys- 
tallized boracic  acid.  The  liquor,  when  evaporated,  leaves  a  non- 
crystalline white  mass,  insoluble  in  alcohol,  but  which  dissolves  in 
IJ  part  of  cold  water,  or  in  J  part  of  boiling  water.  The  formula 
of  this  substance,  dried  at  212°,  is 

KO,(C,H,0„,B03). 

At  545°  it  loses  2  equiv.  of  water,  becoming  K0(CgH208,B03),  and 
the  organic  compound  which  it  then  contains  presents  no  longer  the 
composition  which  we  have  assigned  to  anhydrous  tartaric  acid, 
although  when  redissolved  in  hot  water  it  reproduces  the  original 
substance.  . 

Soda  also  forms  two  tartrates,  2NaO,CgH^O^Q-f4HO,  which  readily 
parts  with  its  water  in  a  dry  vacuum,  and  (Na04-HO),CgH40,o. 

Ammonia  also  yields  two  tartrates,  of  which  the  formulae  are 
2(NH3,HO),CgH,0,o+HO,  slightly  soluble  in  water, 
and         (NH3HO + HO),  Cfifi,,. 

Lime  forms  2  tartrates:  the  neutral  salt  2CaO,CgH40io  +  8HO, 
which  is  nearly  insoluble  in  cold  water,  and  is  frequently  found  in 
beautiful  crystals  in  crude  tartar,  and  the  acid  tartrate  (CaO  +  HO), 

By  saturating  cream  of  tartar  with  carbonate  of  soda  and  crys- 
tallizing it,  a  double  tartrate  of  potassa  and  soda  is  obtained  (KO  + 
NaO),C8H40io4-8HO,  called  Bochelle  salt,  which  is  used  in  me- 
dicine, and  is  generally  prepared  by  dissolving  in  boiling  water  1 
part  of  crystallized  carbonate  of  soda  and  1 J  part  of  cream  of  tar- 
tar, when  the  salt  is  obtained  in  large  prismatic  crystals. 

All  the  tartrates,  when  dissolved  in  water,  exert  rotation  to  the 
right,  while  tartrate  of  lime,  dissolved  in  chlorohydric  acid,  turns 
the  plane  of  polarization  to  the  left. 

Tartar  Emetic  (KO+Sb03),C8H,Oio+2HO. 
§  1458.  Tartar  emetic,  one  of  the  most  valuable  medicines  used,  is 
a  double  tartrate  of  potassa  and  oxide  of  antimony,  according  to 
the  formula  (KO+Sb03),C8H40io+2HO.     It  is  prepared  by  boil- 


TARTARIC   ACID.  601 

ing  in  5  or  6  parts  of  water  equal  parts  of  oxide  of  antimony  and 
cream  of  tartar,  and  then  glass  of  antimony;  the  oxychloride  or 
subsulphate  may  be  substituted  for  the  oxide.  The  hot  solution, 
when  filtered,  deposits  colourless  crystals,  soluble  in  2  parts  of  boil- 
ing and  14  of  cold  water,  which,  when  heated  to  212°,  part  with 
their  2  equiv.  of  water  of  crystallization,  while,  if  heated  to  442.4°, 
they  lose  2  more  equiv.,  and  the  remaining  product  (K0  +  Sb03), 
CgHgOg  no  longer  presents  the  formula  of  the  tartrates,  although  if 
it  be  redissolved  in  water  it  reproduces,  by  crystallization,  the 
original  salt,  tartar  emetic. 

Acids  decompose  solutions  of  tartar  emetic,  bitartrate  of  potassa 
and  a  basic  salt  of  oxide  of  antimony  being  separated.  Alkalies 
and  the  alkaline  earths  also  decompose  them,  but  this  precipitate  is 
frequently  not  formed  for  some  time,  as  is  the  case  in  potassa  and 
soda ;  by  using  an  excess  of  which  bases  no  precipitate  is  formed, 
because  the  oxide  of  antimony  remains  dissolved  in  the  alkaline 
liquid.     Ammonia  and  limewater  immediately  efi'ect  a  precipitate. 

Sulf  hydric  acid  decomposes  the  solution  of  tartar  emetic,  and  an 
orange-coloured  precipitate  of  sulphide  of  antimony  is  formed.  Tar- 
tar emetic  is  decomposed  by  heat,  and,  when  calcined  in  a  close  ves- 
sel, yields  a  residue  of  antimoniuret  of  potassium,  (§  1017,)  while  in 
Marsh's  apparatus  it  produces  abundantly  antimonial  deposits. 
(§1016.) 

By  dissolving  in  boiling  water  9  parts  of  tartar  emetic  and  4  parts 
of  tartaric  acid,  evaporating  the  solution  by  a  gentle  heat,  and  then 
leaving  it  to  itself,  crystals  of  tartar  emetic  first  separate,  and  then, 
by  continuing  the  evaporation,  a  crystalline  compound,  efiiorescent 
and  very  soluble  in  water,  is  deposited,  the  formula  of  which  is 
(KO+Sb03),2C8H40jo+7HO,  corresponding  to  that  of  a  neutral 
tartrate.  Tartar  emetic  can  also  combine  with  3  equiv.  of  bitartrate 
of  potassa,  which  compound  is  obtained  by  dissolving  together  10 
parts  of  tartar  emetic  and  15  of  cream  of  tartar. 

Lastly,  by  pouring  into  a  solution  of  tartar  emetic  nitrate  of  silver 
,or  acetate  of  lead,  precipitates  are  obtained  which  are  species  of 
tartars  emetic,  in  which  the  oxides  of  silver  or  lead  replace  the 
potassa.  Their  formulae  are  (AgO  +  Sb03),CgH^Oio  and  (PbO  + 
Sb03),C8H40io,  etc.  etc. ;  and,  like  tartar  emetic,  they  lose  2  equiv. 
of  water  at  a  high  temperature. 

Modifications  of  Tartaric  Acid  hy  Seat, 

§  1454.  When  tartaric  acid  is  rapidly  heated  in  an  oil-bath  to 
the  temperature  of  338°,  it  fuses  without  losing  any  water,  while  its 
composition  is  remarkably  modified;  for  when  redissolved  in  water 
and  combined  with  the  various  bases,  it  yields  salts  which  difier  in 
their  forms  and  solubility  from  the  ordinary  tartrates.  The  name 
of  metatartaric  has  been  given  to  this  modified  tartaric  acid.  The 
bimetatartrate  of  ammonia  (NH3HO+HO),C8H^Oj(j  is  much  more 


602  VEGETABLE  ACIDS. 

soluble  than  the  bitartrate,  and  produces  crystals  of  a  totally  dif- 
ferent form,  and  the  former  salt  does  not  precipitate  a  solution  of 
chloride  of  calcium,  while  the  bitartrate  does.  Boiling  converts 
metatartrates  into  bitartrates. 

By  maintaining  melted  tartaric  acid  for  a  long  time  at  a  tempera- 
ture of  338°  it  undergoes  a  second  isomeric  modification,  and  forms 
an  acid  called  isotartaric  acid,  which,  while  exhibiting  the  same 
composition  as  tartaric  acid,  appears  to  differ  from  it  by  saturating 
only  1  equiv.  of  base.  Isotartrate  of  lime  (Ca04-HO),C8H40jo  dis- 
solves readily  in  cold  water,  producing  a  solution  behaving  perfectly 
neutral  with  litmus  paper,  which,  when  boiled,  becomes  acid  and 
deposits  crystals  of  neutral  metatartrate  of  lime.  Isotartrate  of 
ammonia  is  a  deliquescent  salt,  easily  converted  by  heat  into  the 
bimetatartrate. 

By  heating  tartaric  acid  rapidly  to  356°,  it  first  melts,  swells  up, 
loses  12  per  cent,  of  water,  and  finally  solidifies  again,  forming  a 
substance  of  the  formula  CgH^OjQ,  which  has  become  insoluble  in 
water,  and  may  be  easily  separated  by  washing  from  the  portions 
which  have  not  yet  undergone  the  transformation.  This  substance, 
which  has  been  called  anhydrous  tartaric  acid  because  it  presents 
the  composition  of  the  acid  in  the  anhydrous  tartrates,  is  equally 
insoluble  in  alcohol  and  ether ;  while,  when  in  contact  with  water, 
it  is  converted  successively  into  the  preceding  modifications  of  tar- 
taric acid,  the  transformation  being  very  rapid  in  contact  with  boil- 
ing water  and  the  bases. 

§  1455.  By  heating  tartaric  acid  to  distillation,  it  undergoes  a 
decomposition  which  produces  two  new  pyrogenated  acids,  which 
have  been  called  pyroracemic  and  pyrotartaric  acid. 

Pyroracemic  acid  is  chiefly  formed  when  tartaric  acid  is  rapidly 
distilled  at  a  temperature  of  428°.  The  product,  subjected  to  a 
second  distillation,  yields  a  very  acid  liquid,  consisting  of  a  mixture 
of  pyroracemic  and  acetic  acids,  which,  when  saturated  with  carbonate 
of  lead,  forms  soluble  acetate  of  lead,  while  the  pyroracemate  of 
lead  remains  in  the  shape  of  an  insoluble  precipitate.  The  preci-  > 
pitate  is  rapidly  washed  in  cold  water,  suspended  in  water,  and  de- 
composed by  a  current  of  sulf  hydric  acid  gas,  and  the  acid  solution, 
when  evaporated,  is  reduced  to  a  syrupy  condition  without  crystal- 
lizing. Pyroracemic  acid  forms  a  great  number  of  salts;  the 
pyroracemate  of  potassa  is  deliquescent,  while  that  of  soda  crystal- 
lizes readily,  and  the  salts  of  lime  and  baryta  are  soluble  in  water. 
Pyroracemate  of  silver  is  obtained  by  double  decomposition,  and 
separates  in  small  crystalline  spangles  of  the  formula  AgOjCgHgO^, 
showing  the  formula  of  anhydrous  pyroracemic  acid  as  it  exists  in 
dry  salts  to  be  CgHgO^.  The  name  given  to  this  acid  is  very  im- 
proper, for  it  seems  to  indicate  that  pyroracemic  acid  is  a  special 
pyrogenated  product  of  racemic  acid,  which  is  presently  to  be 
described. 


RACEMIC   ACID.  603 

If  tartaric  acid  be  rapidly  heated  to  about  570°  the  products  of 
its  decomposition  differ  from  those  just  indicated,  and  the  receiver 
contains  a  brown  liquid,  which  is  subjected  to  a  second  distillation. 
The  first  products  are  collected  separately,  and  the  receiver  changed 
when  the  substance  in  the  retort  becomes  syrupy.  The  liquid  which 
then  distils  sets  into  a  crystalline  mass  under  the  receiver  of  an 
air-pump,  and  the  crystals  are  pressed  between  several  folds  of 
tissue-paper,  in  order  to  free  them  from  adherent  empyreumatic 
matter,  redissolved  in  water,  and,  after  having  discoloured  the  solu- 
tion by  boiling  it  with  a  small  quantity  of  animal  black,  it  is  again 
evaporated,  and  yields  crystals  of  pure  fyrotartaric  acid.  A  much 
larger  proportion  of  pyrotartaric  acid  is  prepared  by  subjecting  to 
the  action  of  heat  an  intimate  mixture  of  tartaric  acid  and  platinum- 
sponge,  or  even  of  powered  pumice-stone,  the  latter  substance  as- 
sisting the  decomposition,  which  then  takes  place  at  a  lower  temper- 
ature. Pyrotartaric  acid  melts  at  about  212°,  and  distils  at  356°, 
while  a  portion  of  it  is  decomposed.  It  is  very  soluble  in  water  and 
alcohol,  and  its  solutions  are  not  precipitated  by  baryta  or  lime- 
water.  Pyrotartaric  acid  is  probably  a  monobasic  acid,  of  which 
the  formula,  in  anhydrous  salts,  is  C5H3O3, 

PARATARTARIC,  RACEMIC,  OR  UVIC  ACID  C,H,0,o,2HO+HO. 

§  1456.  The  acid  to  which  these  various  names  have  been  given, 
has  only  been  obtained  once,  accidentally,  in  making  tartaric  acid 
on  a  large  scale,  and  never  has  been  since  produced.  We  shall  re- 
tain the  name  of  racemic  acid  alone.  The  composition  of  racemic 
acid,  when  dried,  is  exactly  the  same  as  that  of  tartaric  acid,  and 
the  composition  of  the  salts  it  forms  with  the  different  bases  is  also 
identical  with  those  of  the  corresponding  tartrates,  the  two  acids 
exhibiting  one  of  the  most  remarkable  examples  of  isomerism,  but 
crystallized  racemic  acid  contains  1  equivalent  of  water  more  than 
tartaric  acid,  which  is  easily  driven  off  by  heat.  Racemic  acid  dif- 
fers from  tartaric  acid  in  the  crystalline  form  and  solubility  of  its 
salts,  and  also  in  its  physical  properties,  particularly  in  the  absence 
of  all  rotatory  action  on  the  plane  of  polarization.  But  we  shall 
soon  see  that  this  neutrality  is  owing  to  its  being  the  union,  in  equal 
weights,  of  two  acids,  one  of  which  is  tartaric  acid  itself,  and  the 
other  an  acid  which  differs  from  it  only  by  an  opposition  of  he- 
mihedrism  in  crystalline  forms,  and  by  an  equally  identical  rotatory 
power,  but  in  an  opposite  direction.  Nevertheless,  for  the  mo- 
ment, we  shall  continue  to  describe  the  properties  of  racemic 
acid  as  though  it  were  simple,  in  order  to  conform  to  the  language 
adopted. 

Racemic  is  much  less  soluble  in  water  than  tartaric  acid,  and  as 
it  only  dissolves  in  5.7  parts  of  cold  water,  it  is  easily  separated 
from  the  latter  acid  by  crystallization.     The  two  acids  are  also  dis- 


604  VEGETABLE   ACIDS. 

tinguished  by  the  manner  in  which  they  behave  with  limewater ,' 
thus,  tartaric  acid  does  not  form  immediately  any  precipitate  in 
lime  water,  and  a  crystalline  deposit  is  not  thrown  down  until  after 
some  time,  while  racemic  acid  immediately  affords  a  white  precipi- 
tate. By  dissolving  separately  in  weak  chlorohydric  acid,  tartrate 
and  racemate  of  lime,  and  carefully  saturating  the  two  liquids 
with  ammonia,  the  racemate  of  lime  is  immediately  precipitated 
in  an  opaque  crystalline  powder,  while  the  tartrate  of  lime,  on 
the  contrary,  is  slowly  deposited  in  the  form  of  small  transparent 
crystals. 

Like  tartaric  acid,  racemic  acid  is  a  bibasic-  acid,  and  forms  two 
salts  with  potassa,  one  (KO-{-RO,)C^E.fi^Q  corresponding  to  cream 
of  tartar,  and  even  less  soluble  than  that  tartrate,  while  the  other 
2K0,Gfifl,,  is  verj  soluble. 

Ammonia  yields  two  salts:  (NH3,HO+HO),C8H40io,  which  only 
dissolves  in  100  parts  of  water ;  and  2(NH3,H0),C8H40n„  which  is 
very  soluble,  and  affords  beautiful  crystals. 

The  salt  of  soda  (NaO+HO),C8H^O,o+2HO  dissolves  in  12  parts 
of  water,  while  the  salt  2NaO,C8H40jo  is  much  more  soluble. 

Racemic,  like  tartaric  acid,  forms  crystallizable  double  salts, 
and  produces,  with  potassa  and  soda,  a  double  racemate,  having  the 
same  composition  as  Rochelle  salt,  but  differing  from  it  in  its  crys- 
talline form  and  in  its  solubility. 

Subjected  to  the  action  of  heat,  raceimc  acid  appears  to  afford  the 
same  modifications  as  tartaric  acid,  and  pyrogenated  acids  identical 
with  those  produced  by  the  latter  substance. 

Dextro-racemic  and  Levo-racemic  Acid, 

§  1457.  The  solution  of  the  neutral  racemates  of  soda,  potassa, 
or  ammonia,  and  even  that  of  a  double  racemate  of  potassa  and  an- 
timony, exert  no  rotatory  power,  and  if  they  be  allowed  to  evaporate 
spontaneously,  the  form  and  all  the  other  physical  properties  of 
the  crystals  progressively  precipitated  are  identical  in  each,  and 
they  are  merely  distinguished  from  each  other  by  their  size. 

Such  is  not  the  case  with  double  racemates  of  soda  and  ammonia, 
or  of  soda  and  potassa.  Their  solutions  are  still  deprived  of  rotatory 
power,  but  the  crystals  deposited  by  each  are  of  two  kinds,  distin- 
guished from  each  other  by  hemihedral  facets  in  opposite  directions. 
If  they  are  separated  according  to  this  character,  and  each  sort  dis- 
solved by  itself,  two  solutions  are  obtained  possessing  equal  and 
inverse  rotatory  powers,  so  that  if  they  are  mixed  together  in  equal 
quantity,  the  resulting  rotatory  power  is  null,  like  that  of  the  ori- 
ginal solution  before  the  separation. 

As  a  single  sorting,  by  hand,  is  never  strictly  exact,  separation 
may  be  effected  more  perfectly  by  redissolving  each  sort  of  crystal 
separately,  and  rejecting  the  first  which  are  deposited.     Those  sub- 


TANNIC   ACIDS.  605 

sequently  obtained  are  generally  formed  alone,  and  of  a  single  sort, 
thus  completing  the  separation.  . 

The  acid  peculiar  to  each  sort  of  crystal  is  extracted  from  its 
salts  in  a  similar  manner  as  tartaric  acid  is  extracted  from  the  tar- 
trates. One  of  the  acids  exerts  rotation  toward  the  right,  like  tar- 
taric acid,  and  with  the  same  special  characters  of  dispersion;  and 
while  its  chemical  composition  is  the  same,  it  also  behaves  exactly 
like  it  in  the  presence  of  boracic  acid  and  the  alkaline  bases,  pro- 
ducing crystals  of  exactly  the  same  form.  In  short,  nothing  dis- 
tinguishes it  from  ordinary  tartaric  acid;  but  it  is  nevertheless, 
called  dextro-racemic  acid,  in  order  to  recall  its  origin,  and  to  not 
decide  too  hastily  on  its  density. 

The  other  acid,  extracted  from  crystals  of  the  opposite  form,  is 
identical  with  tartaric  acid  in  its  ponderable  composition,  but  ex- 
actly inverse  in  its  rotatory  properties.  They  are  exerted  toward 
the  left,  as  those  of  tartaric  acid  toward  the  right,  with  the  same 
energy,  the  same  laws  of  dispersion,  and  evincing  similar  reactions 
in  the  presence  of  the  same  substances.  It  has  been  called  levo- 
racemic  acid,  and  it  crystallizes  in  the  same  form  as  tartaric  acid, 
except  that  its  crystals  have  hemihedral  facets  in  opposite  direc- 
tions. 

Levo-racemic  and  dextro-racemic  acid  being  dissolved  together 
in  equal  weights,  combine  immediately,  and  reproduce  racemic  acid, 
the  mixed  solution  becoming  neutral  in  polarized  light,  and  the 
crystals  deposited  by  it  exhibiting  no  distinctive  characters.  The 
individual  dissymmetry  of  the  two  compounds  has  disappeared  in 
their  union,  and  when  combined  they  are  identical  with  racemic 
acid  which  has  not  been  decomposed. 

TANNIC  ACIDS. 

§  1458.  The  name  of  tannin  has  been  given  to  several  sub- 
stances, probably  of  different  composition,  which  possess  the  property 
of  forming  insoluble  compounds  with  albumen,  gluten,  gelatin,  fi- 
brin, the  animal  tissues  in  general,  and  the  epidermis  and  skin  of  ani- 
mals. These  compounds  will  not  putrefy,  and  are  unchangeable 
by  water ;  on  which  properties  is  founded  the  process  of  tanning  of 
skins,  to  be  described  at  the  close  of  this  work.  Tannins  exist  in 
almost  all  vegetables,  in  the  bark  and  leaves  of  trees,  and  the  seeds 
of  fruits;  the  oak,  chestnut,  elm,  and  willow  containing  large 
quantities  of  it,  while  it  occurs  most  abundantly  in  galls,  a  sort  of 
excrescence  which  grows  on  the  leaves  of  the  oak  when  they  have 
been  punctured  by  a  certain  insect. 

In  order  to  extract  tannin,  the  galls  are  finely  powdered  and 
introduced  into  a  displacer,  (fig.  683,)  the  neck  of  which  has 
been  previously  stopped  with  a  plug  of  cotton,  the  powder 
being  heaped  upon  it,  and  ordinary  ether  of  commerce  poured 


606 


VEGETABLE   ACIDS. 


on.  The  tube  is  corked,  and  adjusted  in  a  flask,  as 
represented  in  the  figure;  when  the  ether  filters  slowly 
through  the  galls,  while  the  tannin  contained  in  the  latter 
dissolves  in  the  water  given  off  by  the  ether,  a  very  small 
portion  being  dissolved  by  the  ether  itself.  The  liquid 
which  falls  into  the  flask  divides  into  two  layers,  the 
inferior  stratum,  of  the  consistence  of  syrup  and  colour 
of  amber,  being  a  highly  concentrated  aqueous  solution 
of  tannin,  while  the  upper  layer  is  ether,  holding  in  solu- 
tion a  small  quantity  of  tannin  and  some  other  substances 
extracted  from  the  galls.  The  ether  is  again  poured  upon 
galls,  in  order  to  abstract  an  additional  portion  of  tannin ; 
and  the  aqueous  solution  of  tannin  is  shaken  several  times 
Fig.  683.  ^-^jj  Y^ure  ether,  and  then  evaporated  under  the  receiver  of 
an  air-pump,  when  a  spongy  mass,  without  any  appearance  of  crys- 
tallization, generally  slightly  yellowish,  remains,  consisting  of  tannin 
in  its  greatest  state  of  purity  known.  It  is  a  spongy,  brilliant,  very 
light,  generally  yellowish  substance,  but  sometimes  is  obtained  of  a 
perfectly  white  colour.  It  dissolves  freely  in  water,  and  gives  it  a 
strongly  astringent  taste  ;  and  as  it  reddens  litmus  and  decomposes 
the  carbonates,  it  is  often  called  tannic  acid.  Tannin  combines 
with  bases,  and  precipitates  the  majority  of  the  metallic  solutions, 
the  colours  of  the  precipitates  being  frequently  characteristic; 
whence  tannin  and  an  infusion  of  galls  are  often  used  as  tests  to 
distinguish  various  metals  from  each  other.  The  composition  of 
tannin  dried  at  248°  corresponds  to  the  formula  CjgHgOjg,  which 
should  probably  be  written  CuH^OgjSHO ;  for,  on  pouring  a  solu- 
tion of  tannin  into  a  boiling  solution  of  acetate  of  lead  and  main- 
taining ebullition  for  some  time,  a  yellow  precipitate  of  the  formula 
3PbO,C,8H509  is  formed. 

Tannin  yields  a  deep-blue  precipitate  with  sesquisalts  of  iron, 
which  compound  is  very  important,  being  the  colouring  principle  of 
ordinary  writing-ink.  In  order  to  prepare  ink,  IJ  part  of  pow- 
dered galls  are  boiled  for  3  hours  with  15  of  water,  filling  up  the 
water  as  it  evaporates ;  after  which  the  liquid  is  filtered,  and  2 
parts  of  gum  and  1  part  of  protosulphate  of  iron  are  added,  besides 
frequently  a  small  quantity  of  a  solution  of  copper.  The  mixture 
is  frequently  shaken,  and  exposed  in  open  vessels,  in  order  that  the 
protoxide  of  iron  may  absorb  oxygen  from  the  air  and  be  converted 
into  sesquioxide,  which  causes  the  colour  of  the  liquid,  at  first 
brown,  gradually  to  deepen  and  become  bluish  black.  Oxidation 
being  arrested  at  the  proper  shade,  the  ink  is  bottled.  This  kind 
of  ink  contains  a  large  amount  of  protoxide  of  iron,  at  the  moment 
of  using  it,  and  the  marks  which  it  leaves  on  paper,  being  at  first 
pale,  turn  black  when  they  have  absorbed  the  oxygen  necessary  for 
the  peroxidation  of  the  iron. 

Tannin  completely  precipitates  gelatin  and  albuminous  substances 


GALLIC  ACID.  607 

from  their  solutions ;  and  animal  membranes  and  skins,  dipped  into 
a  solution  of  tannin,  ultimately  abstract  all  this  substance  which  is 
incorporated  in  the  membrane,  thus  rendering  it  unchangeable  and 
imputrefiable. 

Tannin  combines  also  with  a  large  number  of  the  mineral  acids, 
and  forms  ill-defined  compounds,  soluble  in  pure  water,  but  very 
slightly  so  in  an  excess  of  acid. 

aallic  Acid  CyHgO^HO. 
1459.  Gallic  acid  is  always  prepared  froia^tannin  or  galls,  and 
several  processes  may  be  adopted. 

1.  By  causing  sulphuric  or  chlorohydric  acid,  diluted  with  8  or 
10  times  their  weight  of  water,  to  act  on  tannin,  and  boiling  the 
mixture  for  about  12  hours,  taking  care  to  fill  up  the  water  as  it 
evaporates,  the  tannin  is  almost  wholly  converted  into  gallic  acid, 
the  greater  portion  of  which  crystallizes  during  the  cooling  of  the 
liquid. 

2.  By  exhausting  powdered  galls  with  cold  water,  concentrating 
the  filtered  liquid  by  evaporation,  and  saturating  it  exactly  with 
caustic  potassa.  Chlorohydric  acid  is  added  to  the  liquid  when  cooled, 
when  a  deposit  of  brown  crystals  of  impure  gallic  acid  is  precipi- 
tated, which  is  dissolved  in  boiling  water;  and  the  hot  solution 
lieing  left  for  some  time  in  contact  with  animal  black,  which  removes 
the  colouring  matter,  the  filtered  liquid  is  allowed  to  cool,  when  the 
gallic  acid  crystallizes  in  a  state  of  purity. 

3.  The  process  usually  employed  in  the  preparation  of  gallic  acid 
is  founded  on  a  peculiar  and  spontaneous  fermentation  experienced 
by  galls,  and  by  which  its  tannin  is  converted  into  gallic  acid. 
Moistened  and  powdered  galls  are  left  for  several  months  at  a  tem- 
perature of  68°  to  86°,  in  an  earthen  vessel,  when  the  substance 
becomes  covered  with  small  whitish  crystals  of  gallic  acid.  Toward 
the  close,  the  substance  is  allowed  to  dry,  and  is  treated  with  boil- 
ing alcohol,  which  dissolves  the  gallic  acid  alone,  and  deposits  the 
greater  portion  of  it  on  cooling.  If  an  extract  of  galls  be  substi- 
tuted for  the  galls,  the  transformation  of  the  tannin  takes  place  in 
the  same  way,  though  more  slowly ;  while  if  a  solution  of  pure  tannin 
be  used,  the  transformation  does  not  ensue.  We  are  hence  naturally 
led  to  infer  that  galls  contain  substances  which  induce  the  conver- 
sion of  tannin  into  gallic  acid,  and  which  behave  like  ferments,  since 
the  transformation  is  arrested  by  all  substances  which  destroy  the 
fermentation  of  the  yeast.  The  presence  of  air  does  not  appear 
to  be  necessary,  because  gallic  fermentation  of  extract  of  galls 
takes  place  even  in  an  hermetically  closed  vessel. 

Gallic  acid  crystallizes  in  long  silky  aciculse,  which  are  some- 
times perfectly  white,  but  more  frequently  slightly  yellowish ;  and 
it  is  deposited  in  larger  prismatic  crystals  from  an  alcoholic  or 
etherial  solution.     It  dissolves  in  100  parts  of  cold  and  in  3  ^ly 


608  VEGETABLE   ACIDS. 

of  boiling  water ;  and  it  neither  precipitates  gelatin  nor  attaches 
itself  to  animal  membranes ;  thus  furnishing  a  ready  method  of 
separating  it  from  tannin. 

The  formula  of  crystallized  gallic  acid  is  CyHgO^jHO,  and  it  loses 
1  equivalent  of  water  at  212°.  The  acid  forms  a  large  number  of 
salts,  the  composition  of  which  has  not  yet  been  sufficiently  studied ; 
and  therefore  chemists  are  not  agreed  upon  the  formula  for  anhy- 
drous gallic  acid. 

By  dropping  an  alcoholic  solution  of  potassa  into  an  alcoholic 
solution  of  gallic  acid,  until  perfect  saturation  is  effected,  white 
flakes  of  a  salt  of  the  formula  KO,  8(0711305)  are  deposited ;  while 
an  excess  of  potassa  decomposes  the  gallic  acid. 

By  exactly  saturating  a  solution  of  gallic  acid  with  ammonia,  a 
salt  is  obtained  by  evaporation,  of  which  the-«©mposition  corresponds 
to  the  formula  (]SrH3,HO),207H3O5+HO  ;  while,  if  only  one-half  of 
the  ammonia  necessary  to  saturation  be  added,  there  results  a  com- 
pound, slightly  soluble  when  cold,  and  corresponding  to  the  formula 
(NH3,HO),C,H03+C,H,0,. 

The  gallate  of  lead,  which  is  precipitated  by  pouring  a  solution 
of  gallic  acid  into  a  boiling  solution  of  acetate  of  lead  in  excess, 
forms  white  flakes,  which  change,  by  heat,  into  yellowish  crystalline 
granules,  corresponding  to  the  formula  2PbO,OyH03. 

It  therefore  frequently  occurs  in  the  gallates,  that  the  acid  in 
combination  with  the  base  presents  the  formula  O^HOg,  which  would 
seem  to  indicate  that  such  is  the  composition  of  anhydrous  gallic 
acid,  and  that  crystallized  gallic  acid  should  be  written  07HO3,2HO 
4- HO;  one  of  the  equivalents  of  water  being  water  of  crystalliza- 
tion, while  the  other  two  are  basic. 

The  aqueous  solution  of  gallic  acid  remains  unchanged  in  well- 
closed  vessels,  but  soon  becomes  mouldy  in  the  air.  Gallic  acid 
dissolves  in  concentrated  hot  sulphuric  acid,  forming  a  red  liquid, 
which,  when  poured  into  cold  water,  yields  a  red  crystalline  preci- 
pitate of  the  formula  C^Ufi^;  which  new  compound  difi'ers  from 
crystallized  gallic  acid  only  in  the  loss  of  2  equivalents  of  water. 

A  solution  of  gallic  acid  colours  sesquisalts  of  iron  of  a  deep  blue ; 
and  when  the  liquid  is  concentrated,  a  precipitate  of  the  same  colour 
is  formed.  Gallic  acid  precipitates  several  metals  from  their  solu- 
tions, particularly  silver  and  gold,  which  reduction  is  more  easily 
efiected  in  the  light  of  the  sun. 

§  1460.  By  heating  gallic  acid  in  a  retort  over  an  oil-bath,  it  first 
loses  1  equivalent  of  water,  and  then  melts,  and  if  the  temperature 
be  raised  to  365°,  and  kept  stationary  for  some  time  at  this  point, 
carbonic  acid  is  disengaged,  while  a  pyrogenated  acid,  pyrogallic 
acid  C6H3O3,  sublimes  in  white  crystalline  spangles,  only  a  small 
brown  residue  being  left  in  the  retort.  The  reaction  which  pro- 
duces pyrogallic  acid  is  expressed  by  the  following  equation : 


ELLAGIC   ACID.  609 

If,  on  the  contrary,  the  temperature  be  suddenly  raised  to  460° 
or  480°,  water  and  carbonic  acid  are  both  disengaged,  and  a  small 
quantity  of  pyrogallic  acid  still  sublimes,  while  the  greater  portion 
of  the  gallic  acid  is  converted  into  a  brown  substance,  which  re- 
mains in  the  retort.  In  its  appearance  and  chemical  properties, 
this  acid  closely  resembles  humic  and  ulmic  acids,  (§  1307,)  being 
insoluble  in  water,  but  dissolving  in  alkaline  liquids  and  forming 
brown  solutions,  from  which  acids  precipitate  the  original  substance 
unchanged.  This  substance  has  been  called  metagallic  acid,  and 
its  composition  corresponds  to  the  formula  CgHgOj ;  the  reaction  by 
which  it  is  derived  from  gallic  acid  being  expressed  by  the  equa- 
tion, 

C,H,0,=C.H,0,+CO,+HO. 

Pyrogallic  acid  may  be  prepared  by  carefully  heating  powdered 
galls,  or  still  better,  its  evaporated  extract,  in  an  earthen  vessel 
covered  with  a  pasteboard  cone,  when  crystals  of  the  acid  sublime 
on  the  sides  of  the  cone.  Pyrogallic  acid,  which  is  very  soluble  in 
water,  alcohol,  and  ether,  melts  at  257°,  sublimes  at  about  410°, 
and  is  decomposed  at  482°  into  water  and  metagallic  acid.  It  turns 
salts  of  the  protoxide  of  iron  of  a  deep  blue  colour,  and  those  of 
the  sesquioxide  of  an  intense  red. 

Ellagic  Acid  Cj^HjO^HO. 

§  1461.  Extract  of  galls,  exposed  for  a  long  time  to  the  air,  con- 
tains, in  addition  to  gallic  acid,  another  acid,  insoluble  in  water, 
and  to  which  the  name  of  ellagic  has  been  given.  This  latter  acid 
is  extracted  from  the  deposit  formed  at  the  bottom  of  the  vessel,  by 
treating  it  first  with  boiling  w^ater  which  dissolves  the  gallic  acid, 
and  then  with  a  solution  of  potassa  which  dissolves  the  gallic  acid 
in  the  state  of  ellagate  of  potassa.  The  alkaline  liquid,  when  eva- 
porated, deposits  the  latter  salt  in  the  form  of  small  crystalline 
spangles,  insoluble  in  fresh  water,  but  dissolving  readily  in  an  al- 
kaline liquid.  Acids  separate  ellagic  acid  in  the  form  of  a  slightly 
yellowish  powder. 

Ellagic  acid  is  insoluble  in  water,  alcohol,  and  ether,  and  its 
composition  corresponds  to  the  formula  C^H^Ojo.  It  loses  2  equi- 
valents of  water  at  248°,  when  its  formula  becomes  C^HgOg.  The 
formula  of  ellagic  acid  in  combination  with  bases  being  Q^Jlfi^, 
that  of  the  dried  acid  is  therefore  Q^fifi^^HO^  and  that  of  the 
hydrated  acid  Q^Jlfi^.KO^^ltLO, 

Ellagic  acid  also  occurs  in  the  animal  economy,  sometimes  form- 
ing concretions  known  by  the  name  of  bezoara. 

Meconic  Acid  Q^^O^^.'^^O. 
§  1462.  Meconic  acid  is  extracted  from  opium.     When  chloride 

Vol.  II.— 39 


610,  VEGETABLE   ACIDS. 

of  calcium  is  poured  into  an  infusion  of  opium,  a  precipitate  of  im- 
pure meconate  of  lime  is  formed,  which,  after  being  washed  succes- 
sively with  water  and  alcohol,  is  treated  with  20  parts  of  hot  water, 
to  which  3  parts  of  chlorohydric  acid  are  added,  when  the  filtered 
liquid  deposits,  on  cooling,  acid  meconate  of  lime.  The  salt  is  di- 
gested with  the  same  quantity  of  hot  acidulated  water,  and,  on  cool- 
ing, the  meconic  acid  separates ;  but  it  is  generally  necessary  to  re- 
peat .this  operation  once  or  twice  before  obtaining  the  acid  entirely 
free  from  lime.  The  impure  meconic  acid  may  also  be  combined 
with  potassa,  and  the  meconate  of  potassa  decomposed  by  chroro- 
hydric  acid,  after  being  purified  by  crystallization. 

Meconic  acid  dissolves  in  4  parts  di  boiling  water,  from  which  it 
is  almost  wholly  deposited,  on  cooling,  in  the  form  of  crystalline, 
pearly  white  spangles.  It  is  decomposed  by  long  boiling  with  water, 
particularly  in  the  presence  of  chlorohydric  acid;  carbonic  acid 
being  disengaged,  while  a  new  acid,  called  comcnic,  is  formed.  It  is 
also  destroyed  by  contact  with  alkaline  liquids,  yielding  compli- 
cated products. 

The  composition  of  crystallized  meconic  acid  is  represented  by 
Cj^HjoOao,  which  formula  should  be  written  Cj^HOjjjSHO-l-BHO, 
because  the  6  equivalents  of  water  of  crystallization  are  driven  off 
at  212°,  while  the  3  equivalents  of  basic  water  may  be  replaced, 
either  wholly  or  partly,  by  bases.  In  fact,  the  three  following 
meconates  of  potassa  have  been  obtained : 

3K0,C,,H0,„    (2K0+H0),C,,H0,„   (K0+2H0),C,,H0i,. 

By  pouring  nitrate  of  silver  into  a  solution  of  meconate  of  am- 
monia, a  yellow  precipitate  of  the  formula  3AgO,Ci4HOu  is  fonjied. 

Meconic  acid  presents  therefore  all  the  characters  of  a  tribasic 
acid.     It  produces  a  beautiful  red  colour  with  sesquisalts  of  iron. 

§  1463.  By  boiling  meconic  acid  for  s6me  time  with  acidulated 
water,  it  is  converted  into  comenic  acid,  while  carbonic  acid  is  dis- 
engaged. The  formula  of  comenic  acid,  is  Ci2H308,2H0,  the  2  equi- 
valents of  water  being  basic,  for  the  formula  of  comenate  of  silver 
is  2AgO,Ci2H308.  Meconic,  by  being  converted  into  comenic  acid, 
loses  only  carbonic  acid,  according  to  the  equation 

C,4HOii,3HO=2CO,+Ci2H,08,2HO. 

Comenic  acid  is  also  largely  formed  in  the  dry  distillation  of  me- 
conic acid,  but  it  is  then  mixed  with  another  acid,  pyromeconic^  into 
which  comenic  acid  itself  is  transformed  when  subjected  to  another 
distillation.  In  order  to  obtain  pure  pyromeconic  acid,  it  must  be 
distilled  several  times ;  and  the  formula  of  the  crystallized  acid  is 
CioH305,HO,  while  that  of  pyromeconate  of  lead  is  VhO^Q^fifi^. 
The  following  equation  shows  how  this  acid  is  derived  from  comenic 
acid :   Cj,H203,2HO=2C03,C,oH30„HO. 


QUINIC  ACID.  611 

Comenic  and  pyrocomenic  acids  turn  sesquisalts  of  iron  of  a  red 
colour. 

CHELIDONIC  ACID  C,«HaO»„2HO. 

§  1464.  In  celandine,  (chelidonium  majus,)  a  plant  of  the  family 
of  the  papaveracese,  there  is  formed  a  peculiar  acid,  called  chelidonic, 
which  is  there  combined  with  lime ;  besides  malic  and  fumaric  acids. 
The  juice  of  the  plant  is  expressed  and  boiled  to  coagulate  the  albu- 
minous substances,  when,  after  having  added  a  small  quantity  of 
nitric  acid,  acetate  of  lead  is  poured  in  until  a  precipitate  no  longer 
forms.  The  chelidonate  of  lead  is  alone  precipitated,  the  malic  and 
fumaric  acids  remaining  in  solution  on  account  of  the  excess  of 
nitric  acid.  The  chelidonate  of  lead,  which  is  mixed  with  chelido- 
nate of  lime,  is  decomposed  by  sulf  hydric  acid,  and  the  acid  liquor 
is  saturated  with  lime ;  after  which  the  chelidonate  of  lime  is  crys- 
tallized several  times.  The  salt  is  subsequently  decomposed  by 
carbonate  of  ammonia,  and  the  chelidonate  of  ammonia  resulting, 
by  chlorohydric  acid ;  when  the  chelidonic  acid  separates  in  long 
crystalline  aciculse  during  the  cooling  of  the  liquid. 

The  formula  of  crystallized  chelidonic  acid  is  C^JIfi^^+bllO, 
and  it  loses  3  equivalents  of  water  at  212°.  From  the  composition 
of  its  salts  it  should  be  regarded  as  a  bibasic  acid 

QUINIC  ACID  CuH„p„,HO. 

§  1465.  This  acid  is  found  in  cinchona  bark,  in  the  state  of  qui- 
nate  of  lime.  The  bark  is  boiled  with^  water  acidulated  with  chlo- 
rohydric acid,  which  is  then  saturated  with  lime,  in  excess ;  when 
the  filtered  liquid  contains  quinate  of  lime  which  mayJbe  crystal- 
lized by  proper  evaporation.  The  salt  is  purified  by  animal  black 
and  several  successive  crystallizations ;  and  in  order  to  separate  the 
quinic  acid  from  it,  6J  parts  of  the  quinate  of  lime  are  heated  with 
1  of  sulphuric  acid  diluted  with  10  of  water,  when  the  lime  sepa- 
rates in  the  state  of  sulphate  of  lime  ;  after  which  alcohol  is  added 
to  efiect  its  complete  precipitation,  and  the  filtered  liquid  is  evapo- 
rated to  the  consistence  of  syrup,  when  the  quinic  acid  crystallizes  in 
large  prisms.  The  formula  of  the  crystallized  acid  is  Cj^H^O^jHO ; 
and  that  of  quinate  of  silver  is  AgOjCj^HuOjj. 

Quinic  acid,  subjected  to  heat,  yields  very  complex  products: 
they  are  benzin,  benzoic  phenic,  and  salicylous  acids,  all  of  which 
shall  subsequently  be  described ;  besides  a  peculiar  crystallizable 
substance  of  the  formula  C^^K^flg,  very  soluble  in  water  and  alco- 
hol, and  which  has  been  called  hydroquinone.  Subjected  to  the 
action  of  sulphuric  acid  and  peroxide  of  manganese,  quinic  acid 
yields  a  volatile  product,  quinone,  of  which  the  formula  is  C^Kfi^, 
In  order  to  obtain  a  small  quantity  of  this  product,  100  gm  of  qui- 
nic acid  are  heated  gently  in  a  small  retort  with  400  gm.  of  per- 
oxide of  manganese  and  100  gm.  of  sulphuric  acid  previously  diluted 


612  ORGANIC   ALKALIES. 

with  one-half  of  its  weight  of  water.  A  great  bubbling  ensues 
in  the  retort,  and  a  mixture  of  formic  acid  and  quinone  is  deposited 
in  the  receiver.  The  latter  substance  crystallizes  in  beautiful  golden- 
jellow  spangles. 

Quinon  is  easily  sublimed  by  the  same  method  as  camphor,  and 
it  has  a  strong  and  irritating  odour,  resembling  that  of  camphor. 
It  dissolves  slightly  in  cold,  but  more  freely  in  boiling  water,  while 
its  true  solvents  are  alcohol  and  etheM  Chlorine  acts  powerfully 
upon  it,  and  gradually  abstracts  all  its  nydrogen,  which  is  replaced 
by  an  equivalent  quantitity  of  chlorine  ;  and  two  crystallized  chlori- 
nated products  have  thus  been  separated :  sechlorinated  quinone 
Ca^HjClgOg  and  perchhrinated  quinone  02401808- 

Quinone  also  gives  rise  to  a  great  number  of  interesting  products, 
but  their  study  would  lead  us  too  far. 


§  1466.  Vegetables  contain  several  other  organic  acids,  named 
generally  after  the  plant  from  which  they  are  extracted,  but  they 
are  as  yet  only  imperfectly  known ;  and  several  of  them  are  proba- 
bly identical  with  those  already  described,  for  which  reason  we  shall 
not  stop  to  mention  them. 


ORGANIC  ALKALIES. 


§  1467.  At  the  present  day  a  large  number  of  organic  substances 
are  known  which  combine  with  acids  after  the  manner  of  mineral 
bases,  forming  compounds  which  exhibit  all  the  characters  of 
salts,  and  to  which  the  -name  of  organic  alkalies,  or  alkaloids,  has 
been  given.  Some  are  found  already  formed  in  vegetables,  while 
others  are  produced  by  the  calcination  or  other  appropriate  treat- 
ment of  organic  matter.  The  majority  of  native  alkaloids  are  ex- 
tremely poisonous,  and  rank  among  the  most  powerful  medicines, 
which  character  lends  them  peculiar  importance. 

All  the  organic  alkalies  contain  nitrogen  and  hydrogen,  and  all, 
with  the  exception  of  ammonia,  contain  carbon ;  while  the  majority, 
in  addition,  contain  oxygen ;  and  lastly,  sulphur  has  been  found  in 
some.  They  all  present  the  remarkable  peculiarity  which  has  been 
described  (§  513)  in  treating  of  ammonia;  that  of  combining  directly 
and  without  decomposition,  with  the  hydracids,  by  forming  chlorohy- 
drates,  iodohydrates,  etc.  etc.,  and  of  fixing,  in  all  salts  which  they 
form  with  the  oxacids,  1  equiv.  of  water,  necessary  to  the  constitu- 
tion of  the  salt,  and  which  cannot  be  driven  off  without  destroying 
its  nature.  The  alkaloids,  like  ammonia,  are  therefore  bases  only 
when  they  have  combined  with  the  elements  of  1  equiv.  of  water. 


QUININ.  613 

We  shall  first  describe  the  alkaloids  which  exist  ready  formed  in 
vegetables,  and  then  some  of  the  numerous  artificial  alkaloids  ob- 
tained in  modern  days,  confining  ourselves  chiefly  to  general  remarks 
on  the  method  of  their  preparation  and  their  properties. 

The  native  alkaloids  may  be  divided  into  two  classes :  alkaloids 
volatile  without  decomposition,  and  non-volatile  alkaloids,  each 
class  requiring  a  special  method  of  extraction.  In  order  to  extract 
those  of  the  first  class,  the  liquid  containing  them  is  distilled  with 
potassa  or  lime,  which  bases  unite  with  the  acid  until  then  com- 
bined with  the  alkaloid,  while  the  latter  passes  over  in  distillation. 
The  majority  of  non-volatile  alkaloids  are  very  slightly  soluble  in 
water,  and  are  prepared  by  boiling  the  vegetables  containing  them 
with  water  acidulated  with  chlorohydric  acid,  when  the  alkaloid  is 
dissolved  in  the  state  of  chlorohydrate,  after  which  the  liquid  is 
then  saturated  with  an  alkali  or  with  lime,  in  order  to  precipi- 
tate the  alkaloid.  The  deposit  is  then  treated  with  boiling  alco- 
hol to  dissolve  the  alkaloid,  which  crystallizes  on  cooling  or  by 
evaporation. 

NON-VOLATILE  NATIVE  ALKALOIDS. 

ALKALOIDS  OF  THE  CINCHONAS. 

§  1468.  The  bark  of  the  cinchonas  contains  two  principal  alka- 
loids, to  which  they  owe  their  medicinal  virtue :  these  are  quinia 
and  cinchonin.  Three  species  of  cinchona  are  known  in  commerce, 
the  yellow,  red,  and  gray ;  and  while  quinin  predominates  in  yellow 
bark,  cinchonin  is  principally  found  in  the  gray ;  and  red  bark  con- 
tains nearly  equal  proportions  of  quinin  and  cinchonin.  Two  other 
less  important  alkaloids  are  also  found  in  the  barks,  chino'idin  and 
cinchovatin,  which  are  present  in  very  small  quantities. 

Quinin  C^U^J^fi^, 

'  §  1469.  Yellow  cinchona  is  preferred  for  the  manufacture  of 
quinin,  to  which  eff*ect  the  bark  is  bruised  and  boiled  with  water 
containing  15  or  20  per  cent,  of  sulphuric  or  chlorohydric  acid, 
when  the  liquid  is  filtered  through  a  cloth,  and  milk  of  lime  added 
until  an  alkaline  reaction  is  produced  with  litmus.  The  deposit 
formed,  which  cqntains  the  quinin,  is  squeezed  in  a  press,  and  the 
cake  resulting  treated  with  boiling  alcohol,  three-fourths  of  which 
being  separated  by  distillation,  sulphuric  acid  is  added  to  the  re- 
mainder until  a  slight  persistent  acid  reaction  is  obtained.  The 
liquid  is  discoloured  by  animal  black,  and  crystallize  when  the 
sulphate  of  quinin  crystallizes  first,  while  the  sulphate  of  cinchonin 
remains  in  the  mother  liquid.  By  decomposing  the  sulphate  of 
quinin  by  ammonia,  quinin  is  obtained  in  the  form  of  a  white  pow- 
der, which,  by  slow  evaporation  from  an  alcoholic  solution,  is  depo- 
sited in  small  prismatic  crystals. 


614  ORGANIC  ALKALIES. 

Quinin  has  a  very  bitter  taste,  requires  for  its  solution  400  parts 
of  cold  and  250  of  boiling  water,  and  turns  litmus  blue.  Boiling 
alcohol  dissolves  one-half  of  its  weight  of  it,  while  ether  also  dis- 
solves a  considerable  quantity,  and  thus  furnishes  a  method  of  sepa- 
rating it  from  cinchonin,  which  is  insoluble  in  ether.  The  formula 
of  quinin,  crystallized  from  an  a(|tteous  solution,  is  C3gH24N204+ 
6H0,  and  it  loses  the  6  equivalents  of  water  at  248°.  Quinin, 
dissolved  in  alcohol  or  acidulated  water,  exerts  a  rotatory  power 
toward  the  left,  at  least  at  the  temperature  of  71.6°,  the  power  de- 
creasing as  the  temperature  rises.  Quinin  forms  crystallizable 
salts  with  nearly  all  the  acids,  its  most  important  compound  being 
the  neutral  sulphate,  used  in  medicine  as  an  anti-intermittent.  Two 
sulphates  of  quinin  are  known. 

1.  The  neutral  sulphate,  crystallizing  in  fine  silky  aciculge,  and 
very  slightly  soluble  in  cold  water,  of  which  it  requires  750  parts 
for  solution,  while  it  dissolves  in  30  parts  of  boiling  water.  Its 
formulae  is  (C38H24Na04,H0),S03-f  7H0,  and  it  loses  its  water  of 
crystallization  by  heat.  It  exerts  rotation  toward  the  left,  like  the 
alkali  which  acts  as  its  base. 

2.  The  acid  sulphate,  soluble  in  10  or  12  parts  of  cold  water,  ths 
formula  of  which  is  (C38H^N204,HO,)2S03+8HO,  the  water  of 
crystallization  being  driven  ofi"  by  heat. 

Cinchonin  Q^Jl^fi^, 

§  1470.  Cinchonin  is  prepared  either  from  the  mother  liquid  of 
sulphate  of  quinin,  or  by  treating  gray  cinchona  in  the  manner  by 
which  quinin  is  extracted  from  yellow  cinchona.  Cinchonin  crys- 
tallizes readily,  and  without  any  water  of  crystallization,  its  formula 
being  CggHg^NgNg,  which  difi'ers  from  that  of  anhydrous  quinin  only 
by  containing  2  equiv.  of  oxygen  less.  Cinchonin  is  still  less  solu- 
ble in  water  and  alcohol  than  quinin,  while  it  is  insoluble  in  ether. 
Salts  of  cinchonin  crystallize  readily,  and  are  generally  more  solu- 
ble in  water  than  the  corresponding  salts  of  quinin. 

When  chlorine  is  made  to  act  upon  a  concentrated  and  hot  solu- 
tion of  chlorohydrate  of  cinchonin,  a  slightly  soluble  salt  is  depo- 
sited, which,  when  redissolved  in  water,  and  treated  with  ammonia, . 
forms  a  precipitate  of  hichlorinated  cinchonin  Q^^QX^fi^.  This 
substance  crystallizes  in  needles,  turns  tincture  of  litmus  blue,  and 
forms  with  acids  crystallizable  salts,  which  closely  resemble  the  cor- 
responding salts  produced  by  ordinary  cinchonin,  and  even  appear 
to  be  isomorphous  with  them.  In  the  same  way  bromine  converts  cin- 
chonin into  hichlorinated  cinchonin  G^fi^fivJ^fi^.  The  elementary 
composition  of  the  bichlorohydrate  of  bibrominated  cinchonin  CggHjjj, 
Br3N30a,2HCl  is  the  same  as  that  of  the  bibromohydrate  of  hichlori- 
nated cinchonin  C38H22Cl3N202,2HBr,  while  the  two  substances  dif- 
fer essentially  from  each  other,  since  the  former  yields  with  potassa 
bibrominated  cinchonin,  and  the  latter  hichlorinated  cinchonin. 


MORPHIN.  615 

Cinchonin,  dissolved  in  alcohol  or  acidulated  water,  exerts  a  *ro- 
tatorj  power  toward  the  right,  while  that  of  quinin  is  toward  the 
left,  and  the  salts  of  cinchonin  also  turns  to  the  right,  like  the  al- 
kali which  forms  their  base,  the  chlorinated  derivatives  of  the  alkali 
exerting  it  in  the  same  direction. 

CJiino'idin. 
§  1471.  The  mother  liquid  of  sulphate  of  quinin,  after  having 
deposited  its  sulphate  of  cinchonin,  may  yield  a  small  quantity  of 
sulphate  of  cMno'idin.  Chino'idin  is  as  yet  but  little  known,  and 
from  the  analyses  which  have  been  made  of  it,  it  would  appear  to 
have  the  same  composition  as  quinin. 

CineJiovatin  C^gHg^NgOg. 

§  1472.  Qinchovatin  is  found  chiefly  in  the  cinchona  from  Jain, 
(cinchona  ovata,)  from  which  it  is  extracted  by  the  same  process  as 
quinin.  It  is  a  substance  insoluble  in  water,  and  soluble  in  alcohol, 
from  which  it  is  deposited  in  crystals  of  the  formula  C^^H^yNgOg.* 

ALKALOIDS  OF  OPIUM. 

§  1473.  On  making  incisions  into  the  head  of  the  white  poppy,  a 
liquid  issues  from  it,  which  hardens  in  the  air  into  a  brown  horn- 
like mass,  constituting  opium,  the  chief  part  of  which  is  imported 
from  the  East,  and  principally  from  Smyrna.  The  poisonous  pro- 
perties of  opium  are  owing  to  the  existence  of  several  alkaloids,  the 
principal  of  which  are  morphin,  narcotin,  and  codein ;  while  several 
others,  less  important,  and  only  existing  in  small  quantity,  are  also 
extracted:  theha'ina,  narce'in,  pseudomorphin,  porphyroxin,  and  a 
non-nitrogenous  crystalline  substance,  which  does  not  act  the  part 
of  a  base,  and  has  been  called  meconin. 

First  quality  opium  contains  about  10  per  cent,  of  morphin  and 
5  per  cent,  of  narcotin. 

Morphin  Q^^^O^. 
§  1474.  In  order  to  obtain  morphin,  the  opium,  cut  into  thin  slices, 
is  macerated  for  some  time  with  water,  and  the  substance,  when 
softened,  is  crushed  with  an  additional  quantity  of  water,  squeezed 
in  bags  under  a  press,  and  the  cake  subjected  to  similar  treatment. 
The  liquid  yielded  by  this  process,  being  evaporated  to  the  consist- 
ence of  an  extract,  is  again  treated  with  a  small  quantity  of  water, 
which  dissolves  the  salts  of  morphin,  and  leaves  the  greater  portion 
of  the  narcotin  mixed  with  a  brown  substance.  By  testing  a  small 
quantity  of  the  liquid,  the  quantity  of  ammonia  necessary  to  wholly 
precipitate  this  substance  is  ascertained,  while  only  J  of  this  quan- 
tity is  poured  into  the  whole  liquid,  when  the  impure  morphin  is 
precipitated,  carrying  with  it  nearly  all  the  colouring  matter.     By 

*  Aricin  is  not  mentioned  by  Regnault,  and  in  fact  much  uncertainty  exists  as 
to  the  alkaloids  in  cinchona  bark,  except  quinine  and  cinchona. — J.  C.  B. 


616  ORGANIC   ALKALIES. 

then  adding  the  balance  of  the  ammonia,  nearly  pure  morphin  is 
precipitated,  and  is  treated  with  alcohol  marking  20°  of  Baumd, 
which  does  not  sensibly  dissolve  the  morphin,  while  it  removes  almost 
entirely  the  resinous  matter  which  adulterates  it.  The  residue  is 
then  treated  with  boiling  alcohol  a^35°  Baum^,  which  dissolves  the 
morphin  and  deposits  the  greater  part  of  it  on  cooling.  Three-fourths 
of  the  alcohol  are  deposited  by  distillation  and  the  residue  .yields 
the  balance  of  the  morphin. 

In  order  to  obtain  the  base  perfectly  pure,  it  is  best  to  redissolve 
it  in  weak  chlorohydric  acid,  crystallize  the  chlorohydrate,  and 
again  decompose  this  salt  by  ammonia. 

Morphin  readily  forms  crystals  of  the  formula  Cj^HjgNOg+SHO, 
which  lose  the  2  equiv.  of  water  by  an  elevation  of  temperature, 
and  may  be  heated  to  570°  without  injury.  Cold  water  dissolves 
about  Yho  of  morphin,  and  hot  water  nearly  double  of  that  quantity; 
the  solution  showing  an  alkaline  reaction  with  litmus.  Weak  alco- 
hol at  20°  B.  dissolves  but  very  little  morphin,  while  boiling  alcohol 
at  35°  B.  dissolves  -^^  of  its  weight,  the  greater  portion  of  the  mor- 
phin crystallizing  on  cooling.  It  is  scarcely  soluble  in  ether,  but  a 
concentrated  solution  of  caustic  potassa  dissolves  it  without  change, 
by  which  process  the  base  may  be  separated  from  narcotin,  the 
latter  being  insoluble  in  alkaline  lixiviae.  Morphin  dissolved  in 
acidulated  w^ter  exerts  a  rotatory  power  toward  the  left,  like  its 
salts. 

Morphin  forms  crystallizable  salts  with  acids,  soluble  in  water  and 
alcohol,  but  insoluble  in  ether.  Chlorohydrate  of  morphin,  which  is 
most  important  on  account  of  its  use  in  medicine,  crystallizes  in 
silky  tufts,  and  dissolves  in  1  part  of  boiling  or  in  20  parts  of  cold 
water.  Its  formula  is  C34HjgNOg,HCH-6HO,  while  that  of  crystal- 
lized sulphate  of  morphin  is 

(C3,H,3NOg,HO),S03+6HO. 

Narcotin  C^gH^^NOi^. 
§  1475.  Narcotin  is  extracted  from  the  residues  left  after  the 
extraction  of  morphin  from  opium  by  treating  them  with  ether, 
which  dissolves  a  mixture  of  narcotin  and  porphyroxin,  the  narcotin 
greatly  predominating.  Fresh  opium  may  also  be  treated  directly 
with  ether,  when  the  salts  of  morphin  remain  in  the  residue  and 
the  ether  contains,  with  the  narcotin  and  porphyroxin,  a  certain 
quantity  of  meconin.  The  ether  being  distilled  in  a  water-bath  and 
the  residue  treated  with  water,  which  dissolves  the  meconin,  the 
narcotin  and  porphyroxin  are  finally  dissolved  in  dilute  chlorohydric 
acid.  The  solution,  when  evaporated,  deposits  chlorohydrate  of 
narcotin,  while  the  chlorohydrate  of  porphyroxin  remains  in  the 
mother  liquid.  The  chlorohydrate  of  narcotin,  decomposed  by  am- 
monia, yields  isolated  narcotin,  which  is  purified  by  crystallizing  it 
in  alcohol. 


STRYCHNIN.  617 

Narcotin  crystallizes  in  small  rhomboidal  prisms,  melting  at  338°, 
decomposing  at  about  390°,  insoluble  in  cold  water,  and  only  dis- 
solving in  500  parts  of  boiling  water.  Alcohol,  when  hot,  dissolves 
about  ^V  of  its  weight,  and  ether  Jg.  Narcotin  is  a  much  more  feeble 
base  than  the  alkaloids  we  have  hitherto  described,  since  its  solutions 
do  not  turn  to  blue  the  reddened  tincture  of  litmus,  although  it  forms 
crystallizable  salts  with  acids.  The  formula  of  narcotin  is  C^H^ 
NOj^,  while  that  of  the  chlorohydrate  is  C^qH^jNOi^jHCI.  Narcotin, 
dissolved  in  alcohol  or  acidulated  water,  exerts  a  rotatory  power  to 
the  right,  opposite  to  that  of  morphin;  the  salts  of  narcotin  pos- 
sessing the  same  power  as  the  alkali. 

Oodein  C,JI,,'NO,, 

§  1476.  Codein  remains  in  the  liquid  from  which  morphin  has 
been  precipitated  by  ammonia,  and  is  extracted  by  concentrating 
them  through  evaporation,  adding  caustic  potassa,  and  then  continu- 
ing the  evaporation  to  dryness.  The  residue  is  treated  with  ether, 
which  dissolves  the  codein,  and  yields,  by  spontaneous  evaporation, 
large  crystals  of  this  substance,  which  are  remarkable  for  the  sharp- 
ness of  their  configuration. 

Codein,  which  is  much  more  soluble  than  the  other  alkaloids 
of  opium,  since  it  dissolves  in  80  parts  of  cold  and  20  of  boiling 
water,  turns  the  reddened  tincture  of  litmus  blue,  and  is  also  highly 
soluble  in  alcohol  and  ether.  The  formula  of  codein,  crystallized 
m  water,  is  C34HJ9NO5+2HO,  and  heat  readily  drives  oflP  its  2 
equiv.  of  water,  while  it  crystallizes  in  the  anhydrous  state  from  its 
solutions  in  ether. 

Codein  has  been  used  for  some  time  In  medicine. 

ALKALOIDS  OF  STRYCHNOS. 

Strychnin  ^^^^^a  ^^^  Brucin  C^gH^gN^Og. 

§  1477.  The  majority  of  the  genus  of  strychnos^  particularly  the 
bean  of  St.  Ignatius,  [strychnos  Ignatia,)  nux  vomica,  {strychnos  nux 
vomica^)  viper-wood,  {strychnos  colubrina,)  and  the  upas  tieut^, 
(strychnos  tieute,)  contain  two  alkaloids  in  various  proportions, 
strychnin  and  brucin,  remarkable  for  the  very  poisonous  effect  they 
exert  on  the  animal  economy. 

The  two  bases  are  generally  extracted  from  nux  vomica  by  boil- 
ing the  powdered  nut  with  water  containing  its  weight  of  sulphuric 
acid,  expressing  the  liquid,  and  precipitating  the  two  bases  by  hy- 
drated  lime.  The  deposit  is  treated  with  boiling  alcohol,  which 
dissolves  th^  strychnin  and  brucin;  and,  on  cooling,  the  greater 
portion  of  the  strychnin  crystallizes.  The  liquid,  concentrated  by 
evaporation,  yields  less  pure  strychnin,  and  the  brucin  crystallizes 
last.  It  is  necessary  to  purify  these  substances  by  several  succes- 
sive crystallizations. 


618  ORGANIC   ALKALIES. 

Strychnin  crystallizes  readily  in  octohedrons  with  rectangular 
bases,  insoluble  in  water,  slightly  soluble  in  alcohol,  and  presenting 
the  formula  C^Jl^J^fi^.  It  forms  easily  crystallizable  salts,  and 
the  formula  of  crystallized  chlorohydrate  of  strychnin  is  CJi^'Nfi^, 
HCH-3H0,  while  that  of  the  crystallized  sulnhate  is  {CJiJSfi^, 
H0),S03.  Strychnin,  dissolved  in  acidulated*water,  exerts  a  rota- 
tory power  toward  the  left,  like  its  salts.* 

Brucin  crystallizes  in -right  prisms  with  a  rhombic  base,  and  its 
formula  is  C^gHggNgOg+SHO;  the  8  equiv.  of  water  being  given  off 
by  heat.  Water  dissolves  a  small  quantity  of  it,  and  it  is  much 
more  soluble  in  alcohol  than  strychnin.  Concentrated  nitric  acid 
produces  an  intense  red  colour  with  brucin,  which  property  dis- 
tinguishes it  from  a  majority  of  the  other  alkaloids.  Brucin  dis- 
solved in  alcohol,  or  in  water  to  which  no  acid  has  been  added, 
deviates  to  the  left  like  strychnin,  its  salts  presenting  the  same 
behaviour. 

ALKALOID  OF  COFFEE  AND  TEA. 
Caffem  or  Them  QJl^fi^. 

§  1478.  Coffee  and  tea  contain  the  same  alkaloid,  which  is  called 
caffe'in  or  the'in,  according  as  it  has  been  extracted  from  either  of 
these  substances,  because  it  was  at  first  supposed  that  they  were 
not  identical.  In  order  to  extract  caffem  from  coffee,  the  bruised 
coffee-grains  are  treated  with  water,  and  subacetate  of  lead  is  poured 
into  the  liquid,  after  which,  the  deposit  being  separated,  sulf  hydric 
acid  is  passed  through  in  order  to  precipitate  the  excess  of  lead. 
The  solution  being  then  evaporated,  the  caffem  crystallizes,  and  is 
purified  by  successive  crystallizations.  Them  is  extracted  in  pre- 
cisely the  same  manner. 

Caffem  crystallizes  in  silky  aciculae,  taking  the  formula  CgH^NjOa 
-f  2H0,  while  it  loses  its  2  equivalents  of  water  at  212°,  melts  at  about 
356°,  and  sublimes  above  570°.  It  is  soluble  in  water,  alcohol,  and 
ether ;  and  its  basic  affinities  are  very  feeble,  for  although  it  dis- 
solves in  acids,  it  generally  leaves  them  when  the  solution  is  eva- 
porated. 

VOLATILE  NATIVE  ALKALOIDS. 

§1479.  Two  native  alkaloids  are  now  known,  which  volatilize 
without  change :  nicotin,  or  the  alkali  of  tobacco,  and  conicin,  the 
alkali  of  cicuta. 

Nicotiii  CaoHj^Nj. 

§  1480.  Certain  varieties  of  tobacco  contain  7  or  8  per  cent,  of 
nicotin,  which  is  extracted  by  digesting  the  tobacco-leaves  with 

*  The  elementary  composition  of  this  most  violent  poison  is,  singular  enough, 
identical  with  that  of  rye  bread,  a  most  wholesome  article  of  food.  The  natives 
of  Borneo  use  the  juice  of  the  different  kinds  of  strychnos  for  poisoning  their  ar- 
row-heads, the  wound  of  which  is  generally  fatal. —  W.  L.  F. 


NICOTIN.  619 

water,  evaporating  the  infusion  to  the  consistence  of  an  extract, 
and  then  treating  with  alcohol,  which  is,  in  its  turn,  concen- 
trated, after  being  decanted.  The  new  extract  is  treated  with 
potassa,  and  then  shaken  with  ether,  which  dissolves  the  nicotin  as 
well  as  some  foreign  substances.  Finely  powdered  oxalic  acid  is 
added  to  the  etherial  solution,  which  is  to  be  frequently  shaken, 
when  oxalate  of  nicotin  is  formed,  and  precipitated  in  drops,  which 
are  washed  several  times  with  water.  The  oxalate  of  nicotin  being 
decomposed  by  potassa,  free  nicotin  is  separated  by  ether.  The 
etherial  solution  is  distilled  in  a  retort  over  a  water-bath,  when  the 
greater  portion  of  the  ether  distils  rapidly,  while  the  last  particles 
do  not  pass  over  at  212°  ;  and  there  exists  also  a  small  quantity  of 
ammonia  and  water,  which  separate  only  at  a  higher  temperature. 
The  retort  must  be  kept,  for  a  whole  day,  at  a  temperature  of  284°, 
and  a  feeble  current  of  hydrogen  must  be  passed  through  it,  after 
which  the  receiver  is  changed,  and  the  temperature  raised  to  356°, 
in  order  to  distil  the  nicotin  in  a  current  of  hydrogen. 

Nicotin  is  an  oleaginous,  lim,pid,  and  colourless  liquid,  smelling 
slightly  of  tobacco,  and  which  boils  at  473°,  but  begins  to  decom- 
pose at  this  temperature ;  so  that  it  is  necessary  to  distil  it  under 
feeble  pressure,  or  in  a  current  of  hydrogen  gas,  so  as  not  to  be 
obliged  to  raise  the  temperature  to  a  degree  at  which  the  elastic 
force  of  the  vapour  is  equal  to  the  pressure  of  the  atmosphere. 
The  density  of  liquid  nicotin  is  1.048,  while  the  density  of  its  vapour 
has  been  found  to  be  5.607.  Nicotin  is  very  soluble  in  water,  which 
then  reacts  powerfully  alkaline ;  and  caustic  potassa  precipitates  it 
from  its  solutions  in  the  form  of  oleaginous  drops,  while  ether  takes 
it  from  water  and  dissolves  it  in  all  proportions,  alcohol  also  dis- 
solving a  large  quantity  of  it.  It  is  one  of  the  most  powerful  poi- 
sons. Nicotin  soon  changes  in  the  air,  by  absorbing  oxygen,  and 
is  converted  into  a  brown  substance  of  a  resinous  appearance. 

The  salts  of  nicotin  are  in  general  very  soluble,  and  crystallize 
with  difficulty.  The  formulae  of  the  sulphate  and  nitrate  of  nicotin 
are  (C2oH,4N2,HO),S03  and  (C2oH,4N2,HO),N05,  according  to  which 
the  formula  of  free  nicotin  is  CgoHj^N^,  corresponding  to  4  volumes 
of  vapour,  like  that  of  ammonia.  Nicotin  exerts  an  extremely  ener- 
getic rotatory  power  toward  the  left,  while  its  chlorohydrate  turns 
the  plane  of  polarization  with  the  same  power  toward  the  right. 

The  various  species  of  tobacco  contain  very  different  proportions 
of  nicotin,  the  following  quantities  having  been  found  in  100  parts 


of  dry  tobacco : 

French  Tobacco. 

Alsace 3.2 


Foreign  Tobacco. 

Havana 2.0 


Maryland 2.3 

Virginia 6.9 


Pas-de-Calais 4.9 

Nord 6.6 

Lot 8.0 

The  tobacco  which  contains  most  nicotin  is  the  best  for  the  manu- 


620  ORGANIC  ALKALIES. 

facture  of  snuff,  since  the  property  possessed  by  tobacco  of  stimu- 
lating the  mucous  membrane  of  the  nose,  is  owing  to  the  pre- 
sence of  nicotin  and  ammoniacal  salts.      V 

Conicin  CjgHj^N 

§  1481.  Conicin  is  extracted  from  the  seeds  of  the  conium,  but 
it  is  also  found  in  the  leaves  and  stalk  of  this  plant,  previous  to 
its  flowering.  The  bruised  seeds  being  distilled  with  a  solution  of 
potassa,  conicin  passes  over  with  water  and  ammonia.  The  liquid 
is  saturated  with  sulphuric  acid,  and  evaporated  to  the  consistence 
of  syrup ;  when,  by  treating  the  extract  with  a  mixture  of  alcohol 
and  ether,  the  sulphate  of  conicin  is  dissolved,  while  the  ammonia- 
cal sulphate  is  left.  The  solution  of  the  sulphate  of  conicin  is  then 
evaporated,  and  afterward  decomposed  by  caustic  potassa ;  when 
the  conicin  arising  from  this  decomposition  is  decanted,  and  then 
left  for  some  time  on  chloride  of  calcium,  which  abstracts  its  water, 
after  which  it  is  purified  by  distillation. 

Conicin  is  a  colourless  liquid,  haying  a  sharp  smell,  which  imme- 
diately produces  sickness,  and  its  density  is  0.89,  while  it  boils  at 
338°.  It  is  one  of  the  most  powerful  poisons.  Conicin  is  slightly 
soluble  in  water,  but  dissolves  in  all  proportions  in  alcohol  and 
ether,  its  solutions  showing  a  strong  alkaline  reaction.  It  rapidly 
absorbs  the  oxygen  of  the  air,  and  then  assumes  various  shades  of 
colour.  The  salts  of  conicin  are  in  general  deliquescent  and  not 
crystalline ;  and  the  composition  of  the  alkaloid  corresponds  to  the 
formula  CjgH^N. 

ARTIFICIAL  ALKALOIDS. 
§  1482.  Chemists  have  long  since  succeeded  in  preparing  a  great 
number  of  alkaloids,  which  have  not  yet  been  found  in  vegetables. 
Almost  all  these  alkaloids  are  volatile  without  decomposition,  and 
contain  no  oxygen ;  and  while  some  resemble,  in  their  properties, 
uicotin  and  conicin,  others  are  so  closely  analogous  to  ammonia, 
that,  in  a  purely  philosophical  classification  of  substances,  it  would 
be  impossible  to  separate  them  from  that  base. 

Quinole'in  C^gHyN. 
§  1483.  Several  native  organic  bases,  particularly  quinin,  cin- 
chonin,  and  strychnin,  yield,  by  distillation  with  potassa,  a  volatile 
alkaloid  called  quinole'in.  It  is  obtained  in  greatest  quantity  from 
cinchonin,  by  heating  in  a  tubulated  retort  some  fragments  of  caustic 
potassa  with  a  small  quantity  of  water,  so  as  to  form  a  pasty  solu- 
tion, and  gradually  adding  powdered  cinchonin.  It  is  heated  with 
an  alcohol-lamp  until  the  substance  appears  to  be  dried,  when 
hydrogen  is  disengaged,  while  water  passes  over,,  as  also  an  oily 
substance,  which  is  rectified  a  second  time  over  potassa.  Quinolein 
is  a  colourless  oil,  of  a  disagreeable  odour,  distilling  at  about  446°, 


ANILIN.  621 

insoluble  in  cold,  and  scarcely  soluble  in  boiling  water,  while  alcohol 
and  ether  dissolve  it  freely.  It  forms  crystallizable  salts  with  chlo- 
rohydric,  sulphuric,  and  nitric  acids,  and  it  contains  no  oxygen,  its 
formula  being  CigH^N.  Quinolein  is  also  found  among  the  products 
of  distillation  of  coal-tar,  and  was  formerly  called  leucole. 

ALKALOIDS  DERIVED  FROM  VARIOUS  CARBURETTED  HYDROGENS. 

Anilin  C12H7N. 

§  1484.  The  majority  of  the  carburetted  hydrogens  yield,  when 
they  are  boiled  with  monohydrated  nitric  acid,  or  a  mixture  of  this 
acid  and  concentrated  sulphuric  acid,  nitrogenous  substances,  which 
result  from  the  substitution  of  1  equivalent  or  2  equivalents  of  the 
compound  NO^  in  the  place  of  1  or  2  equivalents  of  hydrogen. 
Thus,  we  shall  soon  see  that  benzin  Q^fi^,  treated  with  mono- 
hydrated nitric  acid,  produces  two  substances,  nitrohenzin  C^aH^ 
(NO4)  and  hinitrohenzin  Q^fiJ^O^^.  These  nitrogenous  com- 
pounds yield  alkaloids  when  they  are  subjected  to  the  action  of 
reducing  substances,  as  e.  g.  the  sulfhydrate  of  ammonia,  or  to 
the  action  of  nascent  hydrogen  obtained  by  causing  dilute  sulphuric 
acid  to  act  on  zinc  in  contact  with  the  nitrogenous  substance. 
'Thus,  by  the  action  of  the  bisulf hydrate  of  ammonia  on  nitrobenzin, 
we  obtain  an  alkaloid,  anilin  CjgH^N,  from  the  following  reaction: 

C,,H,(NOj4-6(NH3,2HSj=C,,H,N+6S+4HO+6(NH3,HS). 
By  the  action  of  nascent  hydrogen,  we  have 

C,,HXNOJ +6H=C,3H,lsr+4HO. 

When  binitrobenzin  is  subjected  to  the  same  treatment,  there 
results  a  second  alkaloid,  nitr anilin  Q.^^Q(J^O^^,  according  to  the 
following  reactions : 

C,,H,(NOJ,+6(NH3,2HS)=C,,He(NO,)N+6S+4HO 
-f6(NH3,HS)„C,,H,{NOJ,+6H==C,A(NOjN+4HO. 

We  shall  describe  only  anilin  and  nitranilin ;  the  properties  of 
the  numerous  alkaloids  obtained  by  applying  the  same  processes  to 
other  carburetted  hydrogens,  or  substances  derived  from  them,  being 
very  similar. 

Anilin  is  a  colourless  liquid,  of  an  agreeable  vinous  smell,  boiling 
at  359.6°,  and  dissolving  slightly  in  watei^but  in  all  proportions 
in  alcohol  and  ether.  Anilin  possesses  no  rotatory  power.  Chlo- 
rine and  bromine  convert  it  into  chlorinated  or  brominated  sub- 
stances, modified  merely  by  substitution,  and  which  often  retain  the 
basic  properties  and  capacity  of  saturation  of  the  original  anilin. 
Monochlorinated  anilin  CigHgClN,  the  monobrominated  CigHgBrN, 
and  nitranilin  Ci2Hg(N04)N,  are  bases  which  form  salts  as  well 
defined  as  anilin  itself;  while  the  terchlorinated  CjjH^CljN  and 
terbrominated  anilins  CjgH^BrjN  possess  no  basic  properties. 


622  ORGANIC   ALKALIES. 

Iodine  may  also  be  substituted  for  hydrogen  in  anilin,  and  a 
moniodinated  anilin  CigHglN  has  been  obtained  which  combines 
with  acids.  Cyanogen  gives  rise  to  no  ph^omena  of  substitution, 
but  combines  directly  with  anilin  with  the  evolution  of  heat,  and 
produces  a  new  crystallizable  base,  cy anilin  Q^J1^0j=Q^Jl^l^^ 
which  forms,  with  the  majority  of  acids,  well-defined  and  crystalli- 
zable salts. 

ALKALOIDS  DERIVED  FROM  CYANIC  AND  CYANURIC  ETHERS, 
PRESENTING  A  CLOSE  ANALOGY  WITH  AMMONIA. 

§  1485.  We  shall  subsequently  describe,  together  with  some  other 
products  of  cyanogen,  two  isomeric  compounds  of  this  substance 
with  oxygen,  cyanic  acid  Cy 0=03^0,  and  cyanuric  acid  CygOg^ 
CgNgOg,  which  are  readily  converted  into  each  other,  as  will  be 
shown  in  its  place.  These  acids  combine  with  bases,  forming  cya- 
nates  and  cyanurates. 

Uthylammonia  CJi^(Nli^, 

§  1486.  By  distilling  cyanate  of  potassa  KO,CyO  with  a  solution 
of  sulphovinate  of  potassa  KO,(C^H^O,2S03)  there  is  obtained  a 
mixture  of  cyanic  ether  C^H^OjCyO  and  cyanuric  ether  SC^H.O. 
CygOg,  which  are  easily  separated  by  distillation,  the  first  being 
very  volatile,  while  the  second  boils  only  at  a  very  high  tempera- 
ture. Cyanic  ether  dissolves  in  ammonia  with  disengagement  of 
heat,  and  the  liquid,  when  evaporated,  deposits  beautiful  prismatic 
crystals,  which  are  fusible,  very  soluble  in  water  and  alcohol,  and 
of  the  formula  CgHgNgOa :  they  result  therefrom  from  the  simple 
combination  of  1  equivalent  of  cyanic  ether  C4H.O,CyO=CeH5N03 
with  1  equivalent  of  ammonia  NH^.  Cyanic  and  cyanuric  ethers, 
treated  with  caustic  potassa,  yield  carbonate  of  potassa  and  an  al- 
kaloid C,H,N : 

C,H,0,C^O+2(KO,HO,=2(KO)CO,)+C,H,N. 

We  shall  call  this  alkaloid  ethylammonia,  and  its  formula  C^H^N 
may  be  written  C^H^NHg,  considering  it  as  resulting  from  the  com- 
bination of  1  equivalent  of  ammonia  with  1  equivalent  of  bicarbu- 
retted  hydrogen  C^H^,  while  it  may  also  be  written  C4H5(NH3), 
and  the  alkaloid  regarded  as  belonging  to  the  series  of  simple  ethers. 
One  of  the  equivalents  of  hydrogen  and  carburetted  hydrogen 
C^Hg,  the  generator  of  the  series,  having  been  replaced  by  1  equi- 
valent of  amide  (NHg). 

In  order  to  obtain  ethylammonia,  cyanic  or  cyanuric  ether  is 
boiled  in  a  distilling  apparatus  with  an  excess  of  potassa,  the  va- 
pours being  collected  in  a  well-cooled  receiver  containing  a  small 
quantity  of  water,  which  takes  the  ethylammonia  in  solution,  and 
thus  becomes  strongly  alkaline,  with  an  intense  ammoniacal  odour, 
although  it  does  contain  a  trace  of  free  ammonia.  This  liquid  is 
saturated  with  chlorohydric  acid  and  evaporated,  when  crystals  are 


METHYLAMMONIA.  623 

obtained  which  dissolve  completely  in  absolute  alcohol,  and  are 
again  deposited,  by  evaporation,  in  crystalline  lamellae.  This 
compound  is  chlorohydrate  of  ethylammonia  C^HyN,HCl,  and  is 
distinguished  from  chlorohydrate  of  ammonia  by  its  solubility  in 
absolute  alcohol. 

The  chlorohydrate  of  ethylammonia,  perfectly  dried,  is  mixed 
with  double  its  weight  of  quicklime,  and  introduced  into  a  long 
tube  closed  at  one  end,  so  as  to  fill  one-half  of  it ;  and  the  other 
half  being  filled  with  fragments  of  caustic  potassa,  a  disengagement- 
tube,  which  enters  a  flask  surrounded  by  a  refrigerating  mixture,  is 
adapted  to  it.  Gentle  heat  being  applied,  the  ethylammonia  set 
free  distils,  and  is  condensed  in  the  receiver.  It  is  important  to 
remark  that  this  process  exactly  resembles  that  used  for  obtaining 
ammonia. 

Ethylammonia  is  a  colourless,  very  volatile  liquid,  boiling  at 
64.4°,  exhaling  a  very  penetrating  ammoniacal  odour,  turning  blue 
the  reddened  tincture  of  litmus,  and  exhibiting  a  causticity  resem- 
bling that  of  potassa.  When  a  glass  rod  moistened  with  chlorohy- 
dric  acid  is*  brought  near  it,  extremely  thick  white  fumes  are  pro- 
duced ;  and  each  drop  of  acid  poured  into  it  produces  a  hissing  at 
the  moment  of  its  mixing  with  the  base.  Ethylammonia  ignites 
when  brought  near  to  a  substance  in  combustion,  and  burns  with  a 
bluish  flame.  It  mixes  with  water  in  all  proportions,  becoming 
very  hot,  and  giving  rise  to  a  solution  of  which  the  basic  properties 
absolutely  resemble  those  of  ammonia.  A  solution  of  ethylam- 
monia precipitates,  in  fact,  the  salts  of  magnesia,  alumina,  manga- 
nese, iron,  bismuth,  chrome,  uranium,  tin,  lead,  and  mercury.  Salts 
of  zinc  throw  down  a  white  precipitate,  which  redissolves  in  a  large 
excess  of  the  reagent.  Salts  of  copper  produce  a  bluish  white  pre- 
cipitate, readily  soluble  in  an  excess  of  the  reagent,  furnishing  a 
deep-blue  liquid,  analogous  to  that  produced  by  an  excess  of  am- 
monia, (§1046.) 

Ethylammonia  combines  with  all  the  acids,  forming  crystallizable 
salts  precisely  resembling  those  of  ammonia,  and  it  also  furnishes 
compounds  analogous  to  the  amides,  (§  514.)  In  fact,  by  mixing  a 
solution  of  ethylammonia  with  oxalic  ether,  the  mixture  becomes 
cloudy,  and  alcohol  is  formed,  while  acicular  crystals  of  a  compound 
CgHgN03= 0^113^,0303  corresponding  to  oxamide  NH^jOgOj  sepa- 
rate. 

Methylammonia  OgH^N  or  (jfiJ^IL^. 

§  1487.  By  boiling  methylocyanic  or  methylocyanuric  ether  with 
a  solution  of  potassa,  and  collecting  the  product  in  a  well-cooled 
receiver  containing  water,  a  strongly  alkaline  solution  is  obtained, 
which  exhales  a  very  penetrating  ammoniacal  odour.  It  is  satu- 
rated with  chlorohydric  acid,  evaporated  to  diyness,  and  again 
treated  with  boiling  alcohol,  which  deposits,  on  cooling,  pearl-like 


624  ORGANIC   ALKALIES. 

crystalline  lamellae  of  cMorohydrate  of  methylammonia  CJI^NjHCl. 
This  salt  heated  with  quicklime,  as  in  tlfe  preparation  of  ammonia 
and  ethylammonia,  yields  methylammonia^  which  may  be  obtained 
in  the  form  of  a  colourless  liquid  by  cooling  the  receiver  with  a 
proper  refrigerating  mixture.  Methylammonia  is  gaseous  at  the 
ordinary  temperature,  and  may  be  collected  in  bell-glasses  over 
mercury,  when  it  resembles  ammoniacal  gas  so  closely  as  to  require 
peculiar  attention  to  distinguish  it  from  it. 

Methylammonia  liquefies  at  about  32°,  and  its  odour  is  strongly 
ammoniacal,  while  its  density  is  1.08,  its  chemical  equivalent  CgHN. 
corresponding,  like  that  of  ammonia,  to  4  volumes  of  gas.  Methyl- 
ammoniacal  gas  is  the  most  soluble  of  all  gases  known,  since,  at 
53.6°,  1  volume  of  water  dissolves  1040  volumes  of  it,  while  at  77° 
water  only  takes  up  906.  Like  ammoniacal  gas,  it  is  instantane- 
ously absorbed  by  charcoal,  but  it  is  distinguished  from  the  latter 
gas  by  igniting  by  contact  with  a  lighted  candle  and  burning  with 
a  yellowish  flame.  It  produces,  with  metallic  solutions,  reactions 
precisely  similar  to  those  of  ammonia  or  ethylammonia. 

Amylammonia  Q^^^^  or  Q^^^^Q^H^, 

§  1488.  The  oil  of  potato-spirit  Q^Jl^fi^  exhibits,  as  shall  soon 
be  shown,  a  perfect  analogy  with  vinic  and  methylic  alcohols,  in  the 
products  which  it  forms  with  chemical  agents,  for  which  reason  it 
has  been  called  amylic  alcohol.  If  amylocyanic  or  amylocyanuric 
ether  be  distilled  with  a  solution  of  potassa,  carbonate  of  potassa 
is  obtained,  besides  anew  base,  amylammonia  CjoH^gN,  which  formula 
may  be  written  CjoHj^NHg,  because  carburetted  hydrogen  Cj^Hjo  is, 
in  the  amylic  series,  the  analogue  of  bicarburetted  hydrogen  in  the 
vinic  series.  It  may  be  also  written  CjoHjj(NH3),  if  it  be  consi- 
dered as  resulting  from  the  replacing  of  1  equivalent  of  hydrogen, 
in  the  amylic  molecule  CjoHj^,  by  1  equivalent  of  amide  (NH^). 
Amyl  is  found  in  solution  in  the  water  which  has  passed  over  in  dis- 
tillation ;  by  saturating  which  with  chlorohydric  acid,  white  crys- 
talline lamellae,  soluble  in  water  and  alcohol,  of  cMorohydrate  of 
amylammonia  Q^fi^^^llQ\  are  obtained  after  evaporation.  This 
salt,  distilled  with  quicklime,  yields  amylammonia  in  the  form  of  a 
colourless  liquid,  of  a  strong  ammoniacal  odour,  and  very  soluble  in 
water. 

Amylammonia  precipitates  all  the  metallic  salts  which  are  precipi- 
tated by  ammonia ;  and  with  solutions  of  copper,  it  yields  a  precipi- 
tate which  dissolves  in  an  excess  of  the  reagent  and  colours  the 
liquid  blue :  nevertheless,  to  effect  perfect  solution,  a  larger  propor- 
tion of  amylammonia  must  be  used  than  of  ethylammonia  or  methyl- 
ammonia. Chloride  of  silver  also  dissolves  in  it,  but  less  readily 
than  in  ammonia. 

Amylammonia  forms  with  acids  a  great  number  of  crystallizable 
acids. 


BUTTRYLAMMONIA.  625 

Butyrylammonia  CgHj^N  or  CgHg(NH5j). 

§  1489.  Butyrylammonia  has  not  yet  been  prepared  by  the  gene- 
ral process  which  has  furnished  the  foregoing  volatile  alkaloids ; 
while  among  the  products  of  distillation  of  animal  substances,  several 
volatile  alkaloids  have  been  found,  among  which  one  called  petinin 
CgHjjN  is  distinguished,  presenting  exactly  the  composition  of  buty- 
rylammonia. The  composition  of  this  substance  presents,  in  fact, 
with  that  of  butyric  acid  CgH^OgjHO,  the  relation  which  exists  be- 
tween ethylammonia  C^HyN  and  acetic  acid  C^HgOgjHO.  It  is  a 
colourless  liquid,  of  a  penetrating  ammoniacal  odour,  and  forming 
well-defined  salts  with  acids.  . 


§  1490.  The  resemblance  with  ammonia  of  the  last  volatile  alka- 
loids which  we  have  described,  is  as  perfect  as  that  observed  between 
potassa  and  soda ;  and  their  composition  presents  the  remarkable 
peculiarity,  that  they  may  be  considered  as  formed  by  the  union  of 
1  equivalent  of  ammonia  with  a  carburetted  hydrogen.  The  other 
volatile  alkalies,  either  native  or  artificial,  which  we  have  described, 
exhibit  a  similar  grouping  in  their  composition,  and  should  probably 
be  included  in  a  single  class,  which  will,  certainly,  be  subsequently 
greatly  extended.     Thus  we  have, 

Ammonia* NHg 

Methylammonia l^H^^Q^^y 

Ethylammonia NH3,C4H^, 

Butyrylammonia NHgyCgHg, 

Amylammonia NH3,CioHjq, 

Nicotin NH3,CioH^, 

Anilin... NH3,Ci2H„ 

Conicin....* NH3,Ci8H^, 

Quinolem NH^C^H^. 


OF  SOME  NEUTRAL  SUBSTANCES  FOUND  IN  VEGETABLES. 

§  1491.  In  the  following  chapter  we  shall  describe  certain  sub- 
stances found  in  vegetables,  exhibiting  no  well-marked  characters 
of  acidity  or  alkalinity,  and  which  have  hitherto  not  been  attached 

*  The  first  five  compounds  in  the  above  table  may  be  considered  as  ammonia 
paired  with  respectively  0,  1,2,  4,  and  5  equivalents  of  the  carburetted  hydrogen 
C3H,,  or  defiant  gas ;  which,  according  to  the  theory  of  pairing,  explained  in  the 
note  to  §1401,  would  fully  explain  the  ammoniacal  properties  of  the  paired  com- 
pounds. They  may  also  be  regarded,  with  equal  propriety,  as  ammonias  in  which 
1  equivalent  of  hydrogen  is  replaced  by  1  equivalent  of  the  radicals  methyl,  ethyl, 
Ijutyril,  and  amyl,  ^respectively ;  which  view  has  gained  much  probability  by  the 
recent  investigations  of  Frankland  and  Kolbe. —  W.  L.  F. 
Vol.  IL— 40 


626  INDIFFERENT  SUBSTANCES. 

to  any  of  the  great  series  of  organi^ompounds.  These  substances 
being  very  numerous,  we  shall  only  mention  the  most  important 
and  those  which  are  best  known. 

Piperin  Ca^Hj^NOg. 
§  1492.  Piperin  exists  in  pepper,  and  is  generally  extracted  from 
white  pepper,  by  treating  it  with  alcohol.  The  alcoholic  solution  is 
evaporated,  the  residue  treated  with  an  alkaline  lye,  which  dissolves 
various  substances,  and  leaves  the  piperin  isolated.  It  is  to  be  puri- 
fied by  several  crystallizations  in  alcohol.  Piperin  forms  colourless 
prisms,  which  melt  at  about  212°,  and  is  slightly  soluble  in  water,  but 
very  soluble  in  alcohol.  Acids  dissolve  it  readily,  without  forming  a 
fixed  compound  with  it,  and,  if  they  are  volatile,  they  part  with  it 
wholly  by  evaporation,  which  operation  is  even  effected  at  the  ordinary 
temperature  in  vacuo.  The  composition  of  piperin  corresponds  to  the 
formula  Cg^H^jNOg,  showing  it  to  be  isomeric  with  morphin. 

Picrotoxin  Q^fi^» 
§  1493.  Picrotoxin  is  the  poisonous  principle  of  the  coculus  Indi- 
CU8,  aijd  is  obtained  by  exhausting  these  berries  by  alcohol,  and 
evaporating  the  liquor,  when  a  mixture  of  picrotoxin  with  fatty 
matter  remains  as  a  residue.  The  residue  is  pressed  between  folds 
of  tissue-paper,  and  then  redissolved  in  alcohol,  after  which  the 
liquor  is  bleached  by  animal  black,  and  picrotoxin  obtained,  by 
evaporation,  in  small  acicular  crystals.  Picrotoxin  dissolves  in  25 
parts  of  boiling  water,  the  greater  portion  of  it  being  again  depo- 
sited on  cooling,  while  it  dissolves  readily  in  alcohol.  Picrotoxin 
does  not  combine  with  acids,  and  it  contains  no  nitrogen,  its  com- 
position corresponding  to  the  formula  Cj2HyOj. 

Cantharidin  Q^Jlfi^, 

§1494.  Cantharidin,  the  active  principle  of  cantharides,  possesses 
extremely  powerful  vesicating  properties,  and  if  any  portion  of  the 
body  be  exposed  to  its  vapours,  swelling  accompanied  by  acute 
pain  immediately  ensues.  It  is  obtained  by  treating  powdered  can- 
tharides with  alcohol,  and  evaporating  the  alcohol,  when  an  aqueous 
liquid  remains,  on  which  floats  an  oily  coat,  solidifying  on  cooling. 
This  coat  being  dissolved  in  alcohol  and  discoloured  by  animal 
black,  crystals  of  cantharidin  are  obtained  by  evaporation.  Can- 
tharidin contains  no  nitrogen,  and  its  composition  corresponds  to 
the  formula  C^oHgO^ ;  but  its  equivalent  has  not  yet  been  deter- 
mined, as  no  definite  compound  of  it  is  known.  Cantharidin  is 
insoluble  in  water,  but  dissolves  readily  in  alcohol  and  ether. 

Asparagin  G^^'^fi^.^O, 

§  1495.  The  name  of  asparagin  has  been  given  to  a  crystallizable 
substance,  first  found  in  the  shoots  of  asparagus,  but  which  also 


ASPARAGIN.  627 

exists  in  liquorice-root,  in  marsh-mallow  root,  comfrey,  potatoes, 
vetches,  and  several  other  plants.  It  is  generally  prepared  by 
macerating  bruised  marsh-mallow  roots  with  very  clear  milk  of  lime, 
filtering  the  liquid,  precipitating  the  dissolved  lime  by  carbonate  of 
ammonia,  and  evaporating  to  the  consistence  of  syrup ;  when,  in 
the  course  of  a  few  days,  granular  crystals  of  impure  asparagin 
separate,  which  are  purified  by  recrystallization. 

Asparagin  does  not  originally  exist  in  the  seeds  of  the  vetch,  but 
is  developed  during  germination  and  vegetation,  to  again  disappear 
at  the  flowering  period.  In  order  to  extract  it,  the  plant  is  cut  at 
the  proper  season,  and  the  juice  expressed  and  boiled,  when  albumin- 
ous substances  coagulate  and  are  separated.  The  liquid  being 
evaporated  to  the  consistence  of  syrup,  and  left  to  itself,  deposits 
crystals  of  asparagin,  which  are  purified  by  being  washed  with  cold 
water  and  recrystallized  several  times. 

Asparagin  forms  beautiful  colourless  prismatic  crystals,  requiring 
for  solution  about  60  parts  of  water,  at  the  ordinary  temperature, 
but  dissolving  more  freely  in  boiling  water.  It  is  not  sensibly  solu- 
ble in  absolute  alcohol  or  in  ether.  Its  aqueous  solution  feebly 
reddens  litmus ;  and  when  it  is  poured  into  a  hot  solution  of  acetate 
of  copper,  a  beautifully  blue  precipitate  is  formed,  consisting  of  a 
compound  with  oxide  of  copper,  oflhe  formula  CuO,CgHyN30^. 
The  formula  of  asparagin  dried  at  2]p°  is  CgHgNgOg,  which  should 
be  written  CgH^NgO^jHO  ;  while  the  formula  of  crystallized  aspara- 
gin is  C3H,N,0„HO+2HO. 

A  solution  of  pure  asparagin,  left  to  itself,  remains  unchanged 
for  an  indefinite  length  of  time,  which  is  not  the  case  if  it  contains 
some  of  the  principles  which  accompany  it  in  the  vegetable,  when 
it  undergoes  a  kind  of  fermentation  which  converts  it  into  succinate 
of  ammonia.  If  we  observe  that  1  equivalent  of  succinate  of  am- 
monia is  equal,  in  its  elementary  composition,  to  1  equivalent  of 
asparagin  plus  2  equivalents  of  water  and  2  equivalents  of  hydrogen^ 

2(NH3-fHO),C3H,08=C3H,N308+2HO+2H, 

we  may  admit  that  asparagin  assimilates  to  itself  2  equivalents  of 
water  and  2  equivalents  of  hydrogen,  produced  by  the  putrefaction 
ensuing  in  the  liquid,  which  excites  a  reducing  action  in  nearly  all 
analogous  cases. 

Under  the  influence  of  sulphuric  and  chlorohydric  acid,  and  of 
nitric  free  from  nitrous  acid,  asparagin  is  decomposed  into  ammonia 
and  a  new  acid,  called  aspartic  CgH5NOg,2HO,  which  is  very  slightly 
soluble  in  water,  but  readily  so  in  the  acids,  with  which  it  afterward 
parts  with  difi&culty  by  evaporation.  It  crystallizes  in  small  pearly 
leaflets;  and  may  also  be  obtained  by  boiling  asparagin  with  a 
solution  of  potassa,  when  ammonia  is  disengaged,  and  the  liquor 
contains  aspartate  of  potassa, 

CsH3N.Oe+2HO=C3H,N08,2HO-fNH,. 


^28  INDIFFERENT   SUBSTANCES. 

If  asparagin  he  treated  with  nitric  a|!id  containing  nitrous  acid, 
a  considerable  quantity  of  bimalate  of  ammonia  (NHgjHO-j-HO), 
CgH^Og  is  formed,  nitrogen  being  disengaged  at  the  same  time. 
Under  the  influence  of  the  nitric  acid,  the  asparagin  is  converted 
into  aspartic  acid  and  ammonia,  while  the  ammonia  has  been  con- 
sumed by  the  nitrous  acid,  yielding  water  and  free  nitrogen ;  and 
the  aspartic  acid,  having  combined  with  2  equivalents  of  water  in 
the  nascent  state,  has  been  changed  into  bimalate  of  ammonia, 
according  to  the  equation, 

C3H,N0«,2H0+2H0=(NH„H0+H0),C3H,03. 

It  is  proper  to  observe  that  aspartic  acid  and  asparagin  may  be 
considered  as  malic  acid,  united  to  1  or  2  equivalents  of  ammonia 
NHg ;  that  is,  as  two  amides  of  malic  acid.  This  view  of  the  con- 
stitution of  these  substances  is  corroborated  by  the  fact  that  the  other 
amides,  such  as  oxamide,  butyr amide,  etc.,  yield,  with  nitric  charged 
with  nitrous  acid,  decompositions  analogous  to  those  produced  by  as- 
partic acid  and  asparagin,  and  are  converted  into  oxalic,  butyric  acid, 
etc.,  with  disengagement  of  nitrogen. 

PMoridzin  Cj^HjgO^. 

§  1496.  Phloridzin  exists  in  the  fresh  bark  of  the  apple,  pear, 
plum,  and  cherry  tree,  and  is  generally  extracted  from  the  bark  of 
the  roots  of  the  apple,  by  digesting  it  in  weak  alcohol,  when  t^ 
phloridzin  dissolves  and  separates  by  evaporation  in  silky  acicu 
which  are  purified  by  recrystallization  in  alcohol.     Boiling  watt 
dissolves  a  large  quantity  of  phloridzin,  while  it  scarcely  retains 
Y5^  part  of  it  after  cooling ;  and  alcohol  dissolves  it  readily,  the 
solution  exerting  no  reaction  on  litmus.      The  solution   of  phlo- 
ridzin in  alcohol  exerts  a  rotatory  power  toward  the  left.     It  loses 
water  when  heated,  and  is  subsequently  decomposed  at  about  392°. 
Dilute  mineral  acids  dissolve  phloridzin  when  cold,  while  if  heat  be 
applied  the  liquid  becomes  clouded,  and  deposits  a  new  substance, 
phloretin  CjaH^Og,  which  is  obtained  in  crystalline  lamellae  by  solu- 
lution  in  alcohol. 

(S-lyeyrrhizin  03eH230ia52HO. 

§  1497.  This  name  has  been  given  to  a  sweet  substance  found  in 
the  aqueous  extract  of  liquorice-root,  {glycyrrhiza glabra,)  from  which 
it  is  extracted  by  adding  to  th^  concentrated  liquid  almost  any 
acid,  which  yields  a  flaky  precipitate  collecting  into  a  tarry  mass. 
This  substance,  when  dried,  is  dissolved  in  absolute  alcohol,  which 
again  deposits  it,  by  eva>poration,  in  the  form  of  an  amorphous 
brownish-yellow  mass.  Glycyrrhizin  is  but  slightly  soluble  in  cold 
water,  and  nearly  insoluble  when  the  water  contains  an  acid ;  while 
it  dissolves  freely  in  absolute  alcohol,  but  is  insoluble  in  ether. 
Analysis  has  assigned  to  it  the  formula  C3gH230i2,2H0,  and  its  so- 
lution produces,  with  acetate  of  lead,  a  precipitate  of  the  formula 
2PbO,C„H^O„. 


j^ 


NITRILS.  629 

NITRILS. 

§  1498.  By  causing  anhydrous  phosphoric  acid  to  act  on  the  am- 
moniacal  salts  formed  by  the  organic  acids,  or  on  the  corresponding 
amides,  a  new  class  of  substances,  called  nitrils,  is  obtained,  the  com- 
position of  which  may  be  represented  by  cyanhydrates  of  carburetted 
hydrogen,  and  which  regenerate,  by  the  action  of  the  alkalies,  the 
acid  of  the  original  ammoniacal  salt,  by  seizing  on  the  water  and 
disengaging  ammonia.  We  shall  give  some  examples  of  their  curi- 
ous reactions. 

Acetonitril  C^HgN. 

§  1499.  By  heating  crystallized  acetate  of  ammonia  with  anhydrous 
phosphoric  acid,  a  liquid  is  obtained  soluble  in  water  in  all  proportions. 
In  order  to  purify  it,  it  is  first  digested  over  chloride  of  calcium,  and 
then  distilled  successively  over  chloride  of  calcium  and  erfcined  mag- 
nesia. The  liquid,  which  is  called  acetonitril^'^  boils  at  170.6°,  and 
its  formula  C^HgN  corresponds  to  4  vol.  of  vapour.  In  contact 
with  hydrated  potassa,  ammonia  and  acetic  acid  are  regenerated ; 

C,H3N+4HO=C,H303,HO+NH3. 

Potassium  decomposes  it  when  cold,  cyanide  of  potassium  being 
formed,  and  a  mixture  of  hydrogen  and  carburetted  hydrogen  dis- 
engaged. 

Acetonitril  appears  to  be  identical  with  methylocyanohydric  ether 
CgHgjCaN,  but  alkalies  do  not  act  upon  it  as  upon  other  compound 
ethers,  since  they  convert  it  into  acetic  acid  and  ammonia. 

Acetonitril  is  also  produced  when  acetamide  C4H302,NH3  is  heated 
with  anhydrous  phosphoric  acid.  Acetamide,  which  is  obtained  by 
treating  acetic  ether  with  ammonia,  is  white,  and  crystallizes  in 
prismatic  aciculae,  melting  at  172.4°,  and  boiling  at  about  428°. 

Chloracetate  of  ammonia  (NH3,H0),C4Cl303  and  chloracetamide 
C^CljOajNHg  furnish,  with  anhydrous  phosphoric  acid,  perchlori- 
nated  acetonitril  C4CI3N,  which  boils  at  177.8°,  and  yields  chlora- 
cetic  acid,  when  the  corresponding  compound  forms  acetic  acid. 

Butyronitril  CgHyN. 
§  1500.  The  butyrate  of  ammonia  and  butyramide,  heated  with 
anhydrous  phosphoric  acid,  yield  butyronitril  CgH^N,  an  oily  liquid, 
boiling  at  245.3°,  and  which  potassium  converts  into  cyamide  of 
potassium,  hydrogen,  and  a  new  carburetted  hydrogen.  Its  for- 
mula CgHyN  corresponds  to  4  vol.  of  vapour. 

Valeronitril,  CjoHgN. 
§  1501.  Valeramide,  heated  with  anhydrous  phosphoric  acid,  pro- 
duces valeronitril  CjoHgNja  colourless  liquid,  boiling  at  257°,  which 
is  decomposed  by  potassium,  when  cold,  into  cyanide,  hydrogen, 
and  a  new  carburetted  hydrogen. 

*  It  may  be  termed  methyooyanhydrio  acid. — J.C.B. 


630  DERIVATIVES   OF   CYANOGEN. 

PRODUCTS  OF  CYAI^GEN. 

§  1502.  Cyanogen  is  always  a  product  of  the  decomposition  by 
heat,  in  the  presence  of  alkalies,  of  nitrogenous  organic  substances. 
Its  study,  and  that  of  its  numerous  derivatives,  should  therefore  find 
a  place  among  substances  of  the  organic  kingdom ;  but  its  compounds 
play  too  considerable  a  part  in  chemical  processes  and  are  too  fre- 
quently used  in  the  examination  of  the  salts  of  various  metals  to 
allow  us  to  postpone  their  consideration  until  the  end  of  the  course. 
These  reasons  have  induced  us  to  describe,  in  the  first  part  of  our 
course,  cyanogen  and  its  compound  with  hydrogen,  cyanohydric 
acid.  We  have  seen  that  cyanogen  behaves,  in  its  compounds,  like 
the  simple  metalloid  substances,  particularly  like  chlorine,  and  we 
have  described  in  detail  the  principal  compounds  it  forms  with  the 
metals,  the  simple  and  multiple  cyanides,  which  are  very  important 
compounds,  both  on  account  of  their  use  in  dyeing,  and  in  chemical 
analysis.  It  still  remains  to  us  to  describe  the  compounds  of  cya- 
nogen with  several  metalloids,  chlorine,  iodine,  oxygen,  sulphur,  and 
several  more  complicated  combinations,  which  present  some  points  of 
peculiar  interest  for  our  chemical  theories. 

COMPOUNDS  OF  CYANOGEN  WITH  CHLORINE. 

§  1503.  As  yet  only  two  compounds  of  cyanogen  with  chlorine 
are  known,  the  elementary  composition  of  which  is  exactly  the  same, 
while  their  properties  are  wholly  difierent,  one  of  the  compounds 
being  gaseous  at  the  ordinary  temperature  of  our  climate,  and  the 
other  solid  and  boiling  only  at  about  390°.  The  gaseous  chloride 
of  cyanogen  CyCl  or  C3NCI  is  obtained  by  causing  chlorine  to  act 
on  moist  cyanide  of  mercury,  which  reaction  is  expressed  by  the  fol- 
lowing equation ; 

HgCy4-2Cl=HgCH-CyCl. 

It  is  also  prepared  by  passing  a  current  of  chlorine  through  a 
concentrated  solution  of  cyanohydric  acid,  when  the  gaseous  chlo- 
ride of  cyanogen  remains  in  solution,  and  may  be  disengaged  by 
gently  heating  the  liquid,  the  gas  being  dried  by  passing  it  over 
chloride  of  calcium.  It  is  a  colourless  gas,  of  a  strong  odour,  caus- 
ing tears,  liquefying  at  about  10.4°,  and  solidifying  at  -—0.4°. 
Thus,  this  substance  passes  through  three  states  in  a  very  small 
change  of  temperature.  Water  dissolves  about  25  times  its  vol., 
and  alcohol  and  ether  50  times  its  vol.  of  it.  Liquid  chloride  of  cy- 
anogen soon  passes  into  the  solid  modification,  called  solid  chloride 
of  cyanogen.  If,  in  fact,  it  be  enclosed  in  a  glass  tube  hermeti- 
cally sealed,  it  undergoes  at  first  no  change,  and  if  the  tube  be 
broken,  it  is  wholly  evolved  in  the  gaseous  state,  while,  in  a  few  days, 
long  prismatic  crystals,  ultimately  occupying  the  whole  mass,  will 
be  found  to  be  developed.     If  the  tube  be  then  broken,  no  gas  is 


CYANURIC   ACID.  631 

disengaged,  and  we  find  only  crystals  melting  at  284°,  and  boiling 
at  374°.  Solid  chloride  of  cyanogen  is  directly  formed,  when  an- 
hydrous prussic  acid  is  poured  into  a  large  bottle  filled  with  dry 
chlorine  and  exposed  to  the  sun.  The  density  of  the  vapour  of 
solid  chloride  of  cyanogen  is  three  times  greater  than  that  of  the 
gaseous  chloride,  for  which  reason  the  formula  CyCl  has  been  as- 
signed to  the  gaseous  chloride,  and  the  formula  CygClg  to  the  solid. 
The  equivalents  of  these  substances  are  therefore  represented  by  4 
gaseous  volumes. 

The  two  chlorides  of  cyanogen  combine  directly  with  ammoniacal 
gas,  and  form  solid  compounds,  of  which  the  formulae  are, 

For  the  gaseous  chloride 2NH3,CyCl. 

"       solid  chloride 3NH3,Cy3Cl,. 

The  first  is  soluble  in  water,  and  the  second  is  insoluble. 
Two  compounds  of  cyanogen  with  bromine  and  iodine  are  also 
known. 

COMPOUNDS  OF  CYANOGEN  WITH  OXYGEN. 

§  1504.  Four  isomeric  compounds  of  cyanogen  and  oxygen  are 
known,  cyanic  acid,  cyanuric  acid,  cyamelide,  Sbud  fulminic  acid,  the 
first  two  of  which  appear  to  present  the  same  relations  of  constitu- 
tion as  the  gaseous  and  solid  chlorides  of  cyanogen. 

By  digesting  solid  chloride  of  cyanogen  with  water,  chlorohydric 
acid  and  a  solid  white  substance,  cyanuric  acid  Gjfi^,  are  formed : 

Cy3Cl,+SHO=3HCl+Cy30,. 

The  same  compound  is  found  under  many  other  circumstances,  and 
particularly  when  certain  substances  of  animal  origin  are  decom- 
posed. A  solution  of  the  substance  in  hot  water  again  deposits  it,  on 
cooling,  in  crystals,  which  are  hydrated  and  present  the  formula  Cjfi^, 
7H0,  while,  when  dried  at  212°,  the  formula  becomes  Cy3033HO  ; 
that  deposited  from  a  nitric  or  chlorohydric  solution  also  present- 
ing the  latter  composition.  The  3  equiv.  of  water  are  basic,  and  may 
be  replaced  partially  or  wholly  by  an  equivalent  quantity  of  base ; 
and,  in  fact,  three  series  of  cyanides  are  known,  of  which  the  general 
formulae  are 

(RO+2HO),Cy30„    (2RO+HO),Cy30„    SRCCy^O,. 

Cyanuric  is  therefore  a  tribasic  acid. 

Cyanuric  acid,  heated  in  a  small  glass  retort,  passes  over  wholly 
in  distillation,  but  is  then  deeply  changed,  for  the  distilled  product 
forms  a  very  volatile  liquid,  of  an  odour  resembling  concentrated 
acetic  acid,  and  which  reddens  litmus  and  behaves  like  a  powerful 
acid.  Its  composition  is  the  same  as  that  of  cyanuric  acid  dried 
at  212°,  but  it  forms  only  one  series  of  salts,  and  should  be  con- 
sidered as  a  monobasic  acid.     The   formula  CyO,HO   has  been 


632  DERIVATIVES   OF   CYANOGEN. 

assigned  to  this  acid,  called  cyanic,  and  to  its  salts  the  general 
formula  RO,CyO. 

Cyanic  acid  is  spontaneously  converted  into  an  isomeric  substance, 
called  cyamelide,  while  the  transformation  does  not  take  place  so 
long  as  the  cyanic  acid  is  kept  at  a  very  low  temperature ;  but,  at 
the  ordinary  temperature,  the  liquid  soon  becomes  clouded,  while  at 
the  same  time  its  temperature  rises  spontaneously,  and  it  is  con- 
verted into  a  solid  mass,  resembling  porcelain.  This  is  cyamelide, 
a  wholly  neutral  substance,  insoluble  in  water,  alcohol,  and  ether, 
and  which  reproduces  the  original  cyanic  acid  by  distillation. 

Cyanic  acid  may  also  be  transformed,  directly,  into  cyanuric  acid, 
by  adding  a  small  quantity  of  nitric  or  acetic  acid  to  a  concentrated 
'Solution  of  cyanate  of  potassa,  which  converts  the  salt  into  cyanurate. 

Cyanic  acid  may  be  prepared,  directly,  in  several  ways : 

1.  By  passing  cyanogen  gas  through  a  solution  of  potassa  or  car- 
bonate of  potassa,  cyanate  of  potassa  and  cyanide  of  potassium  are 
formed,  the  reaction  being  similar  to  that  of  chlorine  on  alkaline 
lixivise,  when  it  converts  them  into  hypochlorites,  (§  450) : 

2KO+2Cy=KO,CyO+KCy. 

2.  By  heating  a  mixture  of  prussiate  of  potash  and  nitrate  of 
potassa  or  peroxide  of  manganese,  when  cyanic  acid  passes  over 
in  distillation.  The  mixture  may  also  be  roasted  in  the  air,  and 
then  treated  with  boiling  alcohol,  which  dissolves  the  cyanate  of 
potassa. 

3.  By  fusing  yellow  prussiate  of  potash  at  a  red-heat,  and  throw- 
ing litharge  into  the  melted  mass  as  long  as  the  former  is  reduced. 
Boiling  alcohol  then  dissolves  the  cyanate  of  potassa  formed. 

The  fourth  isomeric  modification  of  cyanic  acid,  fulminic  acidy 
is  formed  under  quite  peculiar  conditions.  Mercury  or  silver  being 
treated  with  a  mixture  of  alcohol  and  nitric  acid,  a  very  powerful 
reaction  ensues,  and  various  products  of  the  oxidation  of  alcohol 
pass  into  the  receiver,  among  which  may  be  distinguished  aldehyde, 
acetic  acid,  formic  acid,  and  nitrous,  acetic,  and  formic  ethers.  A 
crystalline  salt,  which  is  the  fulminate  of  mercury  or  silver,  is  de- 
posited in  the  retort. 

The  composition  of  fulminic  acid  is  the  same  as  that  of  cyanic 
and  cyanuric  acids,  but  it  is  a  bibasic  acid,  the  formula  of  which, 
should  be  written  Cy203,2H0,  since  it  forms,  in  fact,  two  series  of 
salts,  of  which  the  general  formulae  are  (R0+H0),Cy203  and  2R0, 
CygOg.  The  formulae  of  the  fulminates  of  mercury  and  silver  are 
2HgO,Cy203  and  SAgOjCyaOg*,  and  by  treating  the  fulminate  of  sil- 
ver with  potassa,  only  one-half  of  the  silver  is  precipitated,  while 
a  double  fulminate,  of  the  formula  (Ag0-|-K0),Cy303,  is  obtained. 

The  dry  fulminates  detonate  with  extreme  violence,  either  by 
percussion  or  when  heated.  Fulminate  of  mercury  is  used  in  the 
manufacture  of  percussion  caps  for  firearms. 


SULPHOCYANIDES.  633 

They  are  prepared  on  a  large  scale,  by  dissolving  1  part  of  mer- 
cury in  12  of  nitric  acid  of  a  density  of  1.36,  adding  to  the  solution 
11  parts  of  alcohol  at  0.80,  and  then  gently  heating  the  mixture  in 
a  distilling  apparatus,  in  order  to  condense  the  disengaged  volatile 
•products,  which  may  be  used  in  another  operation.  The  liquid 
remaining  in  the  retort  deposits  the  fulminate  on  cooling. 

Metallic  SulphooyanideB  and  Sulphocyanohydrie  Acid. 

§  1505.  By  heating  to  a  dull-red  an  intimate  mixture  of  2  parta 
of  prussiate  of  potash  and  1  part  of  sulphur,  and  then  treating  it 
with  boiling  alcohol,  sulphocyanide  of  potassium  KS,CyS  is  depo- 
sited in  small  crystalline  aciculae ;  and  it  may  be  regarded  as  a 
cyanate  of  potassa,  in  which  the  oxygen  of  the  acid  and  the  base 
is  replaced  by  a  corresponding  quantity  of  sulphur.  A  larger  quan- 
tity is  obtained  by  heating  46  parts  of  prussiate  of  potash,  17  parts 
of  carbonate  of  potassa,  and  16  of  sulphur,  and  treating  the  mass 
with  boiling  alcohol. 

If  sulphocyanide  of  potassium  be  distilled  with  phosphoric  acid, 
sulphoeyanohydric  acid  CyS,HS  is  obtained,  a  large  proportion  of 
which  is,  however,  decomposed.  Acetate  of  lead  may  also  be 
poured  into  the  solution  of  the  sulphocyanide  of  potassium,  when 
sulphocyanide  of  lead  PbS,CyS  is  precipitated,  and  is  decomposed 
by  sulf  hydric  acid,  a  colourless  acid  liquor,  reddening  litmus,  being 
formed. 

Free  sulphocyanohydrie  acid,  and  the  alkaline  sulphocyanides, 
yield,  with  sesquisalts  of  iron,  precipitates  of  a  blood-red  colour, 
which  reaction  is  often  used  to  detect  these  salts. 

By  pouring  into  a  solution  of  an  alkaline  sulphocyanide,  6  or  8 
times  its  volume  of  concentrated  chlorohydric  acid,  a  deposit  of 
small  white  aciculae  is  formed,  which  are  to  be  washed  with  a  small 
quantity  of  cold  water.  It  is  a  new  acid,  called  persulphocyanohy- 
dric,  of  the  formula  Cy 8^,118.  This  acid  may  be  dissolved  in  boiling 
water,  and  is  deposited  from  it,  on  cooling,  in  small  crystalline  aci- 
culae. It  is  a  feeble  acid,  which  combines  directly,  without  altera- 
tion, under  certain  conditions,  while  under  other  conditions  it  is 
decomposed.  Persulphocyanohydric  acid,  and  sulphocyanohydrate 
of  ammonia,  yield,  when  heated,  a  great  number  of  new  substances, 
as  yet  but  imperfectly  known. 


634  ESSENTIAL   OILS. 


ESSENTIAL  OILS. 

§  1506.  A  large  number  of  volatile  substances,  possessing  gene- 
rally a  powerful  and  frequently  an  agreeable  odour,  adapting  them 
for  the  toilet,  are  extracted  from  vegetables ;  and  the  greater  por- 
tion of  them  are  liquid,  while  some  are  solid  at  the  ordinary  temper- 
ature. These  substances  are  in  general  prepared  by  expressing 
the  juice  of  the  vegetables  which  contain  them,  and  distilling  it  with 
water,  when  the  essential  oil  passes  over  with  the  water,  and,  as  it 
is  generally  less  volatile  than  the  latter,  the  proportion  which  passes 
over,  compared  with  the  quantity  of  water,  is  the  greater  as  the 
difference  between  the  boiling  point  of  water  and  that  of  the  oil  is 
less.  Parts  of  the  vegetables  themselves,  the  flowers  for  example, 
are  frequently  distilled  with  water,  and  when  the  essential  oil  is 
lighter  than  water,  the  products  are  collected  in  a  bottle  of  peculiar 
shape,  (fig.  684,)  called  aflorence  receiver.  The  bottle  is 
conical,  and  has  a  lateral  tube  communicating  with  the  bot- 
tom, and  of  which  the  orifice  is  at  a  lower  level  than  the 
mouth  a  of  the  bottle.  The  water  and  oil  distilled  pass 
into  the  bottle  through  the  mouth  a,  the  oil  forming  the 
upper  stratum ;  and  when  the  bottle  is  filled  above  the 
level  of  the  orifice  c,  the  water  escapes  through  the  lat- 
ter, and  the  essential  oil  floats  on  its  surface,  in  a  layer 
of  a  thickness  in  proportion  to  the  diameter  of  the  neck 
Eig.  684.  q£  ^-^q  bottle,  and  which  is  removed  from  time  to  time 
with  a  pipette.  An  ordinary  alembic  is  used  for  distillation,  but 
the  vegetables  subjected  to  the  operation  must  not  be  allowed  to 
reach  a  temperature  above  212°,  in  order  to  avoid  the  generation  of 
empyreumatic  products,  which,  distilling  at  the  same  time  as  the 
essential  oil,  would  injure  its  flavour.  In  order  to  prevent  these 
accidents,  the  vegetables  are  placed  in  bags,  or  metallic  vessels 
pierced  with  holes,  and  kept  above  the  liquid  in  the  cucurbit,  in  the 
space  traversed  by  the  vapour. 

As  the  water  which  has  distilled  over  with  the  essential  oil  gene- 
rally dissolves  a  small  quantity  of  it,  sufficient  to  impart  to  it  its 
odour,  it  is  carefully  collected  and  sold.  Thus,  while  distilling 
orange-flowers  with  water,  a  certain  quantity  of  essence  of  orange- 
flower  collects  at  the  top  of  the  florence  receiver,  while  a  water, 
possessing  a  very  agreeable  smell,  and  which  is  sold  under  the  name 
of  orange-flower  water,  is  found  under  it. 

The  quantity  of  essential  oil  which  exists  in  the  portions  of  vege- 
tables subjected  to  distillation  is  frequently  so  small  that  no  sepa- 
rate oil  can  be  obtained,  but  only  an  odoriferous  water.     The  same 


TERPENTINE.  6^5 

thing  occurs  when  the  boiling  point  of  the  essential  oil  is  very  high ; 
and  in  the  latter  case,  the  fresh  water  in  the  cucurbit  is  replaced 
by  water  saturated  with  salt,  which  boils  at  230°,  and  the  vessel 
containing  the  flowers  is  suspended  in  this  water ;  when  the  tension 
of  the  vapour  of  the  oil  is  necessarily  greater  in  this  hotter  space, 
and  a  larger  quantity  of  it  passes  over. 

Some  essential  oils  would  be  very  easily  injured  by  heat,  and  at 
other  times  the  flowers  in  which  they  exist  contain  alterable  princi- 
ples, and  the  distilled  oil  is  far  from  possessing  the  odour  of  the 
flower.  They  are  then  not  distilled,  and  we  are  satisfied  with  sepa- 
rating the  oil  by  dissolving  it  in  a  fixed  oil,  of  itself  inodorous, 
poppy-oil  for  example ;  for  which  purpose  the  flowers  are  spread 
thinly  over  woollen  cloths  soaked  in  poppy-oil,  when  the  cloths  are 
piled  on. each  other,  and  the  whole  placed  under  a  press. 

Essential  oils  difier  materially  from  each  other,  both  in  their  com- 
position and  chemical  reactions ;  and,  if  due  regard  be  paid  to  the 
nature  of  the  compounds  from  which  they  are  derived,  we  are  led  to 
divide  them  among  those  series  most  differing  from  organic  bodies. 
A  great  number  of  oils  contain  only  carbon  and  hydrogen,  while 
others  also  contain  oxygen,  and,  lastly,  some  few  contain  sulphur. 
We  shall  therefore  divide  them  into  three  groups,  and  include  in  the 
first,  those  oils  which  are  composed  of  hydrogen  and  carbon  alone ; 
in  the  second,  those  which  contain,  in  addition,  oxygen ;  and  in  the 
third,  the  sulphuretted  essential  oils. 

HYDROCARBURETTED  ESSENTIAL  OILS. 

§  1507.  The  composition  of  the  greater  number  of  these  oils  cor- 
responds to  the  formula  C^H^,  and  we  therefore  here  find  a  great 
number  of  isomeric  substances,  the  chemical  properties  of  which  are 
so  similar  that  recourse  must  be  had  to  very  delicate  characters  to 
prove  their  non-identity.  The  mobility  of  their  molecular  constitu- 
tion is  such,  that  by  distilling,  or  forming  them  into  compounds 
from  which  they  are  subsequently  separated,  their  nature  is  changed. 

Essential  Oil  of  Terpentine  or  Terehethene  CgoHjg. 

§  1508.  This  is  the  most  important  of  the  essential  oils,  on  ac- 
count of  its  application  in  the  arts,  being  used  in  the  preparation 
of  varnishes,  and,  i;i  general,  as  a  solvent  for  certain  substances, 
which  it  deposits,  by  spontaneous  evaporation,  on  the  surface  of 
bodies  coated  with  the  solution. 

A  viscous  substance,  called  terpentine,  consisting  essentially  of  a 
resin,  colophony,  or  common  resin  dissolved  in  oil  of  terpentine, 
exudes  from  the  trees  of  the  family  of  the  coniferse,  chiefly  from  the 
pines.  By  distilling  terpentine  with  water,  the  greater  portion  of  the 
essential  oil  is  carried  over  by  the  vapour  of  water,  in  which  state  it 
still  contains  a  small  quantity  of  resin,  partly  formed  by  the  oxida- 
tion of  the  oil  by  contact  with  the  air.  In  order  to  purify  it,  it  is 
again  distilled  with  water,  dried  by  leaving  it  for  some  time  over 


ESSENTIAL   OILS. 

chloride  of  calcium,  and  again  distilled  for  the  last  time  by  itself, 
avoiding  as  much  as  possible  the  contact  of  the  air. 

The  essential  oil  extracted  from  the  various  terpentines  of  com^ 
merce  is  far  from  being  identical,  and  appears  to  vary  according  to 
the  tree  which  has  produced  it.  French  oil  of  terpentine,  produced 
by  the  pinus  maritima  which  grows  in  the  south  of  France,  is  a 
colourless,  very  volatile  liquid,  of  a  characteristic  smell  and  an 
acrid  and  burning  taste.  Its  density  at  32°  is  0.875,  while  the 
density  of  its  vapour  is  4.76  ;  and  if  it  be  admitted  that  its  equiva^ 
lent  is  represented  by  4  volumes  of  vapour,  like  that  of  the  carbu^ 
retted  hydrogen  hitherto  described,  its  formula  should  be  written 
CgoHjg.  Oil  of  terpentine,  which  we  shall  call,  for  brevity's  sake, 
terehenthen^"^  boils  at  about  300°,  the  boiling  point  being  rarely 
constant.  It  deviates  polarized  light  to  the  left,  while  the  various 
oils  differ  from  each  other  in  the  intensity  of  their  rotatory  power ; 
some  even  producing  deviation  to  the  right,  as  the  oil  extracted 
from  the  pinus  tada  of  Carolina,  which  is  chiefly  used  in  England. 
Moreover,  the  same  terebenthen  does  not  maintain  an  identical 
rotatory  power  when  it  is  subjected  to  successive  distillations, 
and  its  molecular  constitution  appears  to  be  modified  by  the  simple 
process  of  distillation ;  these  modifications  being  much  more  decided 
when  the  distillation  is  effected  under  high  pressure,  and,  conse- 
quently, at  a  more  elevated  temperature.  An  oil  of  terpentine 
having  been  kept  boiling,  for  several  hours,  under  a  pressure  of  8 
or  10  atmospheres,  more  than  one-half  of  it  was  converted  into  an 
isomeric  product  which  did  not  boil  under  464°. 

Terebenthen  dissolves  but  slightly  in  water,  communicating  to 
it,  however,  its  characteristic  odour ;  and  it  dissolves  freely  in  alco- 
hol, ether,  and  the  fixed  oils.  It  dissolves  a  large  proportion  of 
sulphur,  phosphorus,  and  several  organic  compounds. 

§  1509.  Terebenthen,  left  for  a  long  time  in  contact  with  water, 
deposits  colourless  crystals,  which  have  been  improperly  called  hy- 
drate  of  terebentheriy  because  their  composition  corresponds  to  the 
formula  C^B.^^6110,  A  much  larger  quantity  of  this  compound  is 
obtained  by  leaving  a  mixture  of  8  parts  of  oil  of  terpentine,  2 
parts  of  ordinary  nitric  acid,  and  1  part  of  alcohol  at  0.80,  to  itself 
for  several  months,  during  which  time  it  is  frequently  shaken; 
when  a  crystalline  magma  is  formed,  which  is  expressed  between 
tissue-paper,  and  redissolved  in  boiling  water,  from  which  it  is  de- 
posited in  small  prismatic  crystals  on  cooling.  By  redissolving  it 
in  boiling  alcohol,  it  yields  large  crystals,  which  melt  at  217.4°, 
^hile,  at  a  more  elevated  temperature,  they  lose  2  equivalents  of 
water,  and  form  a  new  hydrate  C^11^q,4:H0,  which  distils  at  about 
482°  without  change.  The  density  of  its  vapour  being  6.26,  the 
equivalent  C2oHjg,4HO  is  represented  by  2  volumes. 

*  galled  Camphine  in  the  U.  S.,  when  purified  by  distillation. — J,  C.  B. 


TERPENTINE.  637 

§  1510.  Terebenthen  combines  readily  with  cHorohydric  acid 
gas,  and  absorbs  large  quantities  of  it,  with  elevation  of  temperar- 
ture,  the  saturated  liquid  depositing  crystals,  on  cooling,  varying 
in  proportion  according  to  the  nature  of  the  oil,  and  which  are 
purified  by  recrystallization  in  boiling  alcohol.  The  crystals  melt  at 
302°,  the  substance  boiling  at  about  338°,  with  partial  decomposi- 
tion ;  and  its  composition  corresponds  to  the  formula  C^oH^gHCl, 
showing  it  to  be  a  MoroJiydrate  of  terebenthen^  which  is  some- 
times called  artificial  camphor :  it  deviates  the  plane  of  polariza- 
tion to  the  left.  The  liquid  which  floats  on  the  crystals,  in  the 
preparation  of  artificial  camphor,  is  itself  a  liquid  chlorohydrate  of 
terebenthen^  of  the  same  composition  as  the  solid  chlorohydrate, 
but  which  does  not  solidify  at  any  temperature. 

If  solid  chlorohydrate  of  terebenthen  be  passed  over  caustic 
lime  heated  to  redness,  a  liquid  carburetted  hydrogen  separates 
from  it,  having  the  same  composition  and  boiling  point  as  the  ori- 
ginal terebenthen,  but  difi"ering  from  it  by  exerting  no  action  on 
polarized  light :  it  has  been  called  camphilen.  It  also  combines  with 
gaseous  chlorohydric  acid,  yielding,  at  the  same  time,  a  solid  and  a 
liquid  chlorohydrate  ;  and  it  is  therefore  composed  of  at  least  two 
distinct  liquids,  like  terebenthen  itself.  By  decomposing  the 
liquid  chlorohydrate  of  terebenthen  by  means  of  lime,  an  essen- 
tial oil  is  separated  having  no  action  on  polarized  light,  and  yield- 
ing only  liquid  chlorohydrate  with  chlorohydric  acid,  which  new  oil 
has  been  called  terebilen,  Bromohydric  and  iodohydric  acids  pro- 
duce compounds  similar  to  those  of  chlorohydric  acid. 

§  1511.  Terebenthen  undergoes  very  curious  isomeric  modifica- 
tions by  contact  with  sulphuric  acid.  By  mixing,  in  a  well-cooled 
flask,  oil  of  terpentine  with  about  ^  of  its  weight  of  sulphuric  acid, 
and  leaving  the  mixture  to  itself  during  24  hours,  shaking  it  fre- 
quently, a  red  and  viscous  liquid  is  obtained ;  and  after  allowing  it 
to  rest  for  some  time,  the  supernatant  oil  is  decanted,  when  a  black 
residue,  saturated  with  acid,  remains  in  the  flask.  If  the  decanted 
oil  be  distilled,  a  small  quantity  of  sulphurous  acid  first  passes  over, 
and  then  an  essential  oil,  having  the  same  composition,  density,  and 
boiling  point  as  terebenthen,  but  differing  from  it  in  exerting  no 
rotatory  power  on  polarized  light,  and  in  forming  with  chlorohy- 
dric acid  gas  a  compound  of  the  formula  2Cj5oHjq,HC1,  which  con- 
sequently contains  one-half  less  chlorohydric  acid  than  the  chlo- 
rohydrate of  terebenthen.  This  essential  oil  has  been  called 
tereben. 

The  essential  oil  modified  by  sulphuric  acid  is  not  solely  com- 
posed of  tereben,  and  when  it  has  separated  by  distillation,  and  the 
temperature  is  raised  to  590°,  a  new  product  is  obtained,  composed 
of  a  viscous  oil,  which  is  bleached  by  being  distilled  over  an  alloy 
of  potassium  and  antimony,  (§  1 017).  This  liquid  is  highly  dichroic  ; 
light  which  passes  through  it  normally  being  colourless,  while  that 


638  ESSENTIAL   OILS. 

obliquely  refracted  by  it,  particularly  at  certain  angles  of  incidence, 
exhibits  a  beautiful  indigo  colour.  Its  density  is  0.940  at  48.2°, 
and  it  has  no  rotatory  power.  It  absorbs  chlorohydric  acid  gas, 
but  without  forming  any  fixed  compound,  for  carbonate  of  lime 
readily  abstracts  the  chlorohydric  acid.  The  name  of  colophen 
has  been  given  to  this  gas,  the  composition  of  which  is  the  same  as 
that  of  terebenthen  ;  and  large  quantities  of  it  are  obtained  by 
the  direct  distillation  of  resin. 

Chlorine  acts  powerfully  on  terebenthen  and  its  isomeric  com- 
pounds, chlorohydric  acid  being  disengaged,  while  a  viscous,  co- 
lourless liquid  is  formed,  having  the  smell  of  camphor,  and  which 
is  quadrichlorinated  terebenthen,  its  formula  being  CgoH^gCl^. 

Oil  of  Lemons,  or  Citrene  C^^^q. 

§  1512.  Lemon-peel  contains  an  agreeable-smelling  essential  oil, 
of  an  identical  composition  with  terebenthen,  and  which  we  shall  call 
citren.  It  may  be  extracted  by  expressing  the  yellow  part  of  the 
lemon  peel,  but  it  is  more  generally  separated  by  distilling  the  peel 
with  water,  in  which  case  the  smell  of  the  oil  is,  however,  less 
grateful.  Citren  boils  at  about  338°,  and  its  density  is  0.847  at 
71.6°,  while  the  density  of  its  vapour  is  the  same  as  that  of  tere- 
benthen, for  which  reason  it  has  received  the  same  formula  Cg^H^g ; 
but  it  polarizes  to  the  right.  It  combines  with  chlorohydric  gas 
forming  a  liquid  and  a  solid  chlorohydrate  having  the  same  composi- 
tion. These  chlorohydrates  of  citren  contain  twice  as  much  chlo- 
rohydric acid  as  the  chlorohydrate  of  terebenthen,  and  their  for- 
mulae is  therefore  C2oHjg,2HCl. 

Oil  of  Oranges,  or  Oil  of  Neroli  CgoH^g. 

§  1513.  Orange-peel,  like  lemon-peel,  contains  an  essential  oil,  to 
which  it  owes  its  fragrance,  and  of  which  the  formula  CgoH^g  is  the 
same.  It  yields,  with  chlorohydric  acid,  a  solid  and  a  liquid  product, 
of  an  identical  composition  with  the  chlorohydrates  of  citren ;  and 
it  polarizes  to  the  right. 

'  In  the  bergamot,  in  juniper-berries,  in  the  seeds  of  parsley,  and 
many  other  vegetables,  essential  oils  of  the  composition  CJi^  are 
found,  but  which  are  distinguished  by  certain  chemical  properties, 
and  by  their  rotatory  powers,  from  the  essential  oils  just  described.  Es- 
sential oils  of  bergamot,  Seville  oranges,  cedrat,  caraway,  and  limes 
rotate  toward  the  right.  Essential  oils  of  the  same  composition  are 
obtained  in  the  distillation  of  several  organic  substances.  Certain 
kinds  of  bitumen  yield  a  yellowish  liquid,  petrolen,  which  may  be 
made  perfectly  colourless  by  distilling  it  over  potassium,  and  pre- 
senting the  same  composition  with  oil  of  terpentine.  But  as  it  boils 
at  536°,  and  the  density  of  its  vapour  is  double,  its  formula  should 
be  written  C^oHga. 


CAMPHOR.  639 

OXYGENATED  ESSENTIAL  OILS. 

§  1514.  These  oils  being  numerous,  and  their  chemical  properties 
very  various,  we  shall  describe  only  the  most  important  and  best 
known  of  them. 

CAMPHORS. 

§  1515.  The  name  of  camphors,  or  stearoptens,  has  been  given  to 
neutral  compounds,  solid  at  the  ordinary  temperature,  volatile,  hav- 
ing an  odour  resembling  those  of  ordinary  camphor,  and  applicable 
to  the  same  uses.  We  shall  here  treat  only  of  the  camphor  from 
Japan  and  that  from  Borneo. 

Japan  Camphor  CgoHjgOao. 

§  1516.  Japan  camphor  is  extracted  from  the  laurus  camphora, 
the  wood  of  which  tree  contains  it  so  abundantly  that  small  crystals 
of  it  are  seen  in  the  fissures.  The  trunk  and  branches  are  split  into 
small  pieces  and  distilled  with  water  in  iron  boilers,  covered  with  an 
earthen  capital  filled  with  straw  or  small  twigs,  on  which  the  cam- 
phor sublimes  and  crystallizes  in  the  shape  of  crude  camphor.  It 
is  distilled  with  a  small  quantity  of  lime  and  charcoal  in  flat-bottomed 
vessels,  resembling  those  used  for  the  sublimation  of  chlorohydrate 
of  ammonia,  (§  516,)  when  the  camphor  sublimes  at  the  upper  part, 
and  forms  crystalline,  colourless,  and  transparent  masses,  such  as 
are  found  in  commerce.  At  the  ordinary  temperature,  the  tension 
of  the  vapour  of  camphor  is  very  feeble,  and,  nevertheless,  it  ex- 
hales an  intense  and  characteristic  odour ;  while,  when  kept  in  a 
close-stoppered  bottle,  the  vapour  condenses  on  its  sides,  and  forms 
small  brilliant  crystals,  remarkable  for  their  sharpness.  Camphor 
melts  at  347°,  and  boils  at  about  410°,  its  density  being  0.986,  and 
the  density  of  its  vapour  5.32.  From  its  great  elasticity  it  is  very 
difficult  to  pulverize.  Its  chemical  composition  corresponds  to  the 
formula  Q^^fi,  which  is  generally  written  Q^^^qO^  ;  its  equivalent 
then  corresponding  to  4  volumes  of  vapour.  Camphor  is  slightly 
soluble  in  water,  but  dissolves  more  freely  in  alcohol,  ether,  and 
concentrated  acetic  acid,  and  it  burns  with  a  white  and  smoky  flame. 
Camphor  obtained  from  the  family  of  the  laurels,  when  dissolved  in 
alcohol,  rotates  toward  the  right. 

Chlorine  does  not  act  readily  on  camphor,  but  when  dissolved  in 
chloride  of  phosphorus  PCI,,  and  subjected  to  the  action  of  chlorine, 
it  yields  chlorinated  camphor  CgoHj^ClgOg,  which  is  separated  from 
the  perchloride  of  phosphorus  by  washing  it  with  water  and  weak 
solutions  of  carbonate  of  potassa. 

Camphor  absorbs  chlorohydric  acid  gas,  and  yields  a  colourless 
liquid  of  the  formula  CgoH^gO^jHCl,  which  is  readily  destroyed  by 
water,  while  camphor  separates  from  it. 

§  1517.  Alkaline  solutions  exert  no  action  upon  camphor,  but  if  its 


640  ESSENTIAL   OILS. 

vapour  be  passed  over  potassic  lime  heated  to  750°  in  a  glass  tube, 
an  acid  called  camphoUc  is  formed,  which  combines  with  the  alkaline 
substance,  and  which  is  then  separated  by  dissolving  in  water  and 
supersaturating  with  chlorohydric  acid.  The  precipitated  cam- 
phoric acid  is  dissolved  in  a  mixture  of  alcohol  and  ether,  from  which 
it  separates  in  crystals,  melting  at  176°,  and  boiling  at  482°.  It  is 
insoluble  in  water,  but  very  soluble  in  alcohol  and  ether.  When 
crystallized,  its  formula  is  G^Jl^fi^,  or  more  properly  C2oHjy03,HO, 
which  corresponds  to  4  volumes  of  vapour,  for  the  density  of  the 
vapour  of  campholic  acid  is  5.9.  The  formula  of  campholic  acid 
differs  from  that  of  camphor  only  by  containing,  in  addition,  the 
elements  of  1  equiv.  of  water.  The  formula  of  campholate  of  silver 
is  AgO,C^H,,03. 

Campholate  of  lime  CaOjCgpH^yOj  is  decomposed  by  heat  into 
carbonate  of  lime  and  a  peculiar  liquid  called  campholone  CjgHjyO. 

CaO,C^H,,03=CaO,CO,+Cj,H,,0. 

Campholic  acid,  distilled  with  anhydrous  phosphoric  acid,  gives 
off  water  and  carbonic  acid,  while  a  carburetted  hydrogen  Cj^H^g, 
called  campholen,  which  boils  at  275°,  is  formed. 

§  1518.  Cold  nitric  acid  dissolves  camphor,  and  parts  with  it 
when  diluted  with  water,  while,  by  the  application  of  heat,  a  peculiar 
acid,  called  camphoric,  is  developed.  In  order  to  prepare  this  acid, 
camphor  is  boiled  for  a  long  time  with  10  times  its  weight  of  nitric 
acid,  and  as  the  latter  distils  over,  it  is  collected  and  poured  back 
into  the  retort.  At  the  close  of  the  operation,  the  excess  of  nitric 
acid  is  driven  off  by  evaporation,  when  the  camphoric  acid  separates 
in  a  crystalline  mass,  which  is  purified  by  dissolving  it  in  carbonate 
of  potassa,  and  again  separating  it  by  means  of  nitric  acid.  Cam- 
phoric acid  is  moderately  soluble  in  boiling  water,  the  greater  por- 
tion of  it  separating  during  cooling,  while  alcohol  and  ether  dissolve 
it  readily.  Its  composition  corresponds  to  the  formula  CaoHjgOg; 
and  the  camphor,  by  being  converted  into  camphoric  acid,  combines 
therefore  with  6  equiv.  of  oxygen,  which  it  takes  from  the  nitric 
acid.  The  formula  of  camphoric  acid  should  be  written  C^H^fig, 
2H0,  because  it  is  a  bibasic  acid,  and  the  general  formula  of  its 
salts  is  2RO,C3oHj40g.  When  heated  it  is  decomposed  into  water 
and  a  crystallized  substance,  boiling  at  518°,  which,  from  its  com- 
position CgoHj^Og,  may  be  regarded  as  anhydrous  camphoric  acid. 
Camphoric  acid,  dissolved  in  alcohol,  rotates  toward  the  right. 

§  1519.  A  species  of  camphor  is  extracted  from  the  labiates,  which, 
in  its  chemical  composition,  appears  identical  with  the  camphor  of 
the  laurels,  but  which  rotates  toward  the  left. 

Borneo  Camphor  Q^Jl^fi^, 

§  1520.  From  the  dryahalanops  camphora  exudes  a  more  or  less 
^viscous  oil,  containing  a  crystallizable  substance,  of  which  the  pro- 


CAMPHORS.  641 

perties  are  analogous  to  those  of  Japan  camphor.  It  has  been  called 
Borneo  campJior,  and  is  often  found  crystallized  in  old  trunks  of 
the  tree  of  the  dryahalanops  eamphora.  The  camphor  imported  from 
Borneo  and  Sumatra  is  in  small,  crystalline,  colourless,  and  trans- 
parent fragments,  insoluble  in  water,  but  dissolving  freely  in  alcohol 
ai»d  ether.  It  melts  at  about  383°,  and  boils  at  about  419°.  Bor- 
neo camphor  differs  from  Japan  camphor  only  by  containing  2  ad- 
ditional equiv.  of  hydrogen,  which  are  consumed  by  heating  it  with 
nitric  acid ;  the  Borneo  being  converted  into  Japan  camphor.  The 
liquid  portion  of  the  essential  oil  of  the  dryahalano'ps  eamphora  is 
essentially  composed  of  a  liquid  carburetted  hydrogen  CgoH^g,  called 
borneen,  boiling  at  about  320°,  and  isomeric  with  oil  of  terpentine, 
similarly  to  which  it  polarizes  to  the  left,  its  rotatory  power  being 
much  greater.  Nitric  acid,  after  some  time,  and  assisted  by  gentle 
heat,  converts  borneen  into  Japan  camphor,  probably  by  the  mere 
absorption  of  oxygen. 

Of  some  other  Stearoptens  analogous  to  Camphor, 

§  1521.  Stearoptens,  exhibiting  properties  analogous  to  the  cam- 
phors, are  found  in  a  great  number  of  vegetables ;  but  we  shall  only 
mention  them,  for  as  yet  they  possess  but  little  interest,  and  are  but 
little  known. 

Peppermint  contains  a  stearopten  of  the  formula  O^^S^fi,^^  called 
menthen  OjoHj ,  which  boils  at  325.4°.  Oil  of  mint  rotates  toward 
the  right. 

Oil  of  cedar  is  composed  of  a  crystallizable  substance  CggHggOg, 
and  a  liquid  carburetted  hydrogen,  cedren  Cg  H^4,  which  boils  at 
478.4°. 

Oil  of  absinth,  when  purified,  boils  at  399.  °2,  and  rotates  to- 
ward the  right :  its  formula  being  CgoH^gOj,  it  is  isomeric  with  Japan 
camphor. 

The  root  of  elecampane  {inula  hellenium)  contains  a  white  crys- 
tallizable substance,  helenm,  very  soluble  in  alcohol  and  ether,  melt- 
ing at  161.6°,  boiling  at  about  536°,  and  presenting  the  formula 

An  essential  oil,  composed  of  a  liquid  portion  and  a  portion  which 
solidifies  at  9.5°,  is  extracted  from  roses;  but  the  composition  of  the 
two  substances  is  not  exactly  known. 

Oil  of  lavender  contains  a  considerable  proportion  of  Japan  cam- 
phor, and  a  volatile  oil,  the  essential  oil  properly  so  called,  which 
has  been  used  in  the  arts. 

BENZOIC  SERIES. 
Oil  of  Bitter  Almonds  Cj^HgO^j. 
§  1522.  Bitter  almonds  contain  an  essential  oil,  and  a  non-vola- 
tile fatty  oil,  which  latter  is  expressed  by  subjecting  them  to  pres- 
sure ;  and  if  the  pulp  moistened  with  water  be  then  distilled  in  an 

Vol.  XL— 41 


642  ESSENTIAL   OILS. 

alembic,  a  volatile  oil,  which  falls  to  the  bottom  of  the  receiver, 
passes  over  with  the  water.  This  is  the  oil  of  hitter  almonds,  mixed 
with  cyanohydric  acid  and  two  new  substances,  henzo'ine  and  hen- 
■zoic  acid,  which  shall  soon  be  described.  They  are  separated  by 
•distilling  the  crude  oil  with  lime  and  protosulphate  of  iron,  reduced 
to  a  paste  with  water ;  the  distilled  oil  being  removed  with  a  pipette, 
and  again  distilled  in  a  glass  retort,  collecting  separately  the  first 
portions,  which  contain  water. 

Oil  i0.f  bitter  almonds  is  a  colourless,  very  fluid  liquid,  having  a 
peculiar  odour  resembling  that  of  cyanohydric  acid ;  and  its  density 
is  1.043,  while  it  boils  at  348.8°.  Water  dissolves  about  -^  of  its 
weight  of  it,  while  it  is  indefinitely  soluble  in  alcohol  and  ether. 
Its  formula  is  Cj^HgOg,  and  it  exerts  no  rotatory  power. 

Oil  of  bitter  almonds  rapidly  absorbs  the  oxygen  of  the  air,  and 
is  converted  into  benzoic  acid  C^Jlfi^,}10, 

C,.H„0,+20=C„H,03,H0. 

Anhydrous  benzoic  acid  is  therefore  derived  from  the  oil  of  bitter 
almonds,  by  the  substitution  of  1  equivalent  of  oxygen  in  the  place 
of  1  equivalent  of  hydrogen.  Benzoic  acid  is  also  formed  when  oil 
of  bitter  almonds  is  boiled  with  a  solution  of  potassa ;  the  hydrated 
potassa  converting,  at  a  high  temperature,  the  oil  of  bitter  almonds 
wholly  into  benzoic  acid,  hydrogen  being  at  the  same  time  disen- 
gaged. Chlorine,  in  contact  with  water,  efi'ects  the  transformation 
in  a  very  short  time. 

§  1523.  Dry  chlorine  acts  powerfully  on  oil  of  bitter  almonds, 
disengaging  chlorohydric  acid.  When  the  evolution  of  the  gas  has 
ceased,  the  liquor  is  heated  to  drive  off  the  dissolved  chlorine,  and 
a  liquid  of  a  penetrating  and  disagreeable  odour  is  obtained,  of  the 
density  1.106,  and  boiling  at  383°,  which  is  monochlorinated  oil  of 
bitter  almonds  C^JifilO^.  Water,  particularly  when  hot,  decom- 
poses it,  forming  chlorohydric  and  benzoic  acids : 

C,,H,C10,+2HO=C,,H303,HO+HCl. 

It  has  not  yet  been  ascertained  if  the  oil  of  bitter  almonds  forms 
still  more  chlorinated  products  with  chlorine.  Bromine  converts  it 
into  monobrominated  oil  Cj^H^BrOg;  and  monoiodinated  oil  Cj^HglOg 
is  obtained,  crystallized  in  laminse,  by  distilling  the  monochlorinated 
oil  over  iodide  of  potassium.  By  replacing  the  iodide  of  potassium 
by  sulphide  of  lead,  or  cyanide  of  mercury,  a  monosulphuretted  oil 
Of  4H5SO2,  or  a  monocyanuretted  oil  Cj^H^CyOg,  is  obtained.  Some 
chemists  take  a  different  view  of  the  composition  of  these  various 
bodies,  and  admit  the  existence  of  an  hypothetical  radical  Q^Jlfi^, 
called  benzoyl,  which,  combined  with  hydrogen,  constitutes  the  oil 
of  bitter  almonds  Q^Jlfi^,YL,  thus  forming  a  hydruret  of  beiizoyl^ 
while  benzoic  acid  is  the  oxide  of  benzoyl  Q^fifi^,0.  The  chlori- 
nated, brominated,  cyanuretted,  and  sulphuretted  oils  are  chlorides^ 
bromides^  sulphides,  and  cyanides  of  benzoyl. 


BENZOIC   SERIES.  643 

§1524.  The  chlorinated  oil  of  bitter  almonds  absorbs  a  large 
quantity  of  ammoniacal  gas,  and  is  converted  into  a  white  crystal- 
line compound  Cj^HyNOg,  or  henzamide : 

C„H,C10,+2NH3=NH3,HC1+C„H.0„NH,. 

By  treating  the  solid  product  of  the  reaction  with  water,  the  am- 
moniacal salt  which  formed  during  the  operation  is  dissolved,  while 
the  benzamide  alone  remains,  and  may  be  crystallized  %om  its  solu- 
tion in  alcohol.  The  relation  of  benzamide  Cj^H^OgjNHg  with  the 
benzoate  of  ammonia  (NH3,H0),Cj4H503  is  the  same  as  that  of  sul- 
phamide  S03,NH3  with  sulphate  of  ammonia  (NH3,H0),S03* 

Benzamide  dissolves  in  boiling  water,  and  separates  from  it,  on 
cooling,  in  crystals,  which  melt  at  239°,  and  boil  without  change 
at  a  higher  temperature.  Benzamide,  treated  with  a  cold  alkaline 
lye,  undergoes  no  change,  while  at  the  boiling  point  it  yields  ben- 
zoate of  potassa  and  ammonia.  Sulphuric  acid  also  decomposes  it, 
sulphate  of  ammonia  and  benzoic  acid  being  formed. 

§  1525.  The  oil  of  bitter  almonds,  kept  for  several  weeks  at  a 
temperature  of  100°  to  120°,  with  20  times  its  volume  of  an  aqueous 
solution  of  ammonia,  gives  rise  to  a  large  number  of  crystals,  which 
are  obtained  isolated  by  removing  the  unaltered  oil  by  ether.  They 
are  dissolved  in  cold  alcohol,  which,  by  evaporation,  deposits  them 
in  a  pure  state,  when  their  composition  is  represented  by  the  formula 
C42Hj3N3.  It  has  been  called  hydrobenzamide,  and  its  formation  is 
represented  by  the  following  equation : 

3,C,,H30,+2NH3=C^H,A+6HO. 

Hydrobenzamide,  dissolved  in  alcohol,  is  readily  converted,  by 
boiling,  into  ammonia  and  oil  of  bitter  almonds.  If  hydrobenzamide 
be  boiled  with  a  solution  of  caustic  potassa,  crystalline  flakes  are 
formed,  which,  by  recrystallization  in  alcohol,  furnish  colourless 
crystals  of  the  formula  C42HjgN2,  like  that  of  the  original  hydroben- 
zamide, but  which  differ  from  it  widely  in  its  properties.  This  new  sub- 
stance, called  amarin,  is  a  true  organic  base,  which  forms  crystal- 
lizable  salts  with  the  acids.  The  formula  of  chlorohydrate  of  amarin 
is  C42HjgN2,HCl+H0,  while  that  of  the  nitrate,  which  is  but 
slightly  soluble  in  water,  is 

(CJI,,N„HO),NO,. 

§  1526.  By  adding  chlorohydric  acid  to  water  which  has  distilled 
with  the  oil  of  bitter  almonds  in  the  preparation  of  the  latter  sub- 
stance, and  evaporating  it  to  dryness  at  a  gentle  heat,  the  residue 
is  composed  of  chlorohydrate  of  ammonia,  and  a  peculiar  substance, 
called  formohenzoylie  acid,  which  is  removed  by  dissolving  it  in 
ether,  when  it  is  deposited  after  evaporation  in  the  form  of  crystal- 
line spangles,  having  the  smell  of  bitter  almonds  and  a  strongly 
acid  reaction.  This  substance  dissolves  readily  in  water,  alco- 
hol, and  ether,  and  its  composition  corresponds  to  the  formula 
C^gHgOg,  or  rather   C^gHyO^jHO,   the  equivalent  of  water  being 


644  ESSENTIAL   OILS. 

replaced,  in  the  salts,  by  1  equivalent  of  base.  The  formula  of  the 
acid  may  be  written  C^Jifi^^G^KO^jllO,  which  would  represent  it 
as  formed  by  the  combination  of  1  equivalent  of  oil  of  bitter  almonds 
and  1  equivalent  of  formic  acid;  and  such,  in  fact,  is  the  constitu- 
tion assigned  to  it  by  its  behaviour  in  a  great  number  of  chemical 
reactions  :  thus,  with  oxidizing  reagents,  it  yields  carbonic  acid,  pro- 
duced by  the  combustion  of  the  formic  acid  and  oil  of  bitter  almonds. 

Benzoic  Acid  Cj^JIfi^,'H.O. 

§  1527.  Oil  of  bitter  almonds  rapidly  absorbs  the  oxygen  of  the 
air,  and  is  converted  into  benzoic  acid  Ci^H^OgjHO,  which  same 
transformation  is  effected  by  exposing  the  oil  to  oxidizing  reagents. 
Benzoic  acid  is  also  extracted  from  a  large  number  of  vegetable  and 
animal  substances,  in  which  it  generally  does  not  exist  already 
formed,  being  the  product  of  chemical  reactions.  In  the  laboratory 
it  is  obtained  from  the  resin  of  benzoin,  by  various  processes,  the 
most  simple  of  which  consists  in  placing  in  an  earthen  or  cast-iron 
capsule  1  kilog.  of  coarsely  powdered  benzoin,  covering  the  capsule 
with  a  sheet  of  tissue-paper,  the  edges  of  which  are  pasted  to  the 
vessel,  and  then  surmounting  it  with  a  pasteboard  cone.  The  cap- 
sule being  heated  in  a  sand-bath  for  3  or  4  hours,  the  vapours  of 
benzoic  acid  condense  on  the  sides  of  the  cone,  after  having  tra- 
versed the  tissue-paper,  which  retains  a  small  quantity  of  the  empy- 
reumatic  oily  substances,  which  would  injure  the  product.  This 
process  yields  very  pure  benzoic  acid,  in  the  form  of  snow-white 
crystals  of  an  agreeable  odour,  but  furnishes  only  a  small  portion 
of  the  acid  which  the  benzoin  contains ;  1  kilog.  of  benzoin  yielding 
only  40  gm.  of  benzoic  acid. 

By  the  following  process,  as  much  as  140  gm.  of  benzoic  acid 
may  be  obtained  from  the  same  quantity  of  benzoin.  The  resin  of 
benzoin,  finely  powdered,  is  mixed  with  ^  of  its  weight  of  carbonate 
of  soda,  and  a  sufficient  quantity  of  water  to  make  a  liquid  paste, 
which  is  gently  heated  for  several  hours,  stirring  it  continually  to 
prevent  the  melting  of  the  resin.  It  is  then  heated  with  a  larger 
quantity  of  water,  to  dissolve  the  benzoate  of  soda,  and  the  benzoic 
acid  is  separated  by  the  addition  of  a  proper  quantity  of  sulphuric 
acid. 

The  resin  of  benzoin  may  also  be  treated  with  3  times  its  weight 
of  alcohol  at  0.75,  and  the  benzoic  acid  saturated  with  carbonate  of 
soda  dissolved  in  8  parts  of  water ;  and  2  parts  of  alcohol  being 
finally  added,  the  liquid,  when  decanted,  is  distilled  in  order  to 
separate  the  greater  portion  of  the  alcohol.  The  resin  which  was 
dissolved  in  the  alcoholic  liquor  separates,  while  the  solution  only 
contains  the  benzoate  of  soda,  which  is  decomposed  by  sulphuric  acid, 
when  the  benzoic  acid  separates  almost  wholly  from  the  liquor  when 
cool.  By  this  method,  1  kilog.  of  benzoin  will  yield  as  much  as  180 
gm.  of  benzoic  acid. 


BENZOIC   SERIES. 


645 


Benzoic  acid  crystallizes  in  lamellae  or  in  flexible  and  brilliant 
silky  aciculse  ;  and  it  has,  of  itself,  but  little  odour,  while  it  gene- 
rally preserves  the  smell  of  benzoin,  particularly  when  it  has  been 
prepared  by  simple  distillation.  It  weakly  reddens  litmus,  melts  at 
248°,  and  boils  at  464°,  exhaling  copious  vapours  ^lieady  at  a  tem- 
perature of  300°  or  400°.  The  density  of  its  vapourbeing  4.27,  its 
equivalent  Ci4Hg03HO  corresponds  to  4  volumes  of  vapour.  It  re- 
quires for  its  solution  25  parts  of  boiling  and  200  parts  of  cold 
water,  while  it  dissolves  in  2  parts  of  alcohol,  and  is  also  very  solu- 
ble in  ether. 

The  general  formula  of  the  benzoates  is  1^0,0 ^Jifi^.  The  ben- 
zoates  of  potassa,  soda,  and  ammonia,  are  very  soluble  in  water,  and 
crystallize  with  difficulty.  The  benzoate  of  lime  is  very  soluble  in 
hot  water,  while  cold  water  retains  only  about  ^  of  its  weight  of  it. 
The  benzoate  of  silver  is  prepared  by  double  decomposition,  by 
pouring  a  hot  solution  of  nitrate  of  silver  into  a  boiling  solution  of 
an  alkaline  benzoate,  when  the  benzoate  of  silver  AgO,C ^Jlfi^  is 
precipitated,  during  the  cooling,  in  the  form  of  colourless  needles. 

Chlorine  acts  on  benzoic  acid  when  assisted  by  the  rays  of  the 
sun,  and  produces  chlorinated  benzoic  acid,  retaining  the  principal 
properties  and  capacity  of  saturation  of  free  benzoic  acid,  the  same 
products  being  obtained  by  heating  benzoic  acid  with  the  alkaline 
hypochlorites  or  with  mixtures  of  chlorohydric  acid  and  chlorate  of 
potassa.     Two  chlorinated  benzoic  acids  have  been  obtained  in  this 


manner 


Monochlorinated  benzoic  acid Ci^H^ClOgjHO. 


Terchlorinated 


C,AC1,03,H0. 


Vinohenzoic  Ether  QJlfi^Q^^fi^. 

§  1528.  In  order  to  prepare  this 
ether,  2  parts  of  alcohol,  1  part  of  ben- 
zoic acid,  and  6  parts  of  concentrated 
chlorohydric  acid  are  heated,  in  a  dis- 
tilling apparatus,  the  liquid  acid  which 
distils  being  returned  several  times  to 
the  retort;  when  the  benzoic  acid  is 
thus  almost  wholly  converted  into  ben- 
zoic ether.  But  it  is  better  to  arrange 
the  operation  as  represented  in  fig.  685 : 
the  mixture  is  placed  over  a  water-bath 
in  a  flask  A  which  is  made  to  commu- 
nicate with  a  refrigerator  so  arranged 
as  to  allow  the  distilled  liquid  to  gra- 
dually fall  back  again.  The  liquid  is 
treated,  first  with  water,  and  then  with 
a  weak  solution  of  carbonate  of  soda  to  remove  the  free  benzoic 


Fig,  685. 


646  ESSENTIAL   OILS. 

acid,  after  whicli  the  benzoic  ether  is  dried  by  digesting  it  over 
chloride  of  calcium. 

Benzoic  ether  is  a  colourless  liquid  of  an  oleaginous  consistence, 
boiling  at  410°,  and  of  the  density  1.054  at  50°.  The  density  of 
its  vapour  being  5.41,  its  equivalent  corresponds  to  4  volumes  of 
vapour,  and  it  is  insoluble  in  water,  but  soluble  in  all  proportions  in 
alcohol. 

Methylbenzoic  Ether  C2H30,Ci4H.0s. 

§  1529.  By  replacing,  in  the  preceding  operation,  vinic  by  me- 
thylic  alcohol,  methylbenzoic  ether*  is  obtained  as  an  oily  liquid, 
boiUng  at  226.4°. 

Sulphohenzoic  Acid  {Q^JLfi^.^fi^.'mO. 

§  1530.  If  vapour  of  anhydrous  sulphuric  acid  be  introduced  into 
a  dry  and  well-cooled  flask  containing  benzoic  acid,  a  semifluid  mass 
is  formed,  which  is  afterward  treated  with  water  to  dissolve  the 
monohydrated  sulphuric  acid,  and  a  peculiar  acid,  called  sulphohen- 
zoic, while  the  benzoic  acid  is  separated  unchanged.  The  acid 
liquid  is  saturated  with  carbonate  of  baryta,  when  sulphobenzoate 
of  baryta  alone  remains  in  the  liquid.  By  adding  chlorohydric 
acid,  crystals  of  acid  sulphobenzoate  of  baryta  (BaO  +  HO), 
(Cj^H^OgjSgOs)  separate,  which  are  redissolved  in  boiling  water  and 
again  crystallized  by  cooling.  Sulphohenzoic  acid  may  be  sepa- 
rated by  decomposing  a  solution  of  this  salt  with  sulphuric  acid 
added  by  drops :  it  is  very  soluble  in  water,  remains  undecomposed 
ev^n  at  300°,  and  may  be  obtained  in  a  crystalline  form  by  evapo- 
ration. 

Sulphohenzoic  acid  forms  two  series  of  salts  of  which  the  general 
formulae  are 

2R0,(C„H,03,S,0), 

(RO+HO),(0„H,0„SA)- 
It  is  therefore  a  bibasic  salt. 

It  will  be  seen  that  when  benzoic  acid  Ci^H^OgjHO  is  treated  with 
anhydrous  sulphuric  acid,  2  equivalents  of  the  latter  enter  into  the 
new  compound,  but  only  after  having  parted  with  1  equivalent  of 
oxygen,  which  has  formed  water  with  1  equivalent  of  hydrogen 
given  off  by  the  benzoic  acid ;  according  to  the  equation 

C,,H,03,HO+2S03=(C,A03,SA),2HO. 

mtrohenzoic  Acid  O^fiJ^^O^O^.'RO, 
§  1531.  Dilute  nitric  acid  does  not  act  readily  on  benzoic  acid, 


*  More  properly  called  benzoic  mether. —  W.  L,  F. 


BENZOIC   SERIES.  647 

but  if  the  fuming  acid  be  used,  and  in  great  excess,  the  benzoic 
acid  is  dissolved  with  the  disengagement  of  nitrous  vapours,  and 
the  liquid  deposits,  on  cooling,  crystals  of  nitrobenpoic  acid  C^^H^ 
(N0J03,H0,  which  is  purified  by  recrystallizations. 

Nitrobenzoic  acid  is  but  slightly  soluble  in  cold,  but  much  more 
so  in  boiling  water ;  and  dissolves  freely  in  alcohol  and  ether.  If 
crystallized  into  benzoate  of  lime,  it  takes  the  formula 

CaO,C,,H,(NOJ03+2HO, 
and  that  of  baryta,  BaO,C,4H,(NOJ03+4HO. 

From  its  composition  it  may  be  admitted  that  the  molecule  of 
nitrobenzoic  acid  Cj4H4(N04)03,H0  is  merely  that  of  benzoic  acid 
Cj^H^OgjHO  in  which  1  equivalent  of  hydrogen  has  been  replaced 
by  the  compound  (NOJ ;  and  many  cases  will  subsequently  be  met 
with  in  which  the  same  substitution  may  be  admitted. 

If  a  current  of  chlorohydric  acid  gas  be  passed  through  an  alco- 
holic solution  of  nitrobenzoic  acid,  nitrobenzoic  ether  Q^fi^Q^Jl^- 
(NOJO3  is  formed,  which  separates  in  colourless  crystals,  fusible  at 
116.6°,  and  boiling  at  about  570°. 

Binitrohenzoic  Acid  Q^fiJ^O ^^0^,^10, 

§  1532.  By  digesting  at  a  gentle  heat  1  part  of  benzoic  acid  with 
12  or  15  parts  of  a  mixture,  in  equal  proportions,  of  Nordhausen 
sulphuric  acid  and  fuming  nitric  acid,  we  effect  the  substitution,  in 
the  molecule  of  benzoic  acid  Q^^.O^^HO,  of  2  equivalents  of  the 
compound  NO^  for  2  equivalents  of  hydrogen,  and  obtain  binitro- 
henzoic acid  C,4H3(N0J203,H0. 

Bromohenzoic  Acid  C^^H^Br 0^,110. 

§  1533.  By  introducing  into  a  very  dry  bottle  benzoate  of  silver, 
and  bromine  contained  in  an  open  tube,  and  leaving  it  to  itself 
after  having  closed  the  bottle,  the  benzoate  of  silver  absorbs  the 
vapours  of  bromine,  bromide  of  silver  being  formed,  while  the  ben- 
zoic acid  combines,  at  the  same  time,  with  the  equivalent  of  oxygen 
given  off  by  the  silver  and  with  1  equivalent  of  bromine.  By 
treating  it  with  ether,  only  the  new  acid  C^^H^Br 0^,110,  dissolves, 
which  remains  in  the  form  of  a  crystalline  mass.  It  is  important 
to  remark  that  bromohenzoic  acid  has  not  preserved  the  constitution 
of  benzoic  acid,  but  that  it  is  fornaed  by  the  addition,  and  not  the 
substitution,  of  new  elements. 

Benzoate  of  Oil  of  Bitter  Almonds, 

§  1534.  When  moist  chlorine  is  passed  through  oil  of  bitter 
almonds,  crystals  insoluble  in  water,  but  very  soluble  in  alcohol,  are, 
after  some  time,  developed  in  it.  The  composition  of  this  substance 
may  be  represented  by  the  ^ormul^  i^Q^Jlfi^^Q^Jlfi^-,  3  mole- 
cules of  the  oil  being  grouped  into  one,  after  one  of  these  molecules 


648  ESSENTIAL   OILS. 

has  been  converted  into  benzoic  acid,  by  the  oxidizing  action  of  the 
moist  chlorine.  Its  composition  would  therefore  be  analogous  to 
that  of  acetal  (§  1368)  and  of  methylal,  (§  1432.) 

Benzoin  Cj^HgOg. 

§  1535.  If  crude  oil  of  bitter  almonds  be  shaken  with  an  alco- 
holic solution  of  potassa,  the  oil  sets,  in  a  few  minutes,  into  a  crys- 
talline mass ;  the  presence  of  a  certain  quantity  of  cyanohydric 
acid  being  necessary  to  the  transformation.  The  new  substance  is 
crystallized  by  purifying  it  in  alcohol.  This  substance,  to  which 
the  name  of  henzo'in  has  been  given,  presents  exactly  the  same 
composition  as  the  oil  of  bitter  almonds,  melts  at  248°,  and  may 
be  distilled  without  change.  Though  insoluble  in  cold,  it  is  slightly 
soluble  in  boiling  water,  and  rather  freely  so  in  alcohol.  Melted 
with  hydrate  of  potassa,  it  yields  benzoate  of  potassa.  If  it  be 
left,  for  a  long  time,  with  an  aqueous  solution  of  ammonia,  a  white 
powder  is  formed,  nearly  insoluble  in  water,  alcohol,  and  ether,  which 
has  been  called  benzo'inamide,  and  presents  the  formula  C^gH^gNg :  it 
may  be  supposed  to  be  formed  by  means  of  3  equivalents  of  ben- 
zoin 3(Cj^Hg02)  and  2  of  ammonia,  from  the  equation 

8C„H„0,+2NH3=C^H,3N,+6HO. 

§  1536.  Benzoin  dissolves  when  heated  with  nitric  acid,  and  a 
new  substance  of  the  formula  C^^H^Oa,  separates  after  cooling, 
called  henzil,  which  therefore  results  by  the  simple  abstraction  of 

1  equivalent  of  hydrogen  from  the  benzoin.  The  same  compound 
is  obtained  when  chlorine  is  caused  to  act  upon  benzoin  heated  to 
fusion,  when  the  equivalent  of  hydrogen  is  disengaged  in  the  state 
of  chlorohydric  acid.  Benzil  is  crystallized  by  purifying  it  in  al- 
cohol, and  is  a  slightly  yellowish  substance,  melting  at  about  194°. 

Benzil  is  not  changed,  even  at  the  boiling  point,  by  an  aqueous 
solution  of  potassa,  while  in  contact  with  an  alcoholic  solution  of 
the  same  alkali,  it  abstracts  1  equivalent  of  water,  and  is  converted 
into  an  acid,  called  benzilic,  of  the  formula  CggHigOg,  which  results 
from  the  combination  of  the  elements  of  2  equivalents  of  water  with 

2  equivalents  of  benzil : 

C^H,A=2C„H,0,+2HO. 

The  same  acid  is  formed  by  heating  benzoin  with  an  alcoholic 
solution  of  potassa,  saturating  the  hot  solution  with  chlorohydric 
acid,  and  allowing  it  to  cool,  when  benzilic  acid  is  deposited  in  crys- 
tals. It  melts  at  248°,  and  decomposes  at  a  higher  temperature, 
giving  off  a  certain  quantity  of  benzoic  acid. 

Benzine  C^JI^ 

§  153Y.  When  benzoic  acid  C^Jifi^,B.O  is  heated  with  3  times 
its  weight  of  hydrate  of  lime,  carbonate  of  lime  is  formed,  while  a 


BENZOIC   SERIES.  649 

colourless,  very  volatile  liquid,  of  the  formula  C^gHg,  and  called 
benzine,  distils  over,  which  is  rectified  over  quicklime.  The  reaction 
is  expressed  by  the  equation 

C,,H303,HO=2(CaO,CO,)+C,3He. 

Benzine  is  also  formed  when  benzoic  acid  in  vapour  is  passed 
through  a  tube  filled  with  fragments  of  pumice-stone  and  heated 
to  redness ;  benzine  and  carbonic  acid  alone  being  formed : 

C„H,03,HO=C^H,+2CO,. 

Benzine  is  also  produced  by  the  decomposition  of  a  great  number 
of  organic  substances  by  heat :  thus,  a  considerable  proportion  of  it 
is  found  in  the  volatile  oils  formed  in  the  manufacture  of  illuminat- 
ing gas. 

Benzine  boils  at  186.8°,  and  its  density  is  0.85,  while  that  of  its 
vapour  is  2.38,  its  equivalent  corresponding  to  4  volumes  of  vapour. 
At  32°  it  sets  into  a  crystalline  mass,  which  melts  only  at  44.6° ; 
and  it  is  insoluble  in  water,  but  very  soluble  in  alcohol  and  ether. 

Benzine  is  easily  acted  on  by  dry  chlorine,  when  exposed  to  the 
rays  of  the  sun ;  and  if  it  be  poured  into  a  large  well-dried  bottle, 
filled  with  chlorine,  and  the  bottle  be  exposed  to  the  sun,  it  becomes 
filled  with  white  vapours,  while  the  sides  are  covered  with  white 
crystals  of  the  formula  C^^HgCl .  The  behaviour  of  this  substance 
with  an  alcoholic  solution  of  potassa  leads  us  to  write  its  formula 
Cj^E[3Clg,3HCl ;  the  solution,  in  fact,  decomposing  it  by  abstracting 
3HC1 ;  while,  if  the  liquid  be  diluted  with  water,  an  oily  and  co- 
lourless liquid,  insoluble  in  water,  and  of  the  formula  C^HgClg, 
separates,  the  density  of  the  vapour  of  which  being  6.37,  its  equiva- 
lent corresponds  to  4  volumes.  This  is  therefore  ter chlorinated 
benzine,  and  the  crystalline  substance  formed  by  the  direct  action 
of  chlorine  on  benzine  may  be  regarded  as  a  terchlorinated  triohlo- 
rohydrate  of  benzine.  This  same  decomposition  of  the  crystalline 
compound  takes  place  when  it  is  distilled  several  times  alone,  or 
still  better,  over  lime. 

Bromine  yields  with  benzine  an  analogous  product  Ci^HgBrg, 
3HBr,  which,  with  the  alcoholic  solution  of  potassa,  also  produces 
terbrominated  benzine  Gj^Ji^Br^. 

§  1538.  Common  nitric  acid  acts  but  feebly  on  benzine,  while  if 
it  be  heated  with  the  fuming  acid,  it  dissolves,  and  an  addition  of 
water  precipitates  from  it  a  yellowish  liquid  Ci2H^(N04),  nitroben- 
zine.  It  may  be  granted  that  this  substance  is  formed  by  the  sub- 
stitution of  1  equivalent  of  the  compound  NO^  for  1  equivalent  of 
hydrogen  of  the  benzine.  Nitrobenzine  solidifies  at  32°,  and  melts 
only  at  37.4°,  while  it  boils  at  415.4°  without  change. 

By  causing  a  large  excess  of  fuming  nitric  acid  to  act  for  a  long 
time  on  benzine,  we  can  succeed  in  replacing  2  equivalents  of  hy- 
drogen by  2  equivalents  of  the  compound  (NOJ,  and  producing 


650  ESSENTIA!  OILS. 

hinitrohefizine  Q^^J^O^^  which,  by  the  addition  of  water,  is 
precipitated  in  the  form  of  a  crystalline  powder.  By  crystallization 
in  alcohol,  it  is  obtained  in  large  brilliant  lamellae. 

By  subjecting  nitrobenzine  and  binitrobenzine  to  certain  re- 
ducing agents,  they  are  converted  into  two  very  remarkable  sub- 
stances :  anilin  C^aH^N,  and  nitraniliii  Ci2Hg(N0JN,  which  are 
true  volatile  organic  bases. 

Sulphohenzinic  acidQ^^^^^fi^,HO,  and  Sulphohenzine  (j^^^^O^, 

§  1539.  Benzine  is  not  appreciably  acted  on  by  ordinary  sul- 
phuric acid,  while  the  anhydrous  acid  dissolves  it  with  elevation  of 
temperature,  a  viscous  liquid  being  formed,  which,  when  treated  with 
water,  deposits  a  crystalline  precipitate,  sulphohenzine,  and  pro- 
duces a  solution  containing,  with  ordinary  sulphuric  acid,  a  new 
acid,  called  sulphohenzinie. 

Sulphobenzine  should  be  purified  by  crystallization  in  alcohol, 
after  which  it  is  a  colourless  substance,  melting  at  212°,  and  boiling 
at  about  750°,  without  change.  Its  formula  is  Cj^HgjSOj,  and  the 
following  equation  expresses  the  reaction  which  produces  it : 

C„H.+2SO.=C.,H„SO,+S03,HO. 

By  saturating  the  acid  liquid  with  carbonate  of  baryta,  the  free 
sulphuric  acid  is  precipitated,  and  a  solution  of  sulphobenzinate  of 
baryta  is  obtained.  By  pouring  sulphate  of  copper  into  the  latter, 
this  salt  is  converted  into  sulphobenzinate  of  copper,  which  crystal- 
lizes readily  according  to  the  formula  CuO,(Ci2H5,S305). 

When  decomposed  by  sulf  hydric  acid,  it  produces  isolated  sul- 
phohenzinie acid,  a  very  acid  liquid  which  may  by  crystallized  by 
evaporation. 

Benzone  CjgH^O. 

§  1540.  When  benzoate  of  lime  is  subjected  per  se,  without  any 
addition  of  an  excess  of  hydrated  lime,  to  the  action  of  heat,  with 
the  benzine,  two  other  products  are  formed :  benzone,  and  a  crystal- 
line substance  of  which  the  nature  is  not  yet  known.  As  these  two 
latter  substances  boil  at  much  higher  temperatures  than  benzine, 
they  are  easily  separated  from  it,  by  heating  the  mixture  to  428°, 
at  which  temperature  the  benzine  is  wholly  volatilized.  The  residue 
being  cooled  to  —  4°,  nearly  all  the  solid  substance  is  deposited,  and 
the  benzone,  which  remains  fluid,  may  be  decanted. 

Benzone  is  an  oily  liquid  of  the  formula  C^^Hfi,  the  reaction 
from  which  it  arises  being  expressed  by  the  equation 

CaO,C,,H,03=CaO,C02+C,3H30. 

AMYGDALIN  C^E„^S>». 
§  1541.  Bitter  almonds  do  not  contain  the  oil  of  bitter  almonds 


BENZOIC   SERIES.  651 

ready  formed,  but  in  its  stead  a  very  remarkable  substance,  called 
amygdalin^  which  is  converted  in  the  oil  by  the  action  of  a  second 
substance,  called  emulsin.  In  order  to  prepare  amygdalin,  bitter 
almonds  are  subjected  to  very  heavy  pressure,  when  a  fatty,  colour- 
less, non-volatile  oil  exudes,  called  oil  of  sweet  almonds,  because  it 
also  exists  in  this  species  of  almond.  The  balance  of  the  oil  is 
then  removed  by  treating  the  crushed  cake  several  times  with  ether ; 
after  which  the  pulp  is  boiled  twice  with  alcohol,  to  dissolve  the  amyg- 
dalin, the  greater  portion  of  the  alcohol  being  afterward  separated 
by  distillation  ;  when  the  residue  deposits  the  amygdalin,  on  cooling, 
in  crystalline  lamellae.  Amygdalin  dissolves  readily  in  water,  and 
is  deposited  from  it  in  beautiful  crystals,  of  the  formula  C^^HgyNgOgg 
4-6H0;  the  6  equivalents  of  water  being  disengaged  at  248°.  It 
dissolves  freely  in  boiling  alcohol,  but  is  nearly  insoluble  in  cold 
alcohol.     Amygdalin  rotates  toward  the  left. 

When  heated  with  a  mixture  of  peroxide  of  manganese  and  sul- 
phuric acid,  it  is  decomposed  into  ammonia,  carbonic  acid,  formic 
acid,  and  oil  of  bitter  almonds,  by  which  process  it  yields  more  than 
one-half  of  its  weight  of  oil. 

§  1542.  By  pouring  into  a  solution  of  amygdalin  in  10  parts  of 
water,  an  emulsion  of  sweet  almonds,  cyanohydric  acid  and  oil  of 
bitter  almonds,  readily  known  by  their  smell,  are  immediately 
formed.  The  name  of  synaptase  has  been  given  to  the  active  sub- 
stance effecting  the  transformation,  which  exists  both  in  sweet  and 
in  bitter  almonds.  In  order  to  prepare  synaptase,  sweet  almonds, 
from  which  the  oil  has  been  previously  expressed,  are  treated  with 
water,  and  to  the  solution  is  added,  first,  acetate  of  lead  in  order 
to  precipitate  a  gummy  matter,  then  acetic  acid  to  coagulate  the 
albumen,  and  lastly,  a  large  quantity  of  alcohol,  after  having  pre- 
cipitated the  excess  of  lead  by  sulfhydric  acid;  when  synaptase  is 
deposited  in  flakes,  which  change,  on  cooling,  into  a  brittle,  gum- 
like substance.  The  action  of  synaptase  on  amygdalin  may  be  com- 
pared to  that  of  yeast  on  sugars,  its  analogy  with  the  phenomena 
of  fermentation  being  perfect,  while  the  products  of  the  reaction 
are  complicated,  and  a  considerable  quantity  of  sugar  is  formed. 
One  part  of  synaptase  is  sufficient  to  decompose  10  parts  of  amyg- 
dalin. Synaptase  is  soluble  in  water,  but  it  coagulates  at  140°, 
and  then  loses  all  its  power  over  amygdalin.  In  order  to  produce 
perfect  transformation,  the  amygdalin  must  be  dissolved  in  a  large 
quantity' of  water. 

From  this  it  will  be  seen  that,  in  order  to  prepare  the  oil  of  bitter 
almonds,  the  pulp  must  not  be  immediately  distilled  with  water,  but 
must  be  digested  in  the  cold,  or  better  still,  at  a  temperature  of  86°, 
long  enough  to  allow  the  amygdalin  to  be  wholly  decomposed  by 
the  synaptase.  The  essential  oil  and  the  cyanohydric  acid  are  then 
separated  by  distillation. 


652  ESSENTIAL   OILS. 

ESSENTIAL  OIL  OF  SPIR^A  ULMARIA,  AND  THE  SALICYLIC  SERIES. 

§  1543.  Bj  distilling  the  flowers  of  the  meadow-sweet  (spiraea 
ulmarid)  with  water,  an  essential  oil  Cj^HgO^  is  obtained,  accompanied 
by  a  carburetted  hydrogen,  isomeric  with  oil  of  terpentine,  and  a 
crystalline  substance  analogous  to  camphor.  The  oil  possesses  acid 
properties,  an(J  has  hence  been  called  spiroylous  acid,  and  salicylous 
acid  from  its  correlations  with  a  neutral  substance,  salicin,  which 
exists  in  the  bark  of  the  willow.  Salicin  treated  with  a  mixture  of 
sulphuric  acid  and  bichromate  of  potassa  yields,  in  fact,  a  large  pro- 
portion of  oil  of  spiraea;  and  we  fehall,  therefore,  commence  with  the 
description  of  this  substance,  which  it  is  impossible  to  separate  from 
the  series  of  salicylic  products. 

Salicin  C^B-^fi^^, 

§  1544.  In  order  to  prepare  salicin,  the  bark  of  the  willow  is  ex- 
hausted by  boiling  water,  and  litharge  is  added  to  the  concentrated 
solution  until  the  liquid  is  deprived  of  colour.  The  oxide  of  lead  is 
then  partially  precipitated  by  sulphuric  acid,  the  precipitation  being 
finished  by  sulphide  of  barium,  added  by  drops  to  prevent  its  being 
in  excess.  The  filtered  liquid  is  evaporated,  and  then  deposits  impure 
salicin,  which  is  purified  by  dissolving  it  in  water,  discolouring  it 
by  animal  black  and  recrystallizing  it. 

Salicin  crystallizes  in  white  inodorous  aciculae  of  a  bitter  taste, 
and  without  any  reaction  on  vegetable  colours.  It  loses  nothing  of 
its  weight  at  212°,  melts  at  248°,  and  is  decomposed  at  a  higher 
temperature.  100  parts  of  water,  at  the  ordinary  temperature,  dis- 
solve 5.6  of  salicin,  while  boiling  water  dissolves  it  much  more  freely, 
and  alcohol  also  dissolves  it,  but  it  is  insoluble  in  ether.  Salicin 
polarizes  toward  the  left. 

Cold  concentrated  sulphuric  acid  dissolves  salicin,  and  it  becomes 
of  a  blood-red  colour ;  which  reaction  is  a  test  of  salicin  in  the  bark 
of  the  willow  and  poplar  tree.  Dilute  sulphuric  and  chlorohydric 
acids  decompose  salicin  at  the  boiling  point  into  glucose  C^JI^fi^^, 
and  a  resinous  substance,  called  saliretin  Cj^HgOg,  according  to  the 
equation 

C^H„0„=C„H„0^+C,,HA. 

§  1545.  Nitric  acid  forms,  with  salicin,  very  various  products,  ac- 
cording as  it  is  more  or  less  dilute.  If  1  part  of  salicin  be  treated 
with  10  parts  of  nitric  acid  at  20°  Baum^,  and  the  mixture  be  left 
to  itself  for  1  or  2  days,  shaking  it  frequently  to  hasten  the  solu- 
tion of  the  salicin,  a  yellow  liquid  is  obtained,  which  deposits  a  white 
substance,  crystallized  in  small  needles,  and  called  helicin.  It  is 
very  soluble  in  hot  water,  but  scarcely  so  in  cold,  and  its  formula  is 
C,oHj,0,,+3HO,  the  3  equiv.  of  water  being  given  off  at  212°,  with- 
out alteration,  while  it  melts  at  about  347°.    A  solution  of  potassa, 


SALICIC   SERIES.  653 

baryta,  or  ammonia  decomposes  it  into  glucose  and  oil  of  spiraea 
C„H,0,: 

C^H,A4+2HO=C„H„0^+C„H,0,. 

Chlorine  acts  readily  upon  helicin  in  the  presence  of  water,  form- 
ing monochlorinated  helicin  CjgHj^ClOj^,  which  is  decomposed  by  a 
solution  of  potassa  into  glucose  O^Jl^fi^^,  and  into  monochlorinated 
oil  of  spiraea  C^^H-CIO^.  Monobrominated  helicin  is  prepared  in 
the  same  manner,  and  undergoes  an  analogous  transformation  with 
potassa. 

Beer-yeast  and  synaptase  exert  a  true  fermenting  action  on  heli- 
cin, decomposing  it  into  glucose  and  oil  of  spiraea,  and  producing 
an  analogous  effect  on  monochlorinated  helicin,  which  they  decom- 
pose into  glucose,  and  monochlorinated  oil  of  spiraea. 

When  the  nitric  acid  is  more  concentrated,  and  it  is  heated,  the 
salicin  is  converted  into  oxalic  acid,  and  an  acid  which  we  shall 
describe  under  the  name  of  picric  acid. 

Chlorine  does  not  act  so  energetically  on  salicin  except  in  the 
presence  of  water,  when  chlorinated  salicins  are  formed,  which  com- 
bine with  a  certain  quantity  of  water,  and  we  thus  have  successively 

Monochlorinated  salicin 026^.^010 ^^+4:B.O,     ' 

Bichlorinated  "      C,,R,fi\fi,^-\-2B.O, 

Trichlorinated  "      C26H,,Cl30i,+2HO. 

Chromic  acid,  or  a  mixture  of  sulphuric  acid  and  bichromate  of 
potassa,  converts  salicin  into  salicylous  and  formic  acids. 

§  1546.  Beer-yeast  and  albuminous  substances  do  not  act  upon 
salicin,  while  synaptase  exerts  over  it  a  very  remarkable  power,  which 
should  be  classed  among  the  phenomena  of  fermentation,  since  it 
decomposes  it  into  glucose,  and  into  a  new  substance,  called  aaligenin 
C^^HgO^,  according  to  the  reaction 

C^H,,0„+2H0=C^H^0.,+C„H,0,. 

In  order  to  effect  this  transformation,  50  parts  of  powdered  salicin, 
diffused  in  200  parts  of  distilled  water,  are  treated  with  about  3 
parts  of  synaptase,  when  the  whole  is  introduced  into  a  bottle,  which 
is  well  shaken,  and  heated  in  a  water-bath  to  104°.  In  10  or  12 
hours  the  transformation  is  completed,  and  the  greater  portion  of  the 
saligenin  is  deposited  in  the  form  of  small  rhombohedral  crystals.  In 
order  to  extract  the  remainder,  the  liquid  is  shaken  with  its  volume 
of  ether,  which  takes  the  saligenin  from  the  water,  and  deposits  it 
on  evaporation.  Glucose  remains  in  the  aqueous  solution,  and  may 
be  easily  recognised  by  its  optical  properties,  or  by  causing  it  to 
ferment  with  yeast. 

Saligenin  dissolves  in  all  proportions  in  boiling  water,  but  it  re- 
quires 15  parts  for  solution  at  the  ordinary  temperature,  and  it  is 
very  soluble  in  alcohol  and  ether,  without  possessing  rotatory  power. 
It  melts  at  179.6°,  while  the  prolonged  action  of  heat  converts  it  into 


654  ESSENTIAL   OILS. 

saliretin,  which  transformation  is  also  very  rapidly  effected  by  dilute 
mineral  acids.  A  mono^  hi,  and  trichlorinated  saligenin  has  been 
obtained  by  causing  synaptase  to  act  on  mono,  bi,  and  trichlorinated 
salicin ;  which  fact  is  remarkable,  because  it  shows  that  the  substitu- 
tion of  chlorine  for  hydrogen  in  salicin  does  not  prevent  fermenta- 
tion. 

Salicylous  Acid  Q^Jlfi^^HO, 

§  1547.  We  have  said  (§  1543)  that  salicylous  acid  is  merely  the 
oil  extracted  from  the  flowers  of  the  meadow-sweet,  by  distillation 
with  water.  It  does  not  exist  in  them  ready  formed,  for  the  flowers 
may  be  exhausted  by  alcohol  without  obtaining  a  trace  of  it ;  but  it 
is  produced  during  the  distillation  of  the  flowers  with  water ;  probably 
by  a  phenomenon  of  fermentation  analogous  to  that  producing  oil 
of  bitter  almonds,  when  the  pulp  of  the  almond  is  digested  with  tepid 
water.  The  distillation  of  the  flowers  of  the  meadow-sweet  with 
water  yields,  in  addition  to  salicylous  acid,  an  essential  oil,  isomeric 
with  oil  of  terpentine,  and  a  volatile  substance  which  crystallizes. 
But  by  shaking  the  distilled  product  with  caustic  potassa,  the  sali- 
cylous acid  alone  combines  with  the  alkali,  and,  if  the  whole  be  again 
distilled,  the  volatile  oil  and  crystalline  substance  volatilize  with  the 
water,  while  the  salicylite  of  potassa  remains  in  the  retort.  The 
salt  being  decomposed  by  sulphurous  acid,  and  the  distillation  re- 
commenced, the  salicylous  acid,  set  free,  condenses  in  the  receiver. 

It  is  more  easy  to  obtain  salicylous  acid  from  salicin  by  introduc- 
ing a  mixture  of  3  parts  of  the  latter  substance  with  3  parts  of  bi- 
chromate of  potassa  and  24  parts  of  water  into  a  retort,  and  shak- 
ing it  frequently  until  complete  solution  is  effected,  when  4J  parts 
of  concentrated  sulphuric  acid,  dissolved  in  12  parts  of  water,  are 
added,  and  the  whole  is  again  shaken.  Reaction  gradually  ensues, 
and  when  it  appears  to  be  terminated,  the  temperature  is  gradually 
raised,  and  the  distilled  products  are  collected  in  a  well-cooled  re- 
ceiver. The  latter  are  composed  of  an  aqueous  solution,  slightly 
acid,  containing  a  small  quantity  of  formic  acid,  and  a  reddish  oil 
which  collects  at  the  bottom  of  the  aqueous  liquid.  The  oil  is  de- 
canted and  digested  for  24  hours  over  chloride  of  calcium,  and  then 
rectified  anew,  by  which  means  perfectly  pure  salicylous  acid  is 
obtained. 

Salicylous  acid,  or  the  essential  oil  of  spirsea  uhnaria,  is  a  colour- 
less liquid,  assuming  a  red  tinge  on  exposure  to  the  air,  of  an  odour 
similar  to  that  of  the  oil  of  bitter  almonds,  and  staining  the  skin 
yellow,  the  stains  disappearing  as  rapidly  as  those  of  iodine.  It 
boils  at  384.8°,  and  its  density  at  55.4°  is  1.173,  while  the  density 
of  its  vapour  is  4.27,  and  its  equivalent  Cj^H^OgjHO  is  represented 
by  4  volumes.  It  has  no  rotatory  power.  It  is  nearly  insoluble  in 
water,  but  dissolves  in  all  propDrtions  in  alcohol  and  ether;  and 
although  its  solutions  do  not  redden  tincture  of  litmus,  they  will 


SALICIC   SERIES.  655 

decompose  the  alkaline  carbonates,  even  when  cold.  It  is  important 
to  remark  that  the  formula  and  density  of  vapour  of  salicylous  acid 
is  the  same  as  that  of  benzoic  acid,  furnishing  a  curious  example  of 
isomerism. 

Salicylous  acid  forms  two  compounds  with  potassa ;  and  salicylite 
of  potassa  }^0,G^^lc{fi^+2110  is  obtained  as  a  yellow  crystalline 
mass  when  salicylous  acid  is  added  to  a  concentrated  solution  of 
potassa.  By  dissolving  it  in  absolute  alcohol,  the  salt  is  deposited 
in  crystalline  lamellae  of  a  golden  yellow  colour.  By  means  of 
this  salt,  the  salycylites  of  baryta,  lime,  zinc,  lead,  mercury,  and 
silver  can  be  prepared  by  double  decomposition.  The  aqueous  solu- 
tion of  salicylite  of  potassa  is  readily  decomposed,  and  yields  formi- 
ate  of  potassa  and  a  salt  of  potassa  formed  by  a  black  substance 
CgoHgO^Q,  to  which  the  name  of  melanic  acid  has  been  given. 

By  dissolving  salicylate  of  potassa  in  hot  alcohol,  and  adding  an 
additional  quantity  of  salicylous  acid,  the  liquid,  on  cooling,  depo- 
sits colourless  aciculse  of  a  salt  of  the  formula  {K^0-\-H.0)^2Q^^fi^, 
which  may  be  called  hisalicylite  of  potassa^  and  is  more  fixed  than 
the  neutral  salicylite. 

Salicylous  acid  absorbs  ammoniacal  gas,  and  is  converted  into 
yellow  and  crystalline  salicylite  of  ammonia  (^^^^HO),(j^Jlfi^^  the 
same  compound  being  formed  when  salicylous  acid  is  dissolved  in  an 
aqueous  solution  of  ammonia ;  while,  if  the  acid  be  first  dissolved  in 
3  times  its  volume  of  alcohol,  and  ammonia  be  added  by  drops,  yel- 
low aciculse  are  formed,  which  readily  dissolve  when  the  temper- 
ature is  raised.  On  cooling,  the  new  product  is  deposited  in  crystals 
of  a  golden  yellow  colour,  with  the  formula  C43Hj8N206=C4aHj4 
(NH2)20g,  ensuing  from  the  following  reaction : 

3(C„H,03,HO)+2NH3=C,H,,(NH,),0,+6HO. 

It  has  been  called  salhydramide,  and  is  insoluble  in  water,  even  at 
the  boiling  point. 

Salicylous  acid  absorbs  chlorine,  even  when  cold,  and  the  reaction 
takes  place  with  elevation  of  temperature,  chlorohydric  acid  being 
disengaged,  and  the  oil  at  last  becoming  solid.  By  dissolving  it  in 
alcohol,  crystalline,  colourless,  and  pearly  lamellae  are  deposited,  of 
monochlorinated  salicylous  acid  0^^1140103+110,  which  forms  well 
marked  salts,  of  the  general  formula  R0,Ci4H4C103,  and  yields,  with 
ammoniacal  gas,  monochlorinated  salicylamide  Q^fi^^QAJ^M^fi^, 

Bromine  forms  a  monochlorinated  salicylic  acid  0i4H4BrO3,HO. 

If  salicylous  acid  be  heated  with  nitric  acid  of  medium  strength, 
hyponitric  acid  is  disengaged,  and  the  oil  is  converted  into  a  crys- 
talline mass,  which  is  purified  by  dissolving  it  in  boiling  water  after 
having  washed  it  with  a  small  quantity  of  cold  water.  The  solution 
deposits,  by  spontaneous  evaporation,  yellow  prismatic  crystals  of 
nitrosalicylous  acid  C^JIJl^O^O^jKO,  which  combines  with  bases, 


Q5Q  ESSENTIAL   OILS. 

and  forms  salts  possessing  detonating  properties  by  an  elevation  of 
temperature. 

Salicylic  Acid  C^JJfi^^HO. 

§  1548.  When  salicylous  acid  is  heated  with  an  excess  of  hydrate 
of  potassa,  hydrogen  is  disengaged ;  and  if  the  operation  be  arrested 
at  the  moment  of  the  cessation  of  the  evolution  of  gas,  the  mass  be 
dissolved  in  water,  and  an  excess  of  chlorohydric  acid  added,  crys- 
tals are  precipitated,  which  are  purified  by  recrystallization  from 
boiling  water.  They  are  formed  by  a  new  acid,  salicylic  Cj^H^O^jHO, 
which  arises  from  the  following  reaction : 

Ci,H,03,HO+KO,HO=KO,C,4Hp,+2H. 

This  acid  results  from  the  simple  combination  of  1  equivalent  of 
salicylous  acid  with  2  equivalents  of  oxygen. 

Salicylic  acid  dissolves  in  boiling  water,  but  is  nearly  insoluble 
in  cold  water :  it  dissolves  freely  in  alcohol  and  ether ;  volatilizes 
without  change,  and  then  produces  crystals  resembling  those  of 
benzoic  acid :  it  reddens  litmus  and  decomposes  the  carbonates. 
It  has  no  action  on  polarized  light.  Bromine  and  chlorine  act  on 
it  readily,  and  produce  mono  and  bibrominated,  mono  and  bichlo- 
rinated  salicylic  acids. 

Treated  with  fuming  nitric  acid,  salicylic  acid  is  converted  into  a 
reddish  resinoid  mass,  which  is  to  be  washed  with  cold  and  dissolved 
in  boiling  water :  yellowish,  fusible,  and  volatile  aciculae,  of  nitro- 
salicylic  acid  Q^fi^i^O^O.^HO  are  deposited  from  the  solution. 

Methylosalicylic  Ether  €21130,0^411505. 

§  1549.  By  distilling  a  mixture  of  2  parts  of  methylic  alcohol,  2 
parts  of  salicylic  acid,  and  1  part  of  sulphuric  acid,  this  compound 
ether  is  readily  obtained,  as  a  colourless  or  slightly  yellowish  liquid, 
boiling  at  428°,  and  of  the  density  1.18  at  50°,  the  density  of  its 
vapour  being  5.42,  and  its  equivalent  031130,01411505  corresponding 
to  2  volumes  of  vapour.  It  is  nearly  insoluble  in  water,  but  dis- 
solves readily  in  alcohol  and  ether. 

Methylosalicylic  ether  exists  ready  formed  in  a  native  essential  oil, 
called  ivintergreen,  and  obtained  from  the  gaultheria  procumbens. 
The  oil  of  gualtheria  comes  principally  from  New  Jersey,  where  the 
plant  grows  in  great  abundance.  By  distilling  the  oil,  there  is  dis- 
engaged, first  a  carburetted  hydrogen  isomeric  with  oil  of  terpen- 
tine, and  subsequently  methylosalicylic  ether.* 

Methylosalicylic  ether  is  a  true  acid,  which  combines  with  potassa, 
forming  a  salt  which  crystallizes  in  pearly  spangles.  But  if  an 
excess  of  potassa  be  used,  particularly  when  assisted  by  heat,  the 

*  The  interesting  discovery  of  the  artificial  formation  of  this  substance,  by  Ca- 
hours,  was  first  indicated  by  W.  Proctor,  of  Philadelphia,  who  first  proved  that  the 
oil  of  gaultheria  belonged  to  the  salicylic  series. — J.  C.  B* 


SALICIC   SERIES.  657 

ether  undergoes  the  ordinary  decomposition  of  compound  ethers, 
and  is  converted  into  alcohol  and  salicylic  acid. 

Chlorine  and  bromine  readily  act  on  methylosalicylic  ether,  and 
yield  chlorinated  and  brominated  products : 

Monochlorinated  methylosalicylic  ether C2H30,Ci4H^C105, 

Bichlorinated  "  "    Cfifi,G,JI,C\fi,, 

Monobrominated  "  "    C2H30,C,,H,Br05, 

Bibrominated  "  "    CJlfi,C,Ji,BYfi^.   ^ 

With  a  hot  solution  of  potassa,  these  substances  are  decomposed 
into  methylic  alcohol  and  mono  or  bichlorinated  or  brominated 
salicylic  acid. 

Fuming  nitric  acid  converts  methylosalicylic  ether  into  nitrome- 
thylosalicylic  ether  Qfifi,Q^Jl^{^0^^)0^. 

By  introducing  into  a  well-corked  bottle  1  volume  of  methylo- 
salicylic ether,  and  5  or  6  volumes  of  a  concentrated  solution  of 
ammonia,  the  ether  disappears  after  some  time,  and  by  then  eva- 
porating the  liquid  and  distilling  the  residue,  a  yellow  mass  is  ob- 
tained, which  may  be  converted  into  crystalline  aciculse,  by  solution 
in  boiling  water.  The  formula  of  this  substance  is  Ci4H5(NH2)0^, 
and  it  is  generated  from  anhydrous  salicylic  acid,  according  to  the 
following  equation : 

C„H,0,+NH3=C„H,(NH,)0,+H0. 

This  substance,  which  has  been  called  salicylamide,  is  soluble  in 
boiling  water,  but  nearly  insoluble  in  cold  water,  and  dissolves 
readily  in  alcohol  and  ether.  It  volatilizes  without  alteration,  and 
with  acids  regenerates  ammonia  and  salicylic  acid.  By  causing 
ammonia,  under  similar  circumstances,  to  act  on  chlorinated,  bro- 
minated, or  nitric  products,  derived  from  methylosalicylic  ether, 
mono  and  bichlorinated,  mono  and  bibrominated,  and  nitric  saliey- 
lamides  are  obtained. 

Lastly,  by  allowing  methylosalicylic  ether  to  fall  on  anhydrous 
lime  or  baryta,  carbonates  of  these  bases,  and  a  new  substance 
Ci4Hg03,  called  amsoZe,  are  formed,  the  reaction  being  expressed 
by  the  following  equation  : 

C2H30,Ci,HA+2BaO=2(BaO,C02)  +  Ci4H302. 

Anisole  is  a  colourless,  very  fluid  liquid,  of  an  agreeable  aromatic 
odour,  boiling  at  302°,  insoluble  in  water,  but  very  soluble  in  alcohol 
and  ether. 

Vinosalicylic  Ether  €41150,01411505. 
§  1550.  By  distilling  a  mixture  of  2  parts  of  absolute  alcohol,  1 J 
part  of  salicylic  acid,  and  1  part  of  sulphuric  acid,  we  obtain  vino- 
salicylic  ether,  which,  like  its  analogue  of  the  methylic  series,  com- 
bines with  bases.  It  also  forms  salicylamide  with  ammonia,  and 
oroduces,  with  chlorine,  bromine,  and  nitric  acid,  chlorinated,  bro- 

VoL.  ix. nA 


658  ESSENTIAL   OILS. 

minated,  and  nitric  ethers,  corresponding  to  those  formed  by  me- 
thylosalicjlic  ether. 

OIL  OF  CINNAMON  AND  THE  CINNAMIC  SERIES. 

§  1551.  Oil  of  cinnamon  is  found  in  commerce,  being  imported 
from  Ceylon  and  China.  That  from  China  is  more  esteemed,  be- 
cause it  has  an  agreeable  smell,  peculiar  to  cinnamon-bark,  while 
the  Ceylon  oil  has  a  mixed  smell  of  cinnamon  and  bed-bugs,  and 
ite  composition  appears  to  be  more  complicated.  By  digesting 
powdered  cinnamon-bark  with  water  for  12  hours,  and  then  saturat- 
ing the  water  with  sea-salt,  and  subjecting  the  whole  to  distillation, 
a  milky  water  passes  over,  which  deposits  an  essential  oil,  of  a  more 
or  less  reddish  yellow,  and  resembling  the  cinnamon-oils  of  com- 
merce. 

Oils  of  cinnamon  appear  to  be  mixtures  of  an  essential  oil,  to 
which  the  name  of  hydruret  of  cinnamyl  has  been  given,  and 
which  we  shall  consider  as  the  oil  of  cinnamon,  properly  so  called, 
with  other  oils  which  have  not  yet  been  studied.  The  oil  of  cinna- 
mon, properly  so  called,  is  separated  by  agitating  the  oil  of  cinnamon 
of  commerce  with  concentrated  nitric  acid,  when,  in  a  few  hours, 
long  prismatic  crystals  are  formed,  which  are  separated  and  pressed 
between  folds  of  tissue-paper.  Water  readily  decomposes  them, 
and  yields  an  essential  oil  C^gHgOg,  which  is  regarded  as  pure  oil 
of  cinnamon ;  the  water  then  containing  nitric  acid.  The  crystals, 
which  may  be  considered  as  a  nitrate  of  the  oil  of  cinnamon,  pre- 
sent the  formula  CigH^O^jNO^+HO. 

Pure  oil  of  cinnamon  is  a  colourless,  oleaginous  liquid,  which  be- 
comes perfectly  solid  with  nitric  acid,  and  reproduces  the  crystalline 
compound  j  ust  mentioned.  It  absorbs  chlorohy dric  acid  gas,  and  forms 
a  compound  CjgHgOgjHCl.  Chlorine  acts  powerfully  upon  it,  and, 
if  its  action  be  exhausted  by  heat,  and  the  product  distilled  in  a 
current  of  chlorine,  we  obtain  white  acicular  -crystals  of  quadri- 
chlorinated  oil  of  cinnamon  CjgH^Cl^O^,  called  also  Morocinnose. 

Oil  of  cinnamon  absorbs  the  oxygen  of  the  air,  and  is  converted 
into  a  peculiar  substance  CjgHyOgjHO,  called  cinnamic  acid,  which 
may  be  regarded  as  being  derived  from  the  oil  Q^Jlfi^,  by  the 
substitution  of  1  equivalent  of  oxygen  for  one  of  hydrogen.*  The 
acid  is  also  formed  when  oil  of  cinnamon  is  treated  with  hydrate 
of  potassa,  hydrogen  being  disengaged ;  while,  if  the  action  of  the 
potassa  be  prolonged,  benzoate  of  potassa  K0,Cj4H503  only  is  found 
in  the  liquid. 

Concentrated  boiling  nitric  acid  converts  oil  of  cihnamon  into  oil 
of  bitter  almonds  and  into  nitrobenzoic  acid. 

*  This  view  is  certainly  incorrect,  because  oxygen  will  not  replace  hydrogen. 
The  oil  of  cinnamon  simply  gains  2  equivalents  of  oxygen,  while  1  equivalent  of 
water  parts  from  it  and  becomes  basic. —  W.  L.  F. 


CINNAMIC  ACID.  659 


Cinnamic  Acid  CigH^OajHO. 

§  1552.  We  have  said  that  cinnamic  acid  is  formed  by  the  oxida- 
tion of  oil  of  cinnamon ;  but  it  exists  already  formed  in  balsams  of 
Tolu  and  Peru,  from  which  it  is  generally  extracted  by  running  the 
the  balsam  of  Peru  into  milk  of  lime,  which  is  constantly  stirred, 
when  the  resins  of  the  balsam  combine  with  the  lime  and  produce 
insoluble  compounds.  By  treating  the  whole  with  boiling  water,  the 
cinnamate  of  lime  only  is  dissolved,  and  crystallizes  on  the  cooling 
of  the  liquid ;  and  by  decomposing  a  boiling  solution  of  cinnamate 
of  lime  with  chlorohydric  acid,  the  cinnamic  acid  is  deposited,  on 
cooling,  in  the  form  of  pearly,  colourless  lamellas,  which  melt  at 
264.2°,  and  boil  at  about  570°.  The  alkaline  and  alkalino-earthy 
cinnamates,  are  soluble  in  water,  while  the  majority  of  the  other 
metallic  cinnamates  are  insoluble ;  and  their  general  formula  is 
RO,Ci8H^03,  when  they  contain  no  water  of  crystallization. 

By  causing  chlorohydric  acid  gas  to  act  on  cinnamic  acid  dis- 
solved in  absolute  alcohol  or  in  anhydrous  wood-spirit,  cinnamic 
ethers  Qfifi^Q^^^O.^  and  (^^fi^Q^^^O^  are  obtained. 

By  heating  1  part  of  cinnamic  with  8  parts  of  concentrated  nitric 
acid,  a  spongy  mass  results,  which  is  to  be  washed  with  water,  and 
afterward  dissolved  in  boiling  alcohol.  The  alcoholic  liquid  depo- 
sits, on  cooling,  acicular  crystals,  fusible  at  a  high  temperature,  of 
nitrocinnamic  acid  Ci8Hg(NOj03,HO. 

Cinnamen  CigHg. 

§  1553.  "When  vapours  of  cinnamic  acid  are  passed  through  a 
glass  tube  heated  to  a  dull-red,  carbonic  acid  is  disengaged,  with  a 
carburetted  hydrogen,  cinnamen  C^gHg,  which  condenses  in  the 
form  of  a  colourless  liquid : 

C„H,03,HO=C,eH3+2CO,. 

The  same  substance  is  obtained  by  decomposing  cinnamate  of  cop- 
per by  heat,  or  subjecting  to  dry  distillation  certain  resins,  particularly 
storax,  a  kind  of  balsam  found  in  commerce.  The  best  method  of 
preparing  cinnamen  consists  in  mixing  10  kilog.  of  storax  with  3J 
kilog.  of  carbonate  of  soda,  and  distilling  the  whole  in  an  alembic 
with  a  sufficient  quantity  of  water,  when  a  milky  water  passes  over, 
which  by  resting,  parts  with  the  cinnamen,  which  floats  on  its  sur- 
face. Storax  thus  yields  rather  more  than  ^^  of  its  weight  of  cin- 
namen ;  and  the  oil  obtained  is  left  for  some  time  on  chloride  of 
calcium,  and  then  distilled. 

Cinnamen  is  a  colourless  liquid,  of  a  penetrating  odour,  of  the 
density  0.95  at  32°,  and  boiling  at  294.8°.  When  heated  to  390° 
in  a  glass  tube  hermetically  closed,  it  is  converted  into  an  isomeric 
substance,  metacinnamen,  which  is  solid,  and  insoluble  in  water,  al- 


660 


ESSENTIAL   OILS. 


cohol,  and   ether.      Heated  to   distillation,  metacinnamen   again 
passes  into  the  state  of  cinnamen. 

Chlorine,  when  cold,  reacts  upon  cinnamen,  and  converts  it  into 
a  viscous  fluid,  of  the  formula  CigHgClg,  but  which  we  shall  write 
CigH^CljHCl.  Distilled  over  quicklime,  or  treated  with  an  alcoholic 
solution  of  potassa,  this  compound  yields  monochlorinated  einiia- 
men  CigH^Cl.  Monobrominated  cinnamen  CjgHyBr  is  also  ob- 
tained, as  well  as  its  bromohydrate  CigHyBrjHBr. 

Balsams  of  Peru. 

§  1554.  Two  species  of  balsam  of  Peru  are  found  in  commerce : 
a  liquid  balsam,  which  alone  has  been  properly  studied ;  and  a  solid 
and  nearly  black  balsam,  which  appears  to  be  a  modification  of  the 
first.  Balsam  of  Peru  is  dissolved  in  alcohol  at  96.8°,  and  an  al- 
coholic solution  of  potassa  added,  when  the  resin  contained  in  the 
balsam  combines  with  the  potassa,  with  which  it  forms  a  compound 
nearly  insoluble  in  water,  while  the  dnnamate  of  potassa  remains 
in  solution.  By  diluting  the  alcoholic  liquid  with  water,  the  cinna- 
mate  of  potassa  remains  in  solution,  while  a  complex  oil  separates, 
retaining  a  small  quantity  of  resin.  This  is  treated  with  oil  of 
naphtha,  which  leaves  the  resin,  and  dissolves  the  oil ;  and  the  latter 
is  cooled  in  a  refrigerating  mixture,  and  treated  with  weak  alcohol, 
equally  cold.  An  oily  portion,  which  is  cinname'in,  is  thus  ex- 
tracted, and  the  residue  is  dissolved  in  boiling  alcohol,  which  depo- 
sits a  crystalline  substance,  metacinname'in, 

Metacinnamein  is  a  solid,  very  fusible  substance,  insoluble  in 
water,  but  readily  soluble  in  alcohol  and  ether,  isomeric  with  oil  of 
cinnamon,  and  being  changed  by  hydrate  of  potassa  into  cincamic 
acid,  with  disengagement  of  hydrogen. 

Cinnamein  is  a  liquid,  which  does  not  volatilize  without  change ; 
and  a  concentrated  solution  of  potassa  decomposes  it,  by  prolonged 
contact,  into  cinnamic  acid  and  a  new  oily  liquid,  lighter  than  wa- 
ter, called  peruvin  CjgHjgOg.  The  composition  of  cinnamein  corre- 
sponds to  the  formula  Cg^HggOg,  and  it  may  be  represented  by  2 
equivalents  of  anhydrous  cinnamic  acid,  and  1  equivalent  of  peru- 
vin, according  to  the  equation 

^54H2608=2(Ci8H703) -I- CigHigOa. 

Balsam  of  Peru  may  therefore  be  considered  as  formed  of  cinna- 
mein, metacinnamein,  cinnamic  acid,  and  resinous  substances. 

Balsam  of  Tolu, 

§  1555.  Balsam  of  Tolu  is  composed  of  resin,  cinnamic  acid,  and 
a  carburetted  hydrogen,  isomeric  with  oil  of  terpentine,  and  called 
tolen.  This  balsam,  heated  with  a  solution  of  caustic  potassa, 
yields  benzoic  acid,  which  is  probably  formed  at  the  expense  of  the 
resin.     Tolen  is  a  colourless  liquid,  boiling  at  about  320°. 


COUMARIN.  661 


COUMARIN  C„H,0«. 


§  1556.  The  name  of  coumarin  has  been  given  to  a  crystalline 
odoriferous  substance  extracted  from  the  Tonka  bean,  but  which 
appears  to  exist  in  the  flowers  of  several  plants :  thus,  its  existence 
has  been  detected  in  the  flowers  of  the  melilot,  and  the  sweet  wood- 
ruff, called  waldmeister  by  the  Germans,  who  use  it  in  the  prepara- 
tion of  an  agreeable  beverage,  called  maitrarik.  Coumarin  is  pre- 
pared by  digesting  bruised  Tonka  beans  with  alcohol  at  96.8°,  when 
the  alcoholic  liquor,  subjected  to  distillation,  yields  a  syrupy  resi- 
due, which,  on  cooling,  sets  into  a  crystalline  mass.  This  is  dis- 
solved in  boiling  water,  and  the  liquid  being  discoloured  by  animal 
black,  the  coumarin  separates  in  white  crystalline  aciculse  during 
the  cooling. 

Coumarin  melts  at  122°,  and  boils  at  518°,  without  any  change, 
and  its  smell  is  agreeably  aromatic,  while  its  vapours  exert  a  pow- 
erful action  on  the  brain.  It  dissolves  freely  in  boiling  water,  but 
is  almost  wholly  deposited  from  it  on  cooling.  It  dissolves  in  cold 
monohydrated  nitric  acid,  with  evolution  of  heat ;  and  if  the  liquid 
be  then  diluted  with  water,  a  cheesy  precipitate  is  formed,  which 
dissolves  in  boiling  alcohol,  and  separates  again,  on  cooling,  in  small 
crystalline  aciculae.  It  is  nitrocoumarin  Q^^J^O^O^^  melting 
at  338°,  and  then  subliming  without  alteration  in  white  and  pearly 
crystals.  If  the  action  of  the  nitric  acid  be  prolonged,  the  couma- 
rin is  converted  into  trinitrophenic  acid  Ci2ll2(N04)03,HO,  which 
shall  hereafter  be  described. 

Coumarin  dissolves  in  a  weak  solution  of  potassa,  and  is  preci- 
pitated from  it  without  change  when  the  alkali  is  saturated  with  an 
acid ;  while,  if  the  solution  is  concentrated,  and  it  be  boiled,  adding 
some  pieces  of  hydrate  of  potassa,  coumaric  acid  Ci8H^.05,HO  is 
formed ;  and  if  the  temperature  be  greatly  raised,  hydrogen  is  dis- 
engaged and  salicylic  acid  formed  at  the  same  time.  The  alkaline 
substance,  treated  with  water,  and  then  supersaturated  with  chloro- 
hydric  acid,  deposits  coumaric  acid,  which  is  washed  with  cold  wa- 
ter, to  dissolve  the  salicylic  acid  which  may  have  been  precipitated 
with  it,  and  then  dissolved  in  ammonia,  which  leaves  the  coumarine 
unchanged.  The  ammoniacal  liquid  is  boiled  to  drive  off  the  excess 
of  ammonia,  when  nitrate  of  silver  is  added,  effecting  a  precipitate 
of  coumarate  of  silver,  which,  with  chlorohydric  acid,  yields  free 
coumaric  acid,  removable  by  means  of  ether. 

Coumaric  acid  is  a  white  crystalline  substance,  very  soluble  in 
alcohol  and  ether,  dissolving  freely  in  boiling,  but  nearly  insoluble  in 
cold  water,  and  melting  at  about  374°.  The  general  formula  of 
the  coumarates  is  ROjCigH^Oj,  from  which  it  will  be  seen  that  an- 
hydrous coumaric  acid  only  differs  from  coumarin  by  the  addition 
of  1  equivalent  of  water. 


662  ESSENTIAL   OILS. 

OIL  OF  ANISEED,  AND  THE  ANISIC  SERIES. 

§  1557.  By  distilling  aniseed  with  water,  a  slightly  yellowish  essen- 
tial oil  is  obtained,  possessing  the  characteristic  odour  of  the  seed,  and 
which,  at  a  low  temperature,  consolidates  almost  wholly  into  a  crys- 
talline mass.  This  mass  is  pressed  between  tissue-paper,  when  a 
liquid  portion,  of  which  the  nature  is  not  yet  known,  separates ;  and 
it  is  redissolved  in  alcohol,  which  deposits,  on  evaporation,  white 
crystalline  lamellae,  fusible  at  64.4°,  and  boiling  at  about  428°. 
This  substance  is  called  concrete  oil  of  aniseed,  and  its  formula 
is  CgoHjgOg.     When  made  liquid  by  heat,  it  rotates  to  the  left. 

Oil  of  aniseed  absorbs  chlorohydric  gas  and  forms  a  compound 
C2oHi202,2HCl ;  while  chlorine  acts  upon  it  and  produces  compounds 
derived  by  substitution :  thus, 

A  trichlorinated  oil C20H9CI3O2 

And  a  quadrichlorinated  oil C20H3CI4O2 

have  been  separated. 

With  bromine,  a  tribrominated  oil  C2oH9Br302,  and,  with  nitric 
acid,  the  binitric  oil  C2oHio(N04)202,  have  been  obtained. 

When  oil  of  aniseed  is  heated  with  dilute  nitric  acid,  a  reddish  oil 
falls  to  the  bottom  of  the  acid  liquid,  by  distilling  which,  after 
having  washed  it  with  water,  two  substances  are  collected;  one 
being  crystalline,  and  a  new  acid,  called  anisic  C^Ji^O^,liO ;  and 
the  other  liquid,  and  consisting  of  a  neutral  substance  CjgHgO^, 
to  which  the  name  of  hydruret  of  miisyle  has  been  given.  It  will 
be  seen  that  anisic  acid  may  be  considered  as  resulting  from  the 
substitution  of  1  equiv.  of  oxygen  for  1  equiv.  of  hydrogen,*  in  the 
molecule  of  hydruret  of  anisyl,  and  there  exists,  therefore,  between 
these  two  su^bstances,  the  same  relation  as  between  oil  of  bitter 
almonds  O^Jlfi^,  ^^^  benzoic  acid  Ci4H503,HO. 

The  mixture  of  the  two  substances  is  treated  with  a  weak  solution 
of  potassa,  which  dissolves  the  anisic  acid,  when  the  hydruret  of 
anisyl  is  distilled  in  a  current  of  carbonic  acid  gas. 

Hydruret  of  anisyl  is  a  colourless  gas,  which  absorbs  the  oxygen 
of  the  air,  and  is  converted  into  anisic  acid.  Chlorine  acts  upon  it 
and  yields  a  monochlorinated  product  CjgH^ClO^.  When  hydruret 
anisyl  is  dropped  on  melted  caustic  potassa,  hydrogen  is  disengaged 
and  anisic  acid  formed. 

Anisic  acid  crystallizes  in  white  inodorous  needles,  which  melt  at 
347°,  and  volatilize  without  change,  and  it  dissolves  readily  in  boil- 
ing water,  alcohol,  and  ether.  The  general  formula  of  its  salts  is 
RO,C„H,0,. 

Chlorine  and  bromine  form  chlorinated  and  brominated  anisic 
acids,  while  nitric  acid  forms  first  a  nitranisic  acid  CioH-Q^i^ 0^)0 ^,110. 

^  The  hydruret  of  anisyl  takes  up  2  equiv.  of  oxygen  and  loses  1  equiv.  of 
>rater,  which  becomes  basic  with  the  acid  formed. —  W.  L.  F. 


ANISEN.  663 

and  then,  if  a  mixture  of  fuming  nitric  and  concentrated  sul- 
phuric acid  be  made  to  act  upon  it,  it  forms  trinitr anisic  acid 
Q-^^J^O^fi^^'E.O,  Anisic  acid  yields  anisole  Ci^HgOg  by  distilla- 
tion with  caustic  baryta : 

Ci,H705,HO+2BaO=2(BaO,C02)+Ci4Hs02. 

Anisen  or  Benzoen  Cj^Hg. 

§  1558.  These  names  have  been  given  to  a  carburetted  hydrogen 
Cj^Hg,  which  is  to  anisic  acid  CigHyOgjHO  what  benzin  Cj^Hg  is  to 
benzoic  acid  Q^Jlfi^^YiO,  It  is  prepared  by  distilling  the  resin  of 
balsam  of  tolu,  and  collecting  the  oil,  which  is  again  distilled  at  a 
temperature  not  exceeding  284° ;  the  distilled  portion  being  recti- 
fied several  times  over  caustic  potassa,  and  dried  over  chloride  of 
calcium.  It  is  a  very  fluid,  colourless  liquid,  boiling  at  226.4°,  and 
its  density  is  0.87  at  64.4° ;  while  that  of  its  vapom-  is  3.26,  its 
equivalent  Cj^Hg  corresponding  therefore  to  4  volumes  of  vapour. 
'  Chlorine  acts  readily  upon  anisen,  and  yields 

Monochlorintated  anisen Ci^H^Cl, 

Trichlorinated  "      Ci^H^Cl^, 

Sesquichlorinated      "      Ci^H2Clg, 

as  well  as  the  following  compounds,  which  these  substances  form 
with  chlorohydric  acid:  Q^Jifi\,YLQ\  Q^Jlfil^^indl,  ^iJ^S^h, 
3HC1. 

§  1559.  Nitric  acid  produces  nitranisen  (j-^J3.^{B0^  and  hini- 
tr anisen  Q^JIJ^O^^-  Nitranisen  yields,  with  sulf  hydrate  of  am- 
monia, an  alkaloid  C14H9N  which  is  called  toluidin;  the  reaction 
being  analogous  to  that  which  forms  anilin  with  nitrobenzin,  (§  1538,) 
according  to  the  equation 

Ci,H7(NOJ+6(NH3,2HS)=Ci,H^-f6S+4HO+6(NH3,HS). 

Nitranisen  must  be  dissolved  in  alcohol,  and  ammonia  and  sulf- 
hydric  gas  be  successively  passed  through  the  liquid,  which,  after 
being  left  for  some  days  to  itself,  and  then  gently  heated,  is  again 
subjected  to  the  successive  action  of  ammoniacal  and  sulf  hydric  gas, 
and  is  finally  saturated  with  chlorohydric  acid,  and  evaporated  to 
one-third,  when  the  residue  is  distilled  with  caustic  potassa.  The 
toluidin  condenses  in  the  receiver  in  the  form  of  a  colourless  oil, 
which,  on  cooling,  sets  into  a  crystalline  mass.  In  order  to  purify 
it,  oxalic  acid  is  added,  and  it  is  treated  with  alcohol,  which  dissolves 
the  oxalate  of  toluidin,  and  leaves  the  oxalate  of  ammonia.  Oxa- 
late of  toluidin  is  decomposed  by  caustic  potassa,  and  the  isolated 
toluidin  coagulates  in  a  crystalline  crust  on  the  surface  of  the 
liquid. 

Toluidin  melts  at  104°,  and  boils  at  about  390°,  and  its  salts 
crystallize  readily;  their  general  formula  being  (Ci4H9N,HO)A. 


664  ESSENTIAL   OILS. 

OIL  OF  CUMIN  AND  THE  CUMINIC  SERIES. 

§  1560.  Cumin  seed,*  distilled  with  water,  yields  an  essential  oil 
composed  of  carburetted  hydrogen  CjoH^^,  cymen,  and  another 
volatile  oil  C2oH^202,  called  cuminole.  When  oil  of  cumin  is  again 
distilled,  the  cymen  passes  over  first,  at  about  392°,  which  tempera- 
ture is  maintained  so  long  as  any  thing  passes  over,  when  the  re- 
ceiver is  changed  and  the  temperature  raised  by  passing  a  current 
of  carbonic  acid  gas  through  the  retort :  the  cuminole  then  distils. 

Cuminole  is  a  colourless  liquid,  having  the  smell  of  cumin,  and  an 
acrid  and  burning  taste,  and  it  boils  at  428° ;  the  density  of  its  vapour 
being  5.24,  and  its  equivalent  Q^^^fi^  being  represented  by  4 
volumes  of  vapour.  It  rapidly  absorbs  the  oxygen  of  the  air,  and 
is  converted  into  euminic  acid  C2oHjj03,HO,  which  transformation  it 
readily  undergoes  when  boiled  with  a  concentrated  solution  of  potassa, 
or  when  dropped  into  melted  hydrate  of  potassa ;  hydrogen  being 
disengaged  in  the  latter  case.  Oxidizing  reagents,  such  as  nitric 
acid,  chlorine  in  the  presence  of  water,  chromic  acid,  etc.,  also  con- 
vert cuminole  into  euminic  acid. 

Chlorine  acts  on  cuminole  when  exposed  to  diffused  light,  and 
produces  monochlorinated  cuminole  Q^^^filO^ ;  while  bromine  forms 
monobrominated  cuminole  Q^^firO^. 

Cuminic  Acid  C2oHii03,HO. 

§  1561.  This  acid  is  generally  prepared  by  melting  hydrate  of 
potassa  in  a  retort  having  a  pointed  tube  fitted  to  its  tubulure,  through 
which  the  crude  oil  of  cumin  drops;  when  the  cymen  is  not  acted 
jon,  and  distils  without  change,  while  the  cuminole  is  decomposed  by 
contact  with  the  alkali,  being  converted  into  cuminic  acid,  which 
remains  combined  with  the  potassa.  The  alkaline  mass  being  dis- 
solved in  water,  and  heated  to  ebullition,  an  excess  of  ehlorohydric 
acid  is  added,  which  precipitates  the  cuminic  acid  in  flakes ;  and  the 
latter,  redissolved  in  alcohol,  are  transformed  into  beautiful  prisma- 
tic tablets. 

Cuminic  acid  melts  at  a  few  degrees  above  212°,  and  boils  at 
about  500°,  subliming  without  alteration  in  crystalline  aciculae. 
Hot  water  dissolves  it  slightly,  and  deposits  it  entirely  on  cooling, 
while  it  dissolves  freely  in  alcohol  and  ether.  The  general  formula 
of  the  cuminates  is 

RO,C2oH,,03. 

Cymen  CgoHj^. 

§  1562.  We  have  described  (§  1560)  the  best  method  of  separat- 
ing cymen  from  crude  oil  of  cumin.  It  is  a  colourless  liquid,  of 
an  agreeable  odour,  resembling  that  of  lemon;  it  boils  at  347°,  and 

*  The  seed  of  cuminum  cyminum. —  W.  L.  F. 


EUGENIC   ACID.  665 

the  density  of  its  vapour  is  4.64,  its  equivalent  being  represented 
bj  4  volumes  of  vapour.  Nordhausen  sulphuric  acid  dissolves  it, 
and  produces  a  compound  acid  C2oHi3,S205,HO  which  forms  a  solu- 
ble salt  with  baryta. 

ESSENTIAL  OIL  OF  CLOVES,  AND  THE  EUGENIC  SERIES. 

§  1563.  Cloves  and  Jamaica  pimento  yield,  by  distillation  with 
water,  a  yellowish  essential  oil  of  a  complicated  character,  for  four  dis- 
tinct substances  have  already  been  separated  from  it:  a  carburuetted 
hydrogen,  isomeric  with  oil  of  terpentine ;  an  oxygenated  essential 
oil  C2oHi^03,HO,  called  eugenic  acid,  because  it  possesses  acid  proper- 
ties ;  and  two  neutral  crystalline  substances,  eugenin  and  cariophyllin. 

Water  which  has  been  distilled  over  cloves  gradually  deposits  a 
substance  crystallized  in  pearly  spangles,  consisting  of  eugenin 
CgoHigO^,  isomeric  with  eugenic  acid. 

Crude  oil  of  cloves  deposits,  after  some  time,  fine  colourless  aci- 
culse  of  cariophyllin  CaoHigOg,  isomeric  with  the  camphor  from  the 
family  of  the  laurels. 

If  crude  oil  of  cloves  be  mixed  with  a  concentrated  solution  of 
potassa,  a  crystalline  mass,  of  the  consistence  of  butter,  is  formed, 
which  is  separated  and  distilled  with  water,  when  the  oil,  isomeric 
with  terpentine  alone,  passes  over,  while  the  eugenic  acid  remains 
in  the  residue  in  the  state  of  eugenate  of  potassa.  The  residue  is 
treated  with  chlorohydric  acid,  which  separates  the  eugenic  acid 
from  it  in  the  form  of  a  colourless,  oleaginous  liquid,  boiling  at  473°, 
which  is  distilled  in  a  current  of  carbonic  acid  gas. 

Eugenic  acid  absorbs  the  oxygen  of  the  air,  and  is  converted  into 
a  resinous  substance.  It  forms  crystallizable  salts  with  potassa, 
soda,  and  lime,  of  the  general  formula  l^O^Q^^i^^^Oy 

OIL  OF  POTATO-SPIRIT,*  OR  AMYLIC  ALCOHOL  C,oH«0,. 
§  1564.  This  oil  is  obtained  when,  in  the  manufacture  of  alcohol, 
the  liquors  resulting  from  the  action  of  ferment  on  the  fecula  of  the 
potato  are  distilled;  and  it  is  also  formed  in  the  distillation  of  cer- 
tain alcoholic  products  obtained  in  the  fermentation  of  the  cerealia 
or  of  grapes;  the  oil,  therefore,  constantly  accompanying  the  pro- 
ducts of  alcoholic  fermentation.  Toward  the  close  of  the  distillation 
of  brandy  from  fecula,  the  largest  proportion  of  the  oil  is  obtained, 
when  a  milky  water  passes  over,  on  the  surface  of  which,  after  rest- 
ing for  some  time,  the  oil  floats.  The  composition  of  this  oil  is  very 
complicated,  and  when  distilled,  it  begins  to  boil  at  about  185°, 
while  its  boiling  point  rises  to  269.6°,  at  which  it  remains  for  some 
time;  the  last  product,  which  is  collected  separately^  being  almost 
wholly  composed  of  the  essential  oil  required.  It  is  purified  by 
several  rectifications,  and  the  oil  which  boils  exactly  at  269.6°  should 
alone  be  regarded  as  pure. 

*  Also  called /oMscZ  ofZ. —  W.  m..  F. 


ESSENTIAL   OILS. 

Oil  of  potato-spirit  is  an  oily,  colourless  liquid,  of  a  strong  and 
disagreeable  odour  and  an  acrid  and  burning  taste.  Its  density  at 
59°  is  0.818,  while  that  of  its  vapour  is  3.15,  its  equivalent  C^oE^fi^ 
corresponding  to  4  volumes.  At  —  4.0°  it  solidifies  in  crystalline 
leaflets ;  and  it  stains  paper  like  the  essential  oils,  but  the  spot 
quickly  disappears,  because  the  oil  volatilizes.  Oil  of  potato-spirit 
does  not  ignite  at  the  approach  of  a  burning  substance,  unless  it 
be  at  a  temperature  of  120°  or  140°,  its  vapour  supporting  com- 
bustion only  at  that  degree.  It  is  not  sensibly  soluble  in  water,  but 
dissolves  in  all  proportions  in  alcohol  and  ether.  Oil  of  potato 
spirit  rotates  toward  the  left. 

A  large  number  of  compounds  is  derived  from  the  oil,  so  analo- 
gous to  those  obtained  by  means  of  alcohol  and  wood-spirit,  that 
chemists  have  not  hesitated  to  regard  this  oil  as  a  true  alcohol,  to 
which  they  have  given  the  name  of  amylic  alcohol.  In  our  subse- 
quent investigation  of  these  compounds,  we  shall  follow  the  same 
order  as  in  those  of  the  vinic  and  methylic  compounds,  since  their 
analogy  will  be  thus  more  easily  understood. 

Aotion  of  Sulphuric  Acid  on  Amylic  Alcohol. 

§  1565.  By  shaking  together  equal  parts  of  oil  of  potato-spirit 
and  concentrated  sulphuric  acid,  a  brown  liquor  is  formed,  which, 
when  saturated  with  carbonate  of  baryta,  yields  sulphate  of  baryta 
and  a  soluble  salt  of  baryta,  the  solution  of  which  is  bleached  by 
animal  black.  The  liquor,  when  evaporated  at  a  gentle  heat,  yields 
small  crystalline  lamellae  of  sulphamylate  of  haryta,  of  the  formula 
BaO,(CioHiiO,2S03)  +  3HO,  which  is  decomposed  at  the  boiling 
point.  Its  solution,  when  decomposed  by  sulphate  of  potassa, 
yields,  after  evaporation  and  dessication  in  vacuo,  a  crystalline  resi- 
due of  sulphamylate  of  potassa  KO,(CioIIiiO,2S03).  If,  on  the 
contrary,  the  baryta  be  precipitated  by  sulphuric  acid  added  drop- 
wise,  a  solution  of  free  sulphamylic  acid  is  obtained,  which,  boil- 
ing readily,  decomposes  into  sulphuric  acid  and  amylic  alcohol 
0,„H,,0,  or  C„H,iO,HO. 

§  1566.  If  an  excess  of  concentrated  sulphuric  acid  be  made  to 
act  on  amylic  alcohol,  and  it  be  heated  to  boiling,  we  obtain  a  car- 
buretted  hydrogen  C^oHjo,  called  amyUn,  which  is  to  amylic  alco- 
hol CioHjjO,HO  what  olefiant  gas  C^H^  is  to  vinic  alcohol  C^H^O, 
HO.  All  reagents  which  abstract  water  from  vinic  alcohol  modify 
amylic  alcohol  in  an  analogous  manner  :  thus  both  concentrated  and 
anhydrous  phosphoric  acid,  fluoboric  and  fluosilicic  gases,  and  chlo- 
ride of  zinc  produce  the  same  efi'ect  as  concentrated  sulphuric  acid. 
As  the  chloride  of  zinc  effects  the  neatest  decomposition,  it  is  gene- 
rally used  in  the  preparation  of  pure  amylen.  Amylic  alcohol  is 
heated  in  a  retort,  with  a  solution  of  chloride  of  zinc  marking  70° 
on  the  hydrometer,  the  retort  being  frequently  shaken  while  the  tem- 
perature rises :  when  the  oil  is  finally  wholly  dissolved,  distillation 


AMYLIC   ALCOHOL.  667 

may  be  begun.  The  liquid,  when  distilled,  is  again  rectified  in  a 
tubulated  retort  furnished  with  a  thermometer,  and  only  the  most 
volatile  part  is  collected. 

Amylen  thus  obtained  is  a  colourless,  very  fluid  liquid,  boiling 
at  102.2°,  and  the  density  of  its  vapour  being  2.45,  its  equivalent 
CjoHio  corresponds  to  4  volumes  of  vapour,  like  that  of  olefiant  gas. 

Amylen  can  form  two  isomeric  products :  paramylen  CgoHgo ;  and 
metamylen^  of  which  the  formula  is  Cg^Hg^  or  C^oH^^.  These  two  pro- 
ducts generally  arise  at  the  same  time  as  the  amylen,  and  are  found 
in  the  last  products  of  distillation  ;  but  they  may  be  obtained  directly 
by  distilling  amylen  with  chloride  of  zinc  several  times  successively. 
Paramylen  boils  at  about  320°,  and  the  density  of  its  vapour  is 
double  that  of  amylen  ;  for  which  reason  its  formula  has  been  writ- 
ten C20H20.  Metamylen  distils  only  at  570°  ;  but  it  probably  has 
not  yet  been  obtained  in  a  state  of  purity. 

§  1567.  Amylio  ether  Q^^^fi  has  not  yet  been  prepared  by  the 
action  of  sulphuric  acid  on  amylic  alcohol ;  but  it  has  been  obtained 
by  causing  an  alcoholic  solution  of  potassa  to  act  on  amylochloro- 
hydric  ether  CioHijCl,  of  which  we  shall  speak  presently.  It  is  a 
colourless  liquid,  of  an  agreeable  odour,  and  boiling  at  230°. 

Compound  Amylic  Ethers,  and  Compound  Amylic  Acids, 

§  1568.  As  yet  we  are  acquainted  neither  with  amylosulphuric 
ether  C-^Ji^fijSO^,  nor  with  amylonitric  ether  Q^^^fi^'^O^;  while 
an  amylonitrous  ether  G^oHL^fi^l^O^  is  produced  by  collecting  in 
amylic  alcohol  the  nitrous  vapours  which  are  disengaged  when 
starch  is  treated  with  nitric  acid.  By  distillation,  the  amylonitrous 
ether  separates  in  the  form  of  a  pale,  yellow  liquid,  which  is  to  be 
washed  several  times  with  water,  and  then  with  a  weak  solution  of 
potassa;  after  which  it  is  dried  over  chloride  of  calcium  and  redis- 
tilled. It  boils  at  204.8°,  and  the  density  of  its  vapour  is  4.03,  so 
that  its  equivalent  CioHijO,N03  corresponds  to  4  volumes  of  vapour, 
like  the  corresponding  product  of  the  vinic  series.  The  same  ether 
is  formed  when  nitric  acid  is  made  to  act  on  amylic  alcohol ;  but  it 
is  then  mixed  with  various  products  of  oxidation,  particularly  with 
valerianic  acid  and  methylic  aldehyde. 

By  causing  boracic  acid,  melted  and  reduced  to  an  impalpable 
powder,  to  act  on  amylic  alcohol,  exactly  under  the  circumstances 
which  have  been  described  for  alcohol,  (§  1248,)  there  remains  a 
residue  of  amylohihoracic  ether  Q^^^fifi^O^,  solid  at  a  low  tem- 
perature, but  assuming  at  about  248°  a  viscous  consistence  resem- 
bling that  of  fused  glass.  This  substance  resists  a  temperature  of 
570°  without  decomposition,  burns  with  a  green  flame,  and  is  decom- 
posed by  water.  « 

If  chloride  of  boron  be  made  to  act  on  amylic  alcohol,  an  oily 
liquid  is  obtained,  which  boils  without  change  at  about  527°,  and 


668  ESSENTIAL   OILS. 

consists  of  triamylhoracic  ether  ZQ^^^fi^'EO^,  The  density  of  iia 
vapour  is  10.55. 

By  dropping  amylic  alcohol  into  chloride  of  silicium,  shaking  the 
mixture  frequently,  then  distilling  it  and  collecting  only  the  product 
which  passes  over  at  from  608°  to  640°,  a  liquid  is  obtained,  which 
is  to  be  purified  by  several  distillations,  and  which  consists  of  tria^ 
■mylosilicic  ether  BCjoHnOjSiOa.     Water  decomposes  it  slowly. 

Amylacetic  ether  ^Q^^W^fi^QJlfi^  is  obtained  by  distilling  1  part 
of  amylic  alcohol,  2  parts  of  acetate  of  potassa,  and  1  part  of  con- 
centrated sulphuric  acid,  the  product  being  washed  with  an  alkaline 
solution,  dried  over  chloride  of  calcium,  and  rectified  a  last  time 
over  litharge.  It  is  a  colourless,  limpid  liquid,  of  an  aromatic 
odour,*  boiling  at  257°,  and  the  density  of  its  vapour  being  4.46, 
its  equivalent  corresponds  to  4  volumes  of  vapour,  like  the  corre- 
sponding ethers  of  the  vinic  and  methylic  series. 

Oxalic  acid  forms  two  compounds  with  amylic  alcohol,  correspond- 
ing to  those  which  it  produces  with  vinic  and  methylic  alcohols. 
When  amylic  alcohol  is  heated  with  oxalic  acid,  a  liquor  is  obtained, 
which,  when  saturated  with  carbonate  of  lime,  yields  a  soluble  salt 
of  lime,  the  amyloxalate  of  lime,  of  which  the  formula  of  the  crys- 
tals is  CaO,(CioHjiO,2C203)4-2HO ;  and  a  great  number  of  other 
amyloxalates  may  be  obtained  by  double  decomposition,'  by  means 
of  this  salt. 

If,  on  the  contrary,  the  mixture  of  amylic  alcohol  and  oxalic  acid 
be  distilled,  a  liquid  is  obtained,  boiling  at  500°,  and  called  amylox- 
alio  ether  C^QH.^fi,G20^,  which  rotates  toward  the  right,  in  an  oppo- 
site direction  to  that  of  amylic  alcohol.  This  liquid,  treated  with 
an  aqueous  solution  of  ammonia,  yields  oxamide ;  while  if  ammo- 
niacal  gas  be  passed  through  a  solution  of  amyloxalic  ether  in  abso- 
lute alcohol,  a  liquid  is  obtained  which  deposits,  on  evaporation, 
crystals  of  amyloxamic  ether  Q^^^fi,[Qfi^ll^. 

Simple  Ethers  of  the  Amylic  Series, 

§  1569.  We  have  described  (§  1567)  the  mode  of  preparing  simple 
amylic  ether  C^oHj^O.  Amylochlorohydric  ether  Q^^^-fil  is  ob- 
tained by  distilling  equal  parts  of  perchloride  of  phosphorus  and 
amylic  alcohol,  when  the  product  is  washed  with  alkaline  water  and 
dried  over  chloride  of  calcium.  The  same  substance  is  also  obtained 
by  causing  chlorohydric  acid  to  act,  for  a  long  time,  on  the  same 
alcohol ;  the  liquid  separating  into  3  layers,  of  which  the  upper  one 
contains  the  amylochlorohydric  ether.  It  is  a  colourless  liquid,  of 
an  aromatic  odour,  boiling  at  215.6°,  and  its  equivalent  corresponds 
to  4  volumes.     Chlorine  acts  on  it,  and  when  its  action  is  exhausted, 


*  The  odour  of  amylacetic  ether  closely  resembles  that  of  the  banana,  and  it  is 
■with  this  substance  that  the  favourite  acidulated  banana-drops  are  flavoured. — 
W.  L.  F. 


VALERIANIC  ACID.  669 

by  exposure  to  the  rays  of  the  sun,  a  chlorinated  product,  of  the 
formula  C10H3CI9,  is  obtained. 

By  causing  15  parts  of  amylic  alcohol,  8  parts  of  iodine,  and  1 
of  phosphorus  to  react  at  a  gentle  heat,  and  then  distilling  the  mix- 
ture, we  obtain  a  liquid,  which  is  to  be  purified  by  several  washings, 
drying  over  chloride  of  calcium,  and  redistillation.  It  is  amyliodo- 
hydric  ether  G^^^J.. 

By  distilling  a  concentrated  solution  of  sulphamylate  of  lime  and 
cyanide  of  potassium,  amylocyanohydric  ether  CjoHijCy  is  obtained; 
and  chlorohydrate  of  amylen  heated  with  an  alcoholic  solution  of 
monosulphide  of  potassium  produces  amylosulfhydric  ether  CioH^jS, 
a  colourless  liquid,  of  a  very  disagreeable  odour,  and  boiling  at 
402.8°.     Its  equivalent  is  represented  by  2  volumes  of  vapour. 

Sulphamylic  alcohol  or  amylic  mercaptan  CioHj^S^HS  is  obtained 
be  distilling  amylochlorohydric  ether  CjoHijCl  with  an  alcoholic 
solution  of  sulf  hydrate  of  sulphide  of  potassium.  It  is  an  oleaginous, 
colourless  liquid,  of  an  alliaceous  smell ;  and  it  boils  at  242.6°,  while 
its  density  at  69.8°  is  0.825.  In  contact  with  oxide  of  mercury  it 
yields  sulphamylomercuric  alcohol  CioHjiS,Hg2S. 

Products  of  the  Oxidation  of  Amylic  Alcohol, 

§  1570.  "When  amylic  alcohol  is  subjected  to  oxidizing  agencies,  it 
is  converted  into  an  acid  CioHgOgjHO,  called  amylic^  identical  with 
an  acid  extract  of  the  valerian  root,  and  called  valerianic  acid. 
This  acid  is  to  amylic  alcohol  CioHiiO,HO  what  acetic  acid  C4H3O3, 
HO  is  tovinic  alcohol  C4H50,HO,  and  what  formic  acid  C2H03,HO 
is  to  methylic  alcohol  C2H30,HO.  An  intermediate  product,  amylic 
aldehyde  CjoHjoOg,  corresponding  to  the  aldehyde  of  the  vinic  series, 
has  also  been  obtained,  but  it  is  difficult  to  isolate  it  among  the  pro- 
ducts of  oxidation  of  amylic  alcohol. 

By  heating  oil  of  potato-spirit  with  a  mixture  of  sulphuric  acid 
and  bichromate  of  potassa,  there  pass  over  in  distillation  valerianic 
acid  CioH903,HO  and  amylovalerianic  ether  Q^^^fi,(j-^^fi^.  If 
it  be  treated  by  a  solution  of  potassa,  the  valerianic  acid,  is  dissolved 
in  the  state  of  valerianate  of  potassa,  while  the  amylovalerianic  ether 
remains,  which  in  its  turn  may  be  wholly  transformed  into  valerianic 
acid,  if  its  vapours  be  passed  over  sodic  lime.  The  oil  of  valerian 
is,  in  fact,  converted  into  valerianic  acid,  when  its  vapours  are  passed 
over  sodic  lime  placed  in  a  flask  heated  in  an  oil-bath  to  a  tempera- 
ture between  400°  and  480° ;  hydrogen  only  being  disengaged  in 
the  beginning,  while  toward  the  close  of  the  operation  this  gas  is 
accompanied  by  carburetted  hydrogens.  The  flask  is  allowed  to 
cool,  and  is  opened  under  water  in  order  to  prevent  the  access  of 
air ;  and  the  substance,  diluted  with  water,  is  distilled  with  an  excess 
of  sulphuric  acid.  The  liquor  collected  in  the  receiver  is  saturated 
with  carbonate  of  soda,  and  the  solution  evaporated  to  dryness ;  and, 
lastly,  the  residue  is  distilled  with  phosphoric  acid,  when  the  vale- 


670  ESSENTIAL   OILS. 

rianic  acid  forms  an  oily  layer  on  the  surface  of  the  water  in  the 
receiver. 

§  1571.  In  order  to  extract  valerianic  acid  from  valerian  root,  it 
is  sufficient  to  distil  the  root  with  a  large  quantity  of  water  acidu- 
lated by  sulphuric  acid ;  a  still  larger  quantity  being  obtained  by 
using  the  following  mixture : — 1  kilog.  of  valerian  root,  100  gr.  of 
sulphuric  acid,  60  gm.  of  bichromate  of  potassa,  and  5  litres  of  water. 
This  is  owing  to  the  fact  that  valerian  contains  an  essential  oil, 
valerole  Q^^^fi^^  which  is  converted,  by  oxidizing  reagents,  into 
valerianic  acid.  The  distillation  should  not  be  commenced  until 
the  mixture  has  macerated  for  24  hours. 

Valerianic  or  amylic  acid  is  a  colourless  liquid,  having  a  strong 
odour  of  valerian,  and  the  density  0.937  at  62.6°,  while  it  boils  at 
175°;  its  equivalent  CioH903,HO  corresponding  to  4  volumes  of 
vapour.  It  dissolves  slightly  in  water,  but  in  all  proportions  in 
alcohol  and  ether.  The  majority  of  the  valerates  are  soluble,  and 
the  alkaline  valerates  crystallize  with  difficulty,  while  that  of  baryta 
forms  small  brilliant  prisms.  Valerate  of  silver  is  insoluble,  and 
presents  the  formula  KgO^Q^^fi^. 

Valerianic  acid  is  acted  on  by  chlorine,  even  when  protected  from 
direct  solar  light,  and  is  then  converted  into  trichlorinated  valerianic 
acid  CioHgClgOgjHO.  In  order  that  the  reaction  may  be  complete, 
heat  must  be  applied  toward  the  close,  and  the  current  of  chlorine 
must  be  kept  up  until  no  more  chlorohydric  acid  is  disengaged.  If 
the  action  of  chlorine  be  continued  in  the  sun,  quadrichlorinated 
acid  CioHgCl^OgjHO  is  obtained. 

Valerate  of  baryta,  distilled  over  the  fire  in  a  retort,  yields  a 
volatile,  oleaginous  product,  which  is  purified  by  redistillation,  col- 
lecting only  the  product  which  boils  at  212°.  The  formula  of  this 
compound  is  Q^Jl^fi^^  and  it  is  amylic  or  valeric  aldehyde,  which 
oxidizing  reagents  readily  convert  into  valerianic  acid;  the  trans- 
formation being  effected  even  by  the  oxygen  of  the  air  in  the  pre- 
sence of  platinum-sponge.* 

ESSENTIAL  OIL  OF  WINE,  OR  (ENANTHIC  ETHER  C^HAC.^H^aO,. 

§  1572.  There  exists  in  wine  an  essential  oil,  to  which  the  peculiar 
odour  of  wines,  called  their  bouquet,  has  been  chiefly  attributed.  It 
consists  of  a  compound  vinic  ether,  containing  an  acid  called  cenan- 
thic  (from  otvoj,  vine,  and  avdo^,  flower.) 

When  large  quantities  of  wine  are  distilled,  an  oil  volatilizes  to- 
ward the  close  of  the  operation,  which  is  a  mixture  of  vinoenanthic 

*  Amylic  ether  is  considered  as  the  oxide  of  a  radical  amyl  CioH,,,  in  the  same 
manner  as  ether  is  regarded  as  oxide  of  ethyl,  which  theor^  has  gained  much 
ground  since  amyl  has  been  actually  isolated. 

Valerianic  acid  then  assumes  the  formula  (C,Hg)CaOa,HO,  or  oxalic  acid  paired 
with  a  radical  valyl  CgHj,,  which  Kolbe  has  isolai.ed. 

See  the  note  to  I  1401.— IF.  L.  F. 


CAOUTCHOUC.  671 

ether  and  free  cenanthic  acid.  As  the  oenanthic  ether  is  much  more 
volatile  than  the  oenanthic  acid,  they  may  be  imperfectly  separated 
by  distillation;  the  first  products  being  much  richer  in  oenanthic 
ether.  In  order  to  obtain  pure  oenanthic  ether,  the  crude  oil  is 
shaken  with  a  hot  solution  of  carbonate  of  soda,  which  dissolves 
the  free  oenanthic  acid,  and  toward  the  close  it  is  heated  to  ebulli- 
tion, so  that  the  oenanthic  ether  may  separate  more  readily  and 
form  an  oily  layer  on  the  surface.  After  being  decanted,  and  again 
subjected  to  the  same  treatment,  it  is  dried  over  chloride  of  calcium 
and  purified  by  distillation. 

CEnanthic  ether  is  a  colourless  liquid,  of  a  very  penetrating  smell 
of  wine,  and  an  acrid  and  disagreeable  taste.  It  is  insoluble  in 
water,  but  dissolves  readily  in  alcohol  and  ether.  Its  density  is 
0.862,  it  boils  at  446°,  and  the  density  of  its  vapour  is  10.48;  its 
equivalent  €41150,01411^303,  being  therefore  represented  by  2  volumes 
of  vapour.  It  is  easily  decomposed  by  a  hot  solution  of  caustic 
potassa,  or  soda,  yielding  alcohol  and  oenanthic  acid  which  remains 
combined  with  the  alkali.  By  decomposing  the  alkaline  oenanthate 
by  dilute  sulphuric  acid,  the  oenanthic  acid  collects  on  the  surface 
of  the  liquid  in  the  form  of  a  colourless  oil,  which  is  merely  washed 
with  hot  water,  and  then  dried  in  vacuo. 

At  the  ordinary  temperature  oenanthic  acid  has  the  consistence 
of  butter,  while  it  becomes  very  fluid  at  a  higher  temperature,  and 
boils  at  about  570°.  It  does  not  sensibly  dissolve  in  water,  but  it 
nevertheless  reddens  litmus.  Alcohol  and  ether  dissolve  it  freely. 
The  distilled  acid  is  anhydrous,  and  presents  the  formula  (j^fi^fi^\ 
while,  when  in  contact  with  water,  it  abstracts  1  equiv.  from  it  and 
becomes  monohydrated  acid  Ci4Hi303,HO.  By  heating  to  302°  a 
mixture  of  5  parts  of  sulphovinate  of  potassa  and  1  part  of  monohy- 
drated oenanthic  acid,  a  vinoenanthic  ether  is  obtained,  which  may 
be  purified  by  a  hot  solution  of  carbonate  of  soda.  If  a  mixture  of 
wood-spirit,  concentrated  sulphuric  acid,  and  oenanthic  acid  be 
heated,  methoenanthic  ether  C2H30,Ci4Hi30  is  formed. 

As  vinoenanthic  ether  cannot  be  detected  in  the  fresh  juices  of 
vegetables,  it  is  probably  a  product  of  fermentation. 

CAOUTCHOUC. 

§  1573.  Caoutchouc  is  contained  in  the  milky  juice  of  several 
vegetables,  where  it  exists  in  the  form  of  small  globules,  suspended 
in  an  aqueous  liquid,  precisely  in  the  same  manner  as  the  fatty 
globules  in  milk.  The  chief  importations  of  caoutchouc  are  from 
Java  and  South  America;  and  it  is  obtained  from  the  siphonia 
cahucha  and  the  ficus  elastica.  The  milky  sap  of  these  trees  con- 
tains about  30  per  cent,  of  caoutchouc;  and  when  left  to  itself,  the 
globules  of  caoutchouc  float  on  the  surface,  because  they  are  lighter 
than  water,  and  form  a  thick  cream  on  it ;  which  separation  is  more 
easily  efiected  if  the  density  of  the  water  is  increased  by  sea-salt. 


672  ESSENTIAL   OILS. 

In  order  to  collect  the  caoutchouc,  deep  incisions  are  made  into 
the  base  of  the  tree  producing  it,  and  the  liquid  which  exudes  is  re- 
ceived in  earthen  vessels,  whence  it  is  transferred  into  bottles,  which, 
when  hermetically  sealed,  may  be  transported  and  preserved  .for  a 
long  time  without  undergoing  any  change.  The  greater  part  of  the 
caoutchouc  found  in  commerce  is  in  the  shape  of  pears,  either  smooth 
or  covered  with  marks,  and  generally  of  a  brown  colour.  The  In- 
dians make  these  pears  by  spreading  successive  layers  of  the  milky 
juice,  which  they  coagulate  in  the  sun,  over  pyriform  clay  moulds ; 
and  when  the  caoutchouc  is  of  sufficient  thickness,  they  dip  the  mould 
in  water  to  soften  the  earth,  which  is  then  emptied  through  the 
mouth  of  the  caoutchouc  bottle.  The  brown  colour  is  owing  to  the 
deposition  of  the  smoke  during  its  desiccation  over  fire. 

Pure  caoutchouc  must  be  obtained  from  the  milky  juice  itself,  by 
mixing  it  with  4  times  its  weight  of  water,  and  allowing  it  to  rest 
for  24  hours,  when  the  globules  of  caoutchouc  float  on  the  surface 
in  the  form  of  cream.  This  cream  is  removed,  and  by  agitation  is 
suspended  with  an  additional  quantity  of  water,  of  which  the  density 
is  increased  by  a  small  quantity  of  sea-salt  and  chlorohydric  acid ; 
when,  after  some  time,  the  caoutchouc  again  collects  on  the  surface, 
and  is  again  removed  and  washed,  and  so  on,  until  the  water  will  dis- 
solve no  more  of  it ;  after  which  the  substance  is  compressed  between 
paper  and  dried  under  the  receiver  of  an  air-pump.  Caoutchouc, 
thus  prepared,  is  a  white,  elastic  substance,  of  th^  density  0.925, 
and  containing  87.2  of  carbon  and  12.8  of  hydrogen. 

All  the  useful  articles  of  caoutchouc,  now  so  extensively  applied  in 
the  arts,  are  manufactured  from  the  pyriform  substance,  by  very 
various  mechanical  processes,  the  description  of  which  would  be  out 
of  place.  The  elasticity  and  impermeability  of  caoutchouc  render 
it  valuable  for  many  purposes  in  surgery,  and  it  also  finds  frequent 
use  in  the  laboratory  of  the  chemist  and  physicist.  It  has  recently 
been  used  for  covering  cloths  and  other  stuffs,  to  render  them  water 
and  air  tight. 

Caoutchouc  is  hard  at  a  low  temperature,  but  softens  readily  by 
heat,  and  at  77°  possesses  great  flexibility ;  while  it  melts  at  about 
248°,  and  then  forms  a  viscous  liquid,  which  does  not  recover  its 
original  condition  for  a  very  long  time.  If  it  be  further  heated, 
the  liquid  becomes  more  fluid,  and  remains  indefinitely  viscous  even 
after  cooling.  Melted  caoutchouc,  diluted  with  a  small  quantity  of 
some  fatty  oil,  is  used  for  greasing  stopcocks.  It  burns  with  a 
brilliant  and  very  smoky  flame ;  and  by  heating  it  to  distillation,  it 
is  converted  into  several  essential  oils,  of  different  volatile  powers, 
and  which  are  themselves  modified  by  redistillation. 

Caoutchouc  is  insoluble  in  water  and  alcohol,  although  boiling 
water  softens  it  and  causes  it  to  swell,  but  without  dissolving  it. 
Ether,  the  essential  oils,  and  sulphide  of  carbon,  on  the  contrary, 
dissolve  it  readily,  and  form  solutions,  which  deposit,  after  sponta- 


RESINS.  673 

neous  evaporation,  on  the  objects  to  whicli  they  have  been  applied, 
an  elastic  and  impervious  coating  of  caoutchouc* 

GUTTA-PERCHA. 

§15T4.  A  substance  of  organic  origin  has  lately  been  found, 
closely  resembling  caoutchouc  in  its  chemical  and  physical  proper- 
ties, and  called  gutta-percha^  which  is  used  in  the  fabrication  of 
bands  to  drive  machinery,  and  several  purposes  which  require  great 
solidity  united  to  a  certain  degree  of  flexibility.  It  is  imported 
from  India  and  China,  and  is  probably  the  product  of  some  vegeta- 
ble, although  as  yet  we  have  no  accurate  account  of  its  origin. 

Gutta-percha  is  of  a  grayish- white  colour,  of  a  consistence  resem- 
bling that  of  horn,  and  not  at  all  elastic ;  but  it  softens  and  be- 
comes more  elastic  by  an  increase  of  temperature,  its  original 
hardness  returning  after  cooling.  It  burns,  like  caoutchouc,  with 
a  brilliant  and  smoky  flame.  Water,  alcohol,  the  acid  or  alkaline 
liquors,  exert  no  action  upon  it ;  but  ether  and  the  essential  oils 
first  soften  and  then  dissolve  it.  Its  elementary  composition  difi*ers 
but  slightly  from  caoutchouc,  for  87.8  of  carbon  and  12.2  of  hydro- 
gen have  been  found  in  it.f 


RESINS. 


§  1575.  The  name  of  resins  has  been  given  to  certain  solid  sub- 
stances, widely  spread  among  vegetables,  and  which  flow  copiously 
from  some  of  them  in  the  state  of  solution  in  the  essential  oil. 
Resins  are  solid,  non-volatile,  sometimes  colourless,  most  frequently 
of  a  yellow  or  brown  tinge ;  insoluble  in  water,  but  dissolving  readily 

*  The  discoveries  of  Goodyear  that  caoutchouc  may  be  modified  in  its  properties 
by  various  processes,  termed  vulcanizing,  are  too  important  to  pass  over  in  utter 
silence.  Charles  Goodyear,  of  Connecticut,  United  States,  discovered,  by  years  of 
patient  and  laborious  experiment,  that  sulphur  heated  with  caoutchouc  produced 
what  he  termed  a  drying  effect  upon  the  latter,  rendering  it  more  elastic,  incapable 
of  becoming  hard  by  frost,  insoluble  in  ether,  the  essential  oils,  &c.  By  a  series 
of  highly  ingenious  mechanical  processes,  the  new  fabric  was  made  to  imitate 
paper,  every  kind  of  leather,  and  various  kinds  of  dry  goods,  still,  however,  re- 
taining more  or  less  of  the  original,  valuable  properties  of  the  rubber.  His  more 
recent  improvements  consist  in  imparting  to  caoutchouc  any  required  degree  of 
hardness  between  its  usually  soft  state  and  the  hardness  and  elasticity  of  ivory, 
effected  by  an  expansion  of  his  sulphurizing  process,  and  by  the  addition  of  mate- 
rials to  the  caoutchouc.  By  this  discovery  of  Goodyear,  and  through  his  enter- 
prise and  patient  perseverance,  a  single  vegetable  product  can  be  made  to  replace 
paper,  leather,  and  dry  goods,  but  with  greater  elasticity  and  durability, — to  re- 
place whalebone,  horn,  tortoise-shell,  horn,  and  ivory. — J.  C.  B. 

t  Gutta-percha  is  similar  in  its  origin  and  composition  to  caoutchouc,  and  yet 
presents  very  different  external  characters.  The  hardening  effect  produced  by 
Goodyear's  sulphuration  of  caoutchouc  seems  to  convert  the  latter  into  a  substance 
resembling  gutta-percha  in  its  properties,  and  enables  us  to  comphrehend  how  the 
same  class  of  plants  may  produce  substances  of  very  different  external  properties. 
The  uses  of  gutta-percha  are  rapidly  extending. — J.  C.  B, 
Vol.  IL— 43 


674  ESSENTIAL   OILS. 

in  absolute  alcohol,  which  frequently  deposits  them,  in  the  form  of 
crystals,  after  evaporation.  The  majority  of  resins  behave  like  weak 
acids,  and  form  definite  compounds  with  the  alkalies  and  with  other 
metallic  oxides.  We  shall  here  describe  only  the  resins  of  ter- 
pentine, which  have,  as  yet,  been  most  accurately  investigated. 

When  the  terpentine  which  exudes  from  the  pinus  maritima  is 
distilled  with  water,  the  oil  of  terpentine  distil3  with  the  water, 
while  a  substance  called  colophony  remains,  consisting  of  three  resins, 
possessing  acid  properties,  and  to  which  the  name  oi  pimarie^  st/lvie, 
and  pinic  acid  have  been  given.  The  elementary  composition  of 
these  three  acids  is  exactly  the  same,  corresponding  to  the  formula 
^40^3004=040112903,  HO. 

Pimaric  acid  predominates  greatly  over  the  other  two  acid  resins, 
and  colophony  appears  sometimes  to  be  wholly  constituted  of  it. 
In  order  to  obtain  it,  powdered  colophony  is  treated  several  times 
with  a  mixture  of  5  or  6  parts  of  alcohol  and  1  part  of  ether,  when 
the  sylvic  and  pinic  acids  are  dissolved,  while  the  greater  portion 
of  the  pimaric  acid  remains  as  a  residue,  and  is  purified  by  being 
crystallized  repeatedly  from  boihng  alcohol.  Pimaric  acid  dissolves 
very  readily  in  ether,  while  it  requires  10  parts  of  cold  and  its  o^vn 
weight  of  boiling  alcohol  for  solution.  It  melts  at  about  257°, 
and  then  undergoes  an  isomeric  modification,  which  is  easily  recog- 
nisable by  dissolving  it  in  cold  alcohol,  of  which  it  then  only  requires 
1  part.  However,  this  modification  is  not  fixed,  since,  after  a  cer- 
tain time,  the  pimaric  acid  is  regenerated,  with  its  original  proper- 
ties, in  the  alcoholic  solution,  and  the  greater  portion  of  it  is  depo- 
sited in  crystals. 

Crystallized  pimaric  acid  is  after  a  time  spontaneously  converted 
into  pinic  acid,  when  it  is  soluble  in  its  own  weight  of  alcohol,  and 
does  not  assume  any  crystalline  form. 

By  distilling  pimaric  acid,  an  oleaginous  substance  is  condensed 
and  congeals  in  the  neck  of  the  retort ;  and  it  is  purified  by  dis- 
solving it  in  boiling  alcohol,  whence  it  is  deposited  in  the  form  of 
crystalline  lamellae.  This  substance  is  identical  with  sylvic  acid, 
of  which  we  mentioned  the  presence  in  colophony,  differing  from 
pimaric  acid  by  its  crystalline  form,  melting  at  nearly  the  same 
temperature  of  257°,  and  dissolving  in  8  or  10  times  its  weight  of 
alcohol. 

A  great  number  of  resins  are  found  in  commerce,  which  are 
generally  called  by  the  name  of  the  vegetable  from  which  they  are 
derived;  and  the  chemical  properties  of  all  of  them  are  analogous 
to  those  of  resins  of  terpentine. 

Resins  yield  by  distillation  very  complicated  products :  carburet- 
ted  hydrogens,  which  burn  with  a  brilliant  flame,  and  are  used  as 
illuminating  gases ;  besides  essential  and  fixed  oils.  The  following 
products  have  been  separated : 


OIL   OF   GARLIC.  675 

Retinaphtha  Ci^Hg,  an  oil  boiling  at  226. 6*^. 
Betini/l   C,,K,,,^         '\       ^      "      ^    302.0°. 
Retinole  CjoHg,  isomeric  with  benzine,  boiling  at  464.0°. 
Retisterin^  isomeric  with  naphthalin,  a  crystalline  substance  melt- 
ing at  149°,  and  boiling  at  617.0°. 


SULPHURETTED  ESSENTIAL  OILS. 

§  1576.  Only  two  sulphuretted  essential  oils  are  as  yet  accurately 
known :  oil  of  mustard,  and  oil  of  garlic ;  while  their  number  will, 
without  doubt,  be  greatly  increased  hereafter. 

OIL  OF  GARLIC  C.H.S. 

§  1577.  This  essential  oil  is  obtained  by  distilling  cloves  of  garlic 
with  water,  when  an  extremely  fetid  brown-coloured  oil  passes  over, 
which  is  decanted,  and,  after  distillation  in  a  salt-water  bath,  is  rec- 
tified over  potassium  until  it  is  no  longer  acted  on  by  this  metal. 
Oil  of  garlic  is  a  colourless  liquid,  of  a  repulsive  odour,  less  dense 
than  water,  distilling  without  alteration,  and  presenting  the  formula 
CgHgS.  It  has  been  called  sulphide  of  allyl^  because  it  has  been 
considered  as  a  compound  of  sulphur  with  a  carburetted  hydrogen 
CgHg,  or  allyl.  This  oil  throws  down  precipitates  with  several 
metallic  solutions :  thus,  if  a  concentrated  solution  of  it  be  mixed 
with  an  equally  concentrated  solution  of  chloride  of  mercury,  a 
white  precipitate  is  formed,  which,  when  purified  by  being  washed 
in  alcohol,  presents  the  formula  (HgS)2,C6H5S+(HgCl)2,C6H5Cl. 
When  alcoholic  solutions  of  oil  of  garlic  and  bichloride  of  platinum 
are  mixed  together,  and  the  liquid  is  diluted  with  water,  a  yellow 
precipitate  is  formed,  of  which  the  composition  corresponds  to  the 
formula  3(PtS2,C6H5S)+PtCl2,C6H5Cl.  When  an  alcoholic  solution 
of  oil  of  garlic  is  added  to  nitrate  of  silver,  a  precipitate  of  sulphide 
of  silver  is  obtained,  mixed  with  a  white  crystalline  compound, 
which  is  deposited  from  a  solution  in  boiling  water,  when  kept  in  the 
dark,  in  the  form  of  brilliant  white  crystals,  of  a  composition  corre- 
sponding to  the  formula  AgO,N05,CgH50,  which  may  be  considered 
as  formed  by  the  combination  of  1  equivalent  of  nitrate  of  silver 
with  1  equivalent  of  oil  of  garlic,  the  equivalent  of  sulphur  in  the 
latter  having  been  replaced  by  1  equivalent  of  oxygen.  By 
treating  this  crystalline  substance  with  ammonia,  the  compound 
CgHgO,  called  oxyde  of  allyl^  is  separated,  in  the  form  of  a  volatile, 
colourless  oil,  of  a  disagreeable  odour,  which  combines  directly  with 
nitrate  of  silver,  reproducing  the  crystalline  compound  of  which  we 
have  just  spoken. 


676  ESSENTIAL   OILS. 


OIL  OF  BLACK  MUSTARD  C^H^NS, 


§  1578.  This  oil  does  not  exist  already  formed  in  mustard-seed, 
"but  is  developed  in  it,  in  the  presence  of  water,  by  a  kind  of  fer- 
mentation taking  place  between  the  substances  contained  in  the 
Feed,  to  which  we  shall  presently  recur.  The  fatty  oil  contained  in 
the  mustard-seed  is  extracted  by  means  of  a  press;  when  the  cake 
being  moistened  with  water,  and  left  to  itself  for  several  hours,  the 
seed,  at  first  inodorous,  soon  exhales  the  pungent  smell  of  mustard. 
It  is  then  distilled  with  water,  when  a  yellow  oil,  denser  than  water, 
passes  over  with  the  aqueous  vapours.  By  a  second  distillation 
with  water,  it  loses  colour  sensibly,  but  as  it  still  contains  foreign 
substances,  it  is  distilled  in  a  retort  furnished  with  a  thermometer, 
and  the  liquid  which  distills  below  293°  is  separated,  the  temper- 
ature being  arrested  at  this  point,  when  pure  oil  of  mustard  passes 
over. 

Oil  of  mustard  is  a  colourless  oil,  boiling  at  293°,  and  furnishing 
vapours  which  irritate  the  eyes  and  nose,  and  show  the  density  3.4, 
its  equivalent  C8H5NS2  corresponding  to  4  volumes  of  vapour.  It 
is  very  soluble  in  alcohol  and  ether,  but  insoluble  in  water,  and  it 
exerts  no  rotatory  power.  Its  formula  CgHgNSg  may  be  written 
€(51158,02^,8,  which  constitutes  oil  of  garlic  CgH^S  and  sulphocya- 
nogen ;  and  in  fact,  the  constitution  of  oil  of  mustard  must  be  thus 
considered,  for  if  it  be  treated  with  monosulphide  of  potassium,  oil 
of  garlic  C6H58  is  obtained  by  distillation,  while  the  liquid  contains 
sulphocyanide  of  potassium.  If  the  vapour  of  oil  of  mustard  be 
passed  over  a  mixture  of  lime  and  caustic  soda,  heated  to  248°, 
oxide  of  allyl  CgH^O  is  obtained,  and  the  residue  contains  sulpho- 
cyanides. 

.  §1579.  Oil  of  mustard  yields,  either  with  ammoniacal  gas  or 
with  liquid  ammonia,  a  crystallized  compound,  thiosinammin 
C8H5NS2NH3,  which  is  a  true  alkaloid.  This  substance  being  re- 
dissolved  in  boiling  water,  the  liquor,  when  bleached  by  animal 
black,  deposits,  by  evaporation,  the  thiosinammin,  in  the  form  of  pris- 
matic crystals,  of  a  brilliant  white  colour.  It  dissolves  in  chloro- 
hydric  acid,  forming  an  uncrystallizable  compound ;  while,  by  adding 
bichloride  of  platinum  to  the  solution,  a  yellow  crystalline  precipi- 
tate is  formed,  of  which  the  formula  is  (C8H5N82,NH3),HCl+PtCl2. 
Thiosinammin  dissolves  also  in  sulphuric,  nitric,  and  acetic  acids, 
but  the  compounds  do  not  crystallize. 

When  heated  with  oxide  of  lead  or  mercury,  it  parts  wholly  with 
its  sulphur,  and  a  new  alkaloid  CgHgNg,  called  sinammin,  is  formed : 

CsH5N82+NH3+2PbO=C8H6N2+2Pb8+2HO. 

Powdered  thiosinammin  is  mixed  with  freshly  precipitated  and 
moist  hydrated  protoxide  of  lead,  and  is  heated  over  a  water-bath 


MYRONIC   ACID.  677 

until  the  filtered  liquid  is  no  longer  blackened  by  the  addition  of 
potassa ;  after  which  it  is  heated  several  times  with  boiling  alcohol, 
to  dissolve  the  sinammin,  leaving,  after  evaporation,  a  syrupy  mass 
in  which  crystals  are  developed. 

Sinammin  has  a  strongly  alkaline  reaction,  but  forms  only  a  small 
number  of  crystallizable  salts  and  its  chlorohydric  solution  yields, 
with  the  bichloride  of  platinum,  a  flaky  yellow  precipitate,  of  the 
formula  CsHeN2,2HCl+2PtCl2. 

If  oil  of  mustard  be  digested  with  hydrated  oxide  of  lead, 
until  an  additional  quantity  of  the  oxide  ceases  to  turn  black,  and 
it  be  then  treated  with  boiling  water,  a  new  substance  C14H12N2O2, 
called  sinapoUn,  is  dissolved,  which  also  possesses  basic  properties, 
the  reaction  from  which  it  arises  being  expressed  by  the  following 
equation : 

Synapolin  crystallizes  from  its  aqueous  solution  in  spangles  of  a 
grayish  lustre,  and  turns  litmus  blue,  while  its  solution  in  chlorohy- 
dric acid  yields  a  crystalline  precipitate  with  chloride  of  mercury. 

Myronic  Acid  and  My  rosin. 

§  1580.  Black  mustard-seed  contains  an  acid  substance,  myronic 
acid,  combined  with  potassa,  which,  by  the  assistance  of  water  and 
a  peculiar  ferment,  called  myrosin,  also  contained  in  the  seed,  is 
converted  into  oil  of  mustard  by  a  peculiar  fermentation,  called 
sinapic  fermentation.  In  order  to  extract  the  myronate  of  potassa, 
black  mustard-seed,  previously  freed  from  its  fatty  oil  by  pressure, 
is  heated  with  alcohol  to  185° ;  when  the  ferment,  myrosin,  in  this 
way  coagulates  and  becomes  inactive.  The  substance  is  again  ex- 
pressed and  heated  with  tepid  water,  which  dissolves  the  myronate 
of  potassa ;  and  by  adding  alcohol  to  this  new  solution,  some  muci- 
laginous substances  are  coagulated,  when  the  liquid,  after  evapora- 
tion, deposits  crystals  of  myronate  of  potassa. 

By  pouring  tartaric  acid  into  a  concentrated  solution  of  myronate 
of  potassa,  the  greater  part  of  the  potassa  is  precipitated,  and  a 
Very  acid  liquor  remains,  which  leaves,  after  evaporation,  an  uncrys- 
tallizable  syrupy  substance.  The  composition  of  myronic  acid  is 
unknown. 

Myrosin  is  separated  by  exhausting  white  mustard-seed  with  cold 
water,  evaporating  the  filtered  liquid  at  a  low  temperature,  and 
adding  alcohol,  which  precipitates  the  myrosin.  Myrosin  cannot  be 
extracted  from  black  mustard-seed,  because  it  forms  oil  of  mustard 
as  soon  as  it  is  moistened  with  water.  No  other  known  ferment 
can  be  substituted  for  myrosin  in  the  sinapic  fermentation. 


678  PRODUCTS   OF   DRY   DISTILLATION. 

OF  SOME  IMPORTANT  PRODUCTS  WHICH  ARE  FORMED  DURING 
THE  DISTILLATION  OF  ORGANIC  SUBSTANCES. 

§  1581.  We  shall  include  in  this  chapter  some  important  sub- 
stances produced  by  the  distillation  of  organic  matter,  which  have 
not  yet  been,  with  certainty,  appended  to  any  great  series.  We 
shall  add  the  native  hydrocarburetted  essential  oils,  known  under 
the  name  of  naphtha  and  petroleum,  which  probably  arise  in  the  same 
manner  from  the  bosom  of  the  earth. 

NAPHTHALIN  CaoH,. 

§  1582.  This  remarkable  substance  is  formed  by  the  decomposition 
of  a  great  number  of  organic  substances  at  a  high  temperature,  a 
considerable  quantity  of  it  being  produced  in  the  manufacture  of 
illuminating  gas  from  bituminous  coal.  Adulterated  with  an  oily 
substance  and  lampblack,  naphthalin  is  deposited  in  crystals  on  the 
sides  of  the  pipes  which  convey  the  gas  from  the  retorts ;  and  it 
must  be  removed,  from  time  to  time,  to  prevent  their  becoming 
completely  choked ;  and  in  the  laboratory,  it  is  generally  extracted 
from  these  deposits.  The  most  simple  method  consists  in  employing 
the  process  described  (§  1527)  for  the  extraction  of  benzoic  acid,  by 
-sublimation  from  the  resin  of  benzoin,  the  naphthalin  thus  obtained 
being  nearly  pure ;  and  to  make  it  perfectly  so,  it  is  dissolved  in 
boiling  alcohol,  whence  it  is  again  deposited,  in  crystals,  on  cooling. 

Naphthalin  crystallizes  in  beautiful  rhomboidal  laminae,  of  a  white 
colour  and  greasy  lustre ;  has  a  peculiar,  very  persistent  odour ; 
melts  at  174.2°,  and  boils  at  413.6°,  the  density  of  its  vapour  being 
4.53,  and  its  equivalent  CgoHg  corresponding  to  4  volumes  of  vapour. 
Hot  water  dissolves  a  very  small  quantity  of  it,  for  water,  heated 
with  naphthalin,  becomes  slightly  cloudy  on  cooling.  Alcohol  dis- 
solves one-fourth  of  its  weight  of  it,  while  ether  and  the  essential 
oils  dissolve  it  more  freely. 

§  1583.  Chlorine  acts  readily  on  naphthalin,  which  first  becomes 
liquid  under  its  action,  but  again  solidifies  if  it  be  prolonged.  If 
the  substance  be  then  expressed  between  tissue-paper  and  crystal- 
lized in  ether,  a  homogeneous  substance  of  the  formula  C2oHg,Cl4is 
obtained,  which  may  be  considered  as  a  combination  of  1  equivalent 
of  naphthalin. and  4  equivalents  of  chlorine.  The  formula  of  the 
liquid  which  precedes  the  formation  of  this  crystalline  compound  is 
CgoHgjClg;  and  it  results  from  the  combination  of  1  equivalent  of 
naphthalin  with  2  equivalents  of  chlorine.  The  formula  of  the  crys- 
talline compound  may  be  written  C2oHgCl2,2HCl,  being  considered 
as  a  compound  of  1  equivalent  of  bichlorinated  naphthalin  CjoHgClg 
with  2  equivalents  of  chlorohydric  acid.  In  fact,  the  substance  is 
in  this  manner  decomposed  by  heat,  chlorohydric  acid  being  disen- 
gaged, while  bichlorinated  naphthalin  CjoHgClg  condenses  in  the  form 
of  a  colourless  liquid.     The  liquid  substance  Q^fi\  being  also 


NAPHTHALIN. '  679 

decomposed  by  heat  into  chlorohydric  acid,  and  into  monochlori- 
nated  naphthalin  C20H7CI;  its  formula  may  therefore  be  written 
C2oH7Cl,HCl.  These  are  not  the  only  substances  which  may  be 
derived  from  naphthalin  by  the  action  of  chlorine,  since  a  great 
numbers  of  others  exist,  which  are  obtained  by  subjecting  the  first 
two  to  various  reagents,  or  by  causing  chlorine  to  act  on  the  pro- 
ducts they  yield  by  distillation.  We  shall  merely  indicate  the  for- 
mulae of  the  principal  of  these  substances : 

Naphthalin CjoHg, 

Monochlorinated  naphthalin C20H7CI, 

Bichlorinated  "  CgoHgClg, 

Trichlorinated  "  C20H5CI3, 

Quadrichlorinated     "  CgoH^Cl^, 

Sesquichlorinated      "  CgoHgClg, 

Perchlorinated  "  CgoClg. 

With  bromine  have  been  obtained 

Monobrominated  naphthalin CgoH^Br, 

Bibrominated  "  CgoHgBrg, 

Tribrominated  "  C2oH5Br3, 

Quadribrominated      "  CgoH^Br^. 

By  the  successive  action  of  bromine  and  chlorine, 

Bromobichlorinated  naphthalin CgoH^BrClg, 

Bibromobichlorinated     "  C2oH4Br2Cl2, 

Bromotrichlorinated       "  CaoH^BrCla, 

Bibromotrichlorinated    "  CggHgBrgClg. 

To  which  may  be  added  the  more  complex  groupings,  considered 
either  as  compounds  with  chlorine  or  bromine,  of  the  original  naph- 
thalin or  chlorinated  or  brominated  naphthalins,  or  as  chlorohydrates 
of  chlorinated  naphthalin,  from  which  two  ways  of  examining  them 
we  shall  write  their  formulae : 

C20H3CI2  or C2oH,Cl,HCl, 

^20^6012,012  , C2oH5Cl3,HCl, 

C2oHgBr2,Cl2       C2oH,Br2Cl,HCI, 

C2oH,Br3,Br2       C2oH,Br„HBr. 

CACl,  C2oHgCl2,2HGl, 

C2oH,Cl,Cl, C2oH,Cl3,2HCl, 

C2oH,Br2Cl2,Br, C2oH2Br,Cl2,2HBr. 

§  1584.  Nitric  acid  reacts  readily  on  naphthalin  at  the  boiling 
point,  converting  it  rapidly  into  an  oil  which  solidifies  on  cooling, 
and  should  be  purified  by  several  crystallizations  in  alcohol.     Its 


680  PRODUCTS' OF   DRY  DISTILLATION. 

formula  being  C2oHy(N04),  it  may  be  considered  as  naphthalin  in 
which  1  equiv.  of  hydrogen  is  replaced  by  1  equiv.  of  the  compound 
NO4.  By  continuing  the  action  of  the  nitric  acid,  we  obtain  suc- 
cessively 

Binitronaphthalin C2oHg(NO^) 

and       Trinitronaphthalin €20115(^04)3. 

By  causing  sulf  hydrate  of  ammonia  to  act  on  an  alcoholic  solu- 
tion of  mononitronaphthalin  C2oH7(NOJ,  an  organic  base  is  obtained, 
naphthalidam  C20H9N: 

C2oH7(NO,)+6(NH3,2HS)=C2oH9N+4HO+6S+6(NH3,HS). 

This  substance  crystallizes  in  white  needles,  melting  at  86°,  and 
boiling  at  about  570°,  without  alteration,  which  combine  with  the 
acids  and  form  crystallizable  salts,  the  formula  of  the  chlorohydrate 
being  C2oH9N,HCl,  and  that  of  the  sulphate  (C2oH9N,HO),S03. 

Under  the  same  circumstances,  binitronaphthalin  C2oHg(N04)2,  and 
the  trinitronaphthalin  €20115(^04)3,  yield  other  alkaloids  CgoHgNg, 
C20H7N3.  y  ^        ^ 

By  causing  nitric  acid  to  act  on  chlorinated  naphthalins,  there  re- 
sult either  substitutions  of  the  compound  NO4  for  hydrogen,  or  pro- 
ducts of  oxidation  in  which  the  molecule  of  naphthalin  is  modified 
by  the  substitution  of  oxygen  in  the  place  of  hydrogen ;  and  in  this 
manner  have  been  obtained 

Trichlorinated  binitronaphthalin €20^^3013(^04)2, 

and  the  products  of  oxidation: €2oH4€l202,02, 

C2oH5€l  02,04, 

C20H   OlgOgyOg. 

It  will  be  seen  that  from  no  carburetted  hydrogen  are  more 
numerous  products  derived  than  from  naphthalin;  which  probably 
arises  from  the  fact  that  no  other  one  has  been  so  carefully  examined 
in  this  point  of  view. 

§  1585.  Concentrated  sulphuric  acid  acts  readily  on  naphthalin, 
and  yields  acid  compounds.  By  heating  naphthalin  to  about  194° 
with  concentrated  sulphuric  acid,  it  dissolves  in  it,  and  forms  a 
syrupy  liquid,  generally  reddish,  which,  when  exposed  to  a  moist  air, 
sets  in  a  crystalline  mass,  readily  soluble  in  water,  producing  an  acid 
liquid  which  forms,  with  carbonate  of  lead,  two  salts  unequally  so- 
luble in  alcohol.  The  acid  of  which  the  salt  of  lead  is  more  soluble 
in  alcohol  is  by  far  the  more  abundant,  and  has  been  called  sulpho- 
naphthalic  acid;  the  general  formula  of  its  dried  salt  being  RO, 
(€201178205.)  The  other  acid  has  received  the  name  of  sulphonaph- 
thic  acid,  but  its  composition  is  not  exactly  known. 

By  causing  concentrated  sulphuric  acid  to  act  on  trichlorinated 


PARAFFIN,  681 

and  on  quadrichlorinated  naphthalin,  there  result  acids  perfectly 
analogous  to  sulphonaphthalic  acid,  forming  salts  of  the  general 
formulae,  when  dried, 

RO,(C2oH4Cl3,S205), 

By  substituting  anhydrous  sulphuric  for  monohydrated  sulphuric 
acid,  two  neutral  crystallizable  substances  are  obtained  in  addition 
to  the  same  acid  compounds :  sulphonaphthalin,  of  which  the  formula 
■  is  CgoHgjSOg,  and  sulphonaphthalide,  the  composition  of  which  ap- 
pears to  correspond  to  the  formula  C24Hjo,S02.  These  substances 
are  generally  accompanied  by  a  red  colouring  matter,  of  which  the 
composition  is  not  yet  exactly  known. 

Paraffin, 

§  1586.  A  small  quantity  of  this  substance  is  found  among  the 
products  of  distillation  of  bituminous  coals,  together  with  a  great 
number  of  organic  substances ;  and  it  is  concentrated  in  the  sub- 
stances which  volatilize  last,  when  these  products  are  subjected 
to  redistillation!  In  order  to  extract  it,  the  substance  is  heated 
with  concentrated  sulphuric  acid,  which  carbonizes  the  greater 
portion  of  the  substances  mixed  with  the  paraffin,  when,  if  the  liquid 
be  allowed  to  rest,  at  a  temperature  of  122°  or  140°,  the  pure  paraf- 
fin forms  an  oily  layer  on  the  surface,  which  solidifies  on  cooling. 
The  substance  is  expressed  several  times  between  tissue-paper, 
which  absorbs  the  oily  portions,  and  it  is  purified  by  solution  in 
boiling  alcohol,  or  in  a  mixture  of  alcohol  and  ether,  whence  it  is 
deposited,  on  cooling,  in  the  form  of  brilliant  spangles  of  a  greasy 
lustre. 

A  large  quantity  of  paraffin  may  be  obtained  by  distilling  a  mix- 
ture of  wax  and  lime,  when  the  oily  product  which  solidifies  on  cool- 
ing, after  being  expressed  between  tissue-paper,  furnishes  pure  paraf- 
fin by  crystallization  in  alcohol  or  in  ether. 

Paraffin  melts  at  116.6°  and  boils^  at  about  700°,  while,  if  it  is 
not  carefully  heated,  a  portion  of  it  is  decomposed  and  yields  gaseous 
products.  It  is  distinguished  by  great  stability,  since  concentrated 
sulphuric  acid,  at  a  temperature  not  exceeding  212°,  ordinary  nitric 
acid,  and  chlorine,  exert  no  action  upon  it,  to  which  property  it 
owes  its  name,  (from  parum  affinis.)  Paraffin  burns  in  the  air  with 
a  brilliant  flame,  and  very  good  candles  are  made  of  it.  100  parts 
of  boiling  alcohol  dissolve  about  3.5  of  it,  nearly  all  of  which  is  de- 
posited on  cooling. 

The  name  of  eupione  has  been  given  to  volatile  oils  obtained,  in 
greater  or  less  quantity,  in  the  preparation  of  paraffin,  which  are 
mixtures  of  various  carburetted  hydrogens,  analogous  to  those  con- 
stituting petroleum. 


682  PRODUCTS    OF   DRY   DISTILLATION. 

PHENIC  ACID,  PHENOLE,  OR  CARBOLIC  ACID  C,,H,0,HO. 

§  1587.  These  various  names  are  given  to  a  product  extracted 
from  coal-tar,  by  distilling  the  oily  part  of  the  tar  atid  collecting 
separately  the  portion  which  passes  over  between  300°  and  400°. 
The  liquid  distilled  between  these  two  degrees  is  shaken  several 
times  with  a  very  concentrated  solution  of  caustic  potassa,  to  which 
fragments  of  hydrate  of  potassa  are  added,  when  the  oil  disengages 
a  disagreeable  odour,  and  sets  into  a  crystalline  mass.  Water  being 
then  added,  and  the  whole  heated  to  boiling,  the  liquid  separates 
into  two  layers :  a  light,  oily  layer,  which  is  removed,  and  a  heavier, 
aqueous  liquid,  which  is  treated  with  chlorohydric  acid.  The  oil 
which  is  thus  separated  by  rising  to  the  surface  is  decanted,  digested 
over  chloride  of  calcium,  and  distilled  several  times.  This  oil, 
which  is  phenic  acid,  and  becomes  solid  at  a  low  temperature,  is 
also  formed  in  the  distillation  of  salicylic  acid  with  lime,  and  in  that 
of  benzoin. 

Phenic  acid  constitutes,  at  the  ordinary  temperature,  a  white  crys- 
talline compound,  melting  at  about  95.0°,  and  boiling  at  370.4° ; 
of  the  density  1.065  at  64.4°;  slightly  soluble  in  water,  and  dis- 
solving in  all  proportions  in  alcohol  and  ether.  It  combines  with 
potassa  to  a  crystalline  salt  KO,Ci2H50,  and  forms  analogous  com- 
pounds with  baryta  and  lime.  It  reduces  several  metallic  salts,  par- 
ticularly the  salts  of  silver  and  mercury. 

Chlorine  acts  readily  on  phenic  acid,  and  the  following  phenic 
acids  have  thus  been  obtained: 

Bichlorinated Ci2H3Cl20,HO, 

and       Trichlorinated Ci2H2Cl30,HO. 

Bromine  forms  analogous  products. 

Nitric  acid  also  acts  on  phenic  acid,  and  yields  successively 
hinitrophenic  acid  Ci2H3(N04)20,HO,  and  trinitrophenic  acid  C12H2 
(N04)30,HO;  which  two  products  are  generally  prepared  by  at- 
tacking directly,  by  nitric  acid,  the  portion  of  oil  of  coal-tar  which 
distils  between  354°  and  374°,  when  a  very  energetic  reaction  ensues, 
furnishing  a  brown  mass,  which  is  washed  with  cold  water  and  dis- 
solved in  ammoniacal  water  heated  to  boiling.  The  liquid  deposits,  on 
cooling,  hinitrophenate  of  ammonia,  which  is  to  be  purified  by  several 
crystallizations;  and  which,  by  decomposition  with  chlorohydric 
acid,  yields  hinitrophenic  acid.  This  acid,  which  crystallizes  in 
right-angled  prisms,  with  a  rectangular  base,  and  of  a  slightly  yel- 
lowish colour,  is  suddenly  decomposed  by  heat.  It  dissolves  slightly 
in  boiling  water,  and  is  wholly  deposited  from  it  on  cooling,  while 
alcohol  and  ether  dissolve  it  largely. 

Boiling  nitric  acid  acts  readily  on  hinitrophenic  acid,  and  con- 
verts it  into  trinitrophenic  acid  Cj2H2(N 0^)30, HO,  which  has  been 
known  for  a  long  time  under  different  names ;  having  been  called 
Welter  8  bitter,  nitrocarbonic  acid,  picric  acid,  etc.     It  is  obtained 


NAPHTHA.  683 

by  the  action  of  nitric  acid  on  the  most  diversified  organic  sub- 
stances, particularly  on  nitrogenous  substances  of  animal  origin, 
such  as  silk,  fibrine,  and  animal  tissues.  Salicin  treated  with  nitric 
acid  yields  a  large  quantity  of  trinitrophenic  acid,  and  we  shall  see 
that  it  is  also  obtained  in  treating  indigo  by  the  same  acid.  It 
crystallizes  in  brilliant  yellow  prisms,  is  but  slightly  soluble  in  cold, 
but  largely  so  in  hot  water,  while  alcohol  and  ether  dissolve  it 
freely.  It  forms  yellow  crystallizable  salts  with  bases  which  detonate 
when  heated. 

CREASOTE  CmH,.0,. 

§  1588.  A  liquid  substance,  called  creasote,  and  possessing  some 
interest  in  being  used  to  allay  toothache,  is  extracted  from  wood-tar 
and  pyroligneous  acid,  by  a  long  and  complicated  process.  The 
wood-tar  is  distilled  until  a  pitchlike  mass  alone  remains,  when  the 
distilled  liquid  separates  in  the  receiver  into  three  layers,  the  lower 
of  which,  containing  the  creasote,  is  saturated  with  carbonate  of 
soda ;  after  which  the  supernatant  oil  is  decanted  and  again  dis- 
tilled ;  the  first  products,  which  are  lighter  than  water,  being  rejected, 
while  the  heavier  oil  is  collected  and  again  distilled.  This  oil  is 
then  shaken  several  times  with  a  weak  and  hot  solution  of  phos- 
phoric acid,  washed  until  it  gives  ofi"  no  more  acid,  and  treated 
with  an  alkaline  solution  of  the  density  1.12,  when  the  creasote 
leaves  the  oil,  and  dissolves  in  the  alkaline  liquid,  which  is  separated 
and  exposed  for  some  time  to  the  air,  to  oxidize  a  foreign  substance 
which  discolours  the  liquid.  Lastly,  the  solution,  after  being  satu- 
rated with  phosphoric  acid,  is  distilled,  when  the  creasote  volatilizes 
with  the  water  and  separates  in  the  receiver  in  the  form  of  an  oily 
layer. 

Creasote  is  a  colourless,  oleaginous  liquid,  of  a  penetrating  and 
disagreeable  odour  and  an  acrid  and  burning  taste ;  cauterizing  the 
organic  tisues,  coagulating  albumen,  and  preventing  the  putrefaction 
of  meat.  It  boils,  without  change,  at  about  390°,  and  is  insoluble  in 
water,  but  readily  so  in  alcohol  and  ether.  It  forms,  with  potassa  and 
soda,  crystalline  compounds,  from  which  acids  separate  it  without 
change ;  and  its  composition  corresponds  to  the  formula  CggHigO^. 

An  alcoholic  solution  of  creasote  is  used  in  medicine. 

NAPHTHA,  OR  PETROLEUM. 

§  1589.  In  many  countries,  odoriferous  oils  exude  from  the  ground, 
accompanied  generally  by  hot  or  cold  water,  and  sometimes  by 
combustible  gases ;  and  when  such  liquids  are  collected  in  natural 
or  artificial  reservoirs,  the  oil  floats  on  the  surface.  The  general 
name  of  petroleum  is  given  to  these  oils,  the  nature  of  which  is  evi- 
dently very  diversified,  for  some  of  them  distil  wholly  without 
change,  while  others  leave  a  considerable  residue  of  fixed  oil,  which 
is  decomposed  by  heat.     The  most  abundant  springs  of  petroleum 


684  FATS. 

are  In  the  neighbourhood  of  Baku  in  Persia,  where  jets  of  com- 
bustible gas,  copious  enough  to  enable  the  inhabitants  to  use  it  for 
cooking  their  food,  issue  simultaneously  from  fissures  in  the  ground ; 
and  some  springs  of  petroleum  are  also  found  at  Amiano,  in  the 
Duchy  of  Parma.  Petroleum  is  purified  by  distillation  with  water, 
and  the  product  is  known  in  commerce  by  the  name  of  oil  of  naphtha^ 
or  oil  of  petroleum. 

Oil  of  naphtha,  which  presents  the  density  of  about  0.84,  and  gives 
a  peculiar  odour,  contains  no  oxygen,  and  appears  to  be  formed  by 
the  mixture  of  several  carburetted  hydrogens.  If  it  be  distilled  in  a 
retort  furnished  with  a  thermometer,  ebullition  is  found  to  com- 
mence when  the  thermometer  marks  250°  to  284°,  while  the  temper- 
ature gradually  rises,  and  the  last  portions  do  not  distil  below  570°. 
If  the  products  of  distillation  be  collected  separately,  the  most  vola- 
tile is  a  liquid  boiling  at  about  194°,  after  which  numerous  products 
pass  over,  boiling  ai^  higher  and  higher  temperatures,  while  it  has 
hitherto  been  impossible  to  separate  a  liquid  presenting  a  constant 
boiling  point,  mixtures  only  having  been  obtained.  The  composition 
of  the  most  volatile  products  correspond  approximately  to  the  formula 
CH,  and  they  are  isomeric  with  olefiant  gas,  while  the  less  volatile 
products  contain  less  hydrogen. 

The  essential  oils  which  form  petroleum  are  remarkable  for  their 
resistance  to  chemical  agents,  since  they  are  scarcely  affected  by 
concentrated  sulphuric  and  nitric  acids  ;  and  they  are  used  in  the 
laboratory  for  the  preservation  of  potassium,  (§  426.) 


THE  FATS. 


§  1590.  The  name  of  fats  is  commonly  assigned  to  substances  of 
organic  origin,  liquid  or  solid,  but  melting  at  a  very  low  tempera- 
ture, which,  when  spread  in  a  liquid  state  on  paper,  render  it  trans- 
lucent, and  make  permanent  stains  on  it,  known  by  the  name  of  grease- 
spots  ;  while  the  chemist  defines  fats  by  certain  chemical  properties, 
and,  particularly,  by  their  manner  of  composition,  as  shall  subse- 
quently be  shown. 

Fatty  substances  are  found  both  in  the  vegetable  and  animal 
kingdoms,  and  seem  to  be  identical  in  both ;  which  has  led  some 
physiologists  to  the  opinion  that  animals  merely  assimilate  to  them- 
selves those  which  exist  in  vegetables,  without  their  undergoing  any 
chemical  change.  Although  we  shall  reserve  for  the  close  of  this  work 
the  study  of  the  principal  substances  constituting  the  animal  eco- 
nomy, we  shall  not,  in  this  place,  separate  the  fatty  substances  of 
the  two  kingdoms. 

Vegetable  fats  are  generally  fluid  at  the  ordinary  temperature, 
while  several  of  them  coagulate  and  solidify,  more  or  less  perfectly, 


FATS.  685 

at  a  low  temperature.  They  are  completely  liquid  only  at  a  high 
heat,  and  at  the  ordinary  temperature  possess  a  certain  degree  of 
viscidity,  called  an  oily  consistence.  The  fat  of  warm-blooded  ani- 
mals is  solid,  its  firmness  varying  according  to  the  position  it  occu- 
pies in  the  body  of  the  animal ;  while  that  of  fishes  and  cold-blooded 
animals  in  general  is  fluid. 

In  plants,  fat  is  found  chiefly  in  the  seeds  and  pericarp  of  the 
fruit,  in  the  form  of  small  drops  which  fill  peculiar  cells,  and  also 
exists  in  the  shape  of  a  waxlike  substance  on  the  surface  of  the 
leaves  and  bark.  The  proportion  existing  in  seeds  is  often  very 
considerable :  thus,  flaxseed  contains  about  20  per  cent,  of  oil,  and 
rapeseed  35  to  40,  while  the  seed  of  ricinus  communis,  which  fur- 
nishes castor-oil,  contains  as  much  as  60.  The  oil  is  generally  ex- 
tracted merely  by  expressing  the  seeds,  but  in  order  to  render  it 
more  fluid  they  are  heated,  and  then  compressed  between  hot  plates. 
When  the  proportion  of  oil  is  smaller,  fermentation  is  sometimes 
resorted  to  for  the  destruction  of  a  portion  of  the  organic  substances 
and  in  order  to  break  up  the  fruit.  Lastly,  in  the  laboratory,  sol- 
vents are  sometimes  used,  chiefly  ether,  which  is  then  driven  off  by 
evaporation. 

Animal  fat  may  be  obtained  either  mechanically  or  by  the  action 
of  heat.  In  order  to  purify  it  in  the  laboratory,  it  is  generally  dis- 
solved in  ether ;  but  it  must  not  be  forgotten  that  this  liquid  can  also 
dissolve  some  of  the  foreign  substances  mixed  with  the  fat.  The 
melting  point  of  fat  varies  from  23°  to  140°,  while  at  temperatures 
above  480°  they  yield  copious  and  very  acrid  fumes,  but  do  not 
distil  without  alteration,  whence  they  are  called  fixed  oils.  At  an 
intense  heat  they  are  wholly  decomposed,  and  produce  gases  of 
great  illuminating  power. 

§  1591.  Oils  generally  absorb  oxygen  from  the  air,  but  in  very 
various  proportions ;  and  while  some  absorb  but  small  quantities  of 
it  without  sensibly  changing  in  appearance,  merely  acquiring  a  dis- 
agreeable smell,  when  they  are  said  to  become  rancid,  others  absorb 
larger  proportions  of  oxygen,  become  covered  with  a  coating  of  a 
resinous  appearance,  and  are  finally  completely  solidified ;  and  these 
are  called  drying-oils,  the  only  ones  which  can  be  used  in  painting. 
Linseed,  nut,  hemp,  poppy,  and  castor-oil  are  drying-oils,  while 
some  fish-oils  appear  to  possess  the  same  property.  The  fat  of 
warm-blooded  animals,  the  oil  of  almonds,  olive-oil,  rapeseed-oil,  &c. 
are  not  drying-oils. 

The  chemical  action  which  produces  the  solidification  of  drying- 
oils  is  sometimes  limited  to  a  simple  combination  with  oxygen ;  as 
in  the  case  with  linseed-oil,  which  absorbs  large  quantities  of  oxy- 
gen without  disengaging  any  gas;  but  more  frequently  carbonic  acid, 
and  sometimes  hydrogen,  is  evolved.  Absorption  goes  on  slowly  at 
first,  but  subsequently  becomes  more  rapid,  especially  when  the  oil 
is  spread  over  a  large  surface  or  on  porous  bodies.     Drying-oils 


686  FATS. 

dry  more  quickly  when  they  have  been  previously  boiled  with 
litharge  oi"  peroxide  of  manganese ;  in  which  case  they  contain  a 
small  quantity  of  these  metallic  oxides  in  solution. 

§  1592.  The  greater  part  of  animal  fats  is  formed  of  several 
proximate  principles  united  in  indefinite  proportions  ;  and  of  which 
chemists  have  distinguished  only  three :  stearin,  margarin,  and  olein. 
These  principles  behave,  in  chemical  reactions,  like  compounds  of 
the  same  substance,  glycerin,  with  a  fatty  acid,  peculiar  to  each  of 
these  principles.  Stearin  and  margarin,  to  which  beef  and  mutton 
fat  owe  their  solidity,  are  converted  into  glycerin,  and  two  fatty  acids, 
which  are  stearic  acid  for  stearin,  and  margaric  acid  for  margarin ; 
while  olein,  to  which  fats  owe  their  oleaginous  character,  is  trans- 
formed into  glycerin  and  oleic  acid.  In  several  fatty  substances, 
such  as  butter,  we  find,  in  addition,  small  quantities  of  peculiar 
fatty  matters,  called  hutyrin,  caprin,  and  caproin,  which  may  be 
considered  as  compounds  of  glycerin  with  volatile  acids,  differing  in 
each  of  these  substances,  and  which  have  been  called  butyric,  capric, 
and  caproic  acids.  We  have  shown  that  butyric  acid  is  formed  in 
a  peculiar  fermentation  of  sugar ;  and  it  will  now  soon  be  seen  that 
the  same  acid  arises,  as  also  capric  and  caproic  acids,  from  the  ac- 
tion of  nitric  acid  on  stearin,  margarin,  and  olein.  The  fat  of  the 
goat  contains,  in  addition  to  the  ordinary  immediate  principles,  a 
small  quantity  of  a  peculiar  fat,  called  hircin,  which  behaves  like  a 
compound  of  glycerin  and  a  peculiar  volatile  acid,  hircic  acid.  Lastly, 
another  fatty  substance  is  found  in  fish-oils,  which  may  be  considered 
as  a  compound  of  glycerin  and  a  peculiar  acid,  called  phocenic,  ap- 
pearing to  be  identical  with  valerianic  acid. 

A  peculiar  fat  substance  is  extracted  from  the  head  of  the  sperm 
whale,  called  spermaceti,  the  constitution  of  which  is  very  different 
from  that  of  other  animal  fats,  since  it  does  not  contain  glycerin,  but 
in  its  stead  another  neutral  substance,  called  ethal ;  while  the  fat 
acid  which  is  combined  with  the  ethal  has  received  the  name  of 
ethalic  acid. 

Lastly,  the  various  kinds  of  wax,  which  should  be  classed  among 
the  fats,  from  the  definition  given  of  the  latter,  (§  1590,)  differ  com- 
pletely from  it  in  their  chemical  composition,  as  shall  presently  be 
shown. 

§  1593.  Stearic,  margaric,  and  oleic  acids  are  weak  acids,  which 
are  displaced  from  their  compounds  by  a  majority  of  the  other 
acids ;  and  they  are  insoluble  in  water,  but  soluble  in  alcohol,  and 
very  feebly  in  ether.  They  are  less  easily  melted  than  the  proxi- 
mate fatty  principles  which  produced  them,  and  they  do  not  distil 
without  alteration  under  the  ordinary  pressure  of  the  atmosphere. 
They  are  then  decomposed  at  a  temperature  above  570°,  yielding 
very  complicated  products ;  but  they  may  be  distilled  in  vacuo,  be- 
cause the  distillation  is  then  effected  at  a  much  lower  temperature. 

§  1594.  The  chemical  operations  by  which  natural  fat  substances 


FATS.  687 

are  converted  into  glycerin  and  fat  acids  are  known  by  the  general 
name  of  saponification.  They  are  various ;  and  the  saponification 
of  fats  may  be  effected  either  by  alkalies  or  by  powerful  acids,  or 
by  the  action  of  heat  alone. 

If  fats  be  heated  to  a  temperature  of  5T0°,  in  an  apparatus  tra- 
versed by  a  current  of  steam,  under  a  pressure  inferior  to  that  of 
the  atmosphere,  the  glycerin  is  converted  into  several  products 
soluble  in  water ;  while  the  fat  acids,  set  free,  distil  without  altera- 
tion ;  thus  furnishing  an  example  of  saponification  by  heat  alone. 

The  action  of  hot  alkaline  lixiviae  decomposes  fats  and  oils  into 
glycerin,  which  dissolves  in  the  aqueous  liquid,  and  into  fat  acids, 
which  combine  with  the  alkali  and  form  salts,  commonly  called 
soaps,  which  are  insoluble  in  the  alkaline  liquor,  but  readily  dissolve 
in  a  sufficient  quantity  of  water.  This  operation,  called  saponifir 
cation  by  bases,  may  be  efi'ected  not  only  by  alkaline  bases,  such 
as  potassa,  soda,  and  ammonia,  but  also  by  other  metallic  oxides 
which  possess  powerful  basic  properties,  such  as  baryta,  strontia, 
lime,  and  the  protoxides  of  lead  and  zinc.  The  other  metallic  oxides 
no  longer  produce  the  saponification  of  fats,  that  is,  their  decom- 
position into  glycerin  and  fat  acids ;  while  they  may  combine  with  the 
isolated  fat  acids  and  form  insoluble  soaps.  Water  is  generated 
during  saponification,  for  the  united  weight  of  the  glycerin  and  fat 
acids  is  greater  than  the  weight  of  the  original  fat.  The  neutral 
alkaline  carbonates  can  also  efiect  the  saponification  of  fats,  in 
which  case  they  part  with  one-half  of  their  alkali,  which  produces 
saponification,  while  the  other  half  retains  all  the  carbonic  acid  in 
the  shape  of  bicarbonate ;  carbonic  acid  being  disengaged  only  if 
heat  is  applied,  because  the  bicarbonate  is  then  decomposed. 

Powerful  acids,  such  as  sulphuric,  also  effect  the  saponification 
of  fats ;  and  if  the  proportion  of  acid  be  not  very  great,  the  fat  acid 
is  isolated,  the  glycerin  combining  with  the  animal  acid  to  form  a 
compound  acid.  If  the  weight  of  the  mineral  acid  exceed  the  half 
of  that  of  the  fat  acid,  it  often  combines  with  the  latter,  producing 
sulpJiogly eerie,  sulphostearie,  sulphomargaric,  and  sulpholeie  acids. 
Smaller  quantities  of  sulphuric  acid  are  however  sometimes  used  to 
purify  the  oils  intended  for  burning  in  lamps,  in  which  case  the  acid 
selects  the  foreign  substances  more  easily  acted  on,  contained  in  the 
oils,  dissolving  them,  and  effecting  only  an  insensible  saponification. 

§  1595.  No  fatty  substance  is  soluble  in  water,  which  does  not 
even  moisten  them;  while  they  are  somewhat  soluble  in  absolute 
alcohol  and  wood-spirit,  ether  and  the  essential  oils  dissolving  them 
much  more  freely.  The  liquid  fats  are  the  best  solvents  of  solid 
fats.  We  have  seen  that  natural  fats  are  rarely  simple,  nearly 
always  mixtures  or  indefinite  compounds  of  various  different  fatty 
substances,  which  are  separated  only  with  the  greatest  difficulty. 
When  the  fat  is  solid,  it  is  sufficient  to  melt  it,  and  allow  it  to  cool 
slowly,  to  observe  in  it  the  forming  of  solid  lumps,  the  nature  of 


688  FATS. 

which  differs  from  the  liquid  part.  So  again,  certain  fatty  oils, 
olive-oil,  for  example,  deposits,  by  slow  cooling,  more  or  less  copious 
flocculi,  which  differ  from  the  liquid  portion ;  and  by  expressing 
these  solidified  portions  between  tissue-paper,  a  large  quantity  of 
interstitial  liquid  oil  can  be  separated,  furnishing  a  mixture  of 
stearin  and  margarin,  adulterated  merely  with  a  small  quantity  of 
olein.  The  proportions  of  stearin  and  margarin  in  the  substances 
expressed  vary  according  to  the  nature  of  the  original  fats.  When 
they  are  yielded  by  mutton  or  beef  fat,  or  lard,  they  are  composed 
almost  wholly  of  stearin ;  while,  if  furnished  by  human  fat  or  olive- 
oil,  they  consist  chiefly  of  margarin.  These  substances  may  be  more 
perfectly  isolated  by  a  proper  use  of  solvents. 

The  immediate  fluid  constituent  of  animal  fats,  olein,  is  still  more 
difficult  to  isolate,  the  oil  which  flows  from  the  compression  of  such 
fats  being  olein  saturated  with  stearin  or  margarin.  The  most  fluid 
vegetable  oils  are  themselves  olein,  containing  more  or  less  stearin 
and  margarin  in  solution ;  and  by  cooling  them  gradually  and  de- 
canting the  fluid,  a  large  portion  of  the  solid  constituent  may  be 
separated ;  or  the  oil  may  also  be  shaken  with  alcohol,  which  dis- 
solves the  olein  much  more  freely  than  the  stearin  and  margarin, 
and  the  alcoholic  solution  may  be  evaporated:  but  all  these  pro- 
cesses never  effect  a  perfect  separation.  It  is  moreover  highly  pro- 
bable that  stearin,  margarin,  and  olein  are  not  merely  mixed  in  the 
majority  of  fats,  and  that  they  are  in  the  state  of  indefinite  com- 
pounds. 

Olein  does  not  appear  to  be  identical  in  the  various  vegetable  oils, 
since  several  chemical  experiments  seem  to  prove  that  it  differs  in 
the  drying  and  non-drying  oils.  If,  for  example,  a  non-drying  oil, 
such  as  olive-oil,  be  agitated  with  a  small  quantity  of  hyponitric 
acid,  or  with  a  solution  of  subnitrate  of  mercury,  which  contains 
hyponitric  acid,  the  oil  becomes  completely  solid  after  some  time, 
and  is  converted  into  a  crystalline  substance,  elaidin.  Drying-oils 
do  not  possess  this  property,  which  thus  furnishes  a  test,  applicable 
to  commercial  purposes,  of  the  purity  of  olive-oil,  which  is  fre- 
quently adulterated  with  other  vegetable  oils,  and  particularly  with 
poppy-oil. 

Fat  acids  which  are  capable  of  crystallization  may  be  obtained 
in  a  state  of  purity,  and  since  they  at  the  same  time  form  a  great 
number  of  definite  compounds,  their  properties  and  chemical  com- 
position have  been  more  accurately  ascertained  than  those  of  the 
fats  which  furnish  them.  Nevertheless,  uncertainties  still  exist,  on 
account  of  the  very  high  value  of  their  chemical  equivalents ;  the 
smallest  errors  in  analyses  corresponding  to  1  or  several  equivalents 
of  simple  elements,  and  sufficing  to  change  the  formulae. 

We  shall  examine  only  the  most  important  and  most  common 
fatty  substances,  commencing  with  the  study  of  glycerin,  which  is 
an  essential  and  constant  principle  of  the  majority  of  these  substances. 


-       GLYCERIN.  689 

aiycerin  CgHyOs^HO. 

§  1596.  The  most  simple  method  of  preparing 'glycerin  consists 
in  heating  fats  with  protoxide  of  lead,  in  the  presence  of  water, 
when  saponification  is  soon  effected,  an  insoluble  soap  of  lead  being 
formed,  while  the  glycerin  remains  dissolved  in  the  water.  The 
aqueous  solution  is  subjected  to  a  current  of  sulfhydric  gas,  which 
precipitates  a  small  quantity  of  oxide  of  lead  dissolved  in  it  in  the 
state  of  sulphide ;  after  which  it  is  concentrated  at  a  gentle  heat, 
and  the  evaporation  completed  in  vacuo. 

Glycerin,  dried  in  vacuo  at  212°,  is  a  syrupy,  colourless,  inodor- 
ous liquid,  tasting  like  sugar,  from  which  circumstance  it  has  de- 
rived its  name,  (yxvxvj,  sweet,)  insoluble  in  water,  but  soluble  in  all 
proportions  in  alcohol  and  ether.  It  is  decomposed  by  heat,  yielding 
very  complex  products ;  among  which  is  remarked  an  oily,  colourless, 
extremely  disagreeable-smelling  liquid,  called  acrolein^  and  present- 
ing the  formula  CgH^Og.  Oxidizing  substances,  such  as  ordinary 
nitric  acid,  or  a  mixture  of  sulphuric  acid  and  peroxide  of  manga- 
nese, form  with  glycerin,  oxalic,  formic,  and  carbonic  acids.  Chlorine 
and  bromine  act  on  glycerin,  and  form  chlorinated  and  brominated 
compounds,  which  can  only  be  expressed  in  equivalents  by  doubling 
the  ordinary  formula  of  glycerin,  that  is,  by  writing  it  G-^^fiy;^^'2i]10, 
which  furnishes. 

Original  glycerin QJl^fi^Q^W.O^ 

Trichlorinated  "  C)i2HiiCl30io, 

Tribrominated  "  CiaHiiBrgOjo. 

But  it  is  difficult  to  decide  the  question,  owing  to  the  want  of  means 
of  ascertaining  the  purity  of  the  chlorinated  and  brominated  sub- 
stances, inasmuch  as  they  do  not  crystallize. 

By  mixing  2  parts  of  concentrated  sulphuric  acid  with  1  part  of 
glycerin,  combination  ensues,  with  elevation  of  temperature;  and 
by  leaving  the  mixture  to  itself  for  some  time,  shaking  it  frequently, 
an  acid  compound,  sulphogly eerie  acid,  is  produced,  which  forms 
soluble  salts  with  lime  and  oxide  of  lead ;  the  lime-salt  being  pre- 
pared by  adding  water  to  the  mixture,  saturating  it  with  chalk,  and 
filtering  to  separate  the  sulphate  of  lime.  The  liquor,  when  evaporated, 
yields  sulphoglycerate  of  lime,  of  which  the  formula,  when  it  is 
dried  at  248°  in  vacuo,  is  Qd.OiQ^^O^fi'^O^,  and  which  dissolves 
in  one-half  of  its  weight  in  water,  but  it  is  insoluble  in  alcohol  and 
ether. 

Glycerin  also  becomes  heated  when  it  is  mixed  with  anhydrous 
or  hydrated  phosphoric  acid ;  a  phosphoglycerie  aeid,  which  dissolves 
in  water,  being  formed.  By  saturating  the  liquid  with  carbonate 
of  baryta,  and  lastly  by  caustic  baryta,  the  free  phosphoric  acid  is 
precipitated  in  the  state  of  phosphate  of  baryta,  while  the  liquid 
contains  phosphoglyeerate  of  baryta,  which  is  separated  by  evapora- 

VoL.  IL— 44 


690  FATS. 

tion.     The  formula  of  this  salt,  dried  at  284°,  is  2BaO,(C6H705, 

Phosphoglyceric  acid  has  been  found  ready  formed  in  the  yolk 
of  eggs. 

Sulphoglyceric  and  phosphoglyceric  acids  yield  a  large  quantity 
of  acrolein  when  they  are  decomposed  by  heat ;  which  is,  in  fact,  the 
best  method  of  preparing  this  substance. 

Stearin  and  Stearic  Acid, 

§  1597.  The  most  efficient  method  of  isolating  stearin  consists  in 
melting  tallow  with  oil  of  terpentine,  when  the  oil,  after  being  de- 
canted, deposits  a  solid  substance  on  cooling,  which  is  subjected  to 
pressure  between  the  folds  of  tissue-paper  in  a  press.  After  being 
similarly  treated  several  times,  it  is  dissolved  in  ether,  with  the  as- 
sistance of  heat,  when  the  greater  portion  of  it  is  again  deposited 
on  cooling.  The  stearin  thus  obtained  is  considered  as  pure. 
Chemical  analysis,  added  to  the  knowledge  of  its  products  of  sapo- 
nification, have  assigned  to  stearin  the  formula  Cj^^H^^^O^q,  which  is 
more  properly  written  {CQH.^0^-\-'H0),2GQjiQQ0y 

Stearin  is  therefore  admitted  to  be  an  acid  compound,  analogous 
to  sulphovinic  acid  (C4H50,HO)2S03,  and  formed  by  the  combination 
of  2  equiv.  .of  stearic  acid  CggH^g^s  ^^^^  ^  equiv.  of  glycerin  and  1 
equiv.  of  water. 

Stearin  crystallized  in  ether  forms  small  white  lamellae,  of  a 
pearly  lustre,  melting  at  from  140°  to  144°,  and  setting,  on  cooling, 
into  a  white  opake  mass,  presenting  no  appearance  of  crystalliza- 
tion. It  is  completely  insoluble  in  water,  but  dissolves  in  8  parts 
of  boiling  alcohol,  separating  from  it  almost  entirely  on  cooling; 
while  ether  dissolves  a  large  proportion  of  it  at  the  boiling  point,  but 
when  cooled  only,  retains  about  tj^. 

§  1598.  Stearic  acid  is  an  important  article  of  commerce,  of  which 
candles,  called  stearic  candles,  are  made.  It  is  prepared  by  sapo- 
nifying beef  or  mutton  suet  by  lime :  500  kilog.  of  suet  and  800 
litres  of  water  are  placed  in  a  wooden  vat,  holding  2000  litres,  and 
lined  with  lead,  and  heated  by  steam  conveyed  directly  into  the  vat 
by  means  of  a  circular  tube  pierced  with  holes ;  and  when  the  suet 
is  melted,  about  600  litres  of  a  solution  of  lime,  containing  60  kilog. 
of  quicklime,  is  added,  and  the  mixture  is  continually  stirred.  After 
6  or  7  hours,  the  saponification  is  terminated,  and  the  soap  of  lime 
has  formed  a  consistent  mass,  which  becomes  very  hard  on  cooling. 
It  is  reduced  to  a  fine  powder,  and  decomposed  by  sulphuric  acid, 
diluted  with  water,  in  vats  similar  to  the  first,  and  heated  by  steam, 
when  the  fatty  acids,  set  free,  form  an  oily  layer  on  the  surface  of 
the  acid  liquids. 

The  melted  fat  is  decanted,  and  washed  several  times,  while  hot, 
with  water  charged  with  sulphuric  acid,  and  then  with  fresh  water; 
and  it  is  finally  run  into  tin  moulds,  forming  cakes  of  3  or  4  kilogs. 


STEARIC   ACIDS.  691 

iti  weight.  This  mass,  which  is  still  a  mixture  of  stearic,  margaric, 
and  oleic  acids,  is  first  powerfully  compressed  when  cold,  in  order 
to  express  the  greater  part  of  the  oleic  acid,  and  then  at  a  tempera- 
ture of  90°  or  100°,  to  drive  out  the  remainder.  The  oleic  acid  thus 
expressed  is  of  a  deep  brown  colour,  and  contains  nearly  all  the 
margaric,  besides  a  certain  quantity  of  stearic  acid.  The  cakes 
remaining  after  this  compression  are  again  melted,  in  contact  with 
a  dilute  solution  of  sulphuric  acid,  which  removes  the  last  traces  of 
lime  from  the  fatty  substance ;  after  which  it  is  freed  from  the  ad- 
hering acid  by  washing  it  in  boiling  water.  It  is  then  poured  into 
moulds,  where  it  becomes  solid,  and  is  thus  brought  into  commerce 
as  refined  stearic  acid,  used  for  the  manufacture  of  candles. 

§  1599.  Large  quantities  of  solid  fat  acids  are  now  prepared  for 
the  manufacture  of  stearic  candles  by  a  very  ingenious  process,  in 
which  saponification  by  sulphuric  acid  is  combined  with  distillation 
of  the  fat  acids,  in  intensely  heated  steam,  having  but  little  tension. 
This  process  enables  the  use  of  fats  of  all  kinds,  and  of  the  most 
inferior  qualities. 

The  fats,  placed  in  boilers  heated  by  steam,  are  first  treated  with 
a  quantity  of  concentrated  sulphuric  acid,  which  varies  from  6  to  15 
per  cent.,  according  to  the  nature  of  the  fat.  The  temperature 
being  raised  to  212°,  and  kept  at  that  point  for  15  or  20  hours, 
under  constant  stirring,  the  fat  acids  are  set  free,  and  the  glycerin 
is  almost  wholly  converted  into  sulphoglyceric  acid ;  while  the  greater 
portion  of  the  foreign  substances  are  destroyed  by  the  sulphuric 
acid,  yielding  carbonaceous  residues  and  products  soluble  in  water. 
The  fat  acids  are  washed  with  water,  and  then  placed  in  a  distilling 
apparatus,  through  which  steam  heated  to  about  600°  is  passed, 
with  an  elastic  force  inferior  to  that  of  the  atmosphere,  when  the 
fat  acids  distil  with  the  water,  and  by  pressure  can  be  brought  into 
a  state  fitted  for  the  manufacture  of  candles. 

§  1600.  Very  pure  stearic  acid  may  be  obtained,  for  laboratory 
purposes,  by  crystallizing  the  stearic  acid  of  commerce  several  times 
in  boiling  alcohol. 

Stearic  acid  yields,  by  slow  cooling,  beautiful  and  pearly  crystals, 
melting  at  158°,  and  at  a  temperature  of  570°  giving  off  vapour 
without  alteration.  It  may  be  distilled  in  vacuo,  and  is  completely 
insoluble  in  water,  but  very  soluble  in  boiling  alcohol  and  ether. 
The  formula  of  crystallized  stearic  acid  is  CggHggOy,  which  should  be 
written  CggHggOgj^HO,  since  2  equiv.  of  a  base  may  be  substituted 
for  2  equiv.  of  water ;  showing  it,  therefore,  to  be  a  bibasic  acid. 

The  acid  forms  two  salts  with  potassa :  bipotassic  stearate  2K0, 
CggHggOs,  and  monopotassie  stearate  (KO+HO),Cg8Hgg05.*  The 
former  is  obtained  by  treating  stearic  acid  with  an  equal  weight  of 


*  These  salts  would  with  more  propriety  be  called  basic  and  neutral  stearates 
of  potassa.—  W.  L.  F.  -       ^ 


692  FATS. 

hydrate  of  potassa,  dissolved  in  20  parts  of  water,  when  the  salt 
remains  in  the  form  of  clots,  which  are  compressed  between  tissue- 
paper.  It  is  then  redissolved  in  15  or  20  parts  of  boiling  alcohol, 
and  the  liquid  allowed  to  cool,  when  the  bipotassic  stearate  is  de- 
posited in  white  crystalline  lamellae.  It  dissolves  without  change 
in  10  times  its  weight  of  water,  but,  when  cold,  produces  only  a 
mucilaginous  liquid,  which  does  not  become  perfectly  fluid  and  limpid 
unless  it  be  heated  to  boiling.  When  a  larger  quantity  of  water  is 
poured  into  this  solution,  a  clouded,  opalizing  liquid  is  obtained,  in 
which  a  large  number  of  small  crystalline  spangles  of  extreme  de- 
licacy swim,  and  which  settle  to  the  bottom  of  the  vessel,  if  it  be 
allowed  to  rest.  These  small  crystals  constitute  monopotassic  stea- 
rate, of  which  the  formula  is  (KO+HO),Cg8Hgg05.  Alcohol  does 
not  effect  this  decomposition  in  the  bipotassic  stearate. 

Soda  forms  two  stearates  analogous  to  those  of  potassa :  stearates 
of  baryta,  strontian,  and  lime,  which  present  the  formula  2R0, 
CggHggOg,  are  prepared  by  double  decomposition  from  the  bipo- 
tassic stearate,  and  are  completely  insoluble  in  water.  The  lead- 
salt  is  obtained  in  the  same  way,  but  the  stearate  of  lead  used  in 
pharmacy  for  the  making  of  plasters  is  prepared  by  directly  sapo- 
nifying fats  by  litharge  in  the  presence  of  water.  Spring-water  is 
generally  hard,  and  is  then  unsuitable  for  washing,  owing  to  the 
presence  of  calcareous  salts,  which  decompose  the  alkaline  soaps  as 
they  form,  and  make  insoluble  soaps ;  and  alkaline  soap  can  only 
dissolve  when  the  calcareous  salts  are  completely  decomposed. 
Water  is  rendered  fit  for  washing  by  adding  a  small  quantity  of 
carbonate  of  soda,  which  decomposes  the  salts  of  lime. 

Stearic  acid  forms  vinostearic  and  methylostearic  ethers,  which 
are  obtained  by  dissolving  stearic  acid  in  absolute  alcohol  or  wood- 
epirit,  and  passing  through  it  a  current  of  chlorohydric  acid  gas ; 
when  the  ethers,  after  being  precipitated  by  water  and  crystallized 
in  alcohol,  form  white  substances  of  a  greasy  lustre,  and  melting  at 
from  86°  to  95°. 

Margaric  Acid  C68Hgg06,2HO. 

§  1601.  By  decomposing  with  acids  a  soap  made  of  human  fat,  a 
mixture  of  fatty  acids  is  obtained,  melting  at  about  135°,  and  which 
is  considered  as  composed  solely  of  margaric  and  oleic  acids.  Mar- 
garic acid  is  supposed  to  be  produced  by  the  saponification  of  a  sim- 
ple fat,  margarin,  but  which  probably  exists  in  combination  with 
olein.  Margaric  acid  is  also  formed  in  the  distillation  of  stearic 
acid  and  the  fats  in  general,  as  well  as  when  the  latter  are  subjected 
to  the  action  of  oxidizing  reagents.  Chemists  are  not  agreed  upon 
the  formula  of  margaric  acid;  and  while  some  write  it  CggHggOg, 
2 HO,  a  formula  which  differs  from  that  of  stearic  acid  by  1  equiva- 
lent of  oxygen,  others  assert  that  its  composition  is  identical  with 
that  of  stearic  acid. 


OLEIC    ACID.  693 

The  best  method  of  preparing  margaric  acid  consists  in  saponify- 
ing human  fat  or  olive-oil  by  potassa,  and  pouring  acetate  of  lead 
into  the  solution,  which  yields  a  precipitate  of  margarate  and  oleate 
of  lead.  The  precipitate  being  treated  several  times  with  ether, 
which  completely  dissolves  the  oleate  of  lead,  and  a  much  smaller 
proportion  of  margarate,  the  remaining  margarate  of  lead  is  decom- 
posed by  dilute  nitric  acid,  and  the  margaric  acid  arising  from  it  is 
purified  by  crystallization  in  alcohol.  In  its  physical  properties, 
margaric  closely  resembles  stearic  acid,  but  it  melts  at  a  lower 
temperature,  viz.  at  140°.  It  forms  two  salts  with  potassa :  the 
bipotassic  margarate  2KO,Cg8HggOg,  and  the  monopotassio  marga- 
rate (KO  +  HO),CggHggOg ;  which  are  formed  under  the  same  circum- 
stances as  the  corresponding  stearates,  and  nearly  resemble  them. 

Oleic  Acid  035113303, HO. 

§  1602.  In  order  to  separate  this  acid,  oils  very  rich  in  olein,  such 
as  olive-oil  and  oil  of  almonds,  are  saponified  by  potassa ;  when  the 
soap  is  decomposed  by  tartaric  acid,  and  the  fatty  acids  which  sepa- 
rate are  decanted.  The  latter  are  digested  in  a  water-bath  with 
one-half  of  their  weight  of  finely-powdered  oxide  of  lead,  thus  form- 
ing a  soap  of  lead,  consisting  of  both  the  oleate  and  the  margarate. 
This  soap  is  digested  for  24  hours  with  twice  its  volume  of  ether, 
which  dissolves  the  oleate,  and  the  etherial  liquor  being  evapo- 
rated, the  oleate  of  lead  is  decomposed  by  chlorohydric  acid.  The 
oleic  acid  thus  obtained  is,  however,  not  pure,  and  must  be  redis- 
solved  in  ammonia,  precipitated  by  chloride  of  barium,  and  the  oleate 
of  baryta  must  be  purified  by  several  crystallizations  in  boiling  alco- 
hol. Lastly,  the  oleate  of  baryta  is  decomposed  by  tartaric  acid, 
operating  in  a  bottle  perfectly  fitted  and  well  corked,  to  prevent  the 
oleic  acid  from  absorbing  the  oxygen  of  the  air. 

Oleic  acid  is  a  colourless  liquid,  solidifying  below  53.6°,  and 
insoluble  in  water,  but  very  soluble  in  alcohol,  ether,  and  the  essen- 
tial oils.  It  does  not  redden  litmus,  even  when  dissolved  in  alcohol ; 
and  it  readily  absorbs  oxygen  from  the  air.  The  formula  C3gH303, 
HO,  which  has  generally  been  assigned  to  this  acid,  should  probably 
be  doubled  and  written  C72HggOg,2HO,  in  which  latter  case  the  acid 
would  be  considered  as  bibasic.  Oleic  acid  is  decomposed  by  heat, 
but  may  nevertheless  be  distilled  in  vacuo.  The  products  of  its 
decomposition  are  very  various ;  and  a  fatty  acid,  called  sebacic, 
which  characterizes  oleic  acid  under  these  circumstances,  is  remarked 
among  them.  Treated  with  nitrous  acid,  oleic  acid  is  easily  trans- 
formed into  an  isomeric  modification,  elaidic  acid,  which  sets  into  a 
crystalline  mass,  and  which  shows  a  very  strong  acid  reaction.  It 
dissolves  in  boiling  alcohol,  and  separates  partly  from  it,  on  cooling, 
in  large  crystalline  lamellae,  which  melt  only  at  111.2°.  ^^  of  ni- 
trous acid  will  efi'ect  the  transformation  of  oleic  acid,  but  it  rapidly 
increases  with  the  quantity  of  nitrous  acid  used.     Elaidic  acid 


694  FATS. 

oxidizes  rapidly  in  the  air,  particularly  if  it  be  heated  to  140°  or 
160^ 

The  alkaline  oleates  are  readily  formed  by  dissolving  oleic  acid 
in  alkaline  lixivige,  or  by  treating  the  alkaline  carbonates  by  an 
alcoholic  solution  of  oleic  acid ;  other  metallic  oleates  being  prepared 
by  double  decomposition.  The  formula  of  oleate  of  baryta  is  BaO, 
C36H33O3.  A  large  quantity  of  water  decomposes  the  alkaline  oleates. 
salts  containing  a  smaller  proportion  of  base  being  deposited ;  which 
decomposition/  is  however  less  readily  effected  than  in  the  stearates 
and  margarates. 

ACTION  OF  SULPHURIC  ACID  ON  THE  NATURAL  FATS. 

§  1603.  When  sulphuric  acid  is  made  to  act  on  stearin,  the  latter 
is  decomposed  in  the  same  manner  as  when  in  contact  with  the 
hydrated  alkalies ;  stearic  acid  being  set  free,  and  the  glycerin 
combining  with  the  sulphuric  acid  to  form  sulphoglyceric  acid.  It 
is  as  yet  unknown  what  reaction  sulphuric  acid  exerts  oh  margarin 
or  on  olein  when  isolated ;  the  reaction  on  the  natural  fats,  which 
are  mixtures  or  compounds  of  these  two  substances,  and  particularly 
on  olive-oil,  having  hitherto  only  been  studied. 

When  olive-oil  is  treated  with  one-half  of  its  weight  of  concen- 
trated sulphuric  acid,  by  placing  the  bottle  containing  the  two  sub- 
stances in  a  refrigerating  mixture,  in  order  to  prevent  an  elevation 
of  temperature,  a  homogeneous  liquid  of  a  viscous  consistence  is 
formed,  composed  of  sulphoglyceric  acid  and  two  new  compound 
acids,  called  sulphomargaric  and  sulpholeic.  By  adding  a  great 
excess  of  cold  sulphuric  acid,  the  sulphomargaric  and  sulpholeic 
acids  are  separated  from  the  sulphoglyceric  acid,  which  remains  in 
solution,  while  they  form  an  oily  coating  on  the  surface,  which  is 
removed  and  washed  with  a  small  quantity  of  water,  to  free  it  from 
the  sulphuric  acid.  These  acids  dissolve  readily  in  water  and  alco- 
hol, and  form  well-defined  salts.  Their  aqueous  solution  decom- 
poses spontaneously  in  the  cold,  and  more  rapidly  at  the  boiling 
point,  into  sulphuric  acid,  and  new  fat  acids,  which  appear  to  differ 
from  margaric  and  oleic  acids  only  by  the  addition  of  1  or  more 
equivalents  of  water.  Margarin  yields  the  three  acids,  metamar- 
garic^  hydromargarie^  and  Jiydromargaritic ;  while  oleic  acid  fur- 
nishes but  two,  metoleic  and  hydroleic  acids.  The  three  acids 
derived  from  margarin  are  solid  at  the  ordinary  temperature,  meta- 
margaric  acid  melting  at  122°,  hydromargaric  at  140°,  and  hydro- 
margaritic  at  154°;  while  metoleic  and  hydroleic  acids  are  oily 
liquids.  All  the  new  fat  acids,  being  insoluble  in  water,  are  readily 
soluble  in  alcohol  and  ether. 

Metoleic  and  hydroleic  acids,  carefully  heated  in  a  retort,  are 
decomposed,  and  disengage  pure  carbonic  acid,  while,  together  with 
some  empyreumatic  substances,  an  oily  liquid,  composed  of  two  iso- 
meric carburetted  hydrogens,  presenting  the  composition  of  olefiant 


DECOMPOSITION   OF    FAT   ACIDS.  695 

gas,  condense  in  the  receiver,  and  may  be  separated  by  distillation 
at  different  temperatures.  The  first,  oleen^  boils  at  131°,  has  a 
disagreeable  and  penetrating  odour,  and  the  density  of  its  vapour 
has  been  found  to  be  2.87,  while  its  formula  is  Q^^^^-)  which  is 
represented  by  4  volumes  of  vapour.  The  second  compound,  elaen, 
the  formula  of  which  appears  to  be  C^gH^g,  boils  at  230°. 

ACTION  OF  NITRIC  ACID  ON  STEARIC,  MARGARIC,  AND  OLEIC  ACIDS. 

§  1604.  Nitric  acid  reacts  energetically  on  the  fat  acids,  forming 
with  them  very  complicated  products,  among  which  are  some  new 
and  highly  interesting  acids.  Since  during  the  first  periods  of  the 
reaction  of  nitric  on  stearic  acid  the  latter  is  converted  into  margaric 
acid,  the  products  afforded  by  margaric  and  oleic  acids  only  remain 
to  be  described.  The  ultimate  products  of  the  reaction  are  very 
complicated,  and  may  be  divided  into  two  classes  :  the  volatile  acids 
which  condense  in  the  receiver,  and  the  fixed  or  slightly  volatile 
acids  which  remain  in  the  retort.  We  shall  here  enumerate  them 
with  their  formula,  in  order  that  the  curious  relation  between  them 
may  be  more  easily  seen.  The  fourth  column  contains  the  carbu- 
retted  hydrogens  from  which  they  may  be  supposed  to  be  derived 
'by  substitution. 

Volatile  Acids.  « 

Formic  acid  Cg  Hg  0^  or  Cg  H  03,H0  C2  H^ 

Acetic  "  C^H.O^  C4H3  03,HO C.Hg 

Acetonic  "  C^  Hg  0^  Cg  H^  03,H0  CgHg 

Butyric  "  Cg  H3  0,  CgH703,HO  Cg  H^o 

Valerianic  "  G,JI,fi^  C^oHg  03,H0  C.^R.^ 

Caproic  "  C12H1A  Ci^H^A^HO  G,,U,, 

(Enanthylic  "  C,fi,fl,  C,JI,fi,,KO  C,J1,^ 

Caprylic  "  G,,R,fi,  C.^H^A^HO  C.^H^g 

Pelargonic  "  C,gH,gO,  C,gH,,03,H0  C,gH^ 

Capric  "  C^oH^O,  C^oH^A^HO  C^oH,^. 

It  will  be  seen  that  if  the  equivalent  of  basic  water  be  not  sepa- 
rated in  the  formula,  all  these  acids  may  be  regarded  as  compounds 
of  4  equivalents  of  oxygen  with  carburetted  hydrogen  isomeric  with 
olefiant  gas.  If,  on  the  contrary,  the  basic  water  be  isolated,  they 
may  be  regarded  as  resulting  from  the  substitution  of  3  equivalents 
of  oxygen  for  3  equivalents  of  hydrogen  in  carburetted  hydrogens 
of  which  the  general  formula  is  C2«H2„+2  (^  being  a  whole  number  :) 
but  only  one  of  these  carburetted  hydrogens,  the  protocarbu- 
retted  CgH^,  is  as  yet  known  with  certainty.* 

^  This  theory  has  already  been  noticed  in  the  note  to  §  1401,  where  it  is  also 
shown  that  the  acids  in  the  above  table  may  more  properly  be  considered  as 
oxalic  acid  paired  with  one  equiv.  of  a  carburetted  hydrogen  of  the  general 


696  FATS. 

The  slightly  volatile  acids  which  remain  in  the  retort  are 

Succinic  acid  Cg  Hg  Og  or  C8H4  06,2HO 

Adipic       "     Ci^H.oOg  Ci2H3  0e,2HO 

Pimelic      "     0,Ji,fi,  C,,H,oO„2HO 

Suberic       «     CieH.A  C,fi,fi,,2R0 

Sebacic      "     C,,B.,fi,  C^oH^A^^HO 

If  we  omit  the  basic  water  contained  in  the  formula,  we  shall 
find  all  these  acids  to  result  from  the  combination  of  8  equivalents 
of  oxygen  with  the  carburetted  hydrogens  of  which  the  general 
formula  is  C2„H2(„_i).  ^  ^  • 

§  1605.  In  order  to  obtain  these  various  products,  it  is  necessary  to 
operate  on  a  somewhat  considerable  quantity  of  oleic  acid.  The  nitric 
acid  should  be  first  introduced  by  itself  into  a  tubulated  retort,  and 
heated  to  120°  or  140°,  the  oleic  acid  being  added  by  small  quantities 
at  a  time.  Violent  reaction  ensues  at  each  addition ;  and  when  all 
the  oleic  acid  has  been  poured  into  the  retort,  the  heat  is  continued 
until  reaction  ceases.  The  liquid  collected  in  the  receiver  consists 
of  water  containing  the  most  soluble  of  the  volatile  acids,  such  as 
formic,  acetic,  acetonic,  and  butyric  acids,  covered  by  an  oily  layer 
which  contains  the  valerianic  and  other  acids.  The  latter  is  de- 
canted, saturated  with  water  of  baryta,  and  the  various  salts  of 
baryta  formed  are  separated  by  successive  crystallizations.  The 
caproate  of  baryta  crystallizes  first,  and  then  successively  the 
oenanthylate,  the  caprylate,  the  pelargonate,  the  caprate,  and 
lastly  the  valerianate  of  baryta. 

The  more  volatile  acids,  when  dissolved  in  water,  are  saturated 
by  carbonate  of  soda,  and  the  solution  evaporated ;  when  the  first 
crystals  deposited  from  the  cold  solution  are  acetate  of  soda ;  while 
if  sulphuric  acid  be  then  poured  into  the  mother  liquid,  an  oily  layer, 
composed  of  butyric  and  metacetonic  acids,  is  separated. 

When  the  slightly  volatile  acids  which  remain  in  the  retort  are 
chiefly  sought  to  be  obtained,  the  action  of  the  nitric  acid  must  not 
be  too  much  prolonged,  since  a  portion  of  them  would  then  be  de- 
stroyed. The  oleic  acid  is  then  acted  on  by  double  its  weight  of 
nitric  acid,  and  the  action  is  continued  until  no  more  reddish 
vapours  are  disengaged,  when  a  portion  of  the  oleic  acid  has  dis- 
appeared, being  converted  into  products  which  dissolve  in  the 
aqueous  liquid.  The  supernatant  oil  is  decanted,  and  again  acted 
on  by  nitric  acid  ;  this  process  being  continued  until  it  has  nearly 
disappeared,  when  the  slightly  volatile  acids  are  found  in  the 
watery  liquids  arising  from  this  treatment. 

formula  C5i„H^^,.  The  substitution  of  oxygen  for  hydrogen  is  in  no  case  admis- 
sible; and  while  of  the  hydrocarbons  assumed  in  the  text  as  the  radicals  only 
one  is  known,  several  of  the  formula  just  mentioned  have  been  isolated,  such 
as  methyl  CaH„  ethyl  C^H,,  valyl  CgHg,  and  amyl  C^.H^^.—  W.  L  .F. 


SUCCINIC  ACID.  697 

Succinic  Acid  C8H^Og,2HO. 

§  1606.  Succinic  acid  is  produced  not  only  by  the  action  of  nitric 
acid  on  fatty  acids,  but  is  also  found  under  other  remarkable  cir- 
cumstances. It  is  generally  prepared  by  distilling  amher,  a  sub- 
stance of  organic  origin,  sometimes  found  in  strata  of  lignite,  and 
occurring  in  large  quantities  in  the  alluvial  sands  of  the  Baltic. 
Amber  distilled  in  a  glass  retort  yields  an  acid  water,  and  empy- 
reumatic  oils,  which  remain  in  the  paper  through  which  the  acid 
liquid  is  filtered.  The  latter  being  saturated  with  chlorine  in  order 
to  destroy  some  foreign  substances,  and  then  evaporated,  the  suc- 
cinic acid  is  deposited  in  crystals. 

An  aqueous  solution  of  impure  asparagin  left  to  itself  for  some  time 
is  converted  by  a  species  of  fermentation  into  succinate  of  ammonia. 
Impure  neutral  malate  of  lime,  such  as  is  directly  obtained  from  the 
berries  of  the  service-tree,  left  for  several  months,  under  a  layer  of 
water,  in  a  vessel  covered  merely  by  a  sheet  of  paper,  undergoes  an 
analogous  fermentation,  the  liquor  becoming  covered  with  mucilage, 
while  crystals  of  hydrated  carbonate  of  lime  are  deposited  on  the 
sides  of  the  vessel,  and  acicular  crystals  of  succinic  acid  are  developed 
on  the  deposit  of  malate  of  lime. 

Succinic  acid  melts  at  365°,  boils  without  alteration  at  473°,  and 
may  be  sublimed  at  much  lower  temperatures.  Cold  water  dissolves 
about  \  of  its  weight  of  it,  and  boiling  water  about  J^;  and  it  also 
dissolves  in  considerable  quantity  in  alcohol,  but  very  slightly  in 
ether.  The  formula  of  succinic  acid,  crystallized  in  water,  is  CgHgOg, 
which  is  generally  written  C8H^Og,2HO,  since  2  equiv.  of  base  may 
be  substitued  for  2  equiv.  of  water.  At  284°  it  loses  1  equiv.  of 
water,  and  after  several  distillations  becomes  perfectty  anhydrous; 
its  composition  then  corresponding  to  the  formula  CgH^Og. 

Nitric  acid  and  chlorine  do  not  sensibly  act  on  succinic  acid,  while 
anhydrous  sulphuric  acid  forms  a  compound  acid  with  it,  called 
sulphosuccinic, 

Adipic  Acid  Ci2H806,2IIO. 

§  1607.  This  acid  is  formed  by  the  reaction  of  nitric  on  oleic  acid, 
being  deposited  after  the  suberic  and  pimelic  acids,  which  are  less 
soluble.  The  best  method  of  preparing  it  consists  in  boiling,  in  a 
large  retort  furnished  with  its  receiver,  tallow  with  nitric  acid  of 
commerce,  renewed  until  the  fatty  substance  has  entirely  disappeared. 
The  distilled  portions  are  returned  to  the  retort,  and  the  reaction 
of  the  nitric  acid  is  continued  until  crystals  appear  in  the  receiver, 
after  which  the  liquid  is  concentrated  in  a  water-bath,  when  it 
c.agulates  into  a  crystalline  mass.  It  is  washed,  first  with  concen- 
trated nitric  acid,  then  with  the  same  acid  more  diluted,  and  lastly 
with  fresh  water.  Treated  again  with  boiling  water,  it  dissolves 
and  deposits,  on  cooling,  very  pure  ciystals  of  adipic  acid. 


698  FATS. 

This  acid  melts  at  266°,  may  be  distilled  without  alteration,  and 
forms  well-marked  salts,  of  which  the  general  formula  is  2R0, 
CjaHgOg.  When  an  alcoholic  solution  of  adipic  acid  is  saturated  with 
chlorohydric  acid  gas,  an  oil  is  obtained  having  the  smell  of  pippin 
apples,  and  known  by  the  name  of  adipic  ether  ^QJlfifi^fi^, 

Suberic  Acid  Q^fi.^fi^.'mO, 

§  1608.  Suberic  acid  is  formed  by  the  action  of  nitric  acid  on  fats, 
being  the  first  deposited  when  the  liquid  is  crystallized ;  while  it  has 
also  been  directly  obtained  by  causing  the  same  acid  to  act  on  cork, 
which  is  the  most  convenient  method  of  preparing  it.  The  rasped 
cork  being  boiled  with  nitric  acid  of  commerce,  the  acid  liquid  is  con- 
centrated by  distillation,  and  allowed  to  cool,  when  suberic  acid  is 
deposited,  and  may  be  purified  by  solution  in  boiling  water  and 
recrystallization. 

Suberic  acid  forms  small,  hard,  granular  crystals,  soluble  in  about 
2  parts  of  boiling  water,  which  scarcely  retains  j^  after  cooling, 
while  it  is  very  soluble  in  alcohol  and  ether,  especially  at  the  boiling 
point.  The  alkaline  suberates  are  soluble  in  water,  and  nitrate  of 
silver  efi'ects  in  their  solution  a  precipitate  of  suberate  of  silver,  of 
the  formula  2KgO,Q^f{.^fi^. 

By  saturating  an  alcoholic  solution  of  suberic  acid  with  chlorohydric 
acid  gas,  vinosuberie  ether  2CjLlfi,G^QH.^2^Q  is  obtained,  as  an  olea- 
ginous, colourless  liquid,  which  boils  at  about  500°. 

Sebacic  Acid  C2oH^gOg,2HO. 

§  1609.  It  has  been  mentioned  (§  1602)  that  sebacic  acid  is  con- 
stantly formed  in  the  distillation  of  substances  containing  olein  or 
oleic  acid,  and  that  it  is  regarded  as  characteristic  of  these  sub- 
stances :  it  is  separated  by  treating  the  distilled  products  several 
times  with  boiling  water.  Acetate  of  lead  is  poured  into  the  solu- 
tion, and  the  salt  of  lead  precipitated  is  decomposed  by  sulphuric 
acid,  when  the  sebacic  acid  is  deposited  from  the  boiling  aqueous 
solution  in  the  form  of  crystalline,  pearly  lamellae.  This  acid  melts 
at  260.6°,  distils  without  alteration,  and  is  slightly  soluble  in  cold, 
but  much  more  freely  in  boiling  water,  while  alcohol  and  ether  dis- 
solve it  readily.  ■  It  forms  crystallizable  salts  with  the  alkalies  of 
the  general  formula  2RO,C2oHigOg.  It  produces  a  compound  ether 
2C4H.O,C2oHigOg  under  the  same  circumstances  as  the  preceding 
acids.* 


*  The  admirable  examination  of  the  fats  and  fat  acids  by  Chevreul  was  the  first 
investigation  which  gave  an  insight  into  the  chemistry  of  organic  compounds. 
But  more  recent  investigations  have  developed  the  singular  transformations  to 
which  they  are  subject;  such  as,  the  action  of  sulphuric  acid,  their  oxidation  into 
other  acids,  &c. —  W.  L.  F. 


CAPROIC  ACID.  699 

OF  SOME  VOLATILE  ACIDS  EXTRACTED  FROM  NATURAL  FATS. 
Sircic  Acid, 

§  1610.  Hircic  acid  is  obtained  by  saponifying  the  fat  of  the  goat 
by  an  alkali,  and  decomposing  the  soap  resulting  by  tartaric  acid; 
after  which  the  aqueous  liquid  is  separated  and  distilled,  when 
the  hircic  acid,  being  volatile,  passes  into  the  receiver.  It  is 
saturated  with  water  of  baryta,  and  the  hircate  of  baryta,  which  is 
obtained  by  evaporation,  is  decomposed  by  distilling  it  with  sulphuric 
acid  diluted  with  its  weight  of  water,  when  the  hircic  acid  forms  an 
oily  stratum  on  the  surface  of  the  water  which  condenses  in  the 
receiver.  It  has  a  decided  goatlike  smell,  is  slightly  soluble  in 
water,  but  easily  so  in  alcohol  or  ether,  and  its  composition  is  un- 
known. 

Phocenic  Acid. 

§  1611.  The  oil  of  the  sperm  whale  and  dolphin  yields,  by  saponi- 
fication, in  addition  to  the  ordinary  fat  acids,  a  peculiar  volatile 
acid,  called  phocenic^  which  appears  to  be  identical  with  valerianic 
acid.  ^ 

Oaproic,  Oapricy  and  Qaprylic  Acids, 

§  1612.  These  three  acids  are  found  among  the  products  of  the 
oxidation  of  oleic  by  nitric  acid,  and  are  also  obtained  mixed  with 
butyric  acid  when  butter  is  saponified  by  the  alkalies.  It  is  admitted 
that  butyric,  capric,  caproic,  and  caprylic  acid  in  butter  are  com- 
bined with  glycerin,  and  form  peculiar  substances :  butyrin,  caprin, 
caproin,  and  caprylin. 

In  order  to  prepare  these  substances,  butter  is  kept  for  a  long  time 
at  a  temperature  approaching  its  melting  point,  when  a  liquid  por- 
tion separates,  in  which  the  butyrin,  caprin,  caproin,  and  caprylin 
are  principally  concentrated.  This  oily  portion  is  treated,  after 
being  decanted,  with  an  equal  part  of  anhydrous  alcohol,  and  shaken 
frequently;  the  alcoholic  solution  leaving  by  evaporation  an  oil  formed 
of  a  mixture  of  butyrin,  caprin,  caproin,  and  caprylin. 

If,  on  the  contrary,  the  butyric,  capric,  and  caproic  acids  are  to 
be  isolated,  the  butter  is  saponified  with  an  alkali,  and  the  soap 
decomposed  by  an  aqueous  solution  of  tartaric  acid,  when  the  acids 
sought  remain  in  the  watery  liquid ;  which  is  separated  and  distilled. 
The  acids,  being  volatile,  pass  over,  and  are  then  saturated  with 
caustic  baryta,  and  evaporated,  which  furnishes  a  mixture  of  buty- 
rate,  caprate,  caprylate,  and  caproate  of  baryta.  The  salts  are 
separated  by  crystallization,  the  caprate  of  baryta  being  first  de- 
posited, then  the  caprylate,  the  caproate,  and  lastly  the  butyrate. 
The  acid  of  each  of  these  salts  may  be  easily  separated  by  distil- 
ling them  with  a  small  excess  of  sulphuric  acid  diluted  with  its 


700  PATS. 

weight  of  water,  when  the.  acid  passes  into  the  receiver  with  the 
water,  and  forms  an  oily  coating  on  its  surface. 

Capric  acid  is  liquid  above  62.6°,  but  solidifies  into  crystalline 
aciculse  when  the  temperature  is  lower ;  and  it  is  very  slightly  solu- 
ble in  water,  but  readily  so  in  alcohol.  The  formula  of  free  capric 
acid  is  CjoHjgOgjHO,  that  of  the  caprates  being  ROjCgoHigOg. 

Caprylic  acid  is  solid  below  57.2°,  and  boils  at  about  464°. 
Water  dissolves  only  a  very  small  quantity  of  it,  even  at  the  boiling 
point,  while,  it  is  very  soluble  in  alcohol  and  ether ;  and  the  general 
formula  of  the  caprylates  is  RO,CigHj503. 

Caproic  acid  is  an  oily  liquid  at  the  ordinary  temperature,  and 
does  not  solidify  even  at  14°,  while  it  boils  at  about  410°,  and  dis- 
solves in  75  parts  of  water  and  in  all  proportions  in  alcohol.  The 
general  formula  of  its  salts  is  ROjCigHuOg. 

These  various  acids  form  compound  vinic  and  methylic  ethers, 
which  may  be  obtained  by  passing  chlorohydric  acid  gas  through 
alcohol  or  wood-spirit  holding  the  acids  in  solution. 

PALM-OIL. 

§  1613.  This  oil,  which  is  imported  chiefly  from  Guinea,  has,  of  late 
years,  become  an  object  of  great  commercial  importance.  It  is  gene- 
rally of  a  reddish-yellow  colour,  and  melts  at  a  temperature  varying 
from  80°  to  86°.  It  is  supposed  to  be  formed  of  olein,  margarin,  and 
a  new  fatty  substance,  called  palmitin,  which  is  extracted  by  express- 
ing the  oil  and  washing  the  residue  several  times  with  alcohol,  when 
the  palmitin  is  isolated  and  purified  by  being  washed  in  ether. 
Palmitin  forms  crystalline  aciculae,  melting  at  118.4°,  but  decom- 
posing at  a  high  temperature ;  and  it  is  nearly  insoluble  in  alcohol, 
even  at  the  boiling  point,  but  dissolves  largely  in  ether.  Alkalies 
convert  it  into  glycerin,  and  into  a  new  acid  called  palmitic.  Its 
composition  corresponds  to  the  formula  CyoHggOg,  which  is  written 
^Q^fi 2,00^^2^.;  the  formula  of  free  palmitic  acid  being  0^^13.^20^, 
2H0. 

CASTOR-OIL. 

§  1614.  Castor-oil  is  extracted  from  the  ricinus  communis^  and 
forms  a  white  or  somewhat  yellowish  oil,  slightly  fluid,  which  soon 
becomes  rancid  in  the  air.  When  saponified,  it  yields  glycerin,  and 
three  new  fatty  acids:  stearoricinic,  called  also  margaritic,  ricinic, 
and  oleorieinic  or  elaiodic  acids.  By  decomposing,  by  an  acid,  soap 
made  with  castor-oil,  an  oil  separates,  which  partially  coagulates  at 
the  ordinary  temperature.  The  solid  part  being  separated  and  ex- 
pressed between  bibulous  paper,  the  residue  is  dissolved  in  boiling 
alcohol,  when,  on  cooling,  pearly  crystalline  lamellae  of  stearoricinic 
acid  separate,  which  melt  only  at  266°.  The  greater  portion  of 
the  oil  which  has  been  separated  by  expression  from  the  stearori- 
cinic acid  coagulates  at  28.4°,  and  is  also  separated,  by  expression 


SPERMACETI.  701 

between  tissue-paper,  from  the  portion  which  remains  liquid,  when 
it  constitutes  ricinic  acid,  which  melts  at  71.6°,  and  may  be  distilled 
without  alteration.  Lastly,  the  name  of  oleoricinic  acid,  has  been 
given  to  the  portion  of  the  acid  oil  which  did  not  become  solid  at 

28.4°. 

SPERMACETI. 

§  1615.  A  peculiar  fat  oil,  which,  by  exposure  to  the  air  for  a  few 
days,  deposits  a  crystalline  substance  called  spermaceti,  is  extracted 
from  the  brain  of  the  sperm  whale.  The  crystalline  mass  is  ex- 
pressed to  separate  the  part  which  remains  liquid,  and  digested  in 
a  hot  lye  of  potassa,  while  the  oily  fluid  is  washed  several  times  with 
boiling  water,  and  poured  into  crystallizing  vessels,  in  which  it 
solidifies  into  crystalline  masses,  constituting  the  cakes  of  spermaceti 
found  in  commerce.  In  order  to  obtain  it  in  a  state  of  purity,  it 
is  necessary  to  crystallize  it  several  times  in  alcohol,  when  it  takes 
the  name  of  eetin. 

Cetin  is  a  white  substance  of  a  crystalline  texture,  almost  inodor- 
ous, melting  at  120.2°,  and  solidifying,  by  slow  cooling,  into  a  mass 
composed  of  large  crystalline  lamellae.  It  is  insoluble  in  water,  and 
100  parts  of  boiling  alcohol  dissolve  16  parts  of  it,  but  retain  only 
3  after  cooling;  while  ether  and  the  essential  oils  dissolve  it  freely. 
Its  composition  corresponds  to  the  formula  C32H32O2.  Spermaceti  is 
saponified  by  potassa,  but  it  differs  from  all  fat  substances  we  have 
hitherto  described  by  yielding  no  glycerin,  but  in  its  place  another 
very  remarkable  neutral  substance,  called  ethal,  while  the  fat  acid 
which  combines  with  the  alkali  has  received  the  name  of  ethalic  acid. 
The  saponification  of  spermaceti  is  much  more  difficult  than  that  of 
the  other  fats,  since  it  can  only  be  effected  by  a  concentrated  solu- 
tion of  potassa,  assisted  by  heat,  and  continued  for  several  days ;  or 
better,  by  melting  2  parts  of  spermaceti  in  a  capsule  and  adding  1 
part  of  caustic  potassa  broken  into  small  pieces,  and  stirring  it  con- 
stantly. After  some  time,  as  soon  as  the  substance  has  become  com- 
pletely solid,  it  is  treated  with  boiling  water  and  chlorohydric  acid, 
when  the  ethalic  acid  separates  and  forms  an  oily  layer  on  the  sur- 
face of  the  liquid.  The  oil  being  decanted,  and  treated  in  the  same 
manner  by  potassa,  is  again  saturated  with  chlorohydric  acid,  and 
the  oil  obtained  is  heated  with  hydrated  lime,  when  the  ethalic  acid 
alone  combines  with  the  lime,  leaving  the  ethal  isolated.  The  latter 
is  removed  by  boiling  alcohol,  which  is  then  driven  off  by  distilla- 
tion, and  it  is  finally  crystallized  by  dissolving  it  in  ether. 

Ethal  melts  at  118.4°,  crystallizing  readily,  on  cooling,  in  brilliant 
lamellae,  and  it  is  insoluble  in  water,  but  dissolves  in  all  proportions 
in  alcohol  and  ether.  It  may  be  distilled  without  alteration.  Its 
composition  corresponds  to  the  formula  €32113^02,  and  exhibits  seve- 
ral reactions  which  assimilate  it  to  alcohol  and  wood-spirit,  on  which 
account  it  has  even  been  called  ethalic  alcohol. 


702  FATS. 

§  1616.  If  a  mixture  of  ethal  and  concentrated  sulphuric  acid  be 
heated,  stirring  it  frequently,  an  acid  product  is  obtained  consist- 
ing of  a  mixture  of  pure  sulphuric  acid  and  a  compound  acid,  sulph- 
ethalic  acid  (C32H330  +  HO),2S03,  which  is  to  ethal  C32H34O2 
what  sulphovinic  acid  (C4H50  +  HO),2S03  is  to  alcohol  C^HgOg. 
The  acid  mass  being  dissolved  in  alcohol  and  saturated  with  potassa, 
.sulphate  of  potassa  is  precipitated,  while  the  sulphethalate  of  po- 
tassa (C32H330  +  HO),2S03  remains  in  solution,  and  crystallizes  by 
evaporating  the  liquid. 

By  heating  in  a  retort  equal  volumes  of  ethal  and  perchloride  of 
phosphorus,  chlorohydric  acid  is  disengaged,  and  protochloride  of 
phosphorus  first  distils,  then  the  perchloride,  and  lastly  an  oily  pro- 
duct of  the  composition  C32H33CI,  which  may  be  regarded  as  the 
chlorohydric  ether  of  ethalic  alcohol  C32H34O2.  In  order  to  obtain 
it  pure,  it  should  be  distilled  a  second  time  with  perchloride  of 
phosphorus,  washed  with  water,  and  distilled  over  a  small  quantity 
of  quicklime. 

By  heating  ethal  with  5  or  6  times  its  weight  of  potassic  lime  to 
a  temperature  of  410°  to  430°,  pure  hydrogen  is  disengaged,  and 
ethalic  acid  C32H3i03,HO  is  formed,  which  is  to  ethalic  alcohol 
€32113^02  what  acetic  acid  €411303,110  is  to  vinic  alcohol  C^HgOg. 
In  order  to  separate  this  acid,  the  alkaline  mass  is  diluted  with 
water  and  saturated  with  chlorohydric  acid,  when  the  ethalic  acid 
separates  in  the  form  of  flocculi,  but  always  mixed  with  unaltered 
ethal.  In  order  to  purify  it,  it  is  heated  with  a  solution  of  caustic 
baryta,  which  combines  with  the  ethalic  acid,  after  which  it  is  eva- 
porated to  dryness,  and  the  residue  treated  with  alcohol  to  dissolve 
the  ethal.  The  residue,  which  is  composed  only  of  ethalate  of  ba- 
ryta, is  decomposed  by  chlorohydric  acid,  while  the  ethalic  acid,  set 
free,  is  purified  by  solution  in  ether. 

§  1617.  We  have  shown  (§1615)  that  spermaceti  is  converted  by 
saponification  into  ethal  and  ethalic  acid ;  and  a  large  quantity  of 
the  latter  acid  may  also  be  obtained  by  decomposing  spermaceti 
soaps  by  acids. 

Ethalic  acid  melts  at  about  140°,  crystallizing,  on  cooling,  in 
brilliant  aciculse ;  and  it  is  insoluble  in  water,  but  very  soluble  in 
alcohol  and  ether.     The  general  formula  of  its  salts  is  RO, (032113^03). 

As  ethalicy  acid  exists  in  palm-oil,  either  isolated  or  combined 
with  glycerin,  it  has  also  received  the  name  0^ palmitic  acid. 

By  distilling  ethal  several  times  with  anhydrous  phosphoric  acid, 
a  volatile  liquid  of  the  formula  C32H32  is  obtained,  which  has  been 
called  ceten^  and  forms  in  the  series  of  ethalic  alcohol  the  analogue 
of  olefiant  gas  in  the  vinic  series.  This  liquid  boils  at  about  527° 
without  alteration,  and  its  formula  corresponds  to  4  volumes  of 
vapour. 


WAX.  703 

WAX. 

§1618.  Chemists  give  the  name  of  wax  to  substances  arising 
from  various  sources,  the  type  of  which,  beeswax,  will  alone  occupy 
our  attention,  because  it  is  best  known  ;  and  we  shall  omit  the  other 
substances  produced  by  vegetables,  which  frequently  resemble  ordi- 
nary wax  only  in  appearance  or  in  physical  properties. 

Wax  forms  the  solid  portions  of  the  honeycomb ;  and  when  the 
honey  has  been  removed  by  expression,  the  wax  is  melted  with  hot 
water,  and  washed  several  times  with  water,  when  a  yellow  substance 
remains,  the  smell  of  which  resembles  that  of  honey.  By  exposing 
it  in  large  sheets  on  the  grass  to  the  action  of  moist  air  and  the 
rays  of  the  sun,  the  odoriferous  and  colouring  substances  are  de- 
stroyed, and  white  wax  remains ;  the  bleaching  being  more  promptly 
effected  by  chlorine  or  the  alkaline  hypochlorites,  and  by  oxidizing 
reagents  in  general.  White  wax  contains  less  carbon  and  more 
oxygen  than  yellow  wax. 

Bleached  wax  is  translucent  to  a  certain  degree,  shows  a  density 
varying  from  0.960  to  0.996,  is  hard  and  brittle  at  32°,  but  very 
malleable  at  86°,  and  melts  at  about  149°.  Boiling  alcohol  sepa- 
rates it  into,  (1)  myriciriy  almost  insoluble  in  boiling  alcohol ; 
(2)  cerin^  also  called  cerotic  acic?,- soluble  in  boiling  alcohol,  but  de- 
posited from  it,  on  cooling,  in  small  crystalline  aciculae ;  and  (3)  into 
ceroleiriy  which  remains  in  solution  in  the  alcohol  when  cooled.  The 
proportions  of  these  substances  vary. 

Wax  yields,  by  distillation,  a  small  quantity  of  acid  water,  com- 
bustible gases,  and  liquid  oils,  isomeric  with  olefiant  gas,  besides  a 
solid  substance,  composed  essentially  of  margaric  acid  and  a  crys- 
tallizable  substance  very  analogous  to  paraffin.  By  distilling  it 
with  lime,  yellow  oils  of  complex  composition  are  first  obtained,  and 
then  a  large  quantity  of  the  crystalline  substance  about  to  be  de- 
scribed. 

Cerin  or  Cerotic  Acid  Q^^^fi^—Q^Jl^O^^^O. 

§  1619.  When  wax  is  boiled  for  some  time  with  alcohol,  and  the 
liquor  allowed  to  cool,  the  deposit  which  is  formed  is  composed 
chiefly  of  cerin  and  myricin,  which  must  be  again  dissolved  in  boiling 
alcohol,  until  the  substance  deposited  during  the  cooling  of  the  liquid 
melts  only  at  158°.  It  is  redissolved  in  boiling  alcohol,  and  acetate 
of  lead  is  added,  the  precipitate  of  cerotate  of  lead  being  washed, 
when  hot,  with  alcohol  and  ether,  and  then  decomposed  by  acetic 
acid.  The  cerotic  acid  is  crystallized  by  dissolving  it  in  boiling 
alcohol ;  and  the  pure  acid,  which  melts  at  172.4°,  is  insoluble  in 
water. 

Myricin, 

§  1620.  Myricin  is  very  slightly  soluble  in  alcohol,  200  parts  of 
boiling  alcohol  being  required  to  dissolve  1  of  it,  which  is  again 


704  ORGANIC    COLOURING   MATTERS. 

deposited,  during  the  cooling,  in  white  flakes ;  while  it  requires 
about  100  parts  of  cold  ether  for  solution.  It  melts  at  161.6°,  and 
partly  sublimes  without  change  at  a  higher  temperature.  Its  ele- 
mentary composition  corresponds  to  the  formula  C82H92O4;  and 
when  heated  for  a  long  time  with  a  concentrated  solution  of  caustic 
potassa,  it  is  converted  into  palmitic  acid  €92113^03,110,  which  re- 
mains combined  with  the  potassa,  and  a  neutral  substance,  melissin 
^60-^62^25  which  in  its  chemical  reactions  resembles  ethal. 

Cerolein. 

§  1621.  Cerolein,  which  remains  in  solution  in  the  cold  alcoholic 
liquor  with  which  wax  has  been  treated,  is  separated  by  evaporation 
from  alcohol,  and  appears  as  a  soft  substance,  fusible  at  84.2°,  very 
soluble  in  alcohol  and  cold  ether,  and  reddening  litmus.  It  contains 
more  oxygen  than  cerin  and  myricin. 


ORGANIC  COLOURING  MATTERS. 

§  1622.  While  vegetables  contain  very  various  colouring  matters, 
unequally  distributed  through  their  various  parts,  they  also  fre- 
quently enclose  substances  which  are  colourless,  or  nearly  so,  con- 
stituting a  part  of  the  living  vegetable,  but  which  acquire  very 
beautiful  colours  by  contact  with  atmospheric  air  or  the  reaction 
of  various  chemical  agents. 

Nearly  all  organic  colouring  matters  change  in  the  air,  especially 
when  exposed  to  the  sun,  and  undergo  partial  combustion,  being 
converted  into  colourless  substances  ;  and  the  quality  of  the  colour- 
ing matter  depends  upon  the  time  in  which  this  change  is  eifected. 
Chemical  agents  generally  modify  the  shade  of  organic  colouring 
matters,  "forming  compounds  with  them  or  converting  them  into 
other  substances  equally  coloured,  which  properties  are  frequently 
applied  in  dyeing.  The  metallic  oxides  especially  combine  with  a 
great  number  of  colouring  matters  possessing  acid  properties ;  and 
the  majority  of  the  oxides,  such  as  that  of  alumina,  tin,  etc.,  thus 
form  insoluble  compounds,  exhibiting  often  very  beautiful  colours, 
and  which  are  used,  under  the  name  of  lakes^  for  painting  in  oil  and 
in  water-colours. 

Very  porous  charcoal,  particularly  animal  black,  absorbs  the 
majority  of  organic  colouring  matters  dissolved  in  water,  without 
alteration,  and  again  deposits  them  if  a  small  quantity  of  alkali  be 
added  to  the  water ;  woody  and  animal  fibre  possessing  the  same 
property.  Moist  chlorine  destroys  all  organic  colouring  matters, 
by  exerting  on  them  a  powerful  oxidizing  action,  owing  to  the  de- 
composition of  water;    and  sulphurous  acid  also  bleaches  them, 


MADDER.  705 

either  by  removing  their  oxygen,  or  by  combining  with  the  substance 
without  altering  it,  and  thus  forming  colourless  compounds. 

A  large  number  of  reducing  substances,  such  as  nascent  hydro- 
gen, sulf  hydric  acid,  the  alkaline  sulphides,  the  hydrated  protoxides 
of  iron  and  manganese,  etc.,  bleach  colouring  matters  by  abstract- 
ing their  oxygen. 

We  shall  here  treat  only  of  the  organic  colouring  matters  used 
in  dyeing. 

COLOURING  MATTERS  OF  MADDER. 

§  1623.  Madder,  (rubia  tinctorum,)  also  known  by  the  name  of 
alizari,  is  one  of  the  most  important  dyestuffs,  which  is  extensively 
cultivated  in  the  Levant  and  the  East  Indies,  as  well  as  in  France, 
particularly  in  Alsace  and  the  county  of  Avignon.  Madder  con- 
tains several  colouring  matters,  the  majority  of  which  are  as  yet 
but  imperfectly  known ;  and  the  plant,  while  growing,  contains  only 
a  yellow  sap,  without  any  red-colouring  principle,  the  same  being 
true  of  the  root ;  while,  when  the  latter  has  been  separated  from 
the  plant  and  dried  in  the  air,  a  red  substance  is  developed  which 
imparts  its  colour  to  all  the  ligneous  portions. 

In  dyeing,  sometimes  crude  madder  is  used,  and  sometimes  that 
which  has  undergone  several  preparations,  of  which  the  intention  is 
to  reduce  the  colouring  matter  to  a  smaller  volume,  or  to  destroy 
some  of  the  colouring  principles,  the  presence  of  which  affect  the 
shade  of  the  red  colour. 

When  ground  madder  is  exhausted  by  cold  water,  a  yellow 
colouring  matter,  or  xanthin,  very  soluble  in  water,  is  extracted 
from  it ;  and  if  the  residue  be  treated  with  one-half  of  its  weight  of 
concentrated  sulphuric  acid  heated  to  212°,  a  large  portion  of  the 
ligneous  matter  is  altered,  becoming  soluble  in  water,  and,  after 
several  washings,  yielding  a  brown  substance,  easily  pulverized  after 
desiccation,  and  constituting  the  article  known  in  commerce  by  the 
name  of  garancin  or  madder-red.  Madder-red  contains  another 
colouring  matter  of  a  beautiful  red  hue,  called  alizarin,  mixed  with 
some  other  colouring  principles.  When  treated  with  boiling  alco- 
hol, it  furnishes  a  beautifully  red  solution,  which  deposits,  on  eva- 
poration, a  substance  of  an  ochrous  yellow  colour,  and  named  colorin, 
Colorin  is  chiefly  formed  of  alizarin,  fatty  matters,  and  a  small  quan- 
tity of  other  colouring  matters ;  and  if  it  be  carefully  heated,  it 
emits  yellow  vapours,  which  condense  in  the  form  of  bright-red 
needles,  constituting  alizarin,  mixed  merely  with  a  small  quantity 
of  empyreumatic  oil,  from  which  it  may  easily  be  freed  by  crystal- 
lizing it  in  weak  alcohol. 

Alizarin  presents  all  the  characters  of  a  definite  compound,  and 
its  analysis  has  led  to  the  formula  CgoHgO^.  It  forms  very  fine 
aciculae  of  an  orange-yellow  colour,  nearly  insoluble  in  cold  water, 
slightly  soluble  in  boiling  water,  but  very  soluble  in  alcohol.     It 

Vol.  II.— 45 


706  ORGANIC   COLOURING  MATTERS. 

dissolves  readily  in  alkaline  lixivise  and  ammonia,  furnishing  solu- 
tions of  a  violet  colour,  and  yielding  bluish  precipitates  with  solu- 
tions of  -baryta,  strontian,  and  lime :  concentrated  sulphuric  acid 
also  dissolves  it,  forming  a  brown  liquid,  from  which  the  alizarin  is 
precipitated  unchanged  upon  the  addition  of  water. 

§1624.  Very  variously  coloured  products  have  been  obtained  by 
different  methods  of  treating  madder-root,  which,  however,  do  not 
exhibit  the  characters  of  definite  substances,  and  are  probably  only 
mixtures.  When  madder-root,  previously  washed,  is  boiled  with 
a  concentrated  solution  of  alum,  a  red  liquid  is  obtained,  depositing, 
on  cooling,  a  brownish-red  substance,  which  is  separated,  while  the 
filtered  liquid  is  of  a  pure  red,  and  by  the  addition  of  sulphuric  acid 
gradually  deposits  the  colouring  matter,  a  mere  trace  of  it  remain- 
ing in  the  solution  after  24  hours.  The  precipitate,  after  being 
washed,  first  with  weak  boiling  chlorohydric  acid,  and  then  with 
cold  water,  is  redissolved  in  alcohol,  which  solution  is  evaporated, 
and  the  residue  treated  several  times  with  ether,  when  a  colouring 
matter  dissolves,  called  purpurin  or  madder-purple,  which  remains 
after  the  evaporation  of  the  ether,  in  the  form  of  a  bright-red  pow- 
der. This  substance  is  insoluble  in  cold  water,  but  very  soluble  in 
boiling  water,  alcohol,  and  ether;  and  its  analysis  has  led  to  the 
formula  CggHjoOig :  but  as  it  has  not  been  obtained  in  a  crystallized 
form,  it  is  difficult  to  assert  that  it  is  a  simple  substance. 

The  name  of  madder-red  is  given  to  a  colouring  matter  found 
in  the  brown  precipitate  deposited  by  a  hot  decoction  of  madder,  on 
cooling ;  which  substance  sublimes  at  about  437°,  forming  crystals 
of  a  yellowish  red  colour,  and  of  a  composition  corresponding  to  the 
formula  C20H10O15. 

By  dissolving  the  colouring  matters  of  madder  in  a  solution  of 
alum,  and  then  adding  carbonate  of  soda,  pecipitates  of  very  beau- 
tiful colour  and  great  stability  are  obtained,  consisting  of  compounds 
of  alumina  with  the  colouring  matters,  and  called  madder-lakes, 
which  are  used  in  painting. 

COLOURING  MATTERS  OF  LOGWOOD. 

§  1625.  The  name  of  hematin  has  been  given  to  the  substance 
to  which  logwood  owes  its  value  as  a  dyestuff.  It  is  readily  ob- 
tained by  making  a  decoction  of  powdered  logwood,  evaporating  it 
to  dryness,  and  treating  the  residue  with  alcohol,  when  hematin  is 
deposited  in  crystals,  varying  in  depth  of  colour  according  to  their 
size,  but  producing  a  yellow  powder.  The  aqueous  solution  of 
hematin  is  colourless  in  the  air,  but  if  ammonia  be  added,  it  assumes 
an  intense  red  hue ;  the  substance  produced  by  this  reaction  being 
named  hematein,  which  is  granular  and  crystalline,  showing  a  violet- 
black  colour  and  metallic  lustre.  It  dissolves  in  water,  and  turns 
it  of  a  deep  purple  colour.  Hematein  appears  to  differ  from  hema- 
tin by  containing  1  equiv.  less  of  water,  the  formula  of  dried 


QUEBCITRON.  707 

hematin  being  G^qH.^Oq,B.O,  and  that  of  hematein  CigHgOg ;  while 
the  formula  of  hematin  crystallized  from  an  aqueous  solution  is 
CigHA,H0+2H0. 

Hematin  possesses  the  properties  of  a  feeble  acid,  its  aqueous 
solution  being  precipitated  by  baryta  and  acetate  of  lead.  Hema- 
tate  of  lead,  decomposed  by  aqueous  sulf  hydric  acid,  forms  a  liquid 
which  deposits  nearly  colourless  crystals  of  hematin  on  evaporation. 

COLOURING  MATTERS  OF  SAFFLOWER. 

§  1626.  The  safflower  is  used  in  dyeing,  and  produces  colours 
which  vary  from  a  delicate  rose  to  a  deep  poppy  hue.  Several  colour- 
ing matters  exist  in  the  flowers ;  and  when  they  are  exhausted  by 
water,  they  yield  a  yellow  colouring  matter,  useless  in  dyeing,  which 
combines  with  bases ;  the  formula  of  its  compound  with  oxide  of  lead 
being  3PbO,C,6H,,0,o. 

If  safflower,  exhausted  by  cold  water,  be  treated  with  a  solution 
of  carbonate  of  soda,  a  red  solution  is  obtained,  by  accurately  neu- 
tralizing which  with  acetic  acid,  and  dipping  cotton  into  it,  the  red 
colouring  matter,  or  carthamin,  is  precipitated.  As  soon  as  the 
liquid  is  nearly  bleached,  the  cotton  is  removed,  and  treated  with 
water  containing  ^^  of  carbonate  of  soda,  when  the  carthamin  dis- 
solves, and,  if  citric  acid  be  added  to  the  liquid,  is  again  precipitated 
in  the  form  of  crimson  flakes.  The  precipitate  being  redissolved  in 
alcohol  and  evaporated,  a  deep-green  substance  is  obtained,  which 
changes  colour  when  seen  in  difi'erent  lights.  The  formula  G^Jlfi^^ 
has  been  assigned  to  carthamin.  • 

BRAZIL  OR  PERNAMBUCO  WOOD. 

§  1627.  Decoctions  of  Brazil  or  Pernambuco  wood  are  used  in 
dyeing,  and  produce  red  colours  which  are  not  very  permanent. 
The  colouring  principle  of  this  wood,  called  brazilin,  has  been  ob- 
tained in  small  orange-coloured  crystalline  aciculse,  soluble  in  water, 
alcohol,  and  ether,  but  of  unknown  composition.  Brazilin  assumes 
a  purple  hue  on  contact  with  the  alkalies,  while  the  action  of  acid 
and  of  ammonia  converts  it  into  a  new  substance,  brazilein,  which  is 
of  a  deep  purple. 

WELD. 

§  1628.  Weld  (reseda  luteola)  contains  a  colouring  principle  of  a 
beautiful  yellow  colour,  called  luteoUn,  which  is  extracted  by  boiling 
water,  and  appears  as  a  yellow  substance,  soluble  without  decompo- 
sition, and  subliming  in  small  aciculae.  It  is  very  slightly  soluble 
in  water,  and  yet  the  small  quantity  which  dissolves  in  it  is  suffi- 
cient to  afibrd  beautiful  dyes,  remarkable  for  their  stability. 

QUERCITRON. 
§  1629.  The  name  of  quercitrin  has  been  given  to  a  colouring 
principle  found  in  the  bark  of  a  certain  species  of  oak,  the  quercus 


708  VEGETABLE   COLOUKING   MATTERS. 

nigra^  from  which  it  is  extracted  by  treating  the  powdered  bark 
with  alcohol,  precipitating  the  tannin  by  gelatin,  evaporating  the 
liquid,  and  dissolving  the  residue  in  alcohol  and  then  in  water. 
Quercitrin  is  a  yellow  crystalline  substance,  of  the  formula  CjgHgOio, 
which  dissolves  in  100  parts  of  cold  water,  and  in  4  or  5  of  absolute 
alcohol. 

ARNOTTO. 

§  1630.  This  is  the  name  of  a  reddish-yellow  substance,  arising 
from  the  fermentation  of  the  hixia  orellana,  and  imported  from 
Brazil,  Guiana,  and  the  East  Indies.  Arnotto  contains  two  dis- 
tinct colouring  matters,  one  of  which  is  yellow,  and  soluble  in  water 
and  alcohol,  but  very  slightly  soluble  in  ether ;  while  the  other, 
which  is  red,  is  slightly  soluble  in  water,  but  highly  so  in  alcohol 
and  ether. 

RED  SANDERS. 

§  1631.  The  name  of  santalin  has  been  given  to  the  collection  of 
colouring  matters  of  the  wood  of  the  pterocarpus  santalinus,  and  it 
is  extracted  by  treating  this  wood,  ground  to  powder,  by  alcohol, 
when  the  solution  is  of  a  reddish-yellow  colour,  and  leaves,  after 
evaporation,  a  resinous  substance  of  the  same  colour.  It  dissolves 
in  the  alkaline  lixiviae,  and  turns  them  of  a  violet  colour. 

INDIAN-YELLOW. 

§  1632.  A  substance  used  in  dyeing,  and  known  by  the  names  of 
purree  and  Indian  yellow,  is  imported  from  China  and  the  Indies, 
but  its  origin  is  unknown.  It  dissolves  in  water  acidulated  with 
chlorohydric  acid,  while  a  crystalline  substance  separates,  called 
euxanthic  acid,  which  forms  nearly  one-half  of  the  weight  of  Indian 
yellow;  some  foreign  substances  being  precipitated  at  the  same 
time.  In  order  to  prepare  pure  euxanthic  acid,  Indian  yellow  is  treated 
with  acetic  acid,  and  acetate  of  lead  is  added  to  the  liquid,  when 
euxanthate  of  lead  is  precipitated,  and  may  be  decomposed  by  sulf- 
hydric  acid.  By  boiling  the  liquid,  the  euxanthic  acid  is  dissolved, 
and  crystallizes,  on  cooling,  in  long,  yellow,  silky  needles,  which 
are  readily  soluble  in  alcohol  and  in  ether.  Its  formula,  when  dried 
at  212°,  is  ^42^1^22  '■)  while,  if  it  be  heated  still  further,  the  euxan- 
thic acid  melts  and  evolves  vapours  w^hich  solidify  in  small  crystals, 
constituting  a  new  substance,  euxanthone  G^Hyfl^2^  which  is  also  ob- 
tained either  by  the  distillation  of  euxanthate  of  lead  or  by  causing 
concentrated  sulphuric  or  chlorohydric  acid  to  act  on  euxanthic 
acid.     We  have,  moreover, 

C^Hi30^=C«H,,Oi,+2CO,+6HO. 

Euxanthone  possesses  no  acid  properties.  With  chlorine,  bromine, 
or  nitric  acid,  euxanthic  acid  yields  products  by  substitution,  with 
the  formulae  C^H.^Cl^O^^,  C^H.^Br^O^^,  CJi,,{l:^0,)0,,.     The  chlo- 


CHLOKOPHYLL.  709 

rinated  and  brominated  euxanthic  acids  dissolved  in  concentrated 
sulphuric  acid,  and  precipitated  by  water,  yield  chlorinated  euxan- 
thone  C40H1QGI2O12  or  brominated  G^IL^qBy^O^, 

CAROTIN. 

§  1633,  Carotin,  the  red-colouring  matter  of  carrots,  is  extracted 
by  diluting  carrot-juice  with  4  or  5  times  its  volume  of  water,  and 
then  adding  sulphuric  acid,  which  precipitates  the  colouring  matter 
with  the  albumen  and  fatty  substances.  The  latter  are  separated 
by  boiling  the  precipitate  for  some  time  with  a  solution  of  caustic 
potassa,  which  dissolves  them ;  and  the  carotin  is  purified  by  boiling 
it  with  dilute  sulphuric  acid,  and  digesting  it,  first  with  ordinary, 
and  then  with  absolute  alcohol.  The  substance,  when  dried,  is 
treated  with  sulphide  of  carbon,  which  dissolves  the  carotin,  after 
which  }  of  the  liquid  are  separated  by  distillation,  anhydrous  alco- 
hol is  added  to  the  residue,  and  the  liquid  is  exposed  to  the  air, 
when,  after  some  time,  small  copper-coloured  crystals  of  pure  caro- 
tin are  deposited.  Carotin  melts  at  about  338°,  but  is  decomposed 
at  a  higher  temperature,  and  it  is  nearly  insoluble  in  water,  alcohol, 
and  ether.  Its  elementary  composition  is  the  same  as  that  of  oil 
of  terpentine,  but  no  means  of  ascertaining  its  equivalent  are  known. 

GREEN  AND  YELLOW  COLOURING  MATTER  OF  LEAVES. 

§  1634.  The  green-colouring  matter  of  leaves,  or  chlorophyll^ 
exists  in  them  but  in  a  very  small  quantity,  and  is  exceedingly  dif- 
ficult to  extract  in  a  state  of  purity.  The  best  method  known  con- 
sists in  digesting  the  leaves  for  several  days  with  ether ;  after  which 
the  liquid  is  filtered  and  evaporated  to  dryness,  when  the  greater 
portion  of  the  residue  is  composed  of  a  substance  analogous  to  wax 
and  of  chlorophyll.  It  is  dissolved  in  boiling  alcohol,  which  deposits, 
on  cooling,  the  greater  part  of  the  wax ;  and  the  alcohol  being  again 
evaporated,  and  the  residue  treated  with  a  smaller  proportion  of  boil- 
ing alcohol,  wax  still  separates  on  cooling.  The  solution  is  finally 
evaporated,  and  the  residue  treated  with  concentrated  chlorohydric 
acid,  which  yields  a  beautiful  green  solution.  The  liquid  is  satu- 
rated and  filtered,  after  having  introduced  some  pieces  of  marble 
into  it,  when  the  chlorophyll,  which  is  rendered  insoluble,  being 
precipitated,  is  washed  with  weak  chlorohydric  acid,  and  then  with 
fresh  water. 

Chlorophyll  is  insoluble  in  water,  but  readily  soluble  in  alcohol 
and  ether,  and  sulphuric  and  chlorohydric  acids  dissolve  it  without 
change ;  a  large  quantity  of  water  precipitating  it  again.  From  an 
analysis  made  of  it,  the  composition  of  chlorophyll,  dried  at  266*^, 
would  correspond  to  the  formula  CjgHgNOg. 

The  name  of  xanthophyll  has  been  given  to  the  yellow-colouring 
matter  of  autumnal  leaves ;  but  nothing  is  with  certainty  known  as 
to  its  nature. 


710  VEGETABLE   COLOURING   MATTERS. 


COCHINEAL. 

§  1635.  The  cochineal  {coccus  cacti)  is  a  small  insect  found  on  the 
nopal)  {opuntia  cocciniUifera,)  and  furnishing  the  most  brilliant  red 
colours  for  dyeing;  those  found  in  commerce  being  composed  only 
of  the  dried  insects.  When  these  are  boiled  with  water,  a  red  liquid 
is  produced,  which  is  clouded  by  the  addition  of  alum  or  bitartrate 
of  potassa;  a  precipitate  being  formed  which  remains  a  long  time 
in  suspension,  and  which  consists  of  the  colouring  matter  and  vari- 
ous fatty  and  albuminous  substances,  constituting  the  carmine  of 
commerce.  If  cochineal  be  boiled  with  a  weak  solution  of  carbonate 
of  soda,  and  alum  be  added  to  the  liquid,  red  precipitates  of  alumina, 
combined  with  the  colouring  matter,  are  formed,  known  by  the  name 
of  carmine  lake. 

The  name  of  carmin  has  been  given  to  the  colouring  matter  of 
cochineal,  but  it  is  doubtful  whether  it  has  been  obtained  in  a 
state  of  purity.  The  powdered  cochineal  is  treated  with  ether  to 
dissolve  the  fatty  matters,  and  then  with  boiling  alcohol  to  dissolve 
the  carmin,  which  is  deposited  during  the  cooling  of  the  liquid. 
In  order  to  purify  it,  it  is  dissolved  in  alcohol  to  which  an  equal 
volume  of  ether  has  been  added,  when  the  carmin  is  slowly  deposited 
in  the  form  of  small  purplish-red  grains.  The  substance  thus 
obtained  melts  at  104°,  and  is  soluble  in  water  and  alcohol,  but 
insoluble  in  ether.  Acids  heighten  its  red  colour,  while  alkalies 
turn  it  of  a  violet  hue. 

ARCHIL  AND  LITMUS. 

§  1636.  The  name  of  archil  is  given  in  commerce  to  some  very  com- 
plex colouring  substances  extracted  from  various  species  of  lichens, 
among  which  may  be  distinguished  the  lecanora  parella,  the  vario- 
laria  dealbata,  the  roccella  tinctoria,  etc.  In  order  to  obtain  the 
archil,  the  lichens  are  mashed,  and  macerated  in  wooden  troughs 
with  a  mixture  of  urine  and  ammonia,  or  urine  and  lime,  when  the 
substance  ferments  after  some  time,  and  is  frequently  stirred  and 
kept  at  a  temperature  of  77°  or  86°.  After  several  months  the 
archil  is  ready  for  commerce,  and  is  put  into  barrels. 

The  litmus  used  in  the  laboratory  is  prepared  from  the  same  lichens, 
and  by  a  similar  fermentation. 

The  colouring  principles  of  archil  and  litmus  have  hitherto  not 
been  isolated  with  certainty,  although  several  red,  non-crystalliQe 
substances  have  been  separated,  to  which  various  names  have  been 
given,  but  which  exhibit  none  of  the  characters  from  which  they 
might  be  supposed  to  be  definite  compounds.  But  by  operating 
directly  on  the  lichens,  perfectly  well-defined  crystallizable  sub- 
stances have  been  extracted,  from  which  the  colouring  matters  of 
archil  and  litmus  probably  originate  during  the  fermentation  of  the 
plant. 


LICHENS.  711 

By  exhausting  the  roccella  tinctoria  or  the  lecanora  parella  by 
ether,  and  concentrating  the  etherial  solution  by  distillation,  greenish 
crystals  of  an  acid  substance,  termed  lecanoric  acid,  are  separated, 
which  are  purified  by  washing  them  with  a  sniall  quantity  of  ether 
and  crystallizing  them  several  times  in  alcohol.  Pure  lecanoric 
acid  is  colourless,  and  requires  for  solution  250  parts  of  boiling  water, 
being  still  less  soluble  in  cold  water;  while  it  dissolves  in  15  parts 
of  alcohol  and  in  80  of  ether.  It  reddens  litmus  and  decomposes  the 
carbonates,  and  the  general  formula  of  its  salts  is  ROjCigHgOg.  If 
lecanoric  acid  be  boiled  for  a  long  time  with  absolute  alcohol,  lecanoric 
etJier  GJifi,G^^ILfi^is  formed,  which  is  separated  by  evaporating  to 
dryness  and  again  treating  with  boiling  water,  which,  on  cooling, 
deposits  it  in  the  form  of  small  crystals,  which  may  be  sublimed 
without  alteration.  A  methyllecanoric  ether  CgHgOjCigHgOg  is  pre- 
pared in  the  same  manner. 

§  1637.  Lecanoric  acid  is  decomposed  by  heat  into  carbonic  acid 
and  a  new  substance,  orein,  which  volatilizes.  It  undergoes  the  same 
decomposition  when  heated  with  the  alkalies,  or  treated  even  with 
cold  sulphuric  acid.  The  best  method  of  preparing  orcin  consists 
in  boiling  lecanoric  acid  with  an  excess  of  water  of  baryta,  precipi- 
tating the  baryta  by  carbonic  acid,  and  filtering  the  boiling  liquid, 
which,  after  evaporation,  furnishes  crystals  of  impure  orcin.  These 
being  redissolved  in  water,  the  liquid  is  boiled  for  some  time  with 
alumina  or  recently  precipitated  sesquioxide  of  iron;  when  the 
filtered  liquor  deposits,  on  evaporation,  pure  orcin,  in  long,  slightly 
yellowish  prismatic  crystals,  which  first  part  with  water  by  heat, 
and  then  sublime  without  alteration.  Orcin  dissolves  readily  in 
alcohol.  The  formula  of  its  hydrated  crystals  is  Ci6H804,3HO,  and 
it  is  precipitated  by  acetate  of  lead,  fui-nishing  a  compound  of  the 
formula  5PbO,Ci6H804. 

Ammonia,  oxygen,  and  water  convert  orcin  into  a  colouring 
substance,  orcein,  which  appears  to  be  one  of  the  colouring  prin- 
ciples of  archil.  The  reaction  is  arrested  when  the  substance 
communicates  a  beautiful  violet  colour  to  the  water;  for  if  it  were 
prolonged,  new  substances  would  be  formed,  which  would  turn  the 
water  to  a  brown  colour. 

According  to  an  analysis,  the  formula  of  orcein  would  be 
CigHgNOy ;  and  it  produces,  with  potassa  and  soda,  violet-red  solu- 
tions, and  with  ammonia  a  beautiful  violet  colour. 

§  1638.  By  exhausting  the  lecanora  parella,  divided  into  small 
pieces,  by  boiling  water,  a  yellowish-brown  liquid  is  obtained,  which 
deposits,  on  cooling,  crystalline  flocculi  of  an  acid  substance,  called 
erythric  acid,  while  the  mother  liquid  contains  another  substance, 
picroerythrin,  which  is  a  product  of  the  alteration  of  erythric  acid 
by  boiling  water.  Erythric  acid  is  purified  by  dissolving  it  in  alcohol, 
and  constitutes  a  white  crystalline  substance,  requiring  more  than 
200  times  its  weight  of  boiling  water  for  solution,  the  greater  por- 


712  VEGETABLE   COLOURING   MATTERS. 

tion  of  it  being  deposited  on  cooling.  It  is  more  soluble  in  alcoliol 
and  in  ether,  and  its  solutions  redden  litmus.  Its  composition  cor- 
responds to  the  formula  C34Hj90i5,4HO ;  and  when  heated,  it  first 
melts,  and  is  then  decomposed,  giving  rise  to  orcin,  which  sublimes. 
The  cold  alkalies  dissolve  it  without  change,  while  if  it  be  heated 
to  the  boiling  point,  orcin  and  carbonic  acid  are  formed.  A  solu- 
tion of  erythrate  of  ammonia,  exposed  to  the  air,  soon  produces  a 
liquid  of  a  deep  purple  colour. 

If  erythric  acid  be  boiled  with  absolute  alcohol,  a  compound, 
erythric  ether  {GJlfi-\-2>110),Q^fl^fi^^^  formerly  called  pseiidoery- 
thrin,  is  formed,  which  is  soluble  in  boiling  water,  and  separates 
from  it,  on  cooling,  in  crystalline  aciculae,  or  in  oily  drops  which 
soon  become  solid. 

The  picroerythrin  remaining  in  the  mother  liquid  which  has  de- 
posited the  erythric  acid,  and  which  is  formed  directly  by  boiling 
erythric  acid  for  a  long  time  with  water,  difiers  in  its  composition 
from  the  latter  acid  only  by  containing  5  additional  equivalents  of 
water,  its  formula  being  C34II24O20.  The  picroerythrin  remains, 
after  evaporation,  in  the  form  of  a  white  crystalline  mass,  which  is 
converted  into  orcin  and  carbonic  acid,  either  by  heat  alone  or  by 
boiling  it  with  alkalies. 

By  exposing  erythric  acid  dissolved  in  hot  water  to  the  air  for 
several  days,  tne  liquor  turns  brown,  and  then  contains  two.  new 
crystallizable  substances,  called  amarythrin  and  telerythrin,  the 
first  of  which  is  very  soluble  in  water  and  alcohol,  while  the  second 
is  insoluble  in  cold  alcohol,  thus  furnishing  an  easy  means  of  sepa- 
rating it  from  the  first.  The  composition  of  these  substances  is 
unknown. 

INDIGO. 

§  1639.  Indigo  is  found  in  a  great  number  of  vegetables,  particu- 
larly in  plants  of  the  genus  indigofera,  in  the  polygonum  tinctorium, 
and  in  woad;  being  chiefly  obtained  from  the  indigoferous  plants. 
After  the  flowering  of  the  plant,  the  leaves  which  contain  the 
greater  proportion  of  indigo  are  removed,  and  dried  in  the  sun ;  and 
then  they  are,  after  being  crushed,  infused  for  2  or  3  hours  with  3 
times  their  volume  of  cold  water.  The  solution,  after  being  strained 
through  a  cloth,  is  stirred  in  the  air  for  some  time ;  after  which  5 
litres  of  lime  water  for  every  10  kilog.  of  dried  leaves  are  added, 
when  the  liquid  soon  turns  blue  and  deposits  indigo.  The  deposit 
is  separated,  washed  with  a  small  quantity  of  boiling  water,  and, 
after  being  drained  on  a  cloth,  is  subjected  to  heavy  pressure.  This 
substance,  after  being  dried  in  the  air  and  cut  in  pieces,  constitutes 
the  indigo  of  commerce,  which  is,  however,  very  impure,  and  con- 
tains only  about  45  per  cent,  of  real  indigo  or  indigotin,  the  balance 
consisting  of  resinous  substances,  fecula,  carbonate  of  lime,  and  a 
large  number  of  other  saline  substances.     In  order  to  remove  the 


INDIGO.  713 

greater  portion  of  these  foreign  substances,  the  powdered  indigo  is 
washed  successively  with  boiling  water,  alcohol,  and  weak  solutions 
of  chlorohydric  acid. 

Pure  indigotin  is  obtained  by  heating  indigo  in  a  glass  tube  in  a 
current  of  hydrogen,  until  crystals  begin  to  sublime  'in  the  anterior 
part  of  the  tube,  the  temperature  being  kept  as  low  as  possible ; 
when  the  indigotin  volatilizes  with  a  violet  vapour,  as  deep  coloured 
as  that  of  iodine,  and  is  deposited  in  the  form  of  beautiful  crystal- 
line needles  of  a  purplish  violet  colour.  The  same  vapours  are 
evolved  when  indigo  is  thrown  on  a  hot  body,  but  the  greater  por- 
tion of  the  indigotin  is  then  decomposed. 

Indigotin  is  wholly  insoluble  in  water,  and  nearly  so  in  alcohol 
and  ether ;  and  its  composition  corresponds  to  the  formula  CigHgNOg. 

§  1640.  Dilute  acids  do  not  act  on  indigotin,  while  concentrated 
and  particularly  Nordhausen  sulphuric  acid  dissolve  it  readily,  and 
produce  a  beautiful  blue  liquid ;  the  reaction  being  not  owing  to  ■ 
solution,  but  rather  to  an  actual  combination  of  the  indigotin  with 
sulphuric  acid. 

When  indigo  is  digested  with  about  5  parts  of  monohydrat^d  sul- 
phuric acid,  raising  the  temperature  to  about  122°,  the  indigo  dis- 
solves, and  forms  a  liquid  of  a  very  intense  purple,  depositing  a  blue 
precipitate  when  diluted  with  water,  which  is  collected  oii  a  filter, 
and  washed  with  water  acidulated  with  chlorohydric  acid  until  the 
washings  contain  no  more  sulphuric  acid,  when  it  is  dried  by  heat- 
ing it  to  248°  in  vacuo.  This  compound,  called  indigo-purple,  or 
sulphopurpuric  acid,  has  the  formula  CigHgNOgjSOg,  and  dissolves 
in  pure,  but  is  insoluble  in  acidulated  water.  It  forms,  with  the 
alkalies,  purple  compounds  which  are  precipitated  in  flocculi. 

By  treating,  on  the  contrary,  1  part  of  indigo  with  15  or  20  parts 
of  monohydrated  sulphuric  acid,  or  8  or  10  parts  of  Nordhausen 
acid,  and  keeping  the  mixture  for  some  time  at  a  temperature  of 
122°  or  140°,  a  beautifully  blue  liquid  is  obtained,  which  contains 
another  compound  of  indigotin  with  sulphuric  acid,  sulphindigotie 
acid.  By  adding  to  this  liquid  40  or  50  times  its  volume  of  water, 
a  small  quantity  of  indigo-purple,  which  is  collected  on  a  filter, 
sometimes  separates.  The  liquid  being  saturated  with  carbonate  of 
potassa,  a  precipitate  of  sulphindigotate  of  potassa  is  formed,  which 
is  soluble  in  fresh  water,  but  insoluble  in  water  highly  charged  with 
sulphate  of  potassa.  It  is  washed  with  a  solution  of  acetate  of  po- 
tassa, which  not  only  dissolves  the  sulphindigotate,  but  also  removes 
the  sulphate  of  potassa ;  and  lastly,  it  is  treated  several  times  with 
alcohol,  which  removes  the  acetate  of  potassa  without  dissolving  the 
sulphindigotate. 

The  formula  of  sulphindigotate  of  potassa  is  KO,(CigH4N02, 
S2O5),  showing  the  indigo  to  have  lost  1  equiv.  of  hydrogen,  which 
combined  with  1  equiv.  of  oxygen  given  off  by  the  sulphuric  acid, 
and  which  separates  in  the  state  of  water  when  sulphindigotie  acid 


714  VEGETABLE   COLOURING  MATTERS. 

is  combined  with  bases.     Several  other  sulphindigotates  may  be 
obtained  from  the  potassa  salt  by  double  decomposition. 

Lastly,  by  causing  a  larger  quantity  of  fuming  sulphuric  acid  to 
act  on  indigo,  a  new  acid  is  formed,  together  with  the  sulphindigotic 
acid,  forming,  tVith  the  alkalies,  more  soluble  salts  than  the  sulphin- 
digotates. This  acid,  the  composition  of  which  is  unknown,  has 
received  the  name  of  hyposulphindigotic  acid. 

White  Indigo. 

§  1641.  When  blue  indigo  is  subjected  to  reducing  agents,  it  com- 
bines with  the  hydrogen  set  free,  and  is  converted  into  a  colourless 
substance,  called  white  indigo^  or  colourless  indigotin,  which  by  expo- 
sure to  the  air  again  passes  into  the  state  of  blue  indigo.  It  is 
prepared  by  placing  in  a  barrel  holding  1  hectolitre,  a  J  kilog.  of 
indigo  of  commerce,  1  kilog.  of  sulphate  of  the  protoxide  of  iron, 
and  1 J  kilog.  of  lime ;  after  which  the  barrel  is  filled  with  tepid 
water,  shaken  actively,  and  hermetically  closed.  After  two  days, 
the  clear  supernatant  liquid  is  drawn  off  by  a  siphon,  and  conveyed 
into  large  bottles  filled  with  carbonic  acid,  at  the  bottom  of  which 
acetic  or  chlorohydric  acid,  charged  with  sulphuric  acid  in  sufficient 
quantity  to  saturate  the  lime,  has  been  placed.  The  liquid  imme- 
diately becomes  clouded,  grayish-white  flakes  being  precipitated, 
which  are  collected  on  a  filter  and  rapidly  washed,  first  with  water 
charged  with  sulphurous  acid,  and  then  with  recently  boiled  fresh 
water.  The  filter  is  expressed  between  tissue-paper  and  the  sub- 
stance dried  in  vacuo. 

This  substance  is  white  indigo,  but  it  is  very  difficult  to  prevent 
it  from  absorbing  a  small  quantity  of  oxygen  from  the  air,  and  it 
should  be  kept  in  bottles  filled  with  carbonic  acid.  It  is  insoluble 
in  water,  soluble  in  alcohol  and  ether,  does  not  act  on  litmus,  and 
is  decomposed  by  heat.  It  rapidly  turns  blue  in  water  containing 
air,  and  does  not  combine  directly  with  the  weak  acids ;  although 
during  the  reduction  of  sulphindigotic  acid  by  sulf  hydric  acid  a 
colourless  substance  is  obtained,  which  is  probably  a  compound  of 
colourless  indigo  with  sulphuric  acid.  Nordhausen  acid  dissolves 
it,  but  the  liquid  is  of  a  beautiful  purple  colour ;  and  all  oxidizing 
agents  convert  it  instantly  into  indigo-blue.  White  indigo  readily 
combines  with  bases,  furnishing  several  soluble  compounds ;  which 
is  the  case  with  the  alkalies,  ammonia,  lime,  baryta,  and  magnesia ; 
the  solutions  being  yellowish,  but  soon  turning  blue  in  the  air.  The 
other  metallic  oxides  form  insoluble  compounds,  which  are  easily 
obtained  by  double  decomposition.  The  composition  of  white  indi- 
go corresponds  to  the  formula  CigHgNOa,  and  difi"ers  from  that  of 
blue  indigo  CigH^NOj  only  by  containing  2  additional  equivalents  of 
hydrogen. 


INDIGO.  715 

Products  of  the  Action  of  Nitric  Acid  on  Indigo. 

§  1642.  The  action  of  nitric  acid  on  indigo  produces  isatin 
CieH5N04,  remarkable  for  the  numerous  substances  which  have  been 
derived  from  it.  A  liquid  paste  is  made  with  1  kilog.  of  indigo  of 
commerce  and  water,  which  is  carefully  heated  in  a  porcelain  cap- 
sule, nitric  acid  being  gradually  introduced  with  constant  stirring, 
until  600  or  700  gm.  of  acid  are  added.  The  indigo  has  then  dis- 
appeared, and  the  liquid,  which  is  more  or  less  brown-coloured, 
contains  the  isatin,  mixed  with  several  other  substances,  which  have 
not  yet  been  examined.  The  liquid,  being  diluted  with  a  large 
quantity  of  water,  is  heated  to  boiling,  and  the  boiling  liquid  rapidly 
filtered,  when  the  isatin  is  deposited,  on  cooling,  in  reddish  mamil- 
lary crystals.  The  deposit  remaining  is  heated  with  the  mother 
liquid  which  has  deposited  the  first  crystallization  of  isatin,  which 
furnishes  an  additional  quantity ;  and  this  process  is  repeated  until 
no  more  isatin  is  deposited. 

Isatin  may  also  be  obtained  by  heating  indigo  with  a  mixture  of 
bichromate  of  potassa  and  sulphuric  acid,  dissolved  in  20  or  30  parts 
of  water. 

Isatin  is  slightly  soluble  in  cold  water,  but  largely  so  in  boiling 
water,  and  still  more  freely  in  boiling  alcohol ;  and  its  solutions  do 
not  act  upon  litmus.  When  heated,  it  first  melts,  and  then  gives 
ofi"  vapours  of  unaltered  isatin,  the  greater  portion  of  the  substance 
being  nevertheless  decomposed,  and  leaving  a  copious  carbonaceous 
residue.  Concentrated  nitric  acid,  when  cold,  readily  dissolves 
isatin,  forming  a  brownish-red  liquid,  which  deposits  unaltered  isa- 
tin ;  while  if  the  liquid  be  boiled,  lively  reaction  ensues,  and  oxalic 
acid  is  formed. 

Isatin  is  easily  acted  on  by  chlorine,  and  yields  products  derived 
by  substitution.  The  isatin  must  be  diluted  with  water,  and  a 
current  of  chlorine  passed  through,  when  monochlorinated  isatin 
Ci3H4Cl]S'04  is  first  formed ;  while  if  the  action  of  the  chlorine  be 
prolonged,  hichlorinated  isatin  CigHgClgNO^  is  produced ;  the  same 
compounds  being  obtained  by  causing  chlorine  to  act  on  indigo. 
Bichlorinated  isatin  is  more  soluble  in  water  and  in  alcohol  than 
monochlorinated  isatin.  Isatin  and  indigo,  in  contact  with  melted 
hydrate  of  potassa,  evolve  hydrogen,  and  anilin  is  formed,  (§  1684 ;) 
while,  under  similar  circumstances,  monochlorinated  isatin  produces 
monochlorinated  anilin,  and  bichlorinated  isatin  bichlorinated  anilin. 

When  a  concentrated  solution  of  potassa  is  poured  over  isatin, 
there  results  first  a  violet-coloured  liquid,  which  by  boihng,  and 
after  being  diluted  with  water,  is  converted  into  a  yellowish  solu- 
tion, depositing  crystals  on  evaporation.  Here  isatin  has  seized 
upon  the  elements  of  1  equiv.  of  water,  and  been  converted  into  a 
new  acid,  called  isatic,  the  formula  of  isatate  of  potassa  being  KO, 
C,eH„NO,. 


716  VEGETABLE   PHYSIOLOGY. 

With  ammonia,  isatin  and  isatic  acid  form  numerous  compounds, 
which  will  not  occupy  our  attention. 

By  subjecting  isatin  to  the  action  of  reducing  agents,  it  is  changed 
into  isathyd  G^^^O^,  by  a  reaction  precisely  similar  to  that  which 
converts  blue  into  white  indigo.  Sulfhydrate  of  ammonia  being 
poured  into  a  hot  alcoholic  solution  of  isatin,  and  the  mixture  al- 
lowed to  rest  for  some  days  in  a  well-corked  bottle,  sulphur  is  depo- 
sited, at  the  same  time  with  laminated  crystals  of  isathyd,  which 
are  colourless  or  slightly  grayish.  They  are  insoluble  in  water, 
but  slightly  soluble  in  boiling  alcohol,  from  which  they  are  depo- 
sited on  cooling ;  and  they  are  decomposed  by  heat.  By  treating 
monochlorinated  and  bichlorinated  isatin  in  the  same  manner,  there 
results  monochlorinated  isathyd  CigH^ClNO^  and  bichlorinated  isa- 
thyd CieH.Cl^NO^. 

If  sulf hydric  acid  be  substituted  for  sulfhydrate  of  ammonia,  the 
isatin  is  not  satisfied  with  1  equiv.  of  hydrogen,  but  also  exchanges 
2  equiv.  of  oxygen  for  2  equiv.  of  sulphur,  and  furnishes  a  new  sub- 
stance, hisulphisathyd  C^gHgNOgSg,  which,  when  treated  with  an 
alcoholic  solution  of  potassa,  forms  a  red  liquid,  depositing  colour- 
less crystals  of  sulphisathyd  C^gHgNOgS. 

If,  on  the  contrary,  the  hisulphisathyd  be  heated  with  a  highly 
concentrated  solution  of  potassa,  the  2  equiv.  of  sulphur  are  removed, 
and  a  rose-coloured  liquid  is  obtained,  holding  a  rose-coloured  sub- 
stance in  solution,  of  the  same  elementary  composition  with  white 
indigo,  and  which  has  received  the  name  of  indin. 


ACTION  OF  VEGETABLES  ON  THE  ATMOSPHERE. 

§  1643.  Vegetables  derive  the  materials  necessary  for  their 
growth,  principally  from  the  atmosphere ;  but  as  the  various  cir- 
cumstances of  this  phenomenon  are  not  well  understood,  we  shall 
only  mention  what  is  most  accurately  known  on  the  subject. 

All  vegetables  spring  from  a  seed  which  is  the  product  of  a  simi- 
lar vegetable,  and  if  properly  dried  and  preserved  from  moisture  and 
the  attacks  of  insects,  appears  to  be  able  to  retain  its  germinating 
principle  for  an  indefinite  length  of  time.  But  if  it  come  into 
contact  with  water,  and  the  temperature  be  not  too  low,  it  soon 
swells,  while  its  woody  envelope  cracks,  and  filaments,  or  radicles, 
which  endeavour  to  penetrate  the  earth,  start  from  one  side,  and 
from  the  other  rises  a  small  stem,  the  germ,  in  an  opposite  direc- 
tion, into  the  air.  These  primary  developments  of  vegetable  life 
take  place  at  the  expense  of  the  amylaceous  matter  of  the  seed,  in 
which  is  formed  a  nitrogenous  principle,  called  diastase  in  the  ce- 
realia,  the  special  ofiice  of  which  is  to  convert  rapidly  the  starch  into 
dextrin  and  sugar,  that  is,  into  soluble  principles,  which,  by  means 
of  agencies  as  yet  unknown,  are  again  organized,  and  transformed 
into  cellulose,  in  its.  turn  serving  for  the  formation  of  the  primary 


VEGETABLE   PHYSIOLOGY.  717 

cellular  tissues  of  the  germ  and  radicles.  During  this  first  epoch  of 
vegetable  life,  carbonic  acid  is  disengaged,  and  the  presence  of  oxy- 
gen appears  essential,  for  moistened  seeds  will  not  germinate  in  an 
atmosphere  deprived  of  this  gas.  The  portions  of  the  seed  which 
furnish  the  amylaceous  substance,  the  cotyledons,  have  then  lost 
their  consistence,  and  wither. 

When  it  reaches  the  air,  the  germ  assumes  a  green  colour,  and 
throws  out  the  primary  leaves.  The  phenomena  of  assimilation  are 
then  wholly  changed,  and  the  new  vegetable  seeks  the  elements  ne- 
cessary to  its  growth,  principally  in  the  atmosphere ;  and  its  green 
portions,  the  leaves  chiefly,  under  the  influence  of  solar  light,  ab- 
sorbing the  carbonic  acid  of  the  air,  assimilate  to  themselves  the 
carbon,  and  give  out  oxygen  into  the  atmosphere ;  while  they  also 
possess  themselves  of  a  certain  quantity  of  nitrogen,  which  serves 
for  the  formation  of  the  nitrogenous  principles  essential  to  them. 
The  hydrogen  is  evidently  furnished  by  the  water  which  arises  both 
from  the  vapour  disseminated  in  the  atmosphere  and  the  moisture 
of  the  soil.  The  greater  portion  of  the  water  remains  as  such  in 
the  vegetable,  and  forms  the  sap,  which  serves  to  transport,  through 
the  various  parts  of  the  plant,  the  nutrient  principles,  rendered  solu- 
ble by  actions  at  present  unknown ;  while  another  part  of  the  water 
is  probably  decomposed,  by  the  action  of  the  vegetative  forces,  into 
hydrogen  which  is  assimilated,  and  into  oxygen  which  is  disengaged 
with  that  arising  from  the  more  or  less  complete  decomppsition  of 
the  carbonic  acid. 

§  1644.  In  this  theory  of  vegetable  growth,  we  have  supposed  the 
earth  to  play  but  an  unimportant  part,  and  to  serve  merely  as  a 
base  on  which  the  plant  is  erected,  and  whence,  by  means  of  its 
roots,  it  can  procure  the  greater  portion  of  water  necessary  for  sap ; 
but  the  daily  experience  of  the  farmer  proves  that  its  part  is  less 
passive.  When  the  soil  is  deprived  of  organic  substances  in  decom- 
position, it  is  known  to  have  lost  its  fertility,  and  to  give  birth  to  a 
small  number  of  dwarfish  plants,  which  struggle  with  difficulty 
through  the  various  phases  of  an  ephemeral  existence ;  and  in  order 
to  restore  its  fertility,  it  must  be  supplied  with  organic  detritus, 
principally  animal  substances,  known  by  the  name  of  manures. 
Manures  supply  the  roots  with  organic,  chiefly  nitrogenous  sub- 
stances, which  the  vegetable  assimilates  to  itself;  while  they  also 
furnish  mineral  principles,  either  already  soluble  or  rendered  so  by 
the  chemical  agencies  developed  in  the  earth.  These  constituents, 
which  are  found  again  in  the  ashes  of  the  vegetable,  are  necessary 
to  its  well-being ;  and  when  they  are  wanting  in  the  soil,  or  do  not 
exist  in  sufficient  quantity,  the  plants  wither,  and  are  unable  to  con- 
struct the  mineral  framework  which  appears  to  be  essential  to  some 
of  them. 

§  1645.  The  following  are  some  experiments  in  support  of  this 
theory : — 


718  '  VEGETABLE   PHYSIOLOGY. 

The  decomposition  of  carbonic  acid  by  the  green  portions  of 
vegetables  can  be  very  easily  demonstrated.  By  placing  fresh 
leaves  in  a  bell-glass,  partly  filled  with  water,  and  partly  with  car- 
bonic acid  gas,  and  exposing  the  glass  to  the  sun,  the  carbonic  acid 
disappears,  and  after  some  time  is  replaced  by  a  rather  smaller 
quantity  of  oxygen ;  and  as  carbonic  acid  contains  a  volume  of 
oxygen  equal  to  its  own,  we  may  conclude  from  this  experiment 
that  all  the  oxygen  of  the  carbonic  acid  is  not  set  free.  The  car- 
bonic acid,  very  probably,  is  only  partially  decomposed  by  the 
vegetable,  being,  for  example,  reduced  to  the  state  of  carbonic  oxide, 
which  enters  into  the  constitution  of  new  organic  substances,  the 
remainder  of  the  oxygen  arising  from  the  decomposition  of  the 
water.  If  part  of  a  branch  of  a  tree  be  placed  in  a  bell-glass  ex- 
posed to  the  sun,  and  into  which  has  been  introduced  a  mixture  in 
known  proportions  of  atmospheric  air  and  carbonic  acid,  it  will  be 
easy  to  ascertain  that  the  gas  which  escapes  from  the  bell-glass  is 
almost  wholly  deprived  of  its  carbonic  acid,  and  that  the  latter  is 
replaced  by  oxygen. 

This  decomposition  of  carbonic  acid  by  the  leaves  takes  place 
only  under  the  influence  of  the  solar  rays  and  the  diffuse  light  of 
day;  while  in  the  dark,  or  when  exposed  to  artificial  light,  an 
inverse  action  ensues.  Experiment  shows  that  in  this  case,  they 
evolve  carbonic  acid  and  absorb  oxygen,  while  if  the  effects  of  the 
day  be  compared  with  those  of  the  night,  the  former  will  be  found 
to  exceed  the  latter  greatly,  and  consequently  the  action  resulting 
is  that  which  takes  place  under  the  infiuence  of  the  solar  rays. 
Those  parts  of  the  vegetable  which  are  unprovided  with  the  green 
parenchyma^  the  roots,  chiefly  behave  with  regard  to  the  atmo- 
spheric air,  even  in  the  sun,  like  the  green  parts  in  the  dark,  since 
they  absorb  oxygen  and  evolve  carbonic  acid.  The  absorption  of 
oxygen  appears  to  be  essential  to  them,  for  a  vegetable  soon 
perishes  when  its  roots  are  in  an  atmosphere  deprived  of  this  gas. 

The  following  experiment  proves  very  conclusively  the  manner  in 
which  a  plant  grows  at  the  expense  of  the  elements  of  atmospheric 
air: — A  known  weight  of  seed  is  sown  in  a  soil  formed  of  pounded 
bricks  or  quartzose  sand  previously  calcined  and  washed,  this 
artificial  soil  being  placed  under  a  bell-glass  so  arranged  as  to  be 
kept  properly  moist,  and  exposed  to  the  sun,  while  a  current  of  air, 
to  which  1  or  2  hundredths  of  carbonic  acid  gas  are  added  to  assist 
the  development  of  the  vegetable,  is  passed  through  the  bell-glass. 
The  seeds  soon  germinate,  the  plants  grow,  and  pass  through  the 
various  phases  of  vegetable  life,  without,  however,  ever  attaining 
the  development  and  strength  they  would  have  acquired  in  a  fertile 
soil.  They  are  then  removed,  and  the  absolute  quantities  of  carbon, 
hydrogen,  oxygen,  and  nitrogen  which  they  contain  are  ascertained 
by  chemical  experiment.  It  is  evident  that  the  soil  could  afford 
them  nothing,  as  it  is  unchangeable,  and  at  all  events  contains  neither 


ANIMAL   CHEMISTRY.  719 

carbon  nor  nitrogen  ;  and  therefore,  if  they  have  not  borrowed  their 
carbon  and  nitrogen  from  the  air,  they  can  contain  only  the  carbon 
and  nitrogen  which  existed  in  the  seeds.  Now,  it  is  easy  to 
analyze  a  sample  of  seed  identical  with  that  which  has  germinated, 
and  determine  by  calculation  the  carbon  and  nitrogen  contained  in 
the  seeds  which  have  vegetated ;  and  by  comparing  this  quantity  of 
carbon  and  nitrogen  with  that  found  in  the  plants,  the  latter  will 
be  found  to  be  much  larger.  It  must  therefore  be  admitted  that 
the  plant  has  absorbed  carbon  and  nitrogen  from  the  atmosphere. 

§1646.  We  have  shown  (§95)  that  atmospheric  air  contains  only 
from  4  to  6  ten-thousandths  of  carbonic  acid,  which  very  small 
proportion  is  still  sufficient  to  furnish  the  carbon  which  accumulates 
in  the  vegetables  covering  the  earth.  But  the  carbonic  acid  of  the 
air,  which  thus  disappears,  is  constantly  reproduced  and  restored  to 
the  atmosphere  by  the  respiration  of  animals,  the  decomposition  of 
vegetables,  and  the  chemical  reactions  taking  place  in  the  interior* 
of  the  globe.  Moreover,  the  terrestrial  atmosphere  is  of  con- 
siderable extent,  and  the  total  amount  of  carbonic  acid  which  it 
contains  includes  a  quantity  of  carbon  greater  than  the  whole 
vegetable  kingdom ;  and  the  continual  agitation  of  the  atmosphere 
mixes  all  its  component  parts,  and  assists  the  absorption  of  carbonic 
acid  by  plants  by  constantly  renewing  the  air  which  surrounds 
them. 


ANIMAL  CHEMISTRY. 


§  1647.  The  body  of  every  animated  being  may  be  considered 
as  a  laboratory  in  which  extremely  numerous  chemical  reactions 
are  performed,  the  majority  of  which  are  very  complicated  and  as 
yet  but  little  understood ;  as  well  upon  the  substances  which  al- 
ready constitute  the  being,  as  on  the  new  substances  taken  in  as  food. 
In  the  present  state  of  science,  it  is  impossible  to  decide  whether 
all  these  reactions  are  owing,  solely,  to  forces  of  the  same  nature 
as  those  which  determine  the  chemical  metamorphoses  witnessed 
in  the  laboratory,  or  the  unknown  and  undefinable  cause,  which  is 
called  life  or  vitality,  introduces  into  it  some  special  forces.*  Even 
admitting  that  we  can  explain,  without  resorting  to  other  agents 
than  the  ordinary  chemical  forces,  all  the  chemical  modifications  of 
substances  in  the  vegetable  or  animal  economy,  we  should  still  be 
obliged  to  admit  the  existence  of  special,  and  so  to  say,  intelligent 
actions,  in  order  to  explain  the  varied,  and  yet  so  clearly  marked 
forms  which  solid  matter  assumes  in  the  composition  of  the  various 

*  We  use  here  the  word /orces,  because  it  is  generally  used  in  this  sense ;  but  it 
must  not  be  forgotten  that  it  in  no  wise  satisfies  the  definition  of  it  given  in  me- 
chanics. It  merely  expresses  the  efficient  and  unknown  cause  of  complicated 
effects,  the  exact  analysis  of  which  is  at  the  present  day  as  yet  impossible. 


720  ANIMAL   CHEMISTRY. 

organic  forms,  so  different  from  those  assumed  by  matter  when  it 
simply  obeys  the  laws  of  molecular  attraction,  without  regard  to 
the  organism.  A  single  substance,  modified  by  the  vital  forces, 
may  assume  the  most  varied  organic  forms,  and  different  states  of 
aggregation,  which  frequently  alter  its  apparent  properties  so 
greatly  as  to  lead  us,  at  first  sight,  to  consider  them  as  different 
substances.  The  progress  of  substances  in  the  economy  is  governed 
by  laws  and  directed  by  mechanical  arrangements,  generally  of 
difficult  explanation,  and  acting  by  instinct,  which  impel  these  sub- 
stances successively  into  the  vessels  in  which  they  are  elaborated 
and  fitted  for  the  special  functions  assigned  to  them  in  the 
organism. 

The  study  of  the  modification  of  matter  in  the  vegetable  and 
animal  economy,  therefore,  presents  difficulties  much  greater  than 
those  of  the  chemical  phenomena  observed  in  the  laboratory.  They 
occur  between  substances  generally  of  very  complex  composition, 
of  extreme  mobility,  and  difficult  definition  by  the  characters  we 
have  adopted  for  mineral  substances.  At  each  step  we  meet  with 
those  mysterious  agencies,  by  which  very  small  quantities  of  certain 
substances  of  a  nature  still  problematical,  execute,  without  any  ap- 
parent intervention  of  their  chemical  elements,  reactions  between 
incomparably  larger  quantities  of  other  substances :  phenomena 
of  which  many  examples  have  already  been  mentioned  in  the  pre- 
sent work,  and  from  the  explanation  of  which  chemists  generally 
extricate  themselves  by  calling  them  'phenomena  of  contact,  or 
fermentations. 

Again,  other  circumstances  increase  the  difficulty  of  this  study. 
Substances  are  modified  in  the  animal  and  vegetable  economy,  suc- 
cessively, and  in  special  organs  which  it  is  impossible  to  detach 
from  the  organized  being  in  order  to  study  the  reactions  which 
take  place  in  each  of  them,  without  altering  completely  the  con- 
ditions which  would  have  existed  in  the  animated  being.  Lastly, 
in  the  laboratory,  chemical  reactions  are  studied  in  unassailable 
vessels  which  play  no  part  in  the  phenomena,  which  is  altogether 
different  in  organized  beings,  chemical  reactions  being  there  effected 
in  vessels  the  substance  of  which,  for  the  most  part,  shares  in  the 
reaction,  and  thus  immeasurably  complicates  the  phenomena. 

We  have  been  satisfied  with  describing  the  substances  of  vegetables, 
uninfluenced  by  vegetative  life,  and  have  not  touched  upon  their 
modifications  in  the  plant,  since  we  could  have  advanced  but  a  few 
vague  and  uncertain  notions.  Our  knowledge  of  the  modifications 
of  substances  in  the  animal  economy  are  not  much  more  accurate ; 
and  to  avoid  the  danger  of  stating  any  rash  opinions,  we  should 
observe  the  same  caution,  and  only  describe  the  property  of  those 
substances  when  they  are  no  longer  influenced  by  vitality.  But 
here  the  question  becomes  much  more  important,  on  account  of  its 
intimate  connection  with  the  medical  sciences,  in  which  our  acquaint- 


BONE.  721 

ance  with  the  chemical  reactions  ensuing  in  the  human  body  in 
health  or  in  disease  is  of  the  highest  importance,  inasmuch  as  it  may 
furnish  valuable  means  of  diagnosis,  or  may  discover  the  treatment 
applicable  to  various  pathological  conditions. 

We  shall  describe  the  most  important  and  best-known  animal 
substances,  with  their  properties,  when  they  are  uninfluenced  by 
vitality ;  and  then  endeavour  to  give  a  general  idea  of  the  opinions 
on  the  chemical  phenomena  which  take  place  in  the  economy. 

SOLID  ANIMAL  SUBSTANCES. 

§  1648.  We  shall  begin  with  the  study  of  the  solids  which  form 
the  various  organs  of  animals,  and  constitute,  as  it  were,  the  labora- 
tory and  apparatus  in  which  are  performed  the  great  phenomena  of 
life.  We  shall  divide  them  into  the  bones,  teeth,  cartilages,  the 
corneous  tissue,  the  skin,  and  the  various  membranes,  muscular  flesh, 
fatty  substances,  and  the  cerebral  substance. 

§  1649.  Bones. — Bones  form  the  framework,  or  what  is  called 
the  skeleton  of  vertebrated  animals.  They  are  composed  of  an  organic 
portion,  the  cartilaginous  substance^  and  of  earthy  matter,  consist- 
ing chiefly  of  carbonate  and  phosphate  of  lime,  and  constituting  in 
the  mammiferse  about  f  of  the  weight  of  the  bone.  The  bones  are 
covered  externally  with  a  fibrous  membrane,  the  periosteum^  which 
contains  the  external  blood-vessels  distributed  to  the  bones,  and 
supplies  them  with  matter  for  increment.  Internally  is  found  an- 
other membrane,  the  medullary,  which  also  receives  blood-vessels. 

When  a  bone  is  suspended  for  several  days  in  a  weak  solution  of 
chlorohydric  acid,  the  earthy  salts  are  dissolved,  and  there  remains 
only  the  cartilage,  retaining  exactly  the  shape  of  the  bone,  but  re- 
duced to  a  soft  and  translucent  substance.  It  is  necessary  to  renew 
the  liquid  several  times,  and  lastly  to  wash  the  cartilage  with  fresh 
water  until  no  traces  of  acid  remain.  When  dried,  the  cartilaginous 
substance  partly  loses  its  translucency  and  becomes  brittle.  Ether 
separates  a  small  quantity  of  fatty  matter  from  it. 

Cartilage  is  insoluble  in  cold  water,  but  ultimately  dissolves  wholly 
in  boiling  water,  being  converted  into  a  substance  commonly  called 
gelatin.  We  subjoin  the  average  composition  of  the  bones  of  an 
adult  man  and  that  of  an  ox,  in  a  state  of  health : 

Man.  Ox. 

Organic  matter 33.30  33.30 

Basic  phosphate  of  lime  with  a  small  quantity 

of  fluoride  of  calcium 53.04  57.35 

Carbonate  of  lime 11.30  3.85 

Phosphate  of  magnesia 1.16  2.05 

Soda  and  chloride  of  sodium 1.20  3.45 

100.00  100.00 

The  composition  of  the  bones  of  the  other  mammalia  and  of  birds 

is  analogous,  while  in  fishes  the  proportion  of  the  organic  and  earthy 

Vol.  IL~46 


722  ANIMAL   CHEMISTRY. 

matters  varies  considerably,  and  they  may  be  divided  into  hony 
fishes,  whose  bones  contain  large  quantities  of  calcareous  salts,  and 
cartilaginous  fishes,  whose  bones  are  nearly  destitute  of  these  salts. 
The  proportion  of  cartilaginous  matter  being  always  greater  in  the 
bones  of  fishes  than  in  those  of  other  vertebrated  animals,  the 
former  are  the  more  flexible. 

§  1650.  Teeth. — The  composition  of  the  teeth  of  the  mammalia 
does  not  differ  much  from  that  of  their  bones,  as  will  be  seen  from 
the  following  analysis: 

Man.  Ox. 

Cartilaginous  matter 28.0  31.0 

Phosphate  of  lime,  with  fluoride  of  calcium 64.3  63.1 

Carbonate  of  lime 5.3  1.4 

Phosphate  of  magnesia 1.0  2.1 

Soda  with  a  small  quantity  of  chloride  of  sodium ...    1.4  2.4 

100.0  100.0 

The  part  of  the  tooth  beyond  the  gum  is  covered  with  a  white, 
very  hard  enamel,  almost  wholly  composed  of  phosphate  of  lime, 
carbonate  of  lime,  and  a  small  quantity  of  fluoride  of  calcium.  The 
enamel  of  human  teeth  has  been  found  to  contain  about  90.0  of  cal- 
careous and  magnesian  phosphates,  and  8.0  of  carbonate  of  lime. 

§  1651.  Cartilages. — The  name  cartilage  has  been  given  to  a 
dry,  elastic  tissue,  containing  only  a  few  hundredths  of  earthy  salts, 
and  very  widely  distributed  in  the  animal  economy,  sometimes  serv- 
ing to  connect  the  ends  of  bones  which  move  on  each  other,  and  some- 
times being  prolongations  of  the  bones,  as  in  the  ribs,  for  example, 
and  furnishing  them  an  elasticity  suitable  to  their  functions;  while 
it  finally  sometimes  forms  the  solid  part  of  certain  organs,  as  the 
nose,  ear,  the  trachea,  etc.  The  chemical  nature  of  all  cartilages 
does  not  appear  to  be  the  same,  for  while  some  seem  to  be  identical 
with  the  cartilage  of  the  bones,  and  are  converted,  by  boiling  water, 
into  gelatin,  others,  such  as  the  cartilages  of  the  nose  and  ear,  do 
not  undergo  this  transformation.  Cartilages  are  characterized  by 
corpuscles  of  peculiar  form,  called  cartilaginous  corpuscles. 

§  1652.  Corneous,  or  horny  matter. — The  horns,  nails,  claws, 
and  hoofs  of  animals  are  formed  of  substances  possessing  very  similar 
properties,  and  which  hitherto  have  been  regarded  as  identical :  they 
are  designated  by  the  general  name  of  horny  matter.  They  are 
insoluble  in  water,  and  soften  in  boiling  water,  and  their  composi- 
tion is  as  follows: 

Cow  Horns.  BuflFalo  Horns.  Human  Nails. 

Carbon 50.8  51.4  ...! 51.1 

Hydrogen 6.8  6.8  6.8 

Oxygen 23.5  \  ^4  4  25  2 

Sulphur 2.6/ ^^-^  ^^-^ 

Nitrogen .16.3 17.4 16.9 

100.0  100.0  100.0 


HAIR.  723 

§  1653.  Hair,  Feathers,  Scales. — Human  hair,  as  well  as  that 
of  animals,  is  composed  of  an  organic  matter  which  does  not  appear 
to  differ  essentially  from  horn  in  its  chemical  composition  and  its 
behaviour  with  reagents.  They  contain  several  fatty  substances, 
generally  coloured,  from  which  their  hue  is  ordinarily  derived.  The 
feathers  of  birds  closely  resemble  horn ;  the  same  being  true  of  the 
scales  of  reptiles.  For  want  of  accurate  experiments,  the  identity 
of  all  these  substances  is  admitted. 

The  composition  of  fish-scales,  on  the  contrary,  resembles  that  of 
bone,  since  they  contain  40  to  50  per  cent,  of  phosphate  of  lime, 
from  3  to  10  per  cent,  of  carbonate  of  lime,  and  from  40  to  55  per 
cent,  of  organic  matter. 

§  1654.  Skin  and  Membranes. — The  skin  of  animals  is  divided 
into  three  principal  parts:  1st,  the  skin,  properly  so  called,  or 
derma,  which  envelops  immediately  the  muscles  and  bones;  2dly, 
the  papillary  tissue,  formed  by  a  delicate,  extremely  sensible  tissue, 
traversed  by  small  blood-vessels  and  nerves,  and  containing  the  pig- 
ment which  colours  the  skin  so  variously  in  the  difi'erent  races  of 
men  throughout  the  globe ;  and,  3dly,  the  outer  covering,  or  epider- 
mis, a  simple  pellicle,  very  thin,  but  very  resisting,  pierced  by 
numerous  small  orifices,  through  some  of  which  the  hairs  pass,  while 
others  give  exit  to  the  fluids  of  perspiration ;  and  still  others  allow 
certain  fatty  substances  to  exude.  The  skin,  which  is  soft  and 
flexible  when  washed  in  water,  becomes  hard  and  coriaceous  by 
drying.  When  dipped  in  a  solution  of  tannin,  it  combines  with  it 
without  falling  to  pieces,  and  becomes  imputrescible,  which  con- 
stitutes the  process  of  tanning.  When  boiled  with  water  it  dissolves 
entirely  into  a  gelatinous  substance,  commonly  called  glue ;  but  the 
transformation  does  not  take  place  in  the  mucous  membranes,  which 
appear  to  consist  of  substances  diflering  from  those  of  the  skin. 

§  1655.  Muscular  Tissue. — Meat,  or  flesh,  is  the  collection  of 
several  organs,  called  muscles,  each  of  which  is  formed  by  an  assem- 
blage of  fibres  united  in  bundles.  A  multitude  of  nerves  and  canals, 
through  which  various  fluids  circulate,  traverse  this  tissue  in  all 
directions ;  thus  rendering  muscular  flesh  a  very  complicated  assem- 
blage. The  substance  which  constitutes  the  muscular  network  is 
called  fibrin,  which  of  itself  is  colourless ;  flesh  owing  its  red  colour 
to  the  blood  which  fills  an  infinity  of  small  capillary  vessels  distri- 
buted throughout  it. 

One  hundred  parts  of  beef  are  reduced,  by  desiccation,  to  25 
parts,  and,  after  incineration,  there  remains  about  1 J  part  of  salts, 
composed  chiefly  of  phosphates  of  potassa,  soda,  and  lime,  and  a 
small  quantity  of  alkaline  chlorides. 

By  exhausting  finely  chopped  beef  by  cold  water,  about  6  hun- 
dredths of  it  are  dissolved,  one-half  of  which  is  composed  of  albu- 
men, and  other  materials  of  the  blood  coagulable  by  heat.  If 
therefore  the  liquid  be  boiled,  there  remains  in  solution  only  3  hun- 


724  ANIMAL   CHEMISTRY. 

dredths  of  matter,  composed  of  soluble  alkaline  salts,  a  crystallizaMe 
nitrogenous  substance,  called  creating  (from  xpfaj,  flesh,)  and  salts 
formed  by  a  peculiar  organic  acid,  called  inosic.  If,  on  the  con- 
trary, flesh  be  treated  with  hot  water,  the  albuminous  substances 
coagulate  immediately,  and  the  same  substances  dissolve  as  in  cold 
water ;  while,  if  the  ebullition  be  prolonged,  a  small  quantity  of 
gelatin  is  dissolved  in  addition,  as  is  the  case  in  making  soup.  A 
portion  of  the  fat  is  also  forced  from  its  cells,  and  floats  on  the 
surface  of  the  liquid. 

Muscular  flesh  yields  leucin  (§  1278)  by  being  boiled  with  dilute 
sulphuric  acid. 

§  1656.  Fibrin. — It  is  difiicult  to  separate  fibrin  from  muscular 
flesh,  because  it  is  intimately  mixed  with  other  substances  which 
behave  in  a  very  analogous  manner  toward  chemical  agents. 

It  is  generally  extracted  from  freshly  drawn  blood  by  beating  it 
with  rods,  to  which  the  fibrin  adheres  in  the  form  of  long  colour- 
less filaments.  They  are  washed  with  much  water,  to  detach  the 
other  soluble  or  insoluble  principles  of  the  blood ;  and  then,  after 
being  dried,  they  are  treated  with  alcohol  and  ether,  which  remove 
the  fatty  matters.  The  fibrin  is  then  washed  with  a  very  dilute 
solution  of  chlorohydric  acid,  and,  lastly,  with  distilled  water. 

Fibrin  is  a  white,  tasteless,  and  inodorous  substance,  completely 
insoluble  in  water,  alcohol,  and  ether,  and,  by  drying,  assuming  a 
horny  consistence.  Prepared  in  the  method  just  stated,  it  leaves 
2  or  3  per  cent,  of  ashes,  composed  chiefly  of  calcareous  and  mag 
nesian  phosphates.  A  long  boiling  with  water  alters  it  and  dis- 
solves a  portion  of  it ;  and  when  left  in  water  and  exposed  to  the 
air  it  soon  putrefies,  but  may  be  preserved  for  an  indefinite  length 
of  time  in  alcohol.  Acids  convert  it  into  a  gelatinous  mass,  insoluble 
in  acid  liquids,  but  soluble  in  fresh  water,  while  it  dissolves  readily 
in  alkaline  lyes,  even  when  they  are  diluted ;  and  if  the  solution  be 
saturated  with  an  acid,  a  precipitate  is  formed,  which,  however, 
cannot  be  considered  as  the  original  fibrin. 

According  to  the  most  reliable  analyses  of  fibrin,  it  contains 

Carbon 62.78 

Hydrogen 6.96 

Nitrogen 16.78 

Oxygen ..13.48 

100.00 
§  1657.  Albuminous  Substances. — We  shall  not  here  again  refer 
to  the  albuminous  substances,   which  have   been  sufiiciently  de- 
scribed, (§1279.)     Their  identity  in  the  two  kingdoms,  though  far 
from  being  demonstrated,  is  generally  admitted. 

§  1658.  Greatin  CgHgNgO^. — In  order  to  obtain  creatin,  finely 
chopped  meat  is  treated  with  an  equal  weight  of  cold  water ;  and 
after  having  stirred  the  mixture  for  some  time,  it  is  expressed  in  a 


CREATIN.  725 

canvas  "bag,  the  filtered  liquid  being  used  in  treating  an  additional 
quantity  of  meat.  The  liquid,  being  then  heated  to  212°  in  a  water- 
bath,  in  orde'r  to  coagulate  the  albuminous  substances,  is  evapo- 
rated after  being  filtered,  and  the  new  deposits  which  form  are  sepa- 
rated. When  the  liquid  is  reduced  by  evaporation  to  ^  of  its  vo- 
lume, water  of  baryta  is  added,  furnishing  a  precipitate  of  various 
phosphates  and  sulphates,  which  are  to  be  separated.  The  evapo- 
ration is  continued  until  the  liquid  is  reduced  to  ^  of  its  original 
volume,  and  it  is  then  allowed  to  evaporate  spontaneously  in  a  warm 
place,  when  crystalline  aciculse  of  creatin  are  formed,  which  are  to 
be  washed  in  cold  water  and  alcohol,  and  redissolved  in  boiling 
water,  which,  on  cooling,  deposits  them  in  a  state  of  purity. 

Lean  meat  is  best  adapted  to  this  purpose,  that  of  fowls  and  the 
weasel  yielding  the  largest  proportion  of  creatin :  100  kilog.  of 
beef  yield  62  gm.,  and  100  kilog.  of  horseflesh  have  furnished 
72  gm. 

Creatin  is  a  neutral,  inodorous,  and  colourless  substance,  soluble 
in  75  parts  of  cold  and  in  a  much  smaller  quantity  of  boiling  water  ; 
and  separating,  on  cooling,  from  its  saturated  aqueous  solution,  in 
the  form  of  prismatic  crystals,  which  lose  18  per  cent,  of  water 
when  dried  at  212°.  It  dissolves  in  90  parts  of  absolute  alcohol ; 
and  the  formula  of  crystallized  creatin  is  CgH9N304+2HO. 

Creatin  it  not  affected  by  very  dilute  acids,  while  concentrated 
acids  abstract  4  equiv.  of  water  from  it,  and  convert  it  into  a  sub- 
stance C8H7N3O2,  or  creatinin,  which  is  a  true  organic  alkali,  pos- 
sessing a  very  strong  alkaline  reaction  comparable  with  that  of 
ammonia,  and  forming  crystallizable  salts  with  all  the  bases. 

Creatin  also  dissolves  without  alteration  in  very  dilute  alkaline 
lyes,  while  the  concentrated  alkalies  decompose  it,  ammonia  being 
evolved,  besides  carbonic  acid  which  combines  with  the  alkali,  and 
a  new  organic  base,  sareosin  QJl^l^O^.  The  decomposition  is  gene- 
rally efl'ected  by  boiling  creatin  with  a  concentrated  solution  of 
baryta,  the  reaction  being  expressed  by  the  following  equation: 

C8HiiN30e+2BaO+2HO=C6H7NO,+2NH3+2(BaO,C02). 

Sareosin  crystallizes  in  right  prisms,  with  a  rhombic  base  ;  exerts 
no  reaction  upon  coloured  reagents ;  but  forms  crystallizable  salts 
with  several  of  the  acids.     It  is  insoluble  in  alcohol  and  ether. 

§  1659.  Inosic  Acid  CioHgN20^o,HO. — This  acid  remains  in  the 
mother  liquid  which  has  deposited  creatin,  and  is  extremely  soluble 
in  water ;  while,  if  alcohol  be  added,  the  liquid  becomes  milky,  and 
in  the  course  of  a  few  days  small  yellowish  crystals  of  inosate  of 
potassa,  or  baryta,  if  the  latter  base  has  been  used  in  the  prepara- 
tion of  the  creatin,  are  developed.  The  crystals  being  redissolved  in 
boiling  water,  and  chloride  of  barium  added,  crystals  of  inosate  of 
baryta  are  deposited,  on  cooling,  which  may  be  purified  by  several 
crystallizations,  and  then  take  the  formula  BaO,CioHgN20io+7HO. 


726  ANIMAL   CHEMISTRY. 

By  decomposing  it  by  sulphuric  acid,  free  inosic  acid  is  obtained, 
which  does  not  crystallize  in  an  aqueous  solution  unless  alcohol 
be  added.     The  formula  of  inosate  of  silver  is  AgO,CioHgN20io. 

§  1660.  Gelatinous  Substances. — We  have  mentioned  that  the 
skin,  the  cartilaginous  substance  of  the  bones,  and  the  cartilages 
properly  so  called,  when  boiled  with  water,  ultimately  dissolve 
wholly,  and  form  a  viscous  liquid,  which  becomes  gelatinous  on  cooling. 
For  a  long  time  it  was  supposed  that  all  the  substances  formed  un- 
der these  circumstances  were  identical,  and  the  general  name  of  gela- 
tin was  assigned  to  them ;  but  it  is  now  admitted  that  there  are  two : 
one  being  afforded  by  the  skin,  intestinal  membranes,  and  tendons, 
which  has  retained  the  name  of  gelatin,  while  the  other,  called 
chondrin,  is  furnished  by  the  cartilaginous  substance. 

The  chemical  reactions  and  composition  of  these  two  substances 
differ  from  each  other,  since  solutions  of  chondrin  are  precipitated 
by  sulphate  of  alumina,  alum,  and  sulphate  of  iron,  which  do  not 
affect  solutions  of  gelatin.  The  formula  C^Ji^Q^fii^^  has  been  given 
to  chondrin,  and  that  of  CigH^oNgOg  to  gelatin ;  but  these  formulae 
are  very  uncertain,  because  there  are  no  means  of  ascertaining  the 
purity  of  the  substances  and  of  determining  their  equivalents,  no 
definite  compound  with  them  being  known  with  certainty.  In  the 
applications  of  the  two  substances  no  distinction  is  made,  and  they 
are  generally  indiscriminately  called  gelatin  and  glue. 

Pure  gelatin  is  colourless  and  transparent,  as  is  the  case  in  the 
fish-glue,  or  ichtJiyocolla,  found  in  commerce.  When  heated  it  melts, 
and  congeals  on  cooling  into  a  remarkably  coherent  mass.  Cold 
water  merely  softens  and  swells,  without  dissolving  it,  while  boiling 
water  dissolves  it,  and  forms  a  viscid  liquid,  which  coagulates  into 
a  more  or  less  consistent  jelly  on  cooling.  Alcohol  precipitates 
gelatin  from  its  aqueous  solution.  Prolonged  ebullition  with  water 
destroys  gelatin,  and  it  afterward  no  longer  coagulates.  We  have 
already  said  (§  1458)  that  tannin  completely  precipitates  gelatin 
from  its  solutions. 

§  1661.  Glue  is  manufactured  from  leather  scraps,  tendons,  horns, 
and  hoofs  of  animals.  As  animal  substances  putrefy  readily,  they 
are  soaked,  if  they  cannot  be  immediately  used,  for  15  or  20  days 
in  milk  of  lime,  and  then  dried  in  the  air,  which  prevents  their  fer- 
mentation. When  required  for  use  they  are  digested  for  some  time 
in  water,  which  causes  them  to  swell  and  removes  the  lime. 

Animal  substances  intended  for  the  manufacture  of  glue  are 
placed  in  boilers  with  water,  rapidly  heated  to  boiling,  which  is 
stirred,  from  time  to  time,  the  operation  being  continued  until  a 
portion  of  the  liquid  taken  from  the  kettle  congeals  on  cooling. 
The  liquid  is  then  decanted  into  a  second  kettle,  kept  at  a  tempera- 
ture of  nearly  212°,  in  order  that  the  liquid  may  not  become  too 
viscid  before  depositing  the  substances  it  holds  in  suspension  ;  and 
after  some  hours,  it  is  run  into  moulds  made  of  pine-wood,  and 


GLUE.  727 

allowed  to  cool.  When  the  glue  sets,  which  generally  takes  place 
in  15  or  18  hours,  the  moulds  are  carried  to  a  well-ventilated  and 
cool  drying-room,  where  the  glue  is  separated  by  a  flexible  and 
wetted  knife,  and  spread  upon  a  table  likewise  wetted.  It  is  imme- 
diately cut  into  small  sheets  by  means  of  a  brass  wire,  and  spread 
on  nets  to  dry,  whence  commercial  glue  usually  shows  the  prints  of 
the  threads  of  the  net.  The  residue  in  the  boiler,  treated  with  a 
fresh  quantity  of  boiling  water,  may  afford  more  glue. 

§  1662.  Gelatin  is  extracted  from  bones  by  two  different  pro- 
cesses. In  the  first,  the  bones  are  subjected  to  the  action  of  steam, 
under  high  pressure,  in  a  Papin's  digester,  when  the  greater  part 
of  the  gelatin  dissolves  in  the  water,  while  the  bones  still  retain  a 
sufficient  quantity  to  allow  of  their  being  used  in  the  manufacture 
of  animal  black.  If  it  be  desired  to  prepare  gelatin  for  alimentary 
purposes,  the  temperature  should  not  be  raised  above  223°  or  226°, 
and  beef-bones  only  should  be  used,  because  the  bones  of  sheep  or 
hogs  would  give  the  gelatin  a  disagreeable  taste  and  smell. 

By  the  second  process,  which  yields  more  gelatin  than  the  pre- 
ceding, the  bones  are  crushed  between  rollers  and  boiled  for  some 
time  with  water,  in  order  to  extract  the  grease  which  is  separated. 
They  are  then  digested  for  24  hours  with  a  dilute  solution  of  chloro- 
hydric  acid,  which  dissolves  the  calcareous  salts;  for  which  purpose 
a  weight  of  chlorohydric  acid,  at  22°  Baum^,  equal  to  that  of  the 
bones,  is  used,  but  it  serves  for  several  times.  The  bones,  deprived 
of  their  calcareous  salts,  are  washed  until  the  water  is  free  from 
acidity ;  after  which  they  are  boiled  with  water  in  a  cast-iron  kettle. 
Not  more  than  the  quantity  of  water  necessary  to  obtain  a  solution 
of  gelatin  which  will  set  on  cooling  should  be  used,  and  added  at 
3  different  times,  because  the  solution  of  gelatin  is  injured  by  too 
long  boiling. 

Fish-glue,  or  iehthyoeolla,  is  prepared  from  the  swimming-bladder 
of  the  sturgeon  by  merely  drying  it ;  and  is  chiefly  used  in  refining 
wines;  but  pure  gelatin,  obtained  from  bones,  will  answer  the  same 
purpose.  Fish-glue  softens  in  cold  water,  and  readily  dissolves  when 
the  temperature  is  raised.  When  poured  into  a  slightly  acidulated 
liquid  the  solution  coagulates,  and  its  filaments  carry  down,  as  in  a 
net,  the  mucilaginous  substances  in  the  liquid. 

Mouth-glue  is  made  of  a  concentrated  solution  of  gelatin,  with  the 
addition  of  a  small  quantity  of  sugar  and  gum-arabic ;  the  solution 
being  boiled  in  order  to  dissolve  the  gelatin  completely,  and  the 
liquid  poured  into  moulds  made  of  oiled  paper,  where  it  becomes 
solid. 

§  1663.  Sugar  of  gelatin^  or  glycocoll^  C4H5NO4. — Sulphuric 
acid  effects  a  very  remarkable  change  in  gelatin,  and  converts  it 
into  a  crystallizable  substance  of  a  sweet  taste,  acting  the  part  of 
a  feeble  alkali,  and  called  glyeocoll,  or,  more  improperly,  sugar 
of  gelatin.     In  order  to  prepare  it,  1  part  of  gelatin  is  digested 


728  ANIMAL   CHEMISTRY. 

for  24  hours  with  2  parts  of  concentrated  sulphuric  acid,  and  10 
parts  of  water  being  added,  it  is  boiled  for  5  hoursw  The  liquid, 
saturated  with  chalk,  and  then  evaporated  to  the  consistence  of 
syrup,  deposits,  after  some  time,  crystals  of  glycocoll ;  their  forma- 
tion taking  place  very  slowly,  sometimes  requiring  a  whole  month 
for  completion.  Boiling  alkaline  solutions  effect  the  same  change 
in  gelatin,  in  which  case  ammonia  is  disengaged. 

Bu,t  the  best  method  of  preparing  pure  glycocoll  consists  in  boil- 
ing, with  4  times  its  weight  of  concentrated  sulphuric  acid,  a  peculiar 
acid  found  in  the  urine  of  herbivorous  animals,  which  we  shall  soon 
describe  under  the  name  of  hippuric.  Hippuric  acid  Ci8HgN0^,H0 
then  separates  into  benzoic  acid  G^fifi^,110,  which  is  almost  wholly 
deposited  on  the  cooling  of  the  liquid,  and  into  glycocoll  C^HgNO^, 
which  remains  in  solution  in  combination  with  the  chlorohydric  acid. 
The  chlorohydrate  of  glycocoll  is  evaporated  to  dryness  in  a  water- 
bath,  and  purified  by  several  crystallizations  in  water,  after  which 
it  is  supersaturated  with  ammonia,  and  again  treated  with  highly 
concentrated  alcohol,  which  precipitates  the  glycocoll  in  the  form 
of  small  crystals.  The  reaction  is  expressed  by  the  following 
equation : 

Ci8H3N05,HO+2HO=Ci,HA,HO+CANO,. 

Glycocoll  is  a  white  substance,  having  a  sweet  taste,  but  which 
does  not  ferment.  It  is  soluble  in  water,  nearly  insoluble  in  alcohol 
and  ether,  and  forms  crystallizable  compounds  with  the  majority  of 
the  acids,  without  exerting  any  action  on  red  litmus.  It  also  com* 
bines  with  potassa  and  several  metallic  oxides. 

§  1664.  Fatty  Substances. — We  shall  not  again  refer  to  the 
fatty  substances  which  are  found  in  animals,  since  they  are  identical 
with  those  existing  in  vegetables,  and  which  have  been  minutely 
described  (§  1590  et  seq.) 

§  1665.  Cerebral  Substance. — The  cerebral  substance  is  com- 
posed essentially  of, 

1st.  A  solid  fat  acid,  containing  phosphorus,  and  called  cerehrie 
acid  ; 

2d.  A  liquid  fat  acid,  also  containing  phosphorus,  called  oleophoS' 
pJiorie  acid; 

3d.  A  peculiar  fatty  matter,  or  cholesteynn,  which  shall  be  de- 
scribed when  treating  of  bile ; 

4th.  Small  quantities  of  ordinary  fatty  substances,  such  as  stearin, 
margarin,  and  olein. 

Cerebric  acid  is  a  white  substance,  which  may  be  obtained  in 
crystalline  granules,  dissolving  readily  in  alcohol  and  boiling  ether, 
while  cold  ether  retains  but  a  small  quantity  of  it.  It  melts  when 
heated,  and  is  very  easily  decomposed.  It  combines  with  bases 
without  forming  crystalhzable  salts,  and  its  analysis  exhibits 


NUTRITION.  729 

Carbon 66.T 

Hydrogen 10.6 

Nitrogen 2.3 

Phosphorus 0.9 

Oxygen 19.5 

iooo 

But  it  is  difficult  to  decide  whether  the  matter  subjected  to  analysis 
was  a  simple  substance. 

Oleophosphoric  acid  is  a  yellowish  oil,  insoluble  in  water  and  cold 
alcohol,  but  very  soluble  in  boiling  alcohol  and  ether.  It  combines 
with  bases,  but  forms  no  crystallizable  salts.  By  contact  with  water, 
it  is  spontaneously  decomposed  into  phosphoric  acid,  which  dis- 
solves, and  an  oily  substance  analogous  to  and  perhaps  identical 
with  olein. 

OF  CERTAIN  CHEMICAL  PHENOMENA  WHICH  OCCUR  IN  THE 
ANIMAL  ECONOMY. 

§  1666.  The  substances  we  have  just  enumerated  form  the  labora- 
tory and  apparatus  in  which  all  the  chemical  reactions  of  the 
economy  take  place ;  but  it  is  important  to  remark  that  these  sub- 
stances do  not  act  an  inert  or  merely  formal  part;  influenced  by 
the  nervous  system,  they  not  only  assume  the  shapes  and  movements 
necessary  for  the  circulation  of  the  fluids,  but  also  intervene  in  the 
chemical  reactions  by  being  constantly  dissolved  and  renewed.  We 
shall  give  the  general  name  of  nutrition  to  the  collection  of  chemical 
phenomena  which  occur  successively  in  alimentary  substances,  from 
the  moment  they  are  taken  into  the  mouth,  until,  after  having  tra- 
versed the  whole  of  the  general  circulation,  they  are  rejected  in  the 
gaseous  state,  with  the  air  expired,  or  in  the  state  of  solids  and 
liquids,  in  the  urine  or  excrements. 

The  phenomena  of  nutrition,  starting  from  the  ingestion  of  foodj 
follow  and  succeed  each  other  in  this  order : 

1st.  Digestion, 

2d.  Respiration, 

3d.  Circulation, 

4th.  Excretion. 
§  1667.  We  shall  give  an  idea  of  the  various  apparatus  in  which 
these  phenomena  are  produced,  by  describing  the  liquids  arising 
from  the  decomposition  of  the  alimentary  substances,  and  to  which 
physiologists  attribute  the  chief  modifications  of  these  substances  in 
the  economy.  In  order  to  render  our  explanation  more  clear,  we 
have  figured  (fig.  686)  the  various  organs  and  circulatory  apparatus 
in  which  the  chemical  phenomena  take  place  in  man,  and  have  en- 
deavoured to  preserve,  as  far  as  possible,  their  actual  form ;  but  we 
have  been  unable  to  represent  the  relative  positions  they  occupy  in 
the  body,  where  they  are  dovetailed  into  and  cover  each  other. 


730 


ANIMAL   CHEMISTRY. 


DIGESTION. 

§  1668.  The  object  of  digestion  is  to  modify,  disaggregate,  and 
dissolve  alimentary  substances,  in  order  to  enable  them  to  pass  sub- 
sequently into  the  general  circulation. 

The  various  acts  of  the  function  of  digestion  are  as  follows : 
From  the  mouth,  where  the  food  is  chewed  by  the  teeth  and 
moistened  with  saliva,  it  is  conveyed  into  the  stomach  A,  passing 
through  the  oesophagus  0.     The  function  of  the  saliva  is  chiefly 


DIGESTION.  731 

physical,  and  assists  the  mastication  and  deglutition  of  food.  The 
saliva  may,  however,  act  chemically,  by  effecting  the  transformation 
of  the  starch  into  dextrin  and  glucose ;  the  latter  action  being  pro- 
bably very  limited,  because  at  a  later  period  the  food  comes  into 
contact  with  several  other  juices  which  effect  the  same  transformation. 

Having  reached  the  stomach  A,  the  food  is  subjected  to  the  action 
of  a  special  juice,  called  gastric^  secreted  by  the  parietes  of  the 
stomach,  and  furnished  by  peculiar  vessels  belonging  to  the  sanguine 
circulation.  The  gastric  juice  modifies,  dissolves,  or  digests  only 
the  nitrogenous  alimentary  principles,  such  as  the  albumen,  fibrin, 
casein,  without  in  any  way  altering  the  fatty  substances,  and  merely 
producing  the  hydration  of  the  amylaceous  matter. 

When  the  food  has  remained  for  some  time  in  the  stomach  A,  it 
leaves  it,  impregnated  with  gastric  juice,  and  passes  into  the  duode- 
num a,  where  it  first  meets  with  the  bile,  brought  from  the  gall- 
bladder B  and  liver  F,  by  the  duct  cd,  called  ductus  choledochus. 
The  action  of  the  bile  on  food  is  not  well  known,  and  some  physio- 
logists even  believe  it  to  act  no  part  in  the  phenomena  of  digestion, 
and  consider  it  as  merely  an  excrementary  fluid. 

§  1669.  In  the  duodenum  the  food  is  moistened,  not  only  by  the 
bile,  but  also  by  the  pancreatic  juice,  supplied  to  the  duodenum  by 
the  pancreatic  duct,  e,  which  juice  is  produced  in  a  peculiar  organ, 
the  pancreas  C,  where  it  is  extracted  from  the  fluids  carried  into 
the  latter  by  the  circulation.  The  pancreatic  juice  acts,  instanta-- 
neously,  on  the  non-nitrogenous  alimentary  substances,  converting 
the  fecula  into  glucose,  and  the  fatty  matters  into  an  emulsion, 
which  renders  them  fit  for  absorption. 

§  1670.  The  alimentary  substances,  modified  by  the  successive 
influence  of  the  gastric  juice,  bile,  and  pancreatic  juice,  pass  from 
the  duodenum  a  into  the  small  intestine  D,D, ...  a  tube  of  considerable 
size,  extending  from  the  duodenum  to  the  caecum  E,  which  itself 
communicates  with  the  large  intestine  EE'E'^E'''.  The  extremely 
long  parietes  of  the  small  intestine  chiefly  effect  the  absorption  of 
the  digested  food  and  its  passage  into  the  circulation.  The  ali- 
mentary substances  which  reach  the  intestine  in  a  condition  to  be 
absorbed,  are  of  two  kinds :  1st.  Nitrogenous  substances,  dissolved 
by  the  gastric  juice,  and  amylaceous  substances,  converted  into 
dextrin  and  sugar  by  the  action  of  the  saliva  and  the  pancreatic 
juice  ;  and,  2d.  The  fatty  substances  which  have  been  made  into  an 
emulsion,  by  the  pancreatic  juice,  without  being  dissolved. 

A  special  system  of  absorbent  vessels,  terminating  in  the  small 
intestine,  is  contrived  for  each  of  these-  peculiar  conditions  of  the 
absorbable  alimentary  substances  :  1st.  The  system  of  the  vena  porta 
ff'f,  which  absorbs  the  nitrogenous  and  saccharine  matters, 
and  conveys  them,  with  the  venous  blood  of  the  intestines  and  the 
spleen  R,  into  the  liver  F,  where  they  undergo  peculiar  modifica- 
tions, to  pass  thence  in  the  right  auricle  G  of  the  heart;  and, 


732  ANIMAL   CHEMISTRY. 

2d.  The  system  of  chyliferous  vessels  g,  g,  g,  which  absorbs  only  the 
fatty  substances,  and  conducts  them  into  the  left  subclavian  vein  z,  i, 
to  pass  thence  directly  into  the  right  auricle  G  of  the  heart,  without 
traversing  the  liver.  In  the  small  intestine  is  effected  the  division 
between  the  digested  alimentary  substances,  which  are  to  be  absorbed 
by  the  organism,  and  are  called,  on  that  account,  accrementitions 
substances,  and  those  which,  remaining  untouched,  or  having  been 
insufficiently  modified  by  the  digestive  fluids,  are  rejected  externally, 
and  consist  of  the  excrementitious  substances  or  faeces. 

§  1671.  The  dimensions  and  developments  of  the  whole  digestive 
apparatus,  stomach,  duodenum,  and  small  intestine,  vary  greatly 
in  diflferent  classes  of  animals  :  in  the  carnivorous,  the  food  of  which 
is  much  more  easily  dissolved  by  the  gastric  and  pancreatic  juices, 
they  are  relatively  much  less  developed  than  in  the  herbivorous  ani- 
mals, of  which  the  food,  being  highly  charged  with  ligneous  matter, 
dissolves  with  much  greater  difficulty. 

§  1672.  The  residue  of  the  alimentary  matter  passes  from  the 
small  into  the  large  intestine  EE'E'^'E''',  where  it  remains  a 
greater  or  less  length  of  time,  and  probably  experiences  new  modi- 
fications and  peculiar  absorptions.  It  there  acquires  a  disagree- 
able and  peculiar  odour,  the  cause  of  which  is  unknown,  and  is 
finally  rejected,  in  the  state  of  excrement,  by  the  anus  H. 

CIRCULATION  OF  THE  BLOOD. 

§  1673.  We  have  followed  the  course  of  the  alimentary  matters 
through  the  primae  viae,  from  their  entrance  at  the  mouth  to  the 
absorption  of  the  digested  portion  into  the  general  circulation,  and 
the  rejection  of  the  residue  by  the  anus.  In  following  the  new  route 
of  the  digested  portion,  we  shall  find  it  ministering  to  the  growth 
and  renovation  of  the  organs,  to  the  production  of  juices  essential 
to  the  chemical  operations  we  have  enumerated,  and  to  the  develop- 
ment of  heat  necessary  to  the  animal,  to  be  excreted,  finally,  either 
in  gaseous  compounds,  with  the  gases  of  respiration,  or  in  solution 
in  the  urine  or  sweat,  or  in  forming  peculiar  fluids,  such  as  milk, 
semen,  etc. 

After  their  absorption  by  the  vena  porta  ff'f",  or  by  the  chyli- 
ferous vessels  g,  g,  g,  the  digested  alimentary  principles  reach,  by 
various  routes,  the  general  circulation,  that  is,  the  riglit  ventricle  I 
of  the  heart,  where  they  are  mixed  with  the  venous  blood,  which 
arrives  from  all  parts  of  the  body  through  the  upper  vena  cava  mm' 
and  the  lower  nn'n" ,  after  having  efi"ected  alimentation,  and  been 
subjected  to  the  phenomena  of  respiration,  etc.,  which  shall  pre- 
sently be  described.  The  instinctive  contractions  of  the  ventricle  I 
drive  all  this  mixture  through  the  pulmonary  artery  IVl"  into  the 
lungs  P,  P,  where  it  meets  with  air,  and  produces  the  phenomena 
of  respiration.  The  blood,  before  reaching  the  lungs,  has  a  deep 
brown  colour,  and  is  venous  blood;  while  as  soon  as  it  comes  into 


DiaESTioN.  733 

contact  with  the  air  in  the  lungs,  it  turns  of  a  bright  red,  and  gives 
off  the  greater  portion  of  the  carbonic  acid  it  contained,  which  is  an 
essential  product  of  the  chemical  reactions  it  experienced  in  its  nu- 
trient functions,  replacing  it  with  a  certain  quantity  of  oxygen,  and 
thus  constituting  arterial  bloody  which  returns  to  the  left  ventricle  J 
of  the  heart  through  the  pulmonary  veins  o,  o.  The  heart  impels 
it  into  the  aortic  or  arterial  system  K,  K,  K, . . .  to  be  distributed  to 
all  the  organs  of  the  body.  The  principal  forces  which  effect  this 
circulation  appear  to  be  the  contractions  of  the  left  ventricle  J,  as 
well  as  the  contractive  forces  of  the  arterial  coats.  If  the  arterial 
blood  experiences  chemical  changes  between  leaving  the  heart  and 
entering  the  organs,  they  are  as  yet  unknown. 

The  arterial  blood,  after  reaching  the  tissues  of  each  organ,  that 
is,  after  having  entered  the  capillary  circulation,  experiences  che- 
mical modifications,  differing  in  each  organ.  The  oxygen  which  it 
had  absorbed  by  contact  with  the  air  in  tjie  lungs,  and  which  had 
effected  its  red  colour,  gradually  disappears,  producing  the  pheno- 
mena of  oxidation,  while  it  is  replaced  more  or  less  completely  by 
carbonic  acid,  which  is  one  of  the  products  of  oxidation ;  the  blood 
then  receiving  its  brown  colour,  and  becoming  venous. 

Arterial  blood  may  be  considered  as  of  the  same  composition  at 
the  moment  of  entering  each  organ,  which  is  not  true  of  venous 
blood,  the  latter  certainly  undergoing  special  modifications  in  the 
various  organs  through  which  it  passes,  and  which  it  nourishes.  It 
is  this  blood,  modified  by  the  various  functions  it  has  fulfilled  in  the 
organs,  which  separates  into  two  different  liquids,  venous  blood 
properly  so  called,  and  lym'ph,  both  of  which  return  to  the  right 
heart  GI  by  special  muscular  systems,  and  are  there  mixed  with  the 
new  liquids  arising  from  digestion,  to  form  a  new  blood,  possessing  all 
the  necessary  nutritive  powers,  and  which  again  resumes  the  round  of 
the  circulation.  The  course  of  the  blood  from  the  right  heart  GI,  to 
the  left  heart  JL,  passing  through  the  capillary  system  of  the  lungs,  is 
called  the  lesser  circulation^  while  its  return  from  the  left  heart  to 
the  right,  passing  through  the  capillary  tissue  of  the  organs  of  the 
body,  is  the  greater  circulation. 

§  1674.  We  have  said  that  the  arterial  blood,  passing  through 
the  capillary  tissue  of  the  organs,  is  chemically  modified  and  con- 
verted into  venous  blood  and  lymph:  now,  it  happens  that  while 
traversing  certain  capillary  tissues,  the  blood  gives  out  certain 
liquid  or  gaseous  products.  When  the  products,  thus  separated, 
are  to  be  used  for  special  purposes,  they  are  called  secretions  ;  but 
when,  on  the  contrary,  they  are  to  be  rejected,  they  are  termed  ex- 
cretions.    The  principal  secretions  are, 

1st.  The  gastric  juice,  secreted  by  the  stomach. 

2d.  The  pancreatic  juice,  formed  in  the  pancreas,  whence  it 
passes  into  the  duodenum. 


734  ANIMAL   CHEMISTRY. 

3d.  The  bile,  produced  in  the  liver,  and  accumulated  in  the  gall- 
bladder. 

4th.  The  intestinal  juice,  which  appears  to  be  secreted  by  the 
intestines,  but  is  perhaps  only  an  alteration  of  the  foregoing  diges- 
tive juices. 

5th.  The  saliva,  secreted  in  the  mouth  by  the  salivary  glands, 

6th.  The  semen  of  male  animals,  formed  in  the  testes. 

7th.  Milk,  secreted  by  the  mammary  glands^  and  collecting  in 
the  spongy  tissue  constituting  the  mammae. 

8th.  The  water  of  the  amnios  surrounding  the  foetus,  in  pregnant 
females. 

Among  the  excretions,  we  distinguish, 

1st.  The  sweat,  excreted  by  peculiar  glands,  the  sudoriferous, 
of  which  the  orifices  open  On  the  surface  of  the  skin. 

2d.  The  urine  which  arises  from  a  peculiar  analysis  of  the  arterial 
blood  in  passing,  during  the  greater  circulation,  through  the  kid- 
neys M,  M,  which  analysis  separates  from  it  a  liquid  charged  with 
mineral  salts  and  highly  oxygenated  organic  substances,  such  as 
urea  and  uric  acid ;  which  substances,  being  only  the  residue  of 
chemical  changes  in  the  food,  must  be  rejected.  The  urine  is  con- 
veyed by  special  ducts,  the  ureters  uu'^  into  the  bladder  V,  where 
it  collects,  until  the  animal  expels  it  by  the  urinary  passages  v. 

3d.  The  gaseous  products  expelled  by  the  act  of  respiration. 

4th.  Gases  arising  in  greater  or  less  quantity  during  the  digestion 
of  the  food  in  the  stomach  or  intestines,  and  which  are  emitted 
either  from  the  mouth  or  from  the  anus. 

RESPIRATION  AND  ANIMAL  HEAT. 

§  1675.  It  has  been  long  since  considered  as  an  established  fact 
that  the  phenomenon  of  respiration  consists  in  a  combustion  constantly 
taking  place  in  the  lungs,  between  a  portion  of  the  carbon  and 
hydrogen  of  the  blood,  and  the  oxygen  of  the  atmospheric  air, 
which  explains  why  arterial  differs  from  venous  blood  by  contain- 
ing less  carbon  and  hydrogen.  Such,  however,  is  not  the  theory 
now  most  received  by  physiologists.  According  to  them,  the  venous 
blood,  having  reached  the  lungs,  disengages  carbonic  acid,  and  ab- 
sorbs oxygen,  which  it  carries  in  a  state  of  solution  into  the  arterial 
system  and  the  capillaries  attached  to  it,  the  dissolved  oxygen  effect- 
ing in  its  course  the  oxidizing  processes  necessary  to  animal  life,  while 
the  carbonic  acid  formed  dissolves  in  the  blood,  and  is  disengaged 
only  when  the  blood,  having  returned  to  the  lungs,  comes  again  in 
contact  with  the  air.  The  exchange  of  the  oxygen  and  carbonic 
acid  is  effected  through  the  very  delicate  membrane  which  lines  the 
air-cells  of  the  lungs,  and  according  to  some,  ensues  merely  in  con- 
sequence of  the  ordinary  laws  of  the  solution  of  gases  in  liquids  ex- 
posed to  atmospheres  of  known  composition,  while  others  regard  it 
as  a  special  endosmose  performed  by  the  porous  membrane.     In  all 


RESPIRATION.  735 

cases,  carbonic  acid  would  no  longer  be  formed  solely  in  the  lungs, 
but  in  all  parts  of  the  circulation. 

The  change  of  colour,  so  well  marked  and  so  instantaneous,  of  the 
venous  blood  by  contact  with  the  air,  is  not  easily  explained  by  a 
simple  solution  of  oxygen  gas ;  and  it  appears  to  us  more  probable 
that  the  oxygen  forms,  with  certain  substances  in  the  blood,  a  true 
chemical  compound,  which  again  gives  off  its  oxygen  readily  enough 
to  effect  instantaneously  the  oxidation  of  other  substances.  The 
carbonic  acid  produced  by  this  oxidation  in  the  capillaries  would 
remain  dissolved  in  the  blood,  on  account  of  the  high  pressure  to 
which  the  latter  is  subjected,  which  pressure  must  be  admitted  in 
order  to  explain  the  passage  of  so  thick  a  fluid  through  such  narrow 
tubes.  The  carbonic  acid  would  be  then  more  readily  evolved  when 
the  blood  reached  the  lungs,  because  it  would  there  be  subjected 
only  to  the  ordinary  pressure  of  the  atmosphere. 

§  1676.  We  shall  regard  all  the  gases  exhaled  by  the  animal  as 
products  of  respiration.  They  belong  to  three  distinct  orders  of 
functions :  the  pulmonary  respiration,  cutaneous  exhalation,  and 
exhalation  through  the  intestinal  canal.  In  warm-blooded  animals 
the  second  is  much  less  active  than  the  first,  while  in  cold-blooded 
animals,  on  the  contrary,  it  is  equally,  and  perhaps  more  energetic ; 
for  example,  in  frogs,  which  can  live  for  several  days  deprived  of 
their  lungs,  by  breathing  through  the  skin ;  or  in  salamanders, 
which  have  lived  for  several  months  after  the  loss  of  their  head, 
and  the  cicatrization  of  the  wound.  The  ensemble  of  these  func- 
tions is  generally  called  by  physiologists  perspiration. 

§1677.  Warm-blooded  animals,  living  on  their  ordinary  food, 
always  exhale  nitrogen,  but  in  very  small  quantities,  since  it  rarely 
exceeds  ih^  of  the  weight  of  all  the  oxygen  consumed  by  respiration. 
When  these  animals  are  in  a  state  of  inanition,  there  is  frequently 
an  absorption  of  nitrogen,  the  quantity  absorbed  being  in  proportions 
as  small  as  that  exhaled  in  the  preceding  case.  It  is  very  frequent 
in  birds  in  a  state  of  inanition,  though  rare  in  mammiferous  animals. 
These  alternations  of  absorption  and  exhalation  of  nitrogen  lead  us 
to  believe  that  the  two  phenomena  always  occur  simultaneously, 
while  experiment  only  demonstrates  the  variable  and  always  small 
result  of  their  opposite  effects,  which  then  might  be  individually 
much  greater  than  is  supposed. 

Cold-blooded  animals  also  appear  to  exhale  small  quantities  of 
nitrogen. 

1678.  The  total  quantity  of  oxygen  which  the  animal  takes  from 
the  air,  in  the  act  of  respiration,  is  not  always  again  found  in  the 
carbonic  acid  exhaled,  a  portion  of  the  oxygen  most  frequently  dis- 
appearing in  other  non-gaseous  compounds,  which  remain  in  the 
animal  economy,  or  are  expelled  from  it  with  the  excrementitious 
matters — principally  with  the  urine.  The  ratio  between  the  quantity 
of  oxygen  found  in  the  carbonic  acid  and  the  whole  quantity  of 


736  ANIMAL   CHEMISTEY. 

oxygen  consumed,  depends  greatly  on  the  nature  of  the  food,  and 
varies  very  little  in  animals  living  on  the  same  aliments,  though 
they  may  belong  to  very  different  species.  The  greatest  absorp- 
tion of  oxygen  in  the  state  of  non-gaseous  compounds  takes  place 
when  animals  are  fed  on  meat ;  the  ratio  between  the  weight  of 
oxygen  contained  in  the  carbonic  acid  and  the  whole  oxygen  con- 
sumed, being  then  comprised  between  0.67  and  0.74.  This  ratio  is 
greater  when  animals  are  fed  on  vegetables ;  and  in  rabbits  sub- 
jected to  this  regimen,  it  has  varied  from  0.85  to  0.95.  It  is  still 
greater  when  animals  are  fed  on  bread  or  grain ;  for  it  may  equal, 
and  sometimes  even  exceed  unity,  so  that  the  animal  then  evolves 
in  the  state  of  carbonic  acid,  a  quantity  of  oxygen  greater  than  that 
which  it  has  taken  from  the  atmospheric  air,  the  excess  of  oxygen 
necessarily  proceeding  from  the  food.  In  a  rabbit  fed  temporarily 
on  bread  and  bran,  the  ratio  between  the  oxygen  contained  in  the 
carbonic  acid  exhaled  and  the  whole  quantity  of  oxygen  consumed 
was  0.997;  while  in  chickens  fed  on  grain  it  varied  from  0.90  to 
1.03 ;  and  lastly,  in  animals  absolutely  dieted,  the  ratio  was  nearly 
the  same  as  when  they  are  fed  on  meat.  In  fact,  the  carbon  fur- 
nished for  respiration  can,  in  this  case,  only  arise  from  themselves, 
that  act  being  then  accomplished  in  them,  as  if  they  were  car- 
niverous,  even  though  they  were  birds  which  naturally  feed  on 
grain. 

1679.  In  the  mammiferse  and  in  birds,  the  quantity  of  carbonic 
acid  formed  by  contact  with  the  body,  and  which  is  disengaged  by 
the  intestinal  canal,  is  always  very  small,  since  it  rarely  reaches  -^ 
of  that  furnished  by  the  pulmonary  respiration.  Small  quantities 
of  hydrogen  and  protocarburetted  hydrogens  traces  of  ammonia,  and 
excessively  small  quantities  of  sulphuretted  gases,  are  disengaged 
through  the  same  passages.  To  recapitulate,  in  warm-blooded 
animals,  the  pulmonary  respiration  predominates  so  greatly  over 
the  secondary  causes  of  exhalation  and  absorption  which  accompany 
it,  that  all  the  peculiarities  which  characterize  it  may  be  inferred 
from  observations  made  on  the  whole  respiration,  as  though  it  alone 
were  active.  On  the  contrary,  in  cold-blooded  animals,  the  cu- 
taneous respiration  predominates  to  so  great  a  degree  that  frogs 
have  continued  to  breathe  for  several  days  when  deprived  of  their 
lungs,  nearly  with  the  same  energy,  absorbing  and  evolving  the 
same  gases,  in  nearly  the  same  proportion,  as  well  as  in  nearly  the 
same  absolute  quantities. 

§  1680.  Hibernating  animals,  as  the  marmot,  during  their  wak- 
ing life,  breathe  precisely  in  the  same  manner  as  other  animals, 
while  the  phenomenon  is  wholly  changed  during  their  sleep,  their 
temperature  then  exceeding  that  of  the  surrounding  medium  only 
by  a  few  degrees,  and  the  consumption  of  oxygen  being  excessively 
feeble,  and  generally  less  than  -^q  of  that  required  by  the  same  ani- 
mals when  awake.     Rather  less  than  one-half  of  this  oxygen  only 


RESPIRATION.  737 

is  found  in  the  carbonic  acid  exhaled,  the  balance  being  assimilated 
internally  in  the  shape  of  non-gaseous  compounds,  and  being  pro- 
bably partly  used  to  form  water,  a  small  portion  of  which  is  lost  by 
perspiration,  on  account  of  the  low  temperature  of  the  animal.  It 
hence  follows  that  the  weight  of  the  carbonic  acid  exhaled  is  less 
than  that  of  the  oxygen  absorbed,  and  the  animal  increases  in 
weight  hy  perspiration.  This  increase,  however,  does  not  take 
place  continuously,  for,  every  few  days,  the  animal  generally  par- 
tially awakens  and  expels  his  urine.  When  the  marmot  fully 
awakes,  his  respiration  becomes  extremely  active,  much  more  so 
than  when  he  has  been  awake  for  some  time;  and  his  temperature 
rises  rapidly,  while  his  limbs  gradually  lose  their  numbness,  and 
the*  animal  is  seized  with  a  violent  shivering,  caused  by  the  sensa- 
tion of  cold,  which  he  did  not  feel  during  sleep.  The  conditions  of 
existence  are  no  longer  the  same  in  the  two  states  of  the  same  ani- 
mal. The  waking  marmot  becomes  asphyxiated,  like  the  other 
mammiferae,  in  an  atmosphere  poor  in  oxygen,  while  in  the  torpid 
state  he  would  be  unaflfected  by  it.  He  cannot,  however,  bring 
himself  voluntarily  to  this  state,  in  order  to  continue  to  live  in  an 
atmosphere  which  his  instinct  tells  him  must  prove  fatal  to  him. 

§  1681.  The  respiration  of  animals  does  not  appear  to  be  changed 
in  an  atmosphere  richer  in  oxygen  than  ordinary  atmospheric  air, 
nor  even  in  pure  oxygen;  the  same  being  true  of  an  atmosphere 
containing  a  large  proportion  of  carbonic  acid,  provided  it  contain 
also  a  sufficient  quantity  of  oxygen.  Lastly,  if  the  nitrogen  of  our 
ordinary  atmosphere  be  replaced  by  an  equal  volume  of  hydrogen, 
the  animal  breathes  as  usual,  without  any  injurious  effects. 

§  1682.  The  internal  combustion  of  the  carbon  which  serves  to 
form  carbonic  acid  is  certainly  one  of  the  sources  of  animal  heat. 
This  fact  is  evident,  not  only  as  being  a  necessary  consequence  of 
the  evolution  of  heat  which  always  ensues  on  the  combustion  of 
carbon,  either  by  active  burning  or  in  solutions,  as  in  alcoholic  fer- 
mentation, but  is  also  manifested  in  the  variations  of  respiration, 
according  to  circumstances,  in  maintaining  the  constancy  of  tem- 
perature. Thus,  the  quantity  of  oxygen  consumed  by  the  same 
animal,  and  the  quantity  of  carbonic  acid  exhaled  in  equal  periods, 
are  the  greater  in  proportion  to  the  depression  of  the  surrounding 
temperature ;  and  it  is  also  greater  when  the  nitrogen  of  its  artificial 
atmosphere  is  replaced  by  hydrogen,  the  relative  refrigerating  power 
of  which  is  much  greater.  On  this  account,  animals  of  the  same  class 
consume,  in  a  given  time,  a  quantity  of  oxygen  in  inverse  ratio  to 
their  size;  the  loss  of  heat  from  the  surface  being  proportionally 
much  greater  in  the  smaller  than  in  the  larger  animal.  For  example, 
the  consumption  of  oxygen  for  100  gm.  of  substance  is  10  times 
greater  in  sparrows  than  in  fowls. 

It  has  long  since  been  admitted  that  the  heat  evolved  by  an  animal 
in  a  given  time  is  precisely  equal  to  that  which,  by  a  vivid  combustion 
Vol.  IL— 47 


738  ANIMAL   CHEMISTRY. 

in  oxygen,  the  carbon  contained  in  the  carbonic  acid  produced  would 
afford,  and  the  hydrogen  which  would  form  water  with  that  portion 
of  oxygen  consumed,  which  is  not  found  in  the  carbonic  acid.  It 
is  highly  probable  that  animal  heat  is  wholly  produced  by  chemi» 
cal  reactions  ensuing  in  the  economy ;  but  the  phenomenon  is  too 
complex  to  allow  of  its  calculation  from  the  quantity  of  oxygen  con- 
sumed. The  substances  consumed  by  respiration  generally  consist 
of  carbon,  hydrogen,  nitrogen,  and  oxygen,  often  in  considerable 
proportion ;  and  when  they  are  completely  destroyed  by  respiration, 
the  oxygen  they  contain  contributes  to  the  formation  of  water  and 
carbonic  acid,  and  the  heat  evolved  is  necessarily  very  different  from 
that  which  carbon  and  hydrogen,  supposed  to  be  free,  would  give 
off  in  burning.  These  substances,  moreover,  are  never  completely 
consumed;  a  portion  being  converted  into  other  substances,  which 
play  special  parts  in  the  animal  economy,  or  which  escape  in  the 
excretions,  in  the  state  of  highly  oxidized  matters,  (urea,  uric  acid.) 
Now,  in  all  these  transformations  and  assimilations  of  substances  in 
the  organs,  heat  is  evolved  or  absorbed;  but  the  phenomena  are 
evidently  so  complicated  that  we  shall  probably  never  be  able  to 
make  them  the  subject  of  calculation. 


5  1683.  We  shall  now  describe  more  in  detail  the  principal  pro- 
perties and  chemical  composition  of  the  liquids  which  are  found  in 
tke  animal  economy. 

BLOOD. 

§  1684,  The  blood  is  a  liquid  which  circulates  in  the  various  parts 
of  the  animal  economy,  and  furnishes  the  organs  with  the  materials 
necessary  for  their  life  and  growth.  In  vertebrated  animals,  such 
as  man,  the  mammiferae,  birds,  reptiles,  and  fishes,  the  blood  is  of  a 
bright  red  colour;  while  in  the  invertebrata,  as  in  insects,  the  crus- 
taceae,  mollusks,  and  zoophytes,  it  is  much  more  fluid  and  colourless, 
or  merely  tinged  of  a  yellow,  green,  rose,  or  lilac  hue.  The  blood  is 
much  denser  and  thicker  in  man  and  the  warm-blooded  animals,  such 
as  the  mammiferae  and  birds,  than  in  cold-blooded  animals;  its 
density  .and  viscidity  varying  according  to  the  food  and  the  more 
or  less  recent  loss  of  blood  which  the  animal  may  have  sustained. 
In  an  adult  man,  the  average  density  of  the  blood  is  1.054  at  59° ; 
being  somewhat  less  in  females,  particularly  during  pregnancy, 
when  it  falls  to  1.045. 

Two  kinds  of  blood  are  distinguished  in  man  and  warm-blooded 
animals :  arterial  blood,  which  is  of  a  vermilion  red,  and  venous  blood, 
the  colour  of  which  is  darker  and  of  a  brownish  red,  which  peculiar 
colour  is  produced,  as  we  have  shown,  (§  1673,)  by  the  action  of  the 
atmospheric  oxygen  on  the  blood;  and  it  therefore  exists  only  in 
animals  which  breathe  in  the  air,  and  is  not  observed  during  intra- 


BLOOD. 


ns9 


Uterine  life.  The  colour  of  foetal  blood  is  intermediate  between  that 
of  the  venous  and  arterial  blood  of  adult  age- 

§  1685.  When  fresh  blood  of  a  vertebrated  animal  is  examined 
under  the  microscope,  it  is  seen  to  be  formed  of  a  colourless,  or 
nearly  colourless  liquid,  in  which  red  bodies,  similar  in  form,  and 
called  blood-globules,  are  disseminated,  which  are  characteristic  of 
each  genug  of  animals.  They  form  in  man  and  the  greater  part  of 
the  other  mammiferae  small,  circular,  flattened  disks ;  while  in  birds, 
reptiles,  and  fishes,  they  are  elliptical.  Their  diameter  in  man  is 
about  y^  of  a  millimetre,  being  smaller  in  the  majority  of  other 
mammiferae,  and  in  the  goat  attaining  only  about  j|g.  In  birds, 
these  globules  are  larger  than  in  the  mammiferae ;  while  they  attain 
their  greatest  size  in  the  family  of  the  batrachians  and  reptiles :  thus, 
in  the  blood  of  the  frog,  they  are  nearly  :^  of  a  millimetre  in  length 
and  ^j  in  breadtL  Lastly,  in  fishes,  the  globules  are -intermediate 
in  size,  between  those  of  birds  and  th-ose  of  reptiles;        "  ' 

Fig.  687  represents  the  blood-^globmles  of  the  frog,  consisting  of 

flatibeaed  elliptical  disks,  of  which 
the  central  part,  less  coloured  and 
protruding,  is  surrounded  by  a 
kind  of  deep-coloured  border. 
Their  anatomical  study  by  the 
microscope  and  powerful  chemical 
reagents  shows  them  to  be  com- 
posed of  two  entirely  distinct  parts, 
a  central  nucleus  and  an  envelope 
resembling  a  small  bladder,  con- 
taining a  coloured  gelatinous  ar.d 
very  elastic  substance.  When  any 
part  of  a  frog,  sufficiently  thin  to 
be  translucent,  such  as  the  web  of 
Fig.  687.  the  foot  or  the  tongue,  is  examined 

under  the  microscope,  the  globlues  will  be  seen  to  be  rapidly  carried 
through  the  capillaries  with  the  watery  fluid,  and  to  be  momentarily 
compressed  in  order  to  pass  through  the  smallest  tubes.  Blood- 
globules  may  be  preserved  for  a  long  time  in  their  natural  liquid ; 
while,  when  water  is  added,  they  swell,  probably  in  consequence  of 
endosmose,  and  tend  toward  a  spherical  shape.  The  central  nucleus 
does  not  appear  to  undergo  any  change.  Certain  acids,  such  as 
phosphoric,  oxalic,  citric,  and  acetic,  rapidly  dissolve  the  external 
envelope  and  expose  the  nucleus ;  while  alkaline  liquids  dissolve  the 
whole  globule.  The  globules  remain  unchanged,  and  without  any 
appreciable  alteration  of  form,  in  a  solution  of  sugar  or  gum,  and  in 
several  saline  solutions,  such  as  those  of  nitrate  of  potassa  or  soda, 
and  chloride  of  potassium  and  of  sodium.  Fig.  688  represents  the 
globules  of  human  blood,  in  which,  as  in  the  blood-globules  of  the 
other  mammiferae,  the  central  portion  is  less  projecting  than  the 


740  ANIMAL  CHEMISTRY. 

border,  while  the  nucleus  is  not  dis- 
tinct, although  we  are  led  to  admit 
the  existence  of  one  by  analogy, 
and  by  the  manner  in  which  the 
globules  are  decomposed  by  chemi- 
cal agents.  In  fig.  688  a  is  a  front 
view  of  the  globules,  and  b  a  profile 
view  of  the  same. 

In  addition  to  the  red  globules 
which  give  colour  to  the  blood,  the 
microscope  detects  a  very  few  co- 
lourless globules,  of  spherical  form, 
closely  resembhng  those  seen  in 
chyle,  and  some  of  which  appear 
^^8-  68a  tQ  l^g  composed  of  fat  alone. 

The  white  or  scarcely  coloured  globules  in  the  blood  of  the  in- 
vertebrata  diifer  greatly  from  those  of  vertebrated  animals,  and 
their  size  varies  in  the  same  individual,  while  their  form  is  generally 
spherical,  and  their  surface  is  covered  with  asperities.  No  central 
Ducleus  can  be  distinguished. 

§  1686.  The  liquid  surrounding  the  blood-globules  of  vertebrated 
animals  is  water,  containing  in  solution  a  great  number  of  different 
substances.  The  presence  of  albumen,  fibrin,  various  fatty  substances, 
some  of  which  contain  sulphur  and  phosphorus,  a  great  number  of 
salts,  such  as  the  chlorides  of  potassium  and  sodium,  chlbrohydrate 
of  ammonia,  the  sulphates  of  soda  and  potassa,  the  phosphates  of 
soda,  lime,  and  magnesia,  the  carbonates  of  soda,  lime,  and  magnesia, 
and  of  alkaline  salts,  formed  by  fatty  acids  and  by  lactic  acid,  ha^^e 
been  detected  in  blood.  This  fluid  contains  also  several  gases  in 
solution :  oxygen,  carbonic  acid,  and  nitrogen,  which  arise  from  th« 
action  of  the  air  in  the  lungs.  It  has  a  peculiar  mawkish  taste,  charac- 
teristic in  some  animals,  and  always  exerts  a  well-marked  alkaline 
reaction,  which  appears  to  be  an  essential  of  its  nature,  for  animal 
life  ceases  when,  by  direct  injections,  the  blood  can  be  made  acid. 

In  a  healthy  man,  100  parts  of  blood  contain,  on  an  average,  T9 
parts  of  water,  1  part  of  mineral  salts,  19  of  albuminous  substances, 
and  some  thousandths  of  fibrin,  besides  the  red  colouring  matter 
known  by  the  name  of  hematosin;  which  proportions  vary  greatly 
with  the  state  of  health.  In  the  blood  of  birds,  the  relative  quan- 
tity of  water  is  generally  somewhat  smaller  than  in  man,  while  it  id 
greater  in  that  of  the  batrachian  reptiles  and  fishes.  As  much  as 
98  per  cent,  of  water  has  been  found  in  the  blood  of  a  frog. 

§  1687*  Blood  drawn  from  a  vein  soon  loses  its  fluidity  and  coa- 
gulates; which  generally  commences  in  5  or  10  minutes  after  its 
extraction,  but  is  not  complete  until  the  lapse  of  8  or  10  hours.  A 
gelatinous  matter  forms,  which  thickens  more  and  more,  until,  after 
a  certain  length  of  time,  the  blood  separates  into  two  portions :  one, 


BLOOD.  741 

fluid,  yellowish  and  transparent,  called  the  serum;  and  the  other, 
gelatinous  and  elastic,  of  a  deep  red  colour,  and  called  the  clot,  co- 
agulurHy  or  erassamentum  of  the  blood.  The  coagulation  of  blood  is 
produced  by  the  fibrin,  which  remains  in  solution  so  long  as  the 
blood  is  under  the  influence  of  vitality,  but  separates  from  it  when 
it  is  removed  from  the  animal  economy,  carrying  with  it  the  blood- 
globules,  in  the  same  way  that  soluble  albumen,  used  for  the  clari- 
fication of  a  muddy  liquor,  carries  down  the  corpuscles  which  exist 
in  it,  as  soon  as  it  is  coagulated  by  heat.  If,  instead  of  allowing 
the  blood  to  rest,  it  is  beaten  with  rods,  the  fibrin  still  coagulates, 
and  forms  whitish  and  elastic  filaments,  which  adhere  to  the  rods, 
the  blood-globules  not  being  included,  because  they  are  detached 
by  the  agitation  of  the  fluid.  Defibrinated  blood  no  longer  coagu- 
lates. It  is  easy  to  demonstrate,  on  the  blood  of  frogs,  the  globules 
of  which  are  too  large  to  pass  through  filtering-paper,  that  fibrin  is 
really  in  solution  in  the  serous  liquid,  and  does  not  constitute  any 
part  of  the  globules,  as  was  long  supposed.  It  is  sufficient  to  pour 
upon  a  filter,  previously  moistened,  the  blood  of  a  frog,  at  the  mo- 
ment of  its  extraction,  to  show  that  a  portion  of  the  liquid  passes 
through  the  filter  before  the  commencement  of  coagulation ;  and 
after  collecting  this  portion  in  a  watch-glass,  the  microscope  will 
exhibit  in  it,  after  a  short  time,  a  colourless  clot,  which  may  be 
made  visible  by  collecting  it  on  a  needle.  This  experiment  does 
not  succeed  in  human  blood,  nor  in  that  of  other  mammiferse,  be- 
cause the  fluid  is  more  viscid  and  the  globules  are  sufficiently  small 
to  pass  through  the  paper. 

The  blood-globules'  are  not  uniformly  distributed  throughout  the 
coagulum,  but  fall  toward  the  lower  part,  while  the  upper  strata 
generally  contain  but  very  few  of  them ;  in  which  case  they  contract 
still  further,  and  form  a  sort  of  pellicle,  called  the  buffi/  coat  of  the 
blood.  By  forcibly  compressing  the  clot,  the  greater  part  of  the 
liquid  serum  may  be  expressed  from  it. 

Serum  is  a  yellow,  slightly  viscid  fluid,  of  a  density  ranging  from 
1.027  to  1.029:  it  has  a  slightly  saline  taste,  and  coagulates  at 
about  168.8°,  which  property  it  owes  to  the  albumen. 

Several  saline  substances  prevent  the  coagulation  of  the  blood: 
as,  for  example,  sulphate  of  soda,  the  chlorides  of  sodium  and  potas- 
sium, nitrate  of  potassa,  borax,  etc. ;  and  the  proportion  of  these 
salts  must  be  about  |  of  the  weight  of  the  blood.  The  dilute  mine- 
ral acids  also  prevent  the  coagulation  of  blood,  but  impart  to  it  an 
oily  consistence.  A  temperature  of  86°  or  104°  appears  to  be  the 
most  favourable  for  coagulation,  while  cold  retards  it  considerably. 

Healthy  human  venous  blood  yields 

Coagulum ...13.0 

Serum .87.0 

100.0 


Serum 


742  ANIMAL   CHEMISTRY. 

r  Fibrin .........0.30^ 

Coagulum<  p,  ,    ,      f  Hematosin 0.20  >13.00 

(^^^^"^^^\  Albuminous  matter 12.60  J 

Water 79.00 

Albumen 7.00 

Fatty  substances 0.06 

^Various  salts  with  mineral  bases 0.94 

100.00 

§1688.  Hematosin,  or  the  red  colouring  matter  of  blood,  has 
probably  not  yet  been  extracted  in  a  state  of  purity,  and  has  not 
been  obtained  crystallized.  In  order  to  obtain  it,  sulphuric  acid  is 
added,  by  small  portions  at  a  time,  to  blood  previously  defibrinated  by 
beating;  until,  by  the  coagulation  of  the  albuminous  substances,  the 
liquid  becomes  like  a  thick  broth  of  a  brown  colour.  This  mass 
being  diluted  in  a  small  quantity  of  alcohol,  filtered  through  mus- 
lin, and  compressed,  the  residue  is  treated  several  times  with  alco- 
hol acidulated  with  a  small  quantity  of  sulphuric  acid,  until  the 
liquid  has  lost  its  colour,  and  the  albuminous  matter  is  thus  almost 
completely  bleached.  The  alcoholic  liquor  is  supersaturated  by 
ammonia,  and  then  evaporated  to  dryness ;  when  the  residue,  which 
is  composed  of  hematosin,  mixed  with  some  fatty  and  some  alkaline 
substances,  is  treated  successively  by  ether,  alcohol,  and  water, 
which  dissolve  the  foreign  substances  and  leave  the  colouring  mat- 
ter. It  is  then  purified  by  dissolving  it  in  ammoniacal  alcohol,  and 
again  separating  it  by  evaporation ;  the  hematosin  remains  in  the 
form  of  a  blackish-red  amorphous  mass,  which  is  tasteless  and  ino- 
dorous, and  insoluble,  when  cold,  in  alcohol,  water,  or  ether ;  while  it 
dissolves  readily  in  alcoholic  solutions  of  potassa,  soda,  and  ammo- 
nia, which  it  colours  intensely  red.  This  substance  contains  as 
much  as  10  per  cent,  of  sesquioxide  of  iron,  which  appears  essential 
to  the  existence  of  the  globules. 

§  1689.  The  quantitative  analysis  of  blood  is  very  difficult,  and 
no  very  accurate  process  is  yet  known ;  the  following  being  that 
most  generally  adopted  by  physiologists  : 

The  blood  is  first  beaten  with  a  brush,  until  the  fibrin  is  separated 
as  perfectly  as  possible,  in  whitish  filaments,  which  are  carefully 
collected,  and  weighed,  after  being  washed,  on  a  cloth,  with  water, 
and  then  dried  at  212°  until  the  weight  remains  constant.  Three 
or  four  times  its  volume  of  a  saturated  solution  of  sulphate  of  soda 
being  added  to  the  defibrinated  liquid,  in  order  to  prevent  the  alter- 
ation of  the  globules,  it  is  rapidly  filtered,  causing  bubbles  of  air 
to  pass  constantly  through  the  liquid  in  the  filter,  to  prevent  the 
globules  from  adhering  to  each  other.  In  this  particular  case,  the 
blood-globules  do  not  pass  through  the  filter,  and  the  sulphate  of 
soda  prevents  the  coagulation  of  the  small  quantity  of  fibrin  which 
may  still  remain  in  the  liquid.     The  globules  are  washed  with  a 


LYMPH.  743 

solution  of  sulphate  of  soda,  dried  in  vacuo,  and  tlien  treated  suc- 
cessively with  ether  which  dissolves  the  fatty  matter,  with  alcohol 
which  dissolves  a  small  quantity  of  foreign  organic  matter,  and 
with  water  which  removes  the  sulphate  of  soda.  The  dried  globules 
are  insoluble  in  these  various  liquids,  and  undergo  no  change ;  and 
after  being  again  dried,  they  are  weighed. 

This  being  done,  another  portion  of  the  same  blood  is  allowed  to 
coagulate  spontaneously,  and  the  crassamentum  being  separated  as 
completely  as  possible  from  the  serum,  they  are  weighed  sepa- 
rately. The  serum  is  then  evaporated  in  a  water-bath,  and  the 
residue  dried  at  212°  or  in  vacuo,  by  which  means  is  ascertained 
the  proportion  of  dry  substances  and  of  water  constituting  the  fluid. 
On  the  other  hand,  the  crassamentum  is  perfectly  dried  at  212°,  ttnd 
its  loss  of  weight  is  supposed  to  represent  the  water  of  the  serum 
which  was  contained  in  the  coagulum;  when,  by  a  proportion 
founded  on  the  knowledge  of  the  composition  of  the  serum,  above 
given,  the  weight  of  the  serum  contained  and  the  weight  of  the 
solid  parts  of  the  serum  which  remained  in  the  dried  coagulum  is 
ascertained.  The  latter  weight,  subtracted  from  that  of  the  dried 
coagulum,  represents  the  united  weight  of  the  fibrin  and  globules, 
which  should  be  equal  to  the  sum  of  the  weights  of  the  fibrin  and 
globules  obtained  separately  in  the  first  analysis.  The  fatty  sub- 
stances are  separated  from  the  dried  coagulum  and  from  the  residue 
of  the  evaporation  of  the  serum  by  treating  them  with  ether, 
•  Lastly,  the  mineral  salts  are  obtained  by  incinerating  separately 
the  coagulum  and  dried  serum,  and  ascertaining  the  weight  of  the 
ashes,  which  may  be  then  subjected  to  a  special  analysis,  if  a  suflS- 
cient  quantity  of  blood  has  been  operated  on.  By  subtracting  the 
weight  of  the  ashes  and  that  of  the  fatty  matter  found  in  the  serum 
from  the  weight  of  the  dried  serum,  and  taking  into  account  the 
serum  interposed  in  the  coagulum,  the  weight  of  the  albuminoid 
substances  is  obtained,  added  to  a  small  quantity  of  other  organic 
substances. 

LYMPH. 

§  1690.  Lymph  is  a  liquid  brought  from  all  the  organs  of  the 
body,  by  a  system  of  vessels  called  lymphatic.  It  is  a  limpid, 
slightly  viscid  fluid,  having  an  alkaline  reaction,  and  coagulating 
spontaneously  like  blood.  Its  composition  resembles  that  of  fluid 
blood,  with  the  exception  of  the  coloured  corpuscles ;  while  fibrin, 
albumen,  and  the  saline  substances  peculiar  to  blood  are  also  found 
in  lymph. 

The  lymphatic  vessels  which  convey  the  lymph  from  the  intes- 
tines, perform,  during  digestion,  the  function  of  absorbing  the  fatty 
matters;  in  consequence  of  which  the  lymph  at  this  time  acquires 
an  opaline  and  whitish  tinge,  resembling  milk.  The  name  of  chyle 
is  given  to  this  mixture  of  intestinal  lymph  with  the  fatty  matter, 


744  ANIMAL   CHEMISTRY. 

and  the  lymphatics  of  the  intestine  have  received  the  name  of  ehy- 
liferous  or  lacteal  vessels,  from  their  function  of  conveying  the 
white  chyle. 


LIQUIDS  WHICH  APPEAR  TO  PLAY  A  PART  IN  DIGESTION. 

§  1691.  Various  liquids  occur  in  the  intestinal  canal  of  animals, 
secreted  by  special  organs  enumerated  §  1667  et  seq.,  and  the  prin- 
cipal duty  of  wliich  appears  to  be  to  effect  the  solution  of  aliment- 
ary substances  and  their  passage  into  the  blood.  Physiologists 
divide  them  into 

1st.  Saliva. 

2d.  Gastric  juice. 

3d.  Bile.  .    . 

4th.  Pancreatic  juice. 

5th.  Intestinal  juice. 
As  the  chemical  nature  of  these  various  fluids  is  far  from  being 
precisely  ascertained,  we  shall  confine  ourselves  to  the  most  general 
information  on  the  subject. 

SALIVA. 

§  1692.  Saliva,  the  liquid  which  moistens  the  mouth,  is  secreted 
by  peculiar  glands,  called  salnmry,  in  various  quantities,  according 
to  the  wants  of  the  animal ;  the  fluid  being  introduced  most  abun- 
dantly into  the  mouth  during  mastication,  while  its  chief  function ' 
appears  to  be  to  assist  deglutition.  The  saliva,  as  it  exudes  from 
the  mouth,  is  a  ropy  and  opaline  fluid,  which,  when  allowed  to  rest, 
separates  into  an  upper  clear  and  fluid  portion,  and  a  lower  more 
viscid  portion,  in  which  swim  filaments  of  mucus  and  remains  of 
organic  substances.  The  density  of  saliva  is  but  little  greater  than 
that  of  water,  since  it  rarely  exceeds  1.008,  and  its  reaction  is  gene- 
rally slightly  alkaline.  It  precipitates  several  metallic  solutions, 
and  deposits,  at  the  boiling  point,  some  coagulated  principles.  Ab- 
solute alcohol  precipitates  from  saliva  a  peculiar  matter,  called  pty- 
alm^  to  which  physiologists  attribute  a  special  function,  because  it 
converts  starch  into  dextrin  in  a  pretty  short  space  of  time,  and 
subsequently  into  glucose ;  but  this  property  is  known  to  belong  to 
all  albuminous  substances.  To  the  saliva  is  attributed  the  forma- 
tion of  the  deposits  which  adhere  to  the  teeth,  commonly  called 
dental  tartar,  but  which  consist  of  earthy  phosphates  and  carbon- 
ates, mixed  with  mucus  and  other  organic  substances  which  are  as 
yet  unknown. 

GASTRIC  JUICE. 
§1693.    The  gastric  juice  is  secreted  by  the  parietes  of  the 
stomach,  varying  in  quantity  with  that  of  the  food  to  be  digested ; 
and  its  duty  is  to  effect  the  solution  of  nitrogenous  organic  sub- 


BILE.  745 

stances,  for  it  appears  to  exert  no  action  on  fecula  or  fatty  matters, 
since  the  latter  leave  the  stomach  without  any  remarkable  change, 
and  meet  in  the  intestine  only  the  fluids  which,  by  affecting  their 
solution  or  disaggregation,  enable  them  to  be  absorbed. 

When  freed  by  filtration  from  certain  mucilaginous  substances 
and  organic  remains,  gastric  juice  is  a  colourless  and  limpid  fluid, 
having  a  saline  taste,  and  a  feeble  but  peculiar  odour,  which  varies 
in  different  animals ;  and  it  always  exerts  a  decided  acid  reaction 
on  litmus.  It  may  be  preserved  unchanged  for  an  indefinite  length 
of  time  in  the  air,  and  without  losing  the  property  of  effecting  the 
solution  of  nitrogenous  alimentary  substances.  The  essential  con- 
stituents of  gastric  juice  are  alkaline  salts,  certain  organic  sub- 
stances, and  a  free  acid ;  the  whole  being  dissolved  in  a  large  quan- 
tity of  water,  which  forms  98  or  99  per  cent,  of  the  juice.  The 
salts  of  gastric  juice  are  chiefly  alkaline  chlorides  and  sulphates,  in 
which  soda  predominates,  the  phosphates  being  found  only  in  a 
very  small  proportion.  In  addition,  small  quantities  of  sulphate, 
carbonate,  and  phosphate  of  lime  are  also  met  with.     • 

Gastric  juice  is  divided  into  two  organic  compounds :  a  mucilagi- 
nous substance,  the  nature  and  functions  of  which  are  not  deter- 
mined, and  a  special  nitrogenous  substance,  to  which  the  greatest 
share  in  the  phenomenon  of  digestion  is  attributed,  known  by  the 
names  of  chymosin,,  pepsin,  and  gasterase.  It  may  be  precipitated 
from  gastric  juice  by  alcohol  and  acetate  of  lead,  or  may  be  sepa- 
rated by  evaporation,  it  being  in  both  cases  obtained  in  an  amor- 
phous form,  from  which  it  is  impossible  to  decide  whether  it  is  a 
simple  and  definite  substance. 

The  acidity  of  gastric  juice  appears  to  be  always  due  to  the  pre- 
sence of  a  small  quantity  of  free  lactic  acid. 

When  meat,  cut  into  thin  slices,  is  dipped  into  gastric  juice,  it  is 
seen,  at  first,  to  swell  and  become  translucent,  after  which  it  gra- 
dually disaggregates,  and  finally  is  wholly  dissolved.  From  this 
powerful  action  we  might  be  led  to  suppose  that  gastric  juice  would 
act  on  the  coats  of  the  stomach ;  but  they  are  covered  by  a  mucus, 
which  is  constantly  renewed,  and  preserves  them  from  contact  with 
the  juice ;  while,  after  death,  this  mucus  becomes  putrid,  and  the 
gastric  juice  then  attacks  the  coats  of  the  stomach. 

BILE. 

§  1694.  Bile  is  a  liquid  secreted  by  the  liver,  and.  collected  in 
a  special  receptacle,  the  gall-bladder,  placed  immediately  below  the 
secreting  organ. 

Bile  is  a  ropy  fluid,  in  man  of  a  yellowish-green  colour,  of  a 
brownish-green  in  the  ox,  and  of  an  emerald-green  in  birds,  amphi- 
bious animals,  and  fishes.  It  has  a  peculiar  nauseous  smell  and  a 
bitter  taste.  When  poured  into  water,  it  first  falls  to  the  bottom 
of  the  fluid,  but  dissolves,  on  stirring,  almost  wholly,  forming  a 


746  ANIMAL    CHEMISTRY. 

frothy  liquor.  The  reaction  exerted  by  bile  on  organic  colouring 
matters  is  not  constant:  it  is  frequently  alkaline,  sometimes  neutral, 
and  sometimes  sensibly  acid.  Bile  soon  undergoes  a  change  in  the 
air,  and  putrefies,  emitting  a  very  disagreeable  odour ;  and  it  coa- 
gulates by  boiling.     Acids  effect  a  copious  precipitate  in  it. 

Although  bile  has  been  studied  by  a  great  number  of  chemists, 
they  are  not  yet  determined  as  to  its  nature,  owing  to  the  great 
mobility  of  its  constituent  principles  in  the  presence  of  chemical 
agents. 

Bile  may  be  considered  as  a  soap,  with  soda  for  its  base,  and 
formed  by  two  acids,  called  cholic  and  choleic,  and  containing,  in  addi- 
tion, small  quantities  of  a  cry  stallizable  fatty  substa,nce,  or  cholesterin, 
fatty  acids,  and  various  salts,  of  which  potassa,  soda,  ammonia,  and 
magnesia,  form  the  bases.  The  formula  of  cholic  acid,  which  con- 
stitutes the  greater  portion  of  bile,  is  C^gH^gNOjg ;  and  by  being  boiled 
with  caustic  potassa,  it  is  converted  into  glycocoll  C^H^NO^,  and  a 
new  acid,  called  cAoZaZic?,  C^HggOg, HO  : 

C«H„N0„=CAN0,+C«H3,0e,H0+H0. 

But  if  the  boiling  be  prolonged  for  some  time,  the  cholalic  acid  is 
itself  converted  into  a  substance  of  a  resinous  appearance,  dyslysin, 
to  which  the  formula  C48H3gOg,2HO  has  been  assigned.  The  fol- 
lowing equation  represents  the  final  reaction : 

C«H„NO,,=C,H,NO.+C«H3,0„2HO. 

Cholalic  acid  crystallizes  readily  in  alcohol  or  in  ether,  the  for- 
mula of  its  crystals  being  C^gHggOcHO+SHO.  They  are  scarcely 
soluble  in  cold  water,  while  they  dissolve  readily  in  solutions  of 
the  caustic  alkalies  and  alkaline  carbonates,  but  the  salts  thus  formed 
do  not  crystallize  by  evaporation.  If,  on  the  contrary,  an  alcoholic 
solution  of  cholalic  acid  be  neutralized  by  potassa,  and  ether  added 
to  it,  colourless  needles  of  cholalate  of  potassa  KO,C^H3gOg  are  de- 
posited. At  a  temperature  of  392°,  crystallized  cholalic  acid 
C48H3gOg,HO+5HO  is  converted  into  a  new  acid,  choloidic 
C^gHggOgjSHO ;  and  if  it  be  heated  to  570°,  it  is  changed  into  dysly- 
sin  C48H3gOg,2HO ;  water  only  being  parted  with  during  these  suc- 
cessive changes. 

The  second  acid  of  bile,  or  choleic  acid,  which  contains  a  large 
amount  of  sulphur,  has  hitherto  not  been  obtained  in  a  state  of 
purity.  Boiling  alkaline  solutions  convert  it  into  cholalic  acid  and 
a  neutral  sulphuretted  substance,  taurin  C^H^NSgOg,  remarkable 
for  its  beautiful  crystalline  forms.  Taurin  is  also  formed  by  boil- 
ing bile  with  chlorohydric  acid.  It  is  a  substance  very  soluble  in 
boiling  water,  but  nearly  insoluble  in  absolute  alcohol,  and  exerting 
no  action  on  coloured  reagents. 


PANCREATIC   JUICE.  747 

Biliary  Caleuli,  and  Cholesterin  C25H22O. 

§1695.  Concretions  of  diversified  forms  and  size,  called  biliary 
calculi,  are  frequently  developed  in  the  gall-bladder  and  biliary- 
ducts.  They  are  essentially  composed  of  a  fatty,  crystallizable 
substance,  cholesterin,  mixed  with  substances  of  a  resinous  appear- 
ance and  mucus.  When  the  powdered  calculi  are  treated  with 
boiling  alcohol,  and  the  liquid  is  bleached  by  animal  black,  beautiful 
crystalline,  brilliant,  and  colourless  lamellae  of  cholesterin  separate 
on  cooling.  It  is  a  neutral,  insipid,  and  inodorous  substance, 
slightly  soluble  in  cold,  and  very  soluble  in  boiling  alcohol.  It 
melts  at  278.6°,  being  decomposed  only  at  a  very  high  temperature, 
and  it  resists  the  action  of  alkaline  lixivise. 

Cholesterin  is  deposited  from  its  alcoholic  solutions  in  the  state 
of  hydrated  cholesterin,  which  loses  all  its  water  at  212°.  The 
composition  of  dried  cholesterin  corresponds  to  CggllggO,  but  its  true 
formula  cannot  be  exactly  determined,  for  no  definite  compound  of 
it  is  known.  Chlorine  forms  products  of  substitution  with  it,  its 
action  stopping  at  quadrichlorinated  cholesterin  CggHigCl^O. 

PANCREATIC  JUICE. 

§  1696.  The  functions  of  the  pancreatic  juice  appear  to  be  to 
effect  the  disaggregation  of  fatty  substances,  and  to  enable  them  to 
pass  into  the  circulation,  (§  1669.)  In  fact,  by  mixing,  at  the  tem- 
perature of  100°  or  104°,  (which  is  that  of  warm-blooded  animals,) 
pancreatic  juice  with  oil,  butter,  or  fat,  these  substances  are  rapidly 
converted  into  an  emulsion,  and  yield  a  whitish  and  creamy  fluids 
being,  moreover,  chemically  altered  and  separated  into  fatty  acids 
and  glycerin.  Of  all  the  various  fluids  in  the  animal  economy,  pan- 
creatic juice  is  the  only  one  which  exerts  this  remarkable  action  on 
fats. 

Pancreatic  juice  is  a  colourless,  adhesive  fluid,  which  becomes 
frothy  by  shaking,  and  constantly  displays  an  alkaline  reaction. 
Heat  coagulates  it  completely  into  a  single  mass,  in  which  respect 
it  closely  resembles  white  of  egg,  but  differs  from  it  in  many  special 
properties.  If  alcohol  be  poured  into  pancreatic  juice,  the  active 
coagulated  principle  is  precipitated,  but  is  wholly  redissolved  in  cold 
water,  even  after  desiccation,  while  the  white  of  egg,  when  coagulated 
by  alcohol,  is  insoluble  in  water.  In  addition  to  the  organic  sub- 
stances, pancreatic  juice  contains  alkaline  carbonates  and  chlorides, 
and  some  few  phosphates ;  the  predominating  base  being  soda. 

INTESTINAL  JUICE. 

§  1697.  The  name  of  intestinal  juice  is  given  to  a  fluid  secreted 
by  the  intestinal  canal,  and  to  which  the  liquefaction  of  amylaceous 
and  ligneous  substances  is  partly  attributed  \  but  the  juice  has  hitherto 
not  been  obtained  separately,  being  always  mixed  with  other  diges- 


748 


ANIMAL   CHEMISTRY. 


tive  juices.  The  mixture  e^^ibits  sometimes  an  alkaline,  sometimes 
an  acid  reaction,  according  to  the  nature  of  the  food;  but  nothing 
accurate  is  known  concerning  its  composition. 

CHYLE. 

§  1698.  Chyle  is  the  fluid  contained  in  the  chyliferous  vessels. 
When  taken  from  the  thoracic  duct,  which  is  the  common  trunk  of 
these  vessels,  it  is  generally  clouded  and  milky;  its  reaction  being 
always  alkaline.  Its  opacity  is  owing  to  the  fatty  matter  which 
exists  in  it  as  an  emulsion;  and  the  microscope  detects  in  it  two 
kinds  of  colourless  globules,  some  of  which  are  fatty,  while  others 
constitute  a  peculiar  substance,  called  chyle-globules,  the  shape  of 
which  is  irregular. 

When  exposed  to  the  air,  chyle  soon  coagulates  and  divides  into 
two  portions:  a  colourless,  or  slightly  reddish  coagulum,  and  a 
colourless  liquid,  termed  serum  of  the  chyle  ;  the  fatty  matter  origin- 
ally in  suspension  collecting  on  the  surface  of  the  serum.  The 
coagulation  of  chyle,  like  that  of  the  blood,  is  owing  to  the  separa- 
tion of  the  fibrin,  which  becomes  insoluble,  and  carries  with  it  other 
substances ;  while  the  serum  chiefly  contains  albumen,  which  coagu- 
lates when  the  fluid  is  boiled.  The  relative  proportions  of  the 
coagulum  and  serum  are  very  variable,  according  to  the  species  of 
animal,  and,  above  all,  accoJ-ding  to  the  food.  The  chyle  of  a  horse 
yields  from  1.1  to  5.6  per  cent,  of  fresh  and  from  0.2  to  1.7  of  dried 
coagulum;  while  that  of  the  dog  yields  from  1.3  to  5.7  of  the  same 
substance  when  moist,  and  from  0.2  to  0.6  when  dried. 

MILK. 

§  1699.  Milk  is  a  liquid  secreted  by  special  glands,  called  mam- 
mary, in  the  females  of  animals,  after  delivery.  It  is  white  and 
opake,  and  serves  as  a  type  of  all  fluids  of  analogous  appearance, 

which  are  then  said  to  be  milky. 
The  opacity  of  milk  is  owing  to  a 
multitude  of  small  fatty  globules,  of 
from  1  to  3  hundredths  of  a  milli- 
metre in  diameter,  which  are  sus- 
pended in  it  in  a  state  of  emulsion. 
These  globules  are  easily  seen  by 
examining  a  thin  film  of  milk  with 
a  microscope,  when  they  present 
the  appearance  represented  in  fig. 
689.  When  milk  is  allowed  to 
rest,  the  fatty  globules,  by  virtue 
of  their  low  specific  gravity,  rise 
to  the  surface,  and  form  a  coat  of 
Fig.  689.  cream. 

Ether  does  not  remove  the  fatty  gloubles  by  simply  being  shaken 


MILK.  74t) 

with  milk ;  while,  if  a  few  drops  of  acetic  acid  be  added  to  it,  and 
the  liquid  be  then  boiled,  the  globules  unite,  and  may  be  dissolved  by 
ether.  If  a  concentrated  solution  of  sulphate  of  soda  or  sea-salt 
be  stirred  in  milk,  and  the  whole  then  filtered,  the  globules  are 
arrested,  and  the  fluid  which  passes  through  is  nearly  transparent. 

Milk  contains,  in  addition  to  the  fatty  substance,  a  nitrogenous 
substance,  which  we  shall  describe  under  the  name  of  casein^  and  to 
which  it  owes  its  principal  nutrient  qualities,  a  peculiar  sugar,  sugar 
of  milk,  albuminous  substances,  and  mineral  salts,  all  of  which 
exist  in  it  in  different  proportions,  not  only  in  the  different  species 
of  animals,  but  even  in  the  same  individual.  They  depend  greatly 
on  the  food,  the  greatest  variations  being  found  in  the  fatty  matter, 
which  does  not  exist  in  the  same  quantity  at  the  beginning  and  end 
of  the  milking.  The  transparent  part  of  milk,  or  whei/,  is  much 
more  constant,  and  is  appreciably  the  same  in  the  different  periods 
of  the  same  milking.  The  fatty  globules,  collected  together,  form 
butter. 

Milk  is  habitually  alkaline,  but  it  soon  sours  in  the  air,  particu- 
larly in  warm  or  stormy  weather,  lactic  acid  being  developed,  which 
causes  the  coagulation  of  the  casein.  The  caseous  matter  separates 
in  clots,  carrying  with  it  the  fatty  globules ;  and  the  milk  is  then 
said  to  be  turned.  This  change  is  avoided,  without  injuring  the 
quality  of  the  milk,  by  the  addition  of  2  or  3  thousandths  of  bicar- 
bonate of  soda;  while  the  addition  of  a  few  drops  of  any  acid  will 
turn  it.  Fresh  milk  does  not  coagulate  by  boiling,  but  its  surface 
becomes  covered  with  white  pellicles  of  an  albuminous  substance, 
which  contains  the  fatty  globules;  and  when  the  milk  boils,  these 
pellicles  prevent  the  escape  of  the  steam,  causing  the  liquid  to  boil 
over  if  the  vessel  be  not  removed  from  the  fire. 

§  1700.  An  accurate  analysis  of  milk  is  a  delicate  operation, 
requiring  a  considerable  length  of  time.  The  milk  being  evaporated 
to  dryness  in  a  procelain  capsule  heated  in  a  water-bath,  the  residue 
is  dried  at  248°,  and  weighed;  the  weight  of  the  residue  reaching 
11  or  12  hundredths  in  cow's  milk  of  good  quality.  It  is  treated 
with  a  mixture  of  alcohol  and  ether,  which  dissolves  only  the  fatty 
matter;  after  which  the  latter,  being  separated,  is  evaporated  and 
weighed.  The  casein,  sugar  of  milk,  and  the  salts  remain  in  the 
residue  after  the  treatment  by  alcohol  and  ether,  and  are  weighed 
together  after  being  dried,  when  the  residue  is  incinerated,  and 
yields  the  mineral  salts,  by  subtracting  the  weight  of  which  from 
that  of  the  residue,  the  casein  and  sugar  of  milk  are  determined. 
The  sugar  is  more  accurately  determined  by  optical  experiments,  for 
it  possesses  considerable  rotatory  power  on  the  plane  of  polarization. 
For  this  purpose  the  rotatory  power  a  of  a  certain  weight  p  of  sugar 
of  milk,  dissolved  in  100  cubic  centimetres  of  water,  and  observed 
in  a  tube  0.3  m.  in  length,  being  first  ascertained,  a  certain  quantity 
of  fresh  milk  is  heated  to  105°  or  120°,  and  treated  with  a  few  cubic 


750  ANIMAL  CHEMISTRY. 

centimetres  of  acetic  acid,  which  coagulates  the  casein  and  fatty 
matter.  It  is  filtered,  and  some  cubic  centimetres  of  a  solution  of 
acetate  of  lead  is  added,  which  precipitates  the  albuminous  sub- 
stances, thus  furnishing  a  perfectly  limpid  liquid  after  filtering. 
The  rotatory  power  a'  of  this  liquid  in  the  tube  of  0.3  m.  in  length 
being  ascertained,  the  proportion  x  of  sugar  contained  in  it  is  then 
given  by  the  proportion 

a:a'  '.'.pix) 

in  which  x  does  not  represent  exactly  the  proportion  of  sugar  exist- 
ing in  100  cubic  centimetres  of  milk,  because,  before  subjecting  the 
liquor  to  optical  examination,  several  liquids  were  added  to  the  milk, 
while,  if  the  quantity  of  the  liquids  added  be  exactly  known,  a  cor- 
rection can  be  made  which  furnishes  the  exact  proportion  of  sugar 
in  the  milk  subjected  to  analysis. 

The  casein  is  ascertained  differentially. 

§  1701.  The  richness  of  various  kinds  of  milk  in  fatty  matters 
may  be  ascertained  by  a  very  simple  experiment  with  a  small  in- 
strument called  a  lactosoope;  the  experiment  being  founded  on  the 
fact  that  the  degree  of  opacity  of  various  kinds  of  milk,  reduced  to 
the  same  density,  is  very  nearly  in  proportion  to  the  quantity  of 
fatty  matter  they  contain  in  suspension.  The  lactoscope  is  a  species 
of  small  opera-glass,  formed  by  two  plane  glasses,  which  may  be 
gradually  brought  into  contact  and  separated  by  means  of  a  very 
fine  screw,  the  separation  of  the  glasses  being  shown  by  a  circular 
graduation  marked  on  their  rims.  A  small  funnel  at  the  upper  part 
serves  for  the  introduction  of  the  milk  between  the  glasses,  while  on 
the  other  side  is  the  handle  of  the  apparatus.  When  the  glasses 
are  in  contact  and  the  division  marks  0,  the  milk  is  poured  into 
the  funnel,  the  glasses  being  separated  by  turning  the  movable 
mounting,  while  the  milk  falls  between  the  glasses.  The  experi- 
menter then  stands  before  a  candle  at  the  distance  of  about  1  metre, 
and  having  brought  the  glasses  together  until  the  flame  becomes 
distinctly  visible,  he  gradually  separates  them  until  the  exact  moment 
at  which  the  flame  ceases  to  be  visible.  The  relative  richness  in 
fatty  matters  of  various  samples  of  milk  is  given  with  sufficient 
accuracy  by  the  degrees  of  separation  of  the  glasses  at  the  moment 
of  the  disappearance  of  the  flame. 

The  mineral  salts  contained  in  1000  parts  of  cow's  milk  have 
been  found  to  consist  of 

Phosphate  of  lime  1.805 

"  magnesia 0.170 

"  iron 0.032 

"  soda 0.225 

Chloride  of  sodium 1.350 

Carbonate  of  soda 0.115 

3.697 


LACTIN.  751 

The  analyses  made  of  various  kinds  of  milk  have  furnished,  as  an 
average,  the  following  compositions : 

Cow.  Ass.  Goat.  Mare.         Bitch.        Human. 

Water 87.4  90.5  82.0  89.6  66.3  88.6 

Butter 4.0  1.4  4.5  trace  14.8  2.6 

Sugar   of    milk    and 

soluble  salts 5.0  6.4  4.5  8.7  2.9  4.9 

Casein,  albumen,  and 

insoluble  salts 3.6  1.7  9.0  1.7  16.0  3.9 

100.0   100.0   100.0   100.0   100.0   100.0 

§  1702.  The  first  milk  furnished  by  the  mammae  after  delivery  is 
called  colostrum^  and  differs  greatly  in  appearance  from  the  milk 
which  flows  some  days  subsequently,  being  less  fluid,  exhibiting  the 
consistence  of  serum,  and  showing  a  yellowish  colour,  while  the 
microscope  detects  in  it  globules  of  fat,  mucus,  and  irregularly 
shaped  granules.  To  the  colostrum  are  attributed  purgative  pro- 
perties, which  free  the  child  from  the  meconium  collected  in  its  in- 
testines. 

Sugar  of  Milk  (j^^zfiu' 

§  1703.  Sugar  of  milk,  or  lactm,  is  extracted  by  pouring  into 
milk  an  acid  which  causes  the  coagulation  of  the  casein,  and  then 
filtering  and  evaporating  the  liquid  to  the  proper  degree  of  concen- 
tration, when  the  latter  gradually  deposits  sugar  of  milk,  which 
forms  semi-transparent  and  very  hard  crusts  on  the  sides  of  the 
vessel.  Sugar  of  milk  is  chiefly  prepared  in  Switzerland,  where 
the  fluids  which  remain  after  the  separation  of  the  butter  and 
casein  are  likewise  used  in  making  Gruyere  cheese. 

The  taste  of  sugar  of  milk  is  sweet  and  agreeable,  and  milk  owes 
its  sweetness  to  it.  It  rotates  toward  the  right.  Heated  to  248°, 
it  loses  2  equiv.  of  water  without  melting,  while  at  300°  it  loses 
3  equiv.,  and  its  composition  is  then  represented  by  the  formula 
Cj^HigOig,  which  is  also  the  case  when  it  is  combined  with  oxide  of 
lead.  Sugar  of  milk  dissolves  in  6  parts  of  cold,  and  2  parts  of 
boiling  water,  but  is  insoluble  in  alcohol  and  ether.  Dilute  acids 
convert  it  into  glucose ;  while  nitric  acid,  when  heated  with  it,  yields 
oxalic  and  mucic  acids,  the  production  of  which  latter  distinguishes 
sugar  of  milk  from  the  other  sugars  we  have  described.  Sugar  of 
milk  undergoes  alcoholic,  lactic,  or  butyric  fermentation,  according 
to  the  nature  of  the  ferment  and  the  circumstances  in  which  it  is 
placed ;  the  casein  and  albuminous  substances  producing  these 
various  fermentations.  If  fresh  milk  be  maintained  at  a  tempera- 
ture of  104°,  sugar  of  milk  undergoes  alcoholic  fermentation,  while 
if  the  milk  be  previously  exposed  to  the  air  for  some  time,  the  casein 
is  changed  and  produces   lactic  fermentation.     It  should  be  re- 


752  ANIMAL   CHEMISTRY. 

marked  that  the  elementary  composition  of  lactic  acid  CgHgO^jHO 
is  the  same  as  that  of  sugar  of  milk ;  and  it  may  therefore  be  sup- 
posed, that  in  lactic  fermentation  the  latter  merely  experiences  an 
isomeric  modification. 

Casein^  or  Caseum. 

§  1704.  In  order  to  separate  casein  from  milk,  a  certain  quantity 
of  sulphuric  acid  is  added,  which  forms  an  insoluble  compound  with 
casein,  precipitated  in  clots,  and  carrying  with  it  the  greater  portion 
of  the  butyrous  matter.  The  precipitate  is  collected  on  a  filter  and 
washed  with  distilled  water,  and  then  treated  with  a  solution  of  car- 
bonate of  soda,  which  dissolves  the  caseous  matter,  forming  a  syrupy 
and  cloudy  liquor.  If  this  be  kept  for  some  time  at  a  temperature 
of  68°  or  77°,  the  fatty  substance  forms  a  coat  on  the  surface.  The 
inferior  aqueous  liquid  being  drawn  off  by  a  siphon,  and  sulphuric 
acid  added  which  again  precipitates  the  casein,  the  latter  is  boiled 
with  water  to  remove  the  sulphuric  acid,  when  a  portion  of  the  casein 
is  dissolved,  which  must  be  precipitated  anew  by  carefully  saturating 
the  acid  liquid  with  carbonate  of  soda.  The  casein  is  collected  on  a 
filter,  washed  with  distilled  water,  and  then,  after  being  dried,  with 
alcohol  and  ether,  which  dissolve  the  balance  of  the  fatty  substances. 
The  casein  is  then  considered  as  pure,  although  it  possesses  no  cha- 
racter by  which  it  may  be  ascertained  to  be  a  simple  substance. 

Casein  is  a  white  substance,  resembling  in  appearance  coagulated 
but  pulverulent  albumen.  It  is.  inodorous,  tasteless,  insoluble  in 
water,  alcohol,  and  ether,  and  always  reddens  litmus,  although  it  is 
difficult  to  decide  if  this  reaction  be  peculiar  to  it.  It  dissolves  in 
alkaline  liquids,  from  which  acids  precipitate  it ;  and  nearly  all  the 
acids  precipitate  it  from  milk,  while  the  precipitate,  which  is  a  com- 
pound of  casein  wdth  the  acid,  is  redissolved  in  an  excess  of  the 
latter  acid.  The  sulphuric  and  chlorohydric  compounds  are  less 
soluble,  and  when  they  are  decomposed  by  the  alkaline  carbonates, 
or  by  that  of  lime  or  baryta,  the  casein  dissolves  and  combines  with 
s,  portion  of  the  base. 

Manufacture  of  Butter, 

§1705.  Butter  which  is  merely  the  aggregation  of  the  fatty 
globules  of  milk,  is  obtained  from  the  cream  which  forms  on  the 
surface  of  this  fluid  when  it  is  allowed  to  rest.  The  cream  is 
poured  into  machines  called  churns,  the  forms  of  which  vary  in 
different  countries ;  one  of  the  best  being  a  small  barrel,  having 
internally  a  dasher  revolving  on  an  axis.  The  dasher  is  rapidly 
turned,  when  the  small  fatty  globules  of  the  milk  adhere  to  each 
other,  and  form,  after  some  time,  grains  of  butter,  which  separate 
from  the  watery  fluid,  or  buttermilk,  containing  the  casein,  sugar  of 
milk,  and  other  soluble  principles.     The  churn  is  then  stopped,  the 


CASEIN.  753 

lid  removed,  and  replaced  by  a  covering  of  thin  muslin  stretched 
over  wire-gauze.  After  churning  slowly  for  a  short  time,  nearly 
all  the  buttermilk  flows  out,  and  fresh  water  being  substituted  for 
it,  the  chum  is  again  set  in  motion;  which  washings  are  repeated 
until  the  w^ater  comes  out  perfectly  clear,  when  the  butter  is  removed 
from  the  churn.  Pure  butter  may  be  considered  as  a  mixture  of 
margarin,  olein,  and  small  quantities  of  butyrin,  caprin,  and 
caproin. 

The  excellence  of  butter  depends  not  only  on  the  quality  of  the 
milk,  but  also  on  its  manufacture,  since  it  is  essential  to  use  fresh 
cream,  which  can  only  be  done  on  large  farms,  for  in  small  ones  it 
is  necessary  to  save  the  cream  of  several  days  to  have  enough  for  a 
churning.  Butter  will  keep  longer  when  well  freed  from  butter- 
milk, since  the  caseous  and  albuminous  principles  of  the  lattef 
change  first,  and  produce  acid  fermentations,  which  separate  the 
butyric  acid  and  other  volatile  acids,  imparting  to  the  butter  a  disa- 
greeable, rancid  taste.  The  decomposition  of  these  substances  is 
prevented  by  the  addition  of  chloride  of  sodium,  or  by  salting  the 
butter. 

Manufacture  of  Oheese, 

§  1706.  Cheese  is  a  mixture,  in  different  proportions,  of  coagu- 
lated caseous  matter  and  butter,  and  is  generally  prepared  from 
skimmed  milk,  which  has  consequently  lost  the  greater  part  of  its 
fatty  substances.  When  sufficiently  compressed  it  is  hard,  trans- 
lucent, yellowish,  and  possessing  a  greasy  lustre,  due  to  the  butter  it 
contains,  and  which  may  be  easily  separated  from  it  by  ether.  The 
caseous  matter  separates  in  the  form  of  cheese,  when  milk  is  left 
for  some  time,  and  at  a  slightly  elevated  temperature,  in  contact 
with  the  mucous  membrane  of  the  stomach  of  young  calves,  called 
rennet.  The  active  principle  of  the  rennet  is  called  chymosin^  but 
it  has  not  yet  been  isolated  with  certainty,  and  nothing  accurate  is 
known  concerning  its  manner  of  action.  By  maintaining  the  tem- 
perature at  77°  or  86°,  the  caseous  matter  sets  into  mass,  which  is 
constantly  agitated  for  some  time  until  it  becomes  sufficiently  solid ; 
after  which  it  is  placed  on  a  cloth,  in  a  mould,  and  allowed  to  drain. 
If  a  hard  cheese,  and  one  that  will  keep  for  a  long  time  is  desired, 
the  substance  is  pressed  in  the  mould,  so  as  to  drive  out  the  greater 
portion  of  the  liquid.  The  cheeses  are  then  laid  on  boards  in  a 
room,  and  left  there  for  some  time,  their  surface  being  frequently 
sprinkled  with  common  salt. 

The  various  kinds  of  cheese  depend  on  the  nature  of  the  milk 
used  in  their  manufacture,  the  proportion  of  cream  left  in  it,  and 
lastly,  on  the  method  employed  for  its  manufacture. 
Vol.  II.— 48 


754  ANIMAL   CHEMISTRY. 

EXCRETIONS  OF  THE  ANIMAL  ECONOMY. 

§  1T07.  A  great  number  of  products,  whicli  have  escaped  assimi- 
lation, are  rejected  from  the  body  of  the  animal.  The  water  which 
existed  in  the  food  or  drink,  or  that  which  was  formed  by  the  che- 
mical reactions  which  take  place  in  the  animal  economy,  are  ex- 
pelled, either  in  the  urine,  or  in  the  excrement  or  fceces  of  the 
intestinal  canal,  or  by  perspiration,  or  lastly,  in  the  state  of  vapour, 
with  the  heated  gases  which  escape  from  the  air-passages  in  the  act 
of  respiration.  The  urine  contains  solid  substances  in  solution, 
which  arise  from  the  various  chemical  reactions  effected  by  vital 
action ;  while  the  excrements  of  the  intestinal  canal  are  composed 
of  insoluble  substances  and  substances  in  solution  in  water.  Lastly, 
gases,  called  intestinal^  frequently  escape  from  the  intestinal  canal, 
which  are  formed  in  the  chemical  reactions  ensuing  in  the  stomach 
and  intestines. 

We  shall  successively  describe,  '  ' 

1st.  The  urine  of  animals. 

2d.  The  excrements,  or  faeces. 

3d.  The  intestinal  gases. 

4th.  The  sweat. 

5th.  The  gaseous  products  formed  by  the  act  of  respiration. 
The  latter  products  having  already  been  described,  the  first  four 
only  will  occupy  our  attention. 

URINE. 

§1708.  The  urine  is  formed  from  the  blood,  by  an  analysis  of 
this  fluid  in  the  kidneys ;  and  its  composition  varies  in  different 
animals,  the  difference"  depending  chiefly  on  the  food.  In  the  car- 
nivorous mammiferae,  the  urine  contains,  in  addition  to  mineral 
salts,  albuminous  and  mucilaginous  matter,  and  two  substances  of 
which  v/e  have  not  yet  spoken,  urea  and  uric  acid.  Urea  often 
constitutes,  of  itself  alone,  more  than  one-half  of  the  solid  sub- 
stances. The  urine  of  herbivorous  animals  contains  much  less  urea, 
while  its  place  is  occupied  by  a  considerable  quantity  of  a  peculiar 
acid,  called  hippuric.  The  urine  of  all  the  mammiferae  in  a  state 
of  inanition  is  similar,  and  resembles  that  of  animals  fed  on  meat, 
which  might  be  expected,  since  the  life  of  an  animal  in  a  state  of 
inanition  is  supported  at  the  expense  of  its  own  substance.  Birds 
and  fishes  have  no  particular  apparatus  for  the  escape  of  the  urine, 
which  is  voided  with  their  excrement.  The  urine  of  the  batrachians, 
of  frogs  for  example,  is  very  liquid,  and  contains  only  a  trace  of  urea, 
while  that  of  reptiles  is  nearly  solid,  and  is  chiefly  composed  of  uric 
acid. 

The  quantity  of  urine  voided  by  the  same  mammiferous  animal 
varies  with  its  food,  and  even  changes  with  the  same  food,  accord- 
ing to  the  surrounding  temperature,  a  condition  of  repose  or  mo- 


UREA.  755 

tion,  and  the  pathological  state  of  the  subject.  The  volume  of  urine 
evacuated  is  in  inverse  proportion  to  the  perspiration:  thus,  all 
other  things  being  equal,  the  urine  is  more  copious  in  winter  than 
in  summer,  and  in  cold  more  so  than  in  hot  climates.  The  chemi- 
cal composition  of  urine  is  not  less  variable  in  the  same  individual, 
that  formed  during  digestion  being  always  more  rich  in  urea.  On 
an  average,  an  adult  man  forms,  in  24  hours,  30  to  40  gm.  of  urea, 
which  are  evacuated  with  the  urine. 

We  shall  describe,  with  some  minuteness,  the  principal  organic 
substances  found  in  the  urine  of  animals,  these  substances  being 
interesting,  not  only  to  the  physiologist,  but  also  to  the  chemist, 
since  they  assist  in  the  production  of  many  curious  metamorphoses. 

Urea  Q.^^fi^, 

§  1709.  Urea  is  obtained  by  evaporating  fresh  urine  until  it  is 
reduced  to  ^^  of  its  volume,  allowing  it  to  cool,  and  gradually  adding 
nitric  entirely  free  from  nitrous  acid,  until  no  more  precipitate  is  ef- 
ected;'when  the  urea  thus  forms  a  compound  with  the  acid,  nitrate 
of  urea,  which  is  very  slightly  soluble  when  cold,  and  is  deposited  in 
small  coloured  crystals.  They  are  collected  on  a  filter,  washed  with 
a  small  quantity  of  cold  water,  and,  after  being  expressed  between 
blotting-paper,  are  redissolved  in  boiling  water,  and  the  liquid 
boiled,  for  a  few  moments,  with  animal  charcoal,  deprived  of  its 
calcareous  salts  by  chlorohydric  acid ;  when  the  salt  is  again  al- 
lowed to  crystallize,  by  cooling.  The  nitrate  of  urea  is  obtained 
perfectly  pure  after  several  crystallizations,  and  is  then  decomposed 
by  carbonate  of  baryta,  which  sets  the  urea  free,  and  with  the  nitrate 
of  baryta  first  formed  remains  in  the  liquid.  The  latter  is  evapo- 
rated to  dryness,  and  the  residue  treated  with  boiling  alcohol,  which 
dissolves  the  urea  alone,  depositing  it  again  on  cooling,  or  by  eva- 
poration, in  long  prismatic  crystals. 

Urea  may  also  be  artificially  produced  by  combining  cyanic  acid 
CgNOjHO  with  ammonia  NH3;  the  composition  of  cyanate  of  am- 
monia (NH3,HO),C2NO  being  identical  with  that  of  urea  CgH^NgOg, 
and  being,  when  left  in  water,  immediately  converted  into  its  iso- 
meric substance,  urea.  The  following  process,  founded  on  the  above, 
furnishes  the  means  of  obtaining  large  quantities  of  very  pure  urea  : 
Cyanate  of  potassa  is  first  formed,  by  heating  to  a  nascent  red-heat, 
in  a  retort,  a  mixture  of  28  parts  of  dried  prussiate  of  potash  and 
14  of  binoxide  of  manganese,  (§  1504 ;)  after  which  it  is  dissolved  in 
water,  treated  with  sulphate  of  ammonia,  evaporated  to  dryness, 
and  again  treated  with  alcohol,  which  dissolves  the  cyanate  of  am- 
monia converted  into  urea,  and  leaves  sulphate  of  potassa.  The 
alcoholic  liquor,  when  evaporated,  yields  beautiful  crystals  of  urea. 

Urea  is  a  colourless,  inodorous  substance,  of  a  fresh  taste,  very 
soluble  in  water,  less  so  in  alcohol,  and  almost  insoluble  in  ether. 
Its  solutions  do  not  act  upon  litmus,  although  it  combines  with  a 


T56  ANIMAL   CHEMISTRY. 

great  number  of  acids,  and  forms  crystallizable  salts  whicli  exhibit 
the  same  rules  of  composition  as  the  organic  alkalies.  There  is, 
however,  this  difference  between  urea  and  the  alkaloids,  that  it  does 
not  combine  indiscriminately  with  all  the  acids :  thus,  it  forms  no 
compound  with  lactic  acid,  the  acid  properties  of  which  are,  never- 
theless, well  marked.  It  melts  at  248°  without  change,  being  at  a 
higher  temperature  decomposed  into  ammonia,  which  is  disengaged, 
and  into  cjanuric  acid,  which  remains  in  the  retort;  and  if  it  be 
further  heated,  the  cyanuric  acid  is  converted  into  its  isomeric  mo- 
dification, cyanic  acid,  which  passes  over  in  distillation.  The  urea 
is  in  this  way  separated  into  ammonia  NH3,  and  into  cyanic  acid 
C2N0,H0;  and  if  these  products  are  united  in  water,  they  again 
form  urea.  A  certain  quantity  of  urea  is  always  formed  in  the 
neck  of  the  retort,  because  the  cyanic  acid,  at  the  moment  of  distil- 
lation, meets  with  the  ammonia  evolved  during  the  first  period  of 
its  decomposition. 

Urea  combines  with  several  metallic  oxides,  particularly  with  the 
oxide  of  lead,  which  it  dissolves ;  and  it  also  forms  definite  and  crystal- 
lizable compounds  with  chloride  of  sodium,  chlorohydrate  of  ammo- 
nia, corrosive  sublimate,  nitrate  of  silver,  and  other  substances. 
Hyponitric  acid  soon  destroys  urea,  by  decomposing  it  into  carbonic 
acid  and  nitrogen,  and  moist  chlorine  produces  the  same  effect. 

Nitrate  of  mercury  dissolved  in  nitric  acid  likewise  decomposes 
urea,  at  the  boiling  point,  into  carbonic  acid  and  nitrogen ;  and  as 
the  other  components  of  urine  do  not  disengage  carbonic  acid  under 
the  same  circumstances,  this  reaction  may  be  used  for  ascertaining 
very  exactly  the  quantity  of  urea  in  a  sample  of  urine,  by  collecting 
the  carbonic  acid  in  a  weighed  bulb-apparatus  containing  a  concen- 
trated solution  of  caustic  potassa;  the  increase  of  weight  of  the 
apparatus,  multiplied  by  the  number  1.371,  giving  the  weight  of  the 
urea. 

A  solution  of  urea,  heated  to  284°  in  a  glass  tube  hermetically 
closed,  is  converted  into  carbonate  of  ammonia,  by  taking  up  the 
elements  of  4  equiv.  of  water : 

CANA+4HO=2[(NH3,HO),COJ. 

A  prolonged  ebullition  with  the  caustic  alkalies  or  mineral  acids 
effects  the  same  decomposition,  which  also  ensues  in  urea  dissolved 
in  urine,  when  the  latter  is  left  to  rest  for  several  days ;  the  albu- 
minous substances  contained  in  it  exerting  a  special  kind  of  fer- 
mentation on  the  urea.  In  consequence  of  this  decomposition,  pu- 
trefied urine  is  highly  ammoniacal. 

Nitrate  of  urea  is  formed  by  the  direct  combination  of  urea  with 
nitric  acid,  and  we  have  mentioned  that  it  is  precipitated  in  the  form 
of  small  crystals  when  nitric  acid  is  poured  into  a  concentrated 
solution  of  urea.    If  heat  be  applied,  the  nitrate  of  urea  crystallizes 


URIC  ACID.  757 

on  cooling  in  beautiful  crystals,  of  the  formula  (C2H4N202,HO),N05, 
and  which  dissolve  in  10  times  their  weight  of  cold  water. 

Oxalate  of  urea  is  still  less  soluble  in  cold  water  than  the  nitrate, 
and  its  formula  is  (C2H4N202,H*0),C203. 

Urea  absorbs  immediately  chlorohydric  acid  gas,  and  is  converted 
into  the  chlorohydrate  C2H^N202,HC1,  which  is  very  soluble  in  water. 

Jlrio  Add  G^^^fi^, 

§  1710.  Healthy  human  urine  generally  contains  1  part  of  uric 
acid  for  every  30  parts  of  urea;  which  quantity  may  vary  according 
to  the  food.  Uric  acid  being  very  slightly  soluble  in  water,  is  often  de- 
posited during  the  cooling  of  urine,  in  the  form  of  small  granular  crys- 
tals, generally  of  a  red  colour.  The  excrement  of  birds  and  serpents 
contains  very  considerable  quantities  of  it;  on^  guano, "^  which  has 
been  used  during  the  last  few  years  as  a  manure,  and  is  merely  the 
excrement  of  sea-birds,  contains  a  large  proportion  of  uric  acid. 

In  the  laboratory,  uric  acid  is  generally  obtained  from  the  excre- 
ment of  the  boa  serpent.  The  powdered  excrement  being  heated 
with  a  solution  of  potassa,  which  dissolves  the  uric  acid  and  some 
other  substances,  the  liquid  is  filtered  and  an  excess  of  chlorohydric 
acid  added,  when  the  uric  acid  is  almost  wholly  precipitated,  since 
it  requires  about  1000  parts  of  water  for  solution.  The  acid  is 
purified  by  dissolving  it  several  times  in  alkalies*  and  precipitating 
it  by  chlorohydric  acid. 

Pure  uric  acid  forms  small  crystalline  lamellae,  white,  soft  to  the 
touch,  inodorous,  and  tasteless :  it  feebly  reddens  litmus,  and  com- 
bines with  all  bases,  the  alkaline  urates  alone  being  soluble.  The 
acid  is  insoluble  in  alcohol  and  ether. 

§  1711.  Oxidizing  reagents  decompose  uric  acid  in  a  very  remark- 
able manner,  producing  many  new  substances,  of  which  we  can  here 
only  give  a  superficial  description. 

By  heating  water  containing  uric  acid  in  suspension  with  bin- 
oxide  of  lead,  the  uric  acid  dissolves  with  a  copious  evolution  of  car- 

*  Bunzen  gives  the  following  as  the  average  composition  of  the  finer  qualities 
of  guano : 

Urate  of  ammonia 9.0 

Oxalate  of  ammonia 10.6 

Oxalate  of  lime 7.0 

Phosphate  of  ammonia 6.0 

Double  phosphate  of  magnesia  and  ammonia 2.6 

Sulphate  of  potassa 6.5 

Sulphate  of  soda 3.8 

Chlorohydrate  of  ammonia 4.2 

Phosphate  of  lime 14.3 

,Clay  and  sand 1.7 

Water  and  undeterminable  organic  substances 35.3 

100.0 

The  result  is  calculated  from  numerous  analyses  of  diflferent  kinds  of  guano, 
made  by  various  chemists. —  W.  L.  F. 


Y58  ANIMAL    CHEMISTRY. 

bonic  acid,  and  the  liquid  deposits,  on  cooling,  a  neutral  substance 
C4H3N2O3,  which  has  already  been  found  in  the  liquor  amnii  of  the 
cow,  and  named  allantoin.  It  crystallizes  in  white  prisms,  much 
more  soluble  in  boiling  than  in  cold  water,  and,  when  heated  with 
nitric  acid,  it  yields  a  considerable  quantity  of  nitrate  of  urea;  while 
it  forms  chlorohydrate  of  urea  with  chlorohydric  acid ;  a  peculiar 
acid  C10H7N4O9,  called  allanturic^  heing  formed  simultaneously  in 
both  cases,  which  is  also  produced  when  uric  acid  or  allantoin  is 
boiled  with  water  and  binoxide  of  lead. 

If  uric  acid  be  heated  with  4  times  its  weight  of  nitric  acid  of 
the  density  1.4,  the  former  dissolves  with  effervescence,  and  the 
liquid  deposits,  on  cooling,  a  crystallized  substance, aZZoa:a.w  CgH^NgOjo, 
which  reddens  litmus.  This  substance,  treated  when  cold  by  alkalies, 
is  converted  into  an  acid  C4HNO4,  called  alloxanie,  which  crystal- 
lizes in  aciculae,  and  forms  perfectly  well-defined  salts.  The  allox- 
anate  of  baryta,  which  may  be  directly  prepared  by  heating  to  140° 
a  mixture  of  alloxan  and  an  excess  of  baryta,  is  decomposed  at  the 
boiling  point  into  carbonate  of  baryta  and  a  new  salt  of  baryta, 
mesoxalate  of  baryta  2BaO,C304,  from  which  the  mesoxalic  acid 
may  be  separated  by  sulphuric  acid.  The  formula  of  crystallized 
mesoxalic  acid  is  C304,2HO ;  its  2  equivalents  of  water  being  basic, 
and  the  anhydrous  acid,  as  it  exists  in  the  salts,  containing  only 
carbon  and  oxygen. 

Alloxanic  acid  alone,  when  boiled  for  some  time  with  water,  gives 
off  carbonic  acid,  and  is  separated  into  two  substances :  leueoturie  acid 
CgHgNgOg,  which  is  almost  wholly  precipitated  in  small  granular 
crystals  during  the  cooling  of  the  liquid ;  and  diffluan  CgH^NgOg,  a 
neutral  substance,  highly  solujble  in  water,  but  insoluble  in  absolute 
alcohol,  and  yielding  alloxan  when  treated  with  nitric  acid. 

Lastly,  when  a  solution  of  alloxan  is  boiled  with  an  excess  of 
ammonia,  a  yellow  nitrogenous  acid  is  formed,' called  mycomelinie 
acid  CigHioNgOio,  almost  insoluble  in  cold  and  very  slightly  soluble 
in  boiling  water.     It  forms  yellow  salts  with  bases. 

We  have  shown  that  by  heating  uric  acid  with  4  times  its  weight 
of  nitric  acid,  alloxan  CgH^NaOjo  is  obtained ;  and  if  the  quantity  of 
nitric  acid  be  doubled,  and  the  action  prolonged,  or  if  the  alloxan 
be  heated  with  this  acid,  a  new  substance,  par«6an2c  acid  Q^fi^fi^l^iO 
is  formed,  which  remains  in  solution,  but  is  deposited  by  evaporation 
in  colourless  crystalline  lamellae.  Parabanic  acid  heated  with  an 
excess  of  ammonia  is  converted  into  oxaluric  acid  CgN2H307,HO 
which  is  itself,  by  continued  boiling  with  water,  separated  into  oxalic 
acid  and  oxalate  of  urea. 

By  causing  sulphurous  acid  and  ammonia  to  act  successively  on 
alloxan,  a  new  acid  of  a  very  complicated  composition  is  produced, 
called  thionuric  acid  CgHgNgOj^Sa.  For  this  purpose,  cold  sulphurous 
acid  is  added  to  a  concentrated  aqueous  solution  of  alloxan,  until 
the  latter  smells  of  the  acid ;  after  which  it  is  saturated  with  carbonate 


URIC  ACID.  759 

of  ammonia,  caustic  ammonia  i^  added,  and  the  whole  boiled,  when 
the  thionurate  of  ammonia  crystallizes  on  cooling.  By  pouring 
acetate  of  lead  into  a  solution  of  this  salt,  thionurate  of  lead  is  pre- 
cipitated, which,  when  decomposed  by  sulf  hydric  acid,  yields  free 
thionuric  acid,  crystallizing  in  small  aciculae  which  redden  litmus. 

If  chlorohydric  acid  be  added  to  a  boiling  solution  of  thionurate 
of  ammonia,  very  fine  silky  needles  of  a  new  substance,  uramil 
CgHgNgOg,  are  deposited,  which,  though  very  slightly  soluble  in  hot 
water,  and  almost  insoluble  in  cold  water,  dissolve  readily  in  am- 
monia. The  ammoniacal  solution  turns  of  a  reddish-purple  colour 
in  the  air,  and  then  deposits  green  crystalline  aciculae  of  a  metallic 
lustre.     Nitric  acid  converts  it  into  alloxan. 

By  adding  sulphuric  acid  to  a  solution  of  thionurate  of  ammonia, 
we  do  not  obtain  uramil,  but  uramilic  acid  ^iJ^i^fii^^  which  is 
deposited  by  evaporation  in  a  water-bath  in  the  form  of  prismatic 
crystals  or  silky  aciculae,  much  more  soluble  in  hot  than  in  cold 
water.     Uramilic  acid  forms  crystallizable  salts  with  bases. 

By  treating  uric  acid  with  an  aqueous  solution  of  chlorine,  or 
boiling  it  with  32  parts  of  water,  and  adding  nitric  acid  by  drops 
until  the  uric  acid  is  dissolved,  it  is  converted  into  a  neutral  sub- 
stance, alloxantin  CgH^NgOio,  which  is  deposited  by  evaporation  of 
the  liquid  in  colourless  or  slightly  yellowish  crystals,  turning  red  by 
contact  with  the  air  and  in  the  presence  of  ammonia,  and  assuming 
a  metallic  lustre.  Oxidizing  reagents  convert  alloxantin  into 
alloxan,  and  the  former  is  also  obtained  by  treating  alloxan  with 
reducing  substances,  particularly  with  sulf  hydric  acid,  protochloride 
of  tin,  or  by  zinc  in  the  presence  of  chlorohydric  acid. 

When  alloxan  is  converted  into  alloxantin  by  sulf  hydric  acid,  the 
liquid,  by  being  boiled,  still  maintaining  the  current  of  sulf  hydric 
gas,  furnishes  a  new  acid,  dialuric  acid  G^YL^fi^,  which  is  deposited 
in  crystals  on  cooling,  and  possesses  active  acid  properties. 

The  majority  of  the  products  derived  from  uric  acid  produce,  in 
the  presence  of  ammonia,  a  neutral  substance,  murexid  Q^^^fi^^ 
remarkable  for  its  beautiful  rose  colour.  In  order  to  prepare  it 
readily,  1  part  of  alloxan  and  27  parts  of  alloxantin  are  dissolved  in 
boiling  water,  and  when  the  liquid  has  cooled  to  158°,  carbonate  of 
ammonia  is  added,  but  not  in  excess.  The  liquid  then  deposits 
crystals  of  murexid,  which  is  but  slightly  soluble  in  water,  while  it 
turns  it  of  an  intense  purple  colour.  Its  crystals  are  red  and  dis- 
play the  greenish  reflection  of  the  wings  of  the  Spanish  fly;  it  is 
insoluble  in  alcohol  and  ether. 

Murexid  is  decomposed  by  the  alkalies  and  acids  into  several 
products,  among  which  may  be  distinguished  alloxan,  alloxantin,  and 
a  new  crystalline  substance,  murexan  CeH^NgOg,  crystallizing  in 
small  silky,  colourless  spangles,  and  nearly  insoluble  in  water.  When 
exposed  to  the  air  and  ammoniacal  vapours,  it  assumes  a  beautiful 
red  colour,  and  is  converted  into  murexid ;  exhibiting  a  phenomenon 


T60  ANIMAL   CHEMISTRY. 

analogous  to  that  of  colourless  orcin,  which  under  the  same  circum- 
stances is  converted  into  coloured  orcein. 

On  evaporating  rapidly  by  boiling  a  solution  of  alloxantin  in 
chlorohydric  acid,  and  allowing  it  to  cool,  the  liquid  deposits  crys- 
tals of  a  new  acid,  called  allituric  acid  CgHgNgOgjHO.  If  dilute 
nitric  be  substituted  for  the  chlorohydric  acid,  and  the  liquid  be 
treated  with  sulf  hydric  acid  as  soon  as  the  alloxantin  is  dissolved, 
alloxan  is  deposited ;  and  when  the  liquid  is  decanted  and  mixed 
with  nitric  acid  it  deposits  an  ammoniacal  salt,  formed  by  a  new 
acid,  called  dilituric,  the  composition  of  which  is  as  yet  unknown. 

§  1712.  The  rapid  enumeration  of  the  numerous  products  derived, 
thus  far,  from  uric  acid,  proves  very  clearly  the  extreme  mobility 
of  certain  organic  molecular  groupings. 

Hippurie  Acid  Ci8HgN05,HO. 

§  1713.  Hippuric  acid  exists  in  the  urine  of  herbivorous  animals 
and  of  young  children.  It  is  prepared  by  evaporating  the  fresh 
urine  of  a  horse  to  \  of  its  volume,  and  adding  chlorohydric  acid ; 
when  the  liquid,  on  being  left  to  itself,  deposits  coloured  crystals  of 
impure  hippuric  acid.  '  They  are  redissolved  in  boiling  water,  when 
the  liquid,  after  being  bleached  by  animal  charcoal,  deposits  white 
prismatic  crystals  of  very  pure  hippuric  acid,  on  cooling.  Hippuric 
acid  is  much  more  soluble  in  hot  than  in  cold  water,  and  dissolves 
freely  in  alcohol,  but  is  almost  insoluble  in  ether;  and  it  forms, 
with  bases,  salts  remarkable  for  their  beautiful  crystalline  forms. 
Under  many  circumstances,  hippuric  yields  benzoic  acid.  When 
heated,  it  first  melts,  and  is  then  decomposed,  giving  rise  to  cyano- 
hydric  acid,  and  a  copious  sublimation  of  benzoic  acid,  besides  se- 
veral other  substances,  the  nature  of  which  is  not  yet  known. 

If  a  solution  of  hippuric  acid  be  boiled  with  powerful  acids,  the 
hippuric  acid  undergoes  a  very  remarkable  decomposition,  already 
mentioned,  (§1663,)  being  separated  into  glycocoll  and  benzoic  acid: 

C,ANO„HO+2HO=C,,H,03,HO+C,H,N03,HO. 

Hippuric  acid  also  furnishes  benzoic  acid  when  it  is  treated  with 
oxidizing  reagents,  as,  for  example,  by  boiling  its  aqueous  solution 
with  brown  oxide  of  lead,  or  with  sulphuric  acid  and  peroxide  of 
manganese;  carbonic  acid  being  disengaged  at  the  same  time. 
Benzoic  acid  is  also  formed  when  it  is  heated  with  sulphuric  acid 
at  a  temperature  exceeding  248°. 

Lastly,  under  the  influence  of  certain  ferments,  hippuric  acid  is 
decomposed,  and  yields  benzoic  acid.  These  ferments  naturally 
exist  in  the  urine  of  herbivorous  animals;  and  if  the  urine  of  a 
horse  be  allowed  to  become  putrid,  and  be  then  concentrated  by 
evaporation,  a  copious  crystallization  of  benzoic  acid  is  separated. 
This  furnishes  an  economical  method  of  preparing  this  acid,  which 


URINE.  761 

is  also  frequently  found,  ready  formed,  though  in  small  quantities, 
in  the  urine  of  the  herbivorae. 

Reciprocally,  benzoic  acid  is  readily  converted,  in  the  animal 
economy,  into  hippuric  acid ;  and,  after  eating  a  small  quantity  of 
benzoic  acid  mixed  with  our  food,  we  shall  find  a  considerable  quan- 
tity of  hippuric  acid  in  the  urine  arising  from  the  digestion  of  this 
food.  Healthy  human  urine  almost  always  contains  a  very  small 
quantity  of  hippuric  acid. 

ANALYSIS  OF  URINE. 

§  1714.  The  substances  generally  looked  for  in  human  urine  are 
urea,  uric  acid,  and  the  salts  ;  the  other  principles,  such  as  creatin, 
hippuric  acid,  and  albuminous  substances,  generally  existmg  in  a 
quantity  too  small  to  allow  of  their  accurate  quantitative  determi- 
nation. 

In  order  to  obtain  the  urea,  the  urine  is  evaporated  at  a  low  tem- 
perature, and  treated  with  alcohol,  which  dissolves  the  urea,  to- 
gether with  a  small  quantity  of  unknown  matter,  while  the  uric 
acid,  urates,  and  mineral  salts  remain  in  the  residue.  It  is  evapo- 
rated to  dryness  at  a  very  gentle  heat,  and  treated  with  a  small 
quantity  of  dilute  nitric  acid,  and  again  evaporated,  when  nitrate  of 
urea  remains  and  is  weighed.  It  is,  however,  always  to  be  feared 
that  some  of  the  urea  may  be  destroyed  during  the  evaporation, 
because  a  small  quantity  of  nitrous  acid  may  be  formed  by  the  reac- 
tion of  foreign  organic  matters  on  nitric  acid,  and  we  have  shown 
(§  1709)  that  nitrous  acid  readily  destroys  urea.  It  is  therefore 
much  more  exact  to  determine  the  urea  by  the  quantity  of  carbonic 
acid  which  is  evolved  when  a  known  weight  of  urine  is  decomposed 
by  a  mixed  solution  of  nitrate  and  nitrite  of  mercury.  (§  1709.) 

The  uric  acid  is  separated  by  pouring  chlorohydric  acid  on  the 
residue  of  urine  which  did  not  dissolve  in  the  alcohol,  and  treating 
it  with  a  sufficient  quantity  of  weak  alcohol,  when  the  mineral  salts 
are  wholly  dissolved,  while  the  uric  acid  alone  remains,  and  is 
weighed  after  desiccation. 

The  mineral  salts  are  obtained  by  evaporating  another  portion 
of  urine  and  incinerating  the  residue.  The  alteration  which  the 
original  salts  may  have  undergone  by  roasting  must  necessarily  be 
taken  into  account. 

We  have  said  that  urea  forms  more  than  one-half  of  the  residue 
after  the  evaporation  of  the  urine ;  and  as  this  substance  contains 
about  one-third  of  its  weight  of  nitrogen,  the  greater  portion  of  the 
nitrogen  of  the  food  will  be  included  in  it.  The  proportion  of 
urea  and  uric  acid  is  much  greater  when  animal  food  is  used  than 
when  the  subject  feeds  on  vegetables. 

§  1715.  In  various  diseases  the  urine  is  greatly  changed,  and  ren- 
ders the  physician  valuable  assistance  in  the  diagnosis  of  altera- 
tions which  have  taken  place  in  the  economy.     In  a  peculiar  disease 


762  .  ANIMAL   CHEMISTRY. 

called  diabetes  mellifus,  the  urine  is  loaded  with  a  considerable  quan- 
tity of  fermentable  sugar,  called  diabetic  sugar,  which  appears  to  be 
identical  with  glucose.  Persons  affected  with  this  disease  suffer 
constantly  from  thirst,  drink  largely,  and  pass  considerable  quanti- 
ties of  urine.  The  sugar  is  separated  by  evaporating  the  urine  in  a 
water-bath,  and  treating  the  residue  with  weak  alcohol,  which  dis- 
solves the  saccharine  matter.  The  liquid  is  bleached  by  animal 
charcoal,  concentrated  by  evaporation  to  the  consistence  of  syrup, 
and  kept  for  a  long  time  at  a  low  temperature ;  when  the  sugar  is 
deposited  in  the  shape  of  little  pyramids,  which  are  washed  with 
absolute  alcohol,  and  purified  by  recrystallization. 

The  proportion  of  sugar  in  diabetic  urine  may  be  ascertained  very 
exactly  by  optical  experiments.     (See  note  to  page  478.) 

CALCULI  OF  THE  BLADDER. 

§  1716.  Concretions,  which  sometimes  attain  a  considerable  size, 
are  frequently  found  in  the  bladder,  and  are  called  urinary  or  vesi- 
cal calculi.  They  are  formed  of  very  various  substances,  and  are 
divided  into, 

1st.  Calculi  of  uric  acid,  which  are  the  most  common,  and  are 
known  by  the  physical  and  chemical  properties  of  uric  acid,  particu- 
larly by  that  of  dissolving  in  nitric  acid,  and  producing  a  rose  colour 
when  the  solution  is  evaporated  in  the  presence  of  ammonia. 

2d.  Calculi  of  urate  of  ammonia,  which  exhibit,  with  nitric  acid, 
the  same  phenomena  as  calculi  of  free  uric  acid,  but  which  evolve, 
in  addition,  ammonia  when  they  are  heated  with  potassa. 

3d.  Calculi  of  phosphate  of  lime,  which  dissolve  readily  and  with- 
out effervescence  in  dilute  chlorohydric  acid.  By  an  excess  of  sesqui 
oxide  of  iron  added  to  the  liquid,  and  then  supersaturating  it  with 
perfectly  caustic  ammonia,  the  phosphoric  acid  is  completely  pre- 
cipitated, in  combination  with  the  sesquioxide  of  iron,  (§  865,)  while 
the  lime  remaining  in  solution ,  may  be  precipitated  by  oxalate  of 
ammonia. 

4th.  Calculi  of  a  compound  phosphate  of  magnesia  and  ammonia, 
which  also  dissolves  readily  in  dilute  chlorohydric  acid.  After 
having  precipitated  the  phosphoric  acid  in  combination  with  the 
sesquioxide  of  iron,  as  in  the  preceding  calculi,  carbonate  or  oxalate 
of  ammonia  is  added,  which  precipitates  the  lime,  if  any  be  present, 
while  the  magnesia  remains  in  solution,  and  may  be  separated  by 
the  processes  indicated,  (§  592.)  The  ammonia  is  separated  by  heat- 
ing another  portion  of  the  calculus  with  hydrated  potassa.  The 
majority  of  urinary  calculi  are  complicated,  being  composed  of  a 
nucleus  of  uric  acid  of  greater  or  less  size,  around  which  are  formed 
concentric  concretions  of  phosphate  of  lime  and  phosphate  of  mag- 
nesia and  ammonia. 

5th.  Calculi  of  oxalate  of  lime,  called  also  mulberry  calculi,  be- 
cause their  rugose  and  mamillated  surface  resembles  that  fruit. 


EXCREMENT.  763 

They  dissolve  with  difficulty  in  chlorohydric  acid,  but  readily  in 
concentrated  nitric  acid,  which  converts  the  oxalic  into  carbonic 
acid.  The  lime  is  separated  by  the  processes  indicated  §  594. 
By  heating  these  calculi  with  concentrated  sulphuric  acid,  a  gaseous, 
inflammable  mixture  of  carbonic  acid  and  oxide  of  carbon  is  disen- 
gaged. 

6th.  Calculi  of  cystin.  These  calculi  are  very  rare,  and  are 
formed  by  a  sulphuretted  organic  matter,  easily  recognised  by  its 
chemical  properties. 

Cystin  is  obtained  in  a  state  of  purity  by  dissolving  powdered 
cystic  calculi  in  ammonia,  filtering  the  solution,  and  then  evaporat- 
ing, when  the  cystin  separates  in  small  crystals,  which  do  not  retain 
the  ammonia.  The  composition  of  cystin  corresponds  to  the  formula 
CgHgNO^Sg,  and  it  is  a  colourless,  crystalline,  inodorous  substance, 
insoluble  in  water  and  in  alcohol,  but  dissolving  readily  in  ammonia. 
With  the  acids  it  plays  the  part  of  a  weak  base,  readily  dissolving 
in  them,  without  forming  fixed  compounds. 

SWEAT. 

§  1717.  Sweat  is  a  liquid  of  acid  reaction,  which  exudes  from 
particular  openings  in  the  skin.  It  contains  some  unknown  animal 
substances,  and  some  mineral  salts,  among  which  have  been  found 
chloride  of  sodium,  chlorohydrate  of  ammonia,  the  sulphates  and 
phosphates  of  potassa  and  soda,  phosphate  of  lime,  and  traces  of 
oxide  of  iron. 

EXCREMENTS. 

§  1718.  The  excrements  of  mammiferous  animals  are  composed 
chiefly  of  animal  substances  which  have  escaped  liquefaction  during 
their  passage  through  the  stomach  and  intestines,  and  contain,  iii 
addition,  fatty  matters,  and  several  soluble  and  insoluble  substances, 
the  nature  of  which  is  unknown.  In  the  newly-born  infant,  the 
intestinal  canal  contains  a  brown  substance,  called  meconium,  which 
the  child  voids  during  the  few  first  days  of  extra-uterine  life,  the 
excrements  soon  changing  when  it  is  fed  on  milk.  Meconium  con- 
tains a  considerable  quantity  of  cholesterin,  and  a  substance  analo- 
gous to  casein  of  milk. 

Birds  void  their  excrement  and  urine  through  the  same  canal, 
and  they  contain  a  large  quantity  of  uric  acid,  besides  some  un- 
known substances. 

INTESTINAL  GASES. 

§  1719.  Gases  are  always  evolved  during  digestion,  their  quantity 
varying  with  the  food  and  the  peculiar  constitution  of  the  individual. 
These  gases  are  essentially  composed  of  nitrogen,  carbonic  acid,  hy- 
drogen, carburetted  hydrogen,  and  frequently  of  a  small  quantity 
of  sulf  hydric  acid.  The  proportions  of  the  gases  range  between 
widely  extended  limits. 


764 


OF  THE  MANUFACTURE  OF  THE  PRINCIPAL  PRODUCTS 
OF  ORGANIC  ORIGIN,  USED  IN  THE  ARTS,  OR  IN  DOMES- 
TIC ECONOMY. 

§  1720.  We  shall  close  the  present  work  by  a  brief  account  of 
the  manufacture  of  the  principal  products,  of  organic  origin,  which 
are  used  in  the  arts,  or  in  domestic  economy.  We  shall,  in  this  de- 
scription, dwell  only  on  the  general  chemical  principles  of  these 
several  manufactures,  without  touching  upon  the  mechanical  part, 
which  is  foreign  to  our  subject,  and  would  require  details,  the  de- 
scription of  which  would  exceed  our  limits. 

MANUFACTURE  OF  BREAD. 

§  1721.  Bread  is  made  from  the  flour  of  the  cerealia,  that  is,  from 
the  product  of  the  grinding  of  the  grain,  freed,  by  sifting  or  bolting^ 
from  the  cortical  portions,  called  bran.  Bran  still  contains  a  con^ 
siderable  quantity  of  starch  and  nutritious  matter,  while  the  woody 
substance  which  constitutes  the  envelope  of  the  grain,  and  which  is 
of  difficult  digestion,  exists  in  the  proportion  of  about  8  hundredths ; 
this  proportion  varying  with  the  method  of  bolting. 

Wheat-flour,  which  is  the  richest  in  gluten,  is  generally  used  in 
making  bread,  although,  in  countries  where  wheat  cannot  be  grown, 
the  inhabitants  use  barley  or  rye-flour,  or  mixtures  of  these  cerealia, 
called  mesUn,  (mdteil,)  which  is  obtained  by  sowing  them  together. 
A  small  quantity  of  rye-flour  is  often  added  to  wheat-flour,  in  order 
to  give  the  bread  more  flavour. 

The  following  is  the  average  composition  of  the  principal  wheat- 
flours  consumed  in  France : 


Water 

Drv  fi^luten  . . . . 

Unbolted  flour  of 
native  wheat. 

10.0 

11.0 

Flour  of  hard 
wheat  from  Odessa. 

12.0 

14.6 

57.6 

8.5 

5.0 

2.3 

100.0 

Flour  of  soft 
wheat  from  Odessa. 

10.0 

12.0 

Starch 

Glucose 

Dextrin 

Bran 

71.0 

4.7 

3.3 

0.0 

100.0 

63.3 

7.4 

5.8 

1.5 

100.0 

§  1722.  The  various  processes  ,in  bread-making  are  mixing  the 
flour  with  water,  kneading,  fermentation  or  rising,  moulding  it  into 
loaves,  and  baking.  By  the  first,  the  starch  and  gluten  are  moist- 
ened with  water,  and  the  soluble  principles,  such  as  dextrin,  glu- 
cose, and  the  albuminous  principles,  dissolved;  but  as  the  paste, 
kneaded  merely  with  water,  would  produce  a  hard  bread,  difficult 
of  digestion,  the  light  and  puffy  consistence  seen  in  well-made  bread 


MAKING   BREAD.  765 

is  imparted  to  the  crumb  through  a  ferment  added  to  the  paste, 
which  acts  on  the  dextrin  and  glucose,  by  eiFecting  alcoholic  fer- 
mentation. The  gases  which  are  disengaged  during  fermentation 
swell  the  paste,  to  which  the  gluten  gives  elasticity;  and,  if  it  be 
well  made,  all  the  small  gaseous  bubbles  remain  in  the  bread.  The 
ferment  is  generally  made  by  taking,  at  the  close  of  each  opera- 
tion, a  portion  of  the  paste,  and  setting  it  aside  for  some  time ; 
when  it  is  called  leaven  or  rising.  In  large  cities,  or  wherever 
breweries  are  found,  a  small  quantity  of  beer-yeast  is  added  to  the 
rising  to  give  it  more  activity ;  but  the  quantity  must  be  carefully 
regulated,  as  too  much  would  give  a  disagreeable  flavour  to  the  bread. 

The  following  is  the  process  adopted  in  the  Paris  bakeries : — The 
leaven  being  left,  for  7  or  8  hours,  in  a  gentle  and  uniform  tem- 
perature, swells  visibly  and  disengages  an  alcoholic  odour,  when  it 
constitutes  what  is  called  head-yeasty  (levain  de  chef.)  It  is  kneaded 
with  a  quantity  of  water  and  flour  sufficient  to  double  its  volume, 
still  retaining  the  consistence  of  a  firm  paste,  and  is  again  allowed 
to  rest  for  6  hours.  After  this  time,  when  the  paste  has  become 
levain  de  premiere,  an  additional  quantity  of  water  and  flour  is 
added,  and  it  is  again  mixed,  the  proportion  of  water  being  greater 
than  in  the  previous  operation;  which  process  yields  levain  de 
seconde.  Lastly,  a  similar  addition  is  made  to  the  levain  de  seconde 
as  was  made  to  the  levain  de  premiere,  the  paste  being  carefully 
worked,  and  a  levain  de  tous  points  obtained,  the  volume  of  which 
should  be,  in  winter,  nearly  one-half  of  that  of  the  dough  intended  for 
baking,  and  in  summer  only  one-third.  A  certain  quantity  of  salt 
is  generally  added,  to  heighten  the  flavour  of  the  bread ;  J  kilog.  of 
salt  being  used  for  every  150  kilog.  of  flour,  in  the  Paris  bakeries. 

The  dough  is  then  kneaded.  The  quantity  of  water  necessary 
for  the  formation  of  the  paste  being  first  added  to  the  rising,  it  is 
mixed  for  a  long  time,  in  order  to  obtain  a  perfectly  homogeneous, 
fluid  paste,  to  which  the  flour  is  gradually  added,  and  which  is  then 
called  the  sponge.  When  the  dough  has  been  sufficiently  worked, 
it  is  collected  into  a  single  mass,  then  again  thoroughly  'worked  by 
turning  it  in  all  directions,  and  finally  let  fall  into  the  trough  with 
its  whole  weight. 

The  kneading  being  terminated,  the  dough  is  divided  into  loaves, 
which  are  weighed  to  ascertain  if  they  reach  the  legal  standard,  ac- 
cording to  which  115  or  117  of  dough  should  give  100  of  baked 
bread.  They  are  then  dusted  with  flour  or  Indian  corn  meal,  and 
placed  on  tables  in  front  of  the  oven,  to  keep  them  at  the  proper 
temperature ;  when  more  active  fermentation  ensues,  while  the  loaves 
gradually  swell,  until  they  have  attained  the  proper  size  to  be  placed 
in  the  oven.  The  fermentation  must  not  be  too  much  prolonged, 
because  it  might  degenerate  into  acetic  fermentation,  which  would 
liquefy  a  portion  of  the  gluten,  and  thus  diminish  the  consistency 
of  the  dough. 


766  TECHNICAL   ORGANIC   CHEMISTRY. 

The  oven  is  generally  of  an  elliptical  form,  and  heated  by  wood 
or  fagots  of  little  value.  The  fuel  should  be  properly  distributed, 
in  order  to  obtain  a  nearly  uniform  temperature ;  and  bakers  remove 
about  30  to  35  per  cent,  of  the  fuel  in  the  state  of  hot  coals. 
The  proper  temperature  for  baking  bread  is  about  570°. 

The  largest  loaves  are  first  introduced,  and  then  the  smallest,  which 
are  placed  in  the  front  part,  because  they  are  to  be  first  withdrawn ; 
and  the  door  is  then  closed.  The  heat  dilates  the  gases,  arrests  the 
fermentation,  vaporizes  a  portion  of  the  water,  and  gives  consist- 
ency to  the  gluten  and  amylaceous  matter,  which  retain  the  shape 
they  have  assumed.  The  inside  of  the  loaf,  or  crumb,  does  not 
attain  a  temperature  above  212°,  on  account  of  the  continual  evolu- 
tion of  steam,  while  the  outer  portion,  or  crust,  is  completely  dried, 
and  has  become  torrefied  by  having  reached  a  temperature  of  about 
400°.  Round  loaves  weighing  8  pounds  remain  about  60  minutes 
in  the  oven,  and  split  loaves  of  4  pounds  from  36  to  40  minutes. 
When  removed  from  the  oven,  they  are  laid  upright,  in  order  that 
they  may  not  break  before  having  acquired  all  their  consistency, 
and  at  some  distance  from  each  other,  that  the  vapours  may  pass 
ofi"  more  easily. 

The  manufacture  of  bread  has  of  late  years  been  much  assisted 
by  the  introduction  of  mechanical  kneading  and  aerothermal  ovens, 
which  eff'ect  a  more  uniform  baking. 

BREWING. 

§  1723.  Beer  is  an  alcoholic  beverage,  made  from  the  amylaceous 
substance  of  the  cerealia,  chiefly  from  barley,  the  price  of  which  is 
lowest.  The  process  of  brewing  may  be  divided  into  four  distinct 
stages:  1.  The  malting,  of  which  the  object  is  to  produce  in  the 
barley  the  principle  which  efi'ects  the  conversion  of  starch  into  dex- 
trin and  glucose,  and  which  essentially  consists  in  causing  the  barley 
to  sprout  under  the  influence  of  a  proper  temperature  and  degree 
of  moisture,  diastase  being  formed  at  the  origin  of  the  sprouts,  and 
in  the  succeeding  operation  converting  the  starch  into  soluble  dex- 
trin and  glucose.  2.  The  preparation  of  the  wort,  (mout,)  or  sac- 
charification  of  the  malt,  which  consists  in  treating  the  ground  malt 
with  water  at  a  suitable  temperature,  in  order  to  cause  the  diastase 
to  act  on  the  starch  and  dissolve  the  dextrin  and  glucose  which 
result  from  this  action.  3.  The  boiling  with  hops,  which  consists 
in  heating  the  wort  with  hops  in  order  to  give  it  a  peculiar  taste  and 
aroma.  4.  Fermentation,  which  consists  in  mixing  the  cooled  wort 
with  a  ferment,  in  order  to  effect  the  conversion  of  glucose  into 
alcohol. 

The  barley  is  first  placed  in  large  vats  of  mason-work,  with  4 
times  its  volume  of  water,  being  stirred  frequently  to  expel  the 
bubbles  of  air  between  the  grains,  while  those  which  arise  on  the 
surface,  being  generally  defective,  are  skimmed  off.     The  object  of 


BREWING.  767 

tills  process  is  chiefly  to  swell  the  grains,  in  order  that  they  may 
sprout  more  easily;  and  it  lasts  24  or  36  hours  in  winter,  during 
which  time  the  water  is  renewed  3  times ;  while  in  summer  it  re- 
quires only  10  or  12  hours,  but  the  water  must  be  renewed  4  or  5 
times. 

The  barley  thus  swollen  is  carried  to  the  malt-house,  a  kind  of 
cave  or  cellar,  the  floor  of  which  must  be  kept  scrupulously  clean  to 
avoid  all  injurious  fermentations.  Germination  requires  the  assist- 
ance of  moisture,  air,  and  a  temperature  of  from  59°  to  62°,  which 
conditions  are  most  readily  realized  in  spring  or  autumn;  whence 
the  name  of  March  beer  is  given  to  that  made  in  the  spring,  and  is 
considered  superior  to  that  made  in  any  other  season.  In  the  malt- 
house  the  barley  is  spread  in  a  layer  of  about  1 J  feet  in  depth,  and 
thus  left  until  it  becomes  heated ;  but  when  it  begins  to  sprout,  the 
thickness  of ,  the  layer  is  reduced  to  1  foot,  and  then  to  3  inches 
when  the  germination  approaches  the  proper  point.  It  is  also  fre- 
quently stirred  in  order  to  renew  the  air  in  the  interior  of  the  layer. 
In  the  hot  season,  the  germination  is  terminated  in  10  or  12  days; 
while  it  requires  15  or  20  days  toward  the  close  of  autumn,  the 
sprout  having  then  become  f  as  long  as  the  grain. 

When  the  barley  has  properly  sprouted,  it  is  dried  rapidly,  in  order 
to  arrest  the  loss  of  the  amylaceous  matter  which  would  ensue  from 
a  longer  growth  of  the  sprout  and  radicles.  The  drying  is  first 
made  in  the  open  air,  by  spreading  the  grain  over  the  floor  of  a 
well-aired  granary,  and  then  in  a  stove  traversed  by  a  current  of 
hot  air,  and  called  a  malt-kiln.  Desiccation  renders  the  radicles  of 
the  barley  very  brittle,  but  they  are  easily  removed  by  sifting  them 
in  a  winnowing-machine  or  fan.  The  sprouted  barley  thus  freed 
from  the  radicles  is  exposed  for  some  time  to  the  air,  when  it  imbibes 
a  small  quantity  of  moisture,  which  facilitates  its  grinding.  This 
operation  is  efiected  between  horizontal  stones,  kept  at  such  a  dis- 
tance from  each  other  that  the  grain  is  broken  and  torn  without 
being  reduced  to  flour.  The  product  is  malt^  which  is  stowed  away 
for  future  use. 

§  1724.  The  saccharification  of  the  malt  is  efiected  in  large  wooden 
vats,  having  a  double  bottom  pierced  with  holes,  intended  to  support 
the  barley  and  facilitate  the  introduction  and  escape  of  the  liquid. 
In  the  space  between  the  two  bottoms  are  the  discharging-tube  and 
one  which  conveys  hot  water.  When  the  malt  is  placed  in  the  vat, 
water  at  140°,  and  equal  in  weight  to  IJ  times  that  of  the  malt,  is 
poured  in,  the  mixture  being  actively  stirred  with  a  kind  of  fork. 
It  is  then  allowed  to  rest  for  J  an  hour,  until  the  malt  is  thoroughly 
moistened,  when  water  at  196°  is  added  until  the  temperature  of 
the  mixture  attains  167°,  which  is  the  most  favourable  for  saccha- 
rification ;  after  which  it  is  again  stirred,  the  vat  covered,  and  the 
reaction  allowed  to  continue  for  3  hours.     The  saccharine  fluid,  or 


768  TECHNICAL   ORGANIC    CHEMISTRY. 

wort,  is  then  conveyed  into  a  reservoir,  and  thence  into  the  boilers 
intended  for  the  decoction  of  hops. 

As  the  first  digestion  with  water  only  abstracts  from  the  malt  0.6 
of  the  saccharine  matter  it  can  furnish,  an  additional  quantity  of 
WAter  at  176°  is  added,  equal  to  one-half  of  that  used  in  the  first 
operation,  and  is  allowed  to  act  for  1  hour,  the  liquid  produced  being 
added  to  the  first.  Lastly,  the  malt  is  exhausted  by  water  at  212°, 
and  a  liquid  obtained  which  is  used  in  making  small-beer.  The 
exhausted  malt*  is  used  as  food  for  animals. 

The  wort  is  heated  to  ebullition  with  hops  in  boilers,  which  must 
be  kept  covered  to  prevent  the  escape  of  the  essential  oil  to  which 
beer  owes  its  aroma,  and  are  furnished  with  an  apparatus  which 
constantly  stirs  the  mixture.  The  strength  of  the  wort  is  sometimes 
increased  by  the  addition  of  glucose,  (§  1306,)  molasses,  or  raw  sugar. 
The  wort  thus  hopped  is  conveyed  into  reservoirs,  where  it  is  clari- 
fied by  rest,  and  then  run  ofi'  into  other  reservoirs,  where  it  is  cooled 
as  rapidly  as  possible,  by  allowing  the  liquid  layer  only  a  thickness 
of  4  or  5  inches ;  the  cooling  vats  being  placed  in  large  rooms  sur- 
rounded by  Venetian  blinds,  in  order  to  afford  a  free  circulation  of 
air.  The  proportion  of  hops  is  about  1  kilog.  for  every  hectolitre 
of  table-beer,  and  2  kilog.  for  every  hectolitre  of  strong-beer. 

When  the  wort  is  cooled,  it  is  poured  into  a  fermenting  vat  or 
tun,  and  a  quantity  of  yeast  added,  varying,  according  to  the  season 
and  strength  of  the  wort,  from  2  to  4  kilog.  for  every  1000  litres, 
and  maintained  at  a  temperature  of  about  68°.  The  fermenting- 
house  should  be  well  aired,  in  order  to  allow  the  carbonic  acid  to 
pass  off  rapidly.  The  fermentation  lasts  from  24  to  48  hours,  pro- 
ducing a  large  quantity  of  froth,  which  falls  from  the  tun  into  spouts 
arranged  for  the  purpose,  and  which,  when  collected  and  expressed 
in  bags,  constitutes  beer-yeast. 

The  tuns  are  always  kept  full  by  adding  the  liquid  separated 
from  the  froth.  The  fermentation  of  table-beer  is  completed  in  small 
casks  filled  to  the  bung,  and  placed  on  a  scafi'olding  over  a  spout  which 
carries  ofi"  the  froth  still  arising  from  the  liquor ;  and  when  the  fer- 
mentation is  finished  the  kegs  are  plugged,  and  the  beer  only  requires 
a  clarification  with  fish-glue. 

Strong-beer  is  allowed  to  ferment  slowly  for  several  weeks  after 
the  fermentation  in  the  tun,  in  large  vats,  holding  as  much  as  2600 
gallons. 

CIDER  AND  PERRY. 

§  1725.  An  alcoholic  liquor,  called  cider,  is  prepared  from  apples, 
and  constitutes  almost  the  sole  drink  in  Normandy  and  Picardy ; 
while  pears  yield  a  similar  beverage,  called  perry.  In  the  making 
of  cider,  a  certain  quantity  of  pears  is  often  added  to  the  apples,  to 
give  the  liquor  a  higher  flavour. 

*  Called,  in  this  country,  grains. — Tkans. 


WINE-MAKING.  769 

In  order  to  make  cider,  the  apples  are  crushed  in  a  vertical  mill, 
turning  in  a  stone  trough,  with  a  pressure  not  great  enough  to  mash 
the  seeds,  which  would  injure  the  flavour  of  the  cider.  About  10 
or  15  per  cent,  of  water  is  generally  added.  The  mashed  apples 
being  put  into  heaps,  and  left  for  24  hours,  the  cellular-tissue  begins 
to  separate,  and  fermentation  develops  a  peculiar  colouring  matter, 
which  gives  cider  its  yellow  tinge.  After  this  maceration,  the  pulp 
is  pressed,  and  500  kilog.  of  juice  are  generally  extracted  from  1000 
kilog.  of  apples.  The  apple-mash  is  again  ground,  after  the  addi- 
tion of  about  250  litres  of  water,  and  expressed;  the  liquid  thus 
obtained  yields  cider  of  an  inferior  quality. 

The  apple-juice  is  allowed  to  ferment  in  vats  or  barrels,  where  it 
is  freed  from  various  substances,  wjiich  are  either  deposited  or  float 
on  the  surface  in  the  shape  of  froth.  It  is  drawn  ofi"  into  large 
hogsheads,  which  are  but  loosely  corked,  in  order  to  give  exit  to 
the  carbonic  acid  generated  during  fermentation.  During  this 
second  stage  of  fermentation,  the  cider  retains  a  sweet  taste,  much 
admired  by  some  persons ;  but  in  countries  where  cider  is  the  general 
beverage,  fermentation  is  allowed  to  continue  to  its  completion,  by 
which  the  liquor  acquires  an  acid  and  slightly  bitter  taste. 

WINE-MAKING. 

§  1726.  Grapes  contain  extremely  numerous  proximate  principles : 
cellulose,  pectin  and  its  congeners,  (§1296,)  grape-sugar,  tannin, 
albuminous  substances,  yellow,  blue,  and  red  colouring  matters,  fatty 
substances,  tartrates  of  potassa  and  lime,  silica,  oxide  of  iron,  etc. 
etc.  Wine  derives  its  alcohol  from  glucose;  while  the  colouring 
matters  and  tannin,  which  exist  chiefly  in  the  skin  of  the  fruit  and 
the  grape-stems  or  stalk,  impart  different  shades  to  the  various  wines, 
according  as  one  or  other  of  the  colouring  principles  predominates. 
These  principles  are  not  all  equally  fixed ;  the  blue  colour  changing 
first,  while  violet-coloured  wines  become  more  red  with  age,  and 
acquire  a  yellowish  tinge  when  they  are  very  old,  because  the  red 
principle  is  destroyed  before  the  yellow. 

In  wine-making,  the  grapes  are,  in  the  first  place,  pressed,  most 
frequently  by  the  feet  of  men,  who  walk  about  in  the  vat.  In  the 
manufacture  of  white  wine,  the  pulp  alone  is  pressed ;  while,  if  red 
wine  is  to  be  made,  the  pulp  is  left  for  several  days  to  itself,  to  allow 
fermentation  to  take  place,  and  the  liquor  to  dissolve  the  colouring 
matters  and  tannin  of  the  skins  of  the  fruit  and  of  the  stalks.  The 
pressing  is  frequently  repeated,  when  the  tissues  are  party  broken 
up  by  fermentation ;  but  this  is  an  operation  requiring  caution,  as 
the  carbonic  acid,  which  is  copiously  evolved,  might  asphyxiate  the 
workmen.  For  wines  of  superior  quality,  a  partial  picking  is  often 
performed,  that  is  to  say,  a  portion  of  the  stalks  are  removed,  when 
the  latter  are  too  abundant,  as  is  the  case  in  years  when  grapes 
are  not  very  plenty.     The  vats  in  which  the  first  fermentation  is 

Vol.  II.— 49 


770  TECHNICAL    ORGANIC    CHEMISTRY. 

eiFected  are  left  open,  though  it  would  probably  be  better  to  keep 
them  closed,  in  order  to  avoid  the  contact  of  air,  which  often  pro- 
duces acetic  fermentation  in  the  scum  collected  on  the  surface.  The 
duration  of  the  fermentation  varies  with  the  temperature  and  nature 
of  the  grape,  and  is  known  to  be  terminated  by  the  almost  complete 
cessation  of  the  evolution  of  gas,  and  the  colour  of  the  wine,  which 
contains  a  sufficient  quantity  of  the  colouring  matter.  For  ordinary 
wines,  it  lasts  from  3  to  8  days ;  while  in  some  localities  it  is  con- 
tinued for  a  month  or  six  weeks,  the  vats  being  then  closed  after 
the  eighth  day. 

When  fermentation  has  ceased,  the  clear  liquid  is  drawn  off  by  a 
stopcock,  and  the  must  is  expressed;  the  latter  being  generally 
diluted  with  a  small  quantity  of  water,  and  again  subjected  to  pres- 
sure, yielding  a  very  weak  wine,  called  piquette,  which  soon  turns 
sour.  The  wine  which  flows  spontaneously  and  that  separated  by 
compression  of  the  pulp  are  generally  mixed  together,  but  are  kept 
separate  in  the  making  of  wines  of  superior  quality,  because  that 
yielded  by  expression  always  contains  some  acid  principles  fur- 
nished by  the  stalks  and  seeds. 

The  wine  is  received  into  hogsheads,  which  are  generally  not 
closed,  because  fermentation  goes  on  slowly,  and  carbonic  acid  is 
for  a  long  time  evolved.  When  this  ceases,  the  wine  is  again  drawn 
off,  and,  about  the  month  of  March  or  April,  the  fining  is  com- 
menced. 

Red  wines  are  commonly  fined  with  white  of  eggs,  bullock's 
blood,  or  gelatin,  which  substances  combine  with  the  tannin  and  a 
portion  of  the  colouring  principle,  and  carry  down,  by  coagulating, 
the  substances  in  suspension  which  muddied  the  wine.  To  fine 
white  wines,  which  contain  but  little  tannin,  it  is  necessary  to  use 
fish-glue,  because  it  coagulates  much  more  rapidly. 

In  bad  years,  when  the  grapes  do  not  ripen  perfectly,  the  quality 
of  the  wines  is  greatly  improved  by  adding  a  certain  quantity  of 
glucose  to  the  fermenting-vat. 

Sparkling  wines,  such  as  champagne,  are  prepared  from  a  black 
grape,  the  juice  of  which  generally  contains  more  sugar  than  the 
white  grape ;  but  in  order  to  avoid  colouring  the  juice,  great  care 
is  taken  not  to  rupture  the  husk  of  the  grape  or  of  the  stalks.  The 
grapes,  gathered  in  warm  weather,  are  carried  with  great  care  to  the 
press,  when,  by  a  first  and  gentle  pressure,  the  juice  which  is  to 
make  wine  of  first  quality  is  obtained,  while  the  must,  being  again 
stamped,  and  more  powerfully  expressed,  furnishes  a  juice  from 
which  pink  champagne  is  made.  A  third  and  fourth  pressing  is 
sometimes  made,  but  the  products  are  added  to  the  ordinary  red 
wines.  The  white  or  pink  juice  is  allowed  to  ferment  in  large 
hogsheads,  where  it  is  freed  from  the  greater  portion  of  its  yeast, 
which  floats  on  the  surface  with  the  scum.  In  24  hours  the  juice 
is  drawn  off  into  other  hogsheads,  which  are  kept  nearly  filled,  and 


MANUFACTURE    OF   BEET-SUGAR.  771 

imperfectly  closed,  so  as  to  allow  the  disengagement  of  carbonic 
acid.  In  a  month  it  is  drawn  oiF  and  fined  for  the  first  time,  a 
second  fining  being  applied  after  the  following  month,  after  having 
drawn  it  off,  and  a  third  one  in  the  month  of  April,  when  it  is 
bottled.  Three  to  five  per  cent,  of  its  weight  of  sugar-candy,  dis- 
solved in  an  equal  weight  of  water,  is  then  added  to  the  wine.  The 
bottles  are  very  carefully  closed  with  corks,  held  down  by  iron  wire, 
and  surmounted  by  a  metallic  cap ;  and  they  are  laid  upon  their 
side,  a  lath  of  wood  being  placed  between  each  two  bottles.  A  por- 
tion of  the  sugar  added  undergoes  alcoholic  fermentation,  under  the 
influence  of  the  yeast  which  still  exists  in  the  wine,  but  the  carbonic 
acid,  finding  no  escape,  remains  in  solution  in  the  liquor,  which  also 
retains  a  sweet  taste,  produced,  by  the  portion  of  the  sugar  which 
has  not  fermented. 

MANUFACTURE  OF  BEET-SUGAR. 

§  1727.  The  sugar-beet  cultivated  in  France  for  the  production 
of  beet-sugar,  is  the  species  called  the  white  Siberian  sugar-heety 
and  shows  the  following  average  composition : 

Water 83.5 

Sugar 10.5 

Cellulose 0.8 

Albuminous  substances 1.5 

Various  organic  substances,  and  mineral  salts    3.7 

100.0 

The  beets  are  taken  out  of  the  ground  when  they  have  acquired 
their  full  growth,  and  carefully  separated  from  those  which  have 
been  injured  by  the  operation,  since  the  latter  do  not  keep,  and 
should  be  used  immediately.  The  beets  are  made  into  heaps  in  the 
field,  and  covered  with  leaves,  until  there  is  danger  of  frost,  when 
they  must  be  housed,  or  buried  in  pits.  The  upper  part  of  the 
root,  at  the  starting-point  of  the  stalk,  is  cut  off,  because  this  por- 
tion is  harder  and  contains  but  little  sugar. 

The  beets,  after  being  cleansed  and  washed,  are  thrown  into  a 
machine  which  reduces  them  to  as  fine  a  pulp  as  possible  and 
breaks  up  the  cells.  The  pulp  is  placed  in  woollen  bags,  laid  on 
each  other,  and  between  which  metallic  plates  are  introduced ;  after 
which  the  mass  is  compressed  by  a  screw-press,  and  the  juice  which 
flows  out,  and  which  constitutes  about  0.4  of  the  juice  contained, 
collected.  The  bags  and  plates  are  then  placed  under  the  platform 
of  an  hydraulic  press,  which  is  unscrewed  after  having  maintained 
the  pressure  for  about  10  minutes,  when  the  bags  are  placed  two 
by  two  between  two  plates,  and  again  still  more  powerfully  com- 
pressed. In  this  manner,  75  to  80  per  cent,  of  beeu-root  juice  may 
be  extracted,  only  about  15  parts  being  left  in  the  pulp. 


772  TECHNICAL   ORGANIC   CHEMISTRY. 

§  1728.  As  the  juice  soon  changes,  it  is  essential  to  raise  it,  as 
quickly  as  possible,  to  a  high  temperature,  in  order  to  destroy  the 
ferments ;  and  to  saturate  with  lime  the  free  acids,  which  would 
soon  convert  a  portion  of  the  sugar  into  sugar  turning  to  the  left. 
For  this  purpose,  the  juice,  on  leaving  the  press,  is  conveyed  into  a 
double-bottomed  boiler,  heated  by  steam,  and  the  temperature  is 
rapidly  raised  to  140°  or  158°,  after  which  it  is  conveyed  into 
another  boiler,  also  heated  by  steam,  where  the  defecation,  or  treat- 
ment with  lime,  is  effected.  Hydrated  lime  is  usually  made  by 
pouring  on  quicklime  10  times  its  weight  of  boiling  water,  and, 
when  the  lime  is  entirely  slacked,  passing  it  over  a  metallic  sieve, 
which  arrests  the  grains  of  sand  and  the  non-decarbonated  portions. 
The  juice  is  first  heated  to  167°  in  the  defecating  boiler,  the 
milk  of  lime  is  then  added,  and  the  whole  is  stirred,  to  render  the 
mixture  homogeneous;  when  the  temperature  is  raised  to  212°,  the 
supply  of  steam  being  cut  off  when  ebullition  commences.  The 
lime  combines  with  the  free  acids,  the  albuminous  substances,  the 
fatty  and  colouring  matters,  and  produces  insoluble  compounds, 
effecting  at  the  same  time  a  kind  of  clarification,  by  carrying 
down,  with  the  insoluble  compounds,  organic  remains  which  were 
suspended  in  the  juice.  A  thick  scum  having  formed  on  the  surface 
of  the  liquid,  the  latter  is  kept  from  boiling,  in  order  to  prevent  its 
rupture  by  the  bubbles  of  steam.  The  proportion  of  lime  added 
varies  with  the  nature  of  the  beets  and  with  their  freshness ;  only 
3  lbs.  for  1000  pints  of  juice  being  used  in  the  beginning  of  the 
season  and  with  fresh  beets,  which  quantity  is  gradually  increased, 
and  frequently  reaches  10  lbs.,  before  the  close  of  the  season.  An 
excess  of  lime  remains  in  the  liquor,  and  forms  a  deliquescent  com- 
pound with  a  portion  of  the  sugar,  which  must  be  lessened  as  much 
as  possible,  because  it  causes  a  loss  of  sugar.  In  some  factories,  it 
has  been  endeavoured  to  saturate  it  with  a  proper  quantity  of  acid. 

§  1729.  When  the  defecation  is  terminated,  the  liquor  is  drawn 
off  and  filtered  through  animal  charcoal,  the  filters  used  for  this  pur- 
pose being  large  sheet-iron  cylinders,  having  a  false  bottom,  pierced 
with  holes,  like  a  cullender.  A  cloth  is  extended  over  the  bottom, 
on  which  is  spread  ver^  coarsely  powdered  animal  charcoal,  added 
m  successive  layers,  until  it  fills  the  cylinders  to  1^  foot  from  the 
top,  when  another  cloth  is  laid  upon  it,  arid  is  covered  by  another  me- 
tallic plate  pierced  with  holes ;  each  filter  receiving  6000  to  8000  lbs. 
of  charcoal.  The  filters  should  be  kept  constantly  filled  with  fluid, 
which  is  easily  done  by  means  of  a  stopcock.  After  this  process,  by 
which  the  juice  loses  a  portion  of  its  colouring  matter,  and  the  lime 
in  excess,  which  adhere  to  the  charcoal,  it  is  conveyed  as  rapidly  as 
possible  into  the  concentrating  boilers,  which  are  generally  shallow, 
and  are  heated  by  the  circulation  of  high-pressure  steam  through 
copper  tubes  arranged  over  their  bottoms.  The  juice  is  raised  to  a 
temperature  of  70°  in  10  or  12  minutes.     The  workman  judges, 


# 

MANUFACTURE    OF   CANE-SUGAR.  773 

by  signs  learned  by  experience  alone,  if  it  is  properly  concentrated, 
or  if  the  boiling  is  completed.  During  the  ebullition,  which  termi- 
mates  at  a  temperature  of  266°  to  275°,  a  considerable  portion  of 
the  sugar  is  altered,  and,  to  diminish  the  loss,  the  evaporation  must 
be  effected  as  rapidly  as  possible.  This  operation  has  been  greatly 
improved  by  boiling  in  vacuo,  that  is  in  close  boilers,  heated  by  steam, 
and  brought  into  communication  with  worms  and  receivers  in  which 
a  vacuum  is  made ;  when  ebullition  takes  place  at  a  lower  tempera- 
ture, the  quantity  of  sugar  changed  is  much  smaller. 

§  1730.  When  the  syrup  is  properly  boiled,  it  is  collected  in  a 
cooler,  which  usually  receives  the  products  of  5  or  6  boilings ;  and 
its  temperature  then  falls  to  about  176°.  Crystallization  then  com- 
mences, but  as  soon  as  any  crystals  form,  they  are  detached  from 
the  sides,  and  the  syrup  stirred  to  bring  them  again  into  suspen- 
sion. When  the  temperature  has  fallen  to  130°  or  122°,  the  syrup 
is  poured  into  large  conical  moulds  of  metal  or  baked  clay,  resting 
on  the  point,  which  is  furnished  with  a  hole  previously  stopped  with 
a  plug  of  wet  muslin.  The  moulds  are  ranged  on  long  benches, 
with  openings  through  which  the  escaping  fluids  fall  into  zinc  gut- 
ters, whence  they  flow  into  reservoirs.  The  temperature  of  the 
room  containing  the  moulds  should  be  about  86°.  Crystallization 
is  completed  in  24  or  36  hours,  when  the  plug  is  removed  from  the 
opening  in  the  mould,  and  the  point  of  the  loaf  pierced  with  an 
awl,  so  as  to  draw  off  the  molasses,  which  is  again  concentrated, 
even  further  than  the  original  syrup,  and  crystallized  in  moulds. 
When  the  molasses  is  too  highly  coloured,  as  happens  sometimes,  it 
is  diluted  with  a  sufficient  quantity  of  water,  filtered  through  animal 
pharcoal,  concentrated  and  recrystallized.  The  syrup  which  drains 
from  the  second  sugar  is  frequently  subjected  to  the  same  process  for  a 
third  time,  but  the  crystallization  then  requires  a  great  length  of  time. 

When  the  sugar  has  drained  sufficiently,  the  loaves  are  loosened, 
that  is,  the  moulds  are  inverted,  and  the  loaves  detached  by  gentle 
blows ;  after  which  they  are  placed  in  the  wareroom,  protected  from 
dampness.  This  is  raw  beet-sugar,  which  requires  refining  before 
being  fitted  for  consumption. 

MANUFACTURE  OP  CANE-SUGAR. 

§  1731.  Of  all  sacchariferous  plants,  sugar-cane  is  the  most  rich 
in  sugar,  since  it  yields  0.90  of  juice,  containing  from  0.17  to  0.22 
of  crystallizable  sugar;  but  in  the  majority  of  the  colonies  its  ma- 
nufacture is  still  so  rude  that  nearly  one-half  of  the  sugar  contained 
in  the  cane  is  lost.  The  richest  variety  of  sugar-cane  is  the  ribbon- 
cane,  or  Otaheite  cane,  containing,  on  an  average, 

Water 72.1 

Sugar 18.0 

Woody  tissue 9.9 

mo 


774  TECHNICAL    OEGANIC   CHEMISTRY. 

It  leaves  about  0.4  of  ash  containing  a  considerable  quantity  of 
silex,  like  that  of  all  the  graminese ;  and  the  ash  consists  of 

Silex 68 

Potassa 22 

Lime 10 

100 

§  1732.  When  the  canes  are  cut,  they  soon  become  damaged  by 
fermentation,  and  should  therefore  be  carried  immediately  to  the 
mill.  The  latter  is  composed  of  large  stone  or  cast-iron  cylinders, 
between  which  the  canes  are  crushed ;  the  best  being  provided  with 
five  crushing-cylinders,  so  that  the  cane  is  compressed  four  times. 
They  are  turned  by  a  water-wheel  or  by  steam ;  and  in  the  major- 
ity of  sugar-works  only  about  50  kilog.  of  juice  are  extracted  from 
100  kilog.  of  cane,  while  in  the  best^ mills  about  65  are  obtained; 
40  kilog.  of  juice  being  in  the  former  case  left  in  the  cane-trash, 
and  25  in  the  latter.  The  woody  fibre  of  the  cane  renders  it  very 
difficult  to  extract  the  juice  completely,  which  would  require  greater 
power;  and  in  the  colonies  the  trash  is,  generally  speaking,  the 
only  fuel  used.  The  rapid  and  perfect  extraction  of  the  juice  is 
the  most  important  part  of  the  process,  and  that  which  produces 
the  greatest  loss  of  sugar  when  not  well  performed.  The  fresh 
cane-juice,  which,  in  addition  to  the  sugar,  contains  merely  very 
small  quantities  of  albuminous  substances,  is  allowed  to  remain  for  an 
hour  in  a  reservoir  to  become  clear,  and  is  thence  conveyed  into  the 
boilers,  five  of  which  generally  make  a  set.  The  first,  which  is  the 
most  remote  from  the  furnace,  is  used  for  defecation,  (or  temper- 
ing ;)  in  which  case  only  ^  of  the  quantity  of  lime  necessary  for  the 
defecation  of  beet-sugar  is  used ;  about  0.2  or  0.3  for  1000  of  juice. 
It  is  then  heated  to  boiling,  and  rapidly  skimmed.  The  defecated 
juice  is  thence  conveyed  into  the  second  boiler,  where  evaporation 
commences ;  the  skimmings  from  this  boiler  being  removed  and 
thrown  back  into  the  first.  The  liquor  then  passes  into  the  third 
boiler,  where  the  evaporation  is  continued ;  and  during  its  sojourn 
in  this  boiler,  the  workman  ascertains  if  it  has  been  properly  defe- 
cated, or  if  it  requires  the  addition  of  a  small  quantity  of  lime.  He 
then  transfers  the  liquid  into  thte  fourth  boiler,  where  it  is  concen- 
trated to  the  consistence  of  syrup ;  and  lastly  into  the  fifth,  where  it 
is  concentrated  to  the  consistence  suitable  for  crystallization. 

In  the  best  establishments  the  boilers  rest  on  pivots  in  their  cen- 
tral line,  and  are  placed  below  each  other,  which  arrangement 
greatly  facilitates  and  accelerates  the  working. 

The  boiling  is  then  run  ofi"  into  large  flat  reservoirs,  where  it  is 
allowed  to  cool  and  crystallize  for  24  hours,  when  the'granular  mass 
is  poured  into  moulds,  in  which  the  crystallization  is  completed, 
and  is  finally  drained. 


SUGAE-REFINING.  775 

The  operation  generally  yields  in  most  of  the  works, 

Brown  sugar 55  to  65 

Sugar  which  remains  in  the  molasses,  for  the  greater 

part  uncrystallizable 25  to  20 

Sugar  left  in  the  trash 80  to  75 

160  to  160 

In  several  important  sugar-works,  an  apparatus  for  evaporating 
in  vacuo  has  been  tried,  which  considerably  diminishes  the  loss  of 
sugar  in  the  molasses,  and  also  furnishes  a  better  article ;  but  the 
primitive  cost  of  such  apparatus,  combined  with  the  want  of  fuel, 
will  for  some  time  prevent  this  more  perfect  process  from  being 
generally  introduced. 

Molasses  is  used  in  the  manufacture  of  several  alcoholic  liquors, 
such  as  rum,  ratafia,  etc. 

SUGAR-REFINING. 

§  1733.  A  large  quantity  of  cane-sugar  is  consumed  in  the  state 
of  brown  sugar,  while  the  greater  portion  of  it  is  refined ;  and  raw 
beet-sugar  must  also  be  refined,  as  otherwise  the  flavour  and  smell 
of  the  beets  would  render  it  unfit  for  use.  The  refiner  generally 
mixes  cane  and  beet-sugar  in  proportions  which  facilitate  the  pro- 
cess. Cane-sugar,  during  its  voyage  from  the  colonies,  has  gene- 
rally undergone  some  change,  and  contains  a  small  quantity  of  acid, 
while  beet-sugar,  on  the  contrary,  contains  a  small  quantity  of  sac- 
charate  of  lime ;  and  by  mixing  them  in  proper  proportions,  the 
acid  of  the  cane-sugar  is  saturated  by  the  lime  of  the  beet-sugar. 

The  raw  sugars  being  mixed  on  a  table  made  of  flag-stones,  and. 
passed  through  a  sieve,  the  mixture  is  dissolved  in  30  per  cent,  of 
its  weight  of  water.  The  solution  is  effected  in  boilers  heated  by 
steam,  and  placed  sufficiently  high  to  allow  the  syrup  to  fall  directly 
into  charcoal  filters,  after  which  the  clarifying  is  commenced.  This 
operation  consists  in  adding  to  the  syrup  5  per  cent,  of  its  weight 
of  finely  powdered  animal  charcoal,  (bone-black,)  and  1  or  2  of  an 
albuminous  substance  coagulable  by  heat ;  bullock's  blood,  defibrin- 
ated  by  beating,  and  diluted  with  4  times  its  weight  of  water,  being 
generally  used.  The  liquid  is  stirred,  and  allowed  to  boil,  when  the 
syrup  is  run  into  peculiarly  shaped  filters,  which  arrest  the  sub- 
stances in  suspension  and  the  scum.  The  best  filters  are  those 
made  of  an  upright  wooden  case,  containing  a  great  number  of 
bags,  made  of  cotton  or  woollen  drugget,  the  mouth  of  which  is 
above  the  top  of  the  case,  while  the  lower  part  passes  through  the 
bottom  and  opens  below.  The  muddy  liquor  being  poured  into  the 
case,  filters  from  without  into  the  bags,  which  are  kept  from  col- 
lapsing by  hoops  of  wood  or  iron,  by  which  means  filtration  ensues 
over  a  large  porous  surface,  and  the  filters  are  moreover  easily 
washed.     The  residue  in  the  case  is  washed  with  fresh  water,  which 


776  TECHNICAL  ORGANIC   CHEMISTRY. 

furnishes  a  weak  solution  of  sugar,  used  to  dissolve  the  new  sugars ; 
and  is  then  sold  as  manure,  under  the  name  of  refinery -black. 

The  clarified  syrup  is  immediately  filtered  through  charcoal,  in 
an  apparatus  resembling  that  used  for  the  bleaching  of  tempered 
sugar-beet  juice,  (§  1729,)  and  is  then  conveyed  into  the  boilers. 
In  almost  all  the  large  refineries,  it  is  now  boiled  in  an  apparatus 
calculated  to  evaporate  in  vacuo.  The  concentrated  syrup  is  col- 
lected in  kettles  in  which  the  temperature  is  raised  to  176°,  in  order 
to  retard  crystallization,  and  redissolve  the  crystals  which  had  be- 
gun to  form  in  the  evaporating  kettles,  where  the  boiling  point  is 
not  very  high.  Crystallization  soon  commences  in  this  kettle,  while 
the  temperature  falls,  and  the  liquid  is  frequently  stirred,  and  the 
mixture  of  syrup  and  crystals  poured  into  moulds,  which  are  placed 
in  a  room  contiguous  to  the  boilers.  The  moulds  are  generally  of 
baked  clay,  and  are  50  centimetres  in  height,  and  from  15  to  22 
wide  at  the  base.  Before  using  new  moulds,  they  are  kept  filled 
for  several  days  with  a  thin  pap  of  clay,  which  closes  the  pores  of 
the  earthenware,  and  prevents  the  absorption  of  the  syrup  and  the 
adhesion  of  the  loaves.  The  moulds  are  perforated  at  the  lower 
part,  the  holes  being  closed  with  a  plug  of  wet  muslin ;  and  the 
moulds  are  arranged  on  a  double  bench,  furnished  with  openings, 
and  of  which  the  lower  part,  made  of  zinc,  conveys  the  drippings 
into  a  canal  communicating  with  a  reservoir  kept  for  the  purpose. 
When  the  moulds  are  filled  to  about  1  centimetre  below  the  top, 
they  are  allowed  to  rest  for  some  time ;  when  there  forms  on  the 
surface  of  the  syrup  a  crystalline  crust,  which  is  broken,  and  the 
broken  crystals  are  thrown  to  the  bottom,  the  syrup  being  stirred 
at  the  same  time  in  order  to  equalise  the  temperature,  which  always 
falls  most  rapidly  toward  the  apex  of  the  cone.  The  crystallizing- 
room  is  kept  at  a  temperature  of  about  95°.  After  remaining  8  or 
12  hours  in  this  room,  the  moulds  are  carried  into  low  apartments 
with  brick  floors,  and  heated  by  steam  conveyed  in  pipes  on  the  floor 
or  around  the  walls.  The  plug  is  then  removed  from  the  hole  in 
the  moulds,  and  the  loaf  pierced  with  an  awl ;  when  it  is  allowed  to 
drain,  and  in  12  hours  the  base  of  the  loaf  is  nearly  white  and  dry. 

The  sugar,  which  now  is  called  drained  green  or  raw  sugar^  is 
then  left  in  the  moulds  for  6  or  7  days  to  complete  the  draining, 
after  which  the  workman  smooths  the  base  of  the  loaf  with  a  plane, 
and  adds  to  it  a  layer  of  purely  white  sugar,  for  which  he  generally 
uses  scrapings  of  refined  sugar,  in  order  to  make  the  base  of  the 
loaf  perfectly  level,  as  it  would  otherwise  be  disfigured  by  a  depres- 
sion in  the  centre.  The  claying  is  then  commenced,  which  consists 
in  pouring  into  each  mould  a  paste  of  clay  diluted  with  water  to  the 
thickness  of  2  or  3  centimetres.  The  water  from  the  clay,  filtering 
slovrly  through  the  loaf,  becomes  saturated  with  nearly  pure  sugar 
in  the  upper  strata,  which  are  nearly  bleached  by  draining,  and  dVi- 
places  in  the  lower  parts  the  coloured  molasses  which  moisten  the 


BONE-BLACK.  777 

porous  crystalline  mass.  After  7  or  8  days  of  claying,  the  clay 
forms  a  firm  coating  on  the  surface  of  the  loaf,  which  is  removed 
by  a  spatula.  The  base  of  the  loaf  is  again  smoothed,  and  it  is  sub- 
jected to  another  claying  resembling  the  first.  These  two  processes 
generally  produce  refined  sugar,  although  a  third  claying  is  some- 
times necessary. 

After  the  last  claying,  the  loaves  are  laid  on  their  sides,  and  the 
bases  being  again  smoothed,  the  moulds  are  slightly  tapped,  in  order 
to  detach  the  loaves  from  their  surfaces,  and  thus  allow  the  last 
portions  of  syrup  to  pass  through  more  easily.  The  moulds  are 
then  placed  in  their  former  position,  to  collect  the  syrup  in  the  apex 
and  cause  it  to  flow  out  as  completely  as  possible ;  after  which  they 
are  set  on  their  bases,  and  thus  left  for  24  hours,  in  order  to  spread 
the  syrup  yet  contained  in  the  apex,  which  would  sensibly  colour 
the  latter,  throughout  the  whole  loaf.  These  alternate  positions 
are  repeated  several  times,  until  the  whole  mass  has  acquired  a 
uniform  colour;  after  which  the  loaves  extracted  from  the  moulds 
are  exposed  to  the  air  for  24  "hours,  and  then  dried  in  ovens  at  a 
temperature  not  exceeding  113°. 

In  some  manufactories,  decolouring  is  substituted  for  claying. 
This  operation  consists  in  pouring  upon  each  loaf,  in  the  mould,  a 
certain  quantity  of  a  syrup  saturated  with  sugar,  and  purer  than 
that  which  moistens  the  loaf,  when  the  latter  syrup  is  displaced  by 
the  syrup  added,  and  escapes  through  the  apex  of  the  mould.  The 
first  '^clairce"  is  replaced  by  a  second,  composed  of  a  syrup  still 
purer  than  the  first,  and  so  on,  until  the  last  clairce  consists  of  per- 
fectly refined  sugar.  This  process  is  much  more  expeditious  than 
that  of  claying. 

The  name  of  lumps,  or  bastards,  is  given  to  sugars  of  inferior 
quality,  for  the  making  of  which  the  coarsest  raw  sugar,  the  green 
syrups,  and  residues  are  used.  They  are  clarified  and  boiled  as  are 
sugars  of  superior  quality,  but  are  crystallized  in  larger  moulds,  and 
the  loaves  are  decoloured  or  clayed  once  oftener  than  sugars  of  first 
quality.  The  apex  of  the  loaf  is  generally  coloured,  and  must  be 
removed. 

A  kind  of  white  loaf-sugar,  called  dried  sugar,  has  been  for  a  long 
time  manufactured  at  Marseilles,  (sucre  tapS.)  It  is  prepared  by 
rasping  the  best  quality  of  lumps  without  allowing  them  to  dry, 
passing  the  substance  through  a  coarse  sieve,  and  introducing  it  into 
small  moulds,  previously  moistened,  into  which  it  is  pressed  with  a 
flat  pestle.  After  some  time  the  loaves  are  taken  out  and  placed  in 
a  stove. 

BONE-BLACK. 

§  1734.  Animal  charcoal,  or  bone-black,  used  for  bleaching  sugar, 
is  generally  made  in  the  vicinity  of  large  cities,  because  bones  are 
there  cheaper  and  more  easily  procured.     The  bones  form  about  \ 


778  TECHNICAL    ORGANIC   CHEMISTRY. 

of  the  "weiglit  of  the  recently  slaughtered  animal;  and  those  which 
are  of  sufficient  size  and  thickness  are  set  apart  for  the  use  of  turners. 

The  fat,  used  in  the  manufacture  of  stearin  candles,  is  first  extracted 
from  the  bones  intended  for  making  bone-black,  by  breaking  them 
into  pieces  and  heating  them  with  water  in  large  boilers,  in  which 
they  are  frequently  stirred,  when  the  fat  separates  and  floats  on  the 
surface.  The  bones  are  removed  from  time  to  time  with  a  strainer, 
and  fresh  ones  added.  A  portion  of  the  bones,  before  being  car- 
bonized, is  used  for  the  preparation  of  gelatin,  (§  1662.) 

The  bones,  after  being  deprived  of  their  fat,  are  drained  and  dried 
in  the  air,  and  then  carbonized  in  cylinders,  or  in  large  cast-iron  or 
earthen  pots,  generally  about  1  foot  in  diameter,  and  IJ  foot  in 
height,  which  are  piled  on  each  other  or  ranged  in  rows  in  large 
furnaces  heated  to  redness  with  bituminous  coal,  which  temperature 
having  been  kept  up  for  6  or  8  hours,  the  pots  are  removed.  When 
they  are  perfectly  cold  the  bone-black  is  removed  and  ground  between 
cylinders ;  all  dust  being  avoided  as  much  as  possible,  because  enough 
is  always  formed  for  the  clarifying  of  sugar,  (§  1733.)  The  dust  and 
variously  sized  grains  are  separated  by  bolting  and  sifting  in  sieves 
■\vith  meshes  of  suitable  size. 

Bone-black  which  no  longer  exerts  any  bleaching  power  on  juices 
and  syrups,  may  have  this  power  restored,  and  be  made  useful  in 
future  operations,  by  removing  the  soluble  substances  in  them  by 
washing,  and  recalcining  them,  which  carbonizes  the  adhering  organic 
matters  and  exposes  the  carbonized  portions.  Their  surface,  how- 
ever, being  still  covered  with  a  pellicle  of  vegetable  charcoal,  which 
diminishes  sensibly  their  activity ;  the  former  is  removed  by  rubbing 
them  slightly  between  horizontal  grindstones  which  do  not  exert 
sufficient  pressure  to  crush  them,  and  by  separating  the  dust  formed 
by  bolting.  By  this  reviving,  bone-black  loses  4  to  5  per  cent,  of 
its  weight ;  but  the  operation  may  be  repeated  20  or  25  times  on 
the  same  charcoal. 

MANUFACTURE  OF  SOAPS. 

§  1735.  We  have  mentioned  (§  1594)  that  the  salts  formed  by 
fatty  acids  with  the  metallic  oxides  are  called  soaps.  Soaps  of 
which  the  base  is  potassa,  soda,  or  ammonia,  are  the  only  ones  soluble 
in  water ;  and  soaps  of  potassa  and  soda  alone  are  used  for  washing 
and  for  the  toilet.  In  commerce,  soaps  are  divided  into  hard  soap, 
of  which  the  base  is  soda,  and  soft  soap,  of  which  the  base  is  potassa  ; 
the  latter  being  more  generally  used  in  northern  countries,  while  in 
France  the  hard  soap  is  preferred.  Soaps  formed  by  the  same  base 
are  harder  in  proportion  to  the  melting  point  of  the  fatty  substances 
uSed  in  saponification. 

Soaps  are  made  by  boiling  fatty  substances  with  more  or  less  con- 
centrated lyes  of  caustic  potassa  or  soda;  which  are  obtained  by 
decomposing  the  alkaline  carbonates,  when  cold,  by  hydrated  lime. 


MANUFACTURE    OF    SOAPS.  779 

False-bottomed  vats  are  generally  used,  and  on  the  upper  bottom, 
which  is  covered  with  straw,  the  slaked  lime  is  placed,  mixed  with 
the  powdered  alkaline  carbonate,  and  it  is  then  covered  with  Avater 
to  the  depth  of  about  5  inches.  In  a  few  hours  the  liquid  has  fil- 
tered through  the  solid  matters,  and  collected  on  the  lower  bottom, 
whence  it  is  then  drawn  off  into  a  separate  vat,  to  be  pumped  back  into 
the  first  vat,  and  once  more  to  filter  through  the  lime ;  this  process 
being  continued  until  the  alkali  is  completely  deprived  of  its  carbonic 
acid.  By  washing  the  remaining  lime  with  water,  alkaline  lyes  are 
obtained,  which  are  generally  used  in  the  first  stage  of  saponifica- 
tion of  fatty  substances.  Saponification  is  effected  in  large  boilers, 
which  are  first  filled  to  one-fourth  with  weak  lye,  and  into  which 
the  fatty  substance  is  gradually  poured,  taking  care  to  constantly 
stir  the  mixture;  weak  lye  and  fat  being  then  added  successively 
until  the  boiler  is  sufficiently  filled.  An  emulsion  of  soap,  with  an 
excess  of  fat,  is  first  formed  in  a  liquor  which  contains  but  little  free 
alkali,  and  which  must  be  kept  uniform  by  continual  stirring,  when 
a  stronger  lye  is  introduced^  which  converts  the  soap  having  an 
excess  of  fatty  acids  into  a  more  basic  and  soluble  soap.  This  more 
highly  charged  lye  is  added  by  different  portions  at  a  time,  and,  in 
the  last  place,  it  is  mixed  with  common  salt,  or  other  alkaline  salts, 
which  entirely  precipitate  the  soap  and  separate  it  from  the  lye. 
It  is  allowed  to  cool,  and  the  aqueous  liquid  containing  the  glycerin, 
the  alkaline  salts  which  have  effected  the  separation  of  the  soap,  and 
the  excess  of  alkali,  is  drawn  off.  A  last  concentrated  lye  being 
then  added,  the  whole  is  heated  to  ebullition,  which  temperature  is 
maintained  until  the  lye  has  attained  a  density  of  1.15  to  1.20,  when 
the  supernatant  soap  is  removed  and  run  into  moulds,  and,  after  it 
has  become  sufficiently  solid,  is  divided  in  parallelopipedons  of  proper 
dimensions  by  means  of  a  wire. 

§  1736.  Marseilles  soap  is  that  most  esteemed,  and  is  made  from 
caustic  soda  and  inferior  quality  olive-oil  yielded  by  the  hot  ex- 
pression of  the  olive-must  from  which  first  quality  olive-oil  has  been 
already  obtained.  Two  kinds  of  artificial  soda  are  used  for  these 
soaps,  one  called  sweet  soda,  which  should  be  as  pure  as  possible, 
since  it  affects  the  saponification,  and  the  other  highly  charged 
with  sea-salt,  and  called  salt  soda,  which  is  used  for  furnishing  to 
the  first  soap,  having  an  excess  of  fatty  acid,  the  quantity  of  base 
necessary  to  entirely  precipitate  it  from  the  liquid. 

The  sweet  soda,  broken  up,  is  mixed  with  J  of  its  weight  of  caus- 
tic lime,  previously  slaked  and  placed  in  vats  of  mason-work,  called 
barquieux,  where  the  mixture  is  lixiviated  several  times,  furnishing 
liquids  of  decreasing  strength.  Saponification  is  effected  in  large 
kettles  with  sloping  sides,  made  of  bricks,  and  with  a  copper  bottom  : 
a  lye  marking  12°  Baum^  being  first  introduced  and  boiled,  the  oil  is 
gradually  added,  and  the  whole  is  constantly  stirred.  After  some 
time  a  lye  marking  15°,  and  at  a  later  period  a  lye  marking  20°, 


780  TECHNICAL  ORGANIC   CHEMISTRY. 

is  introduced.  The  whole  operation,  called  empdtage,  lasts  about 
24  hours,  and  produces  a  soap  with  an  excess  of  fatty  acid;  it  being 
important  that  the  soda  should  be  as  free  as  possible  from  sea- 
salt.  Having  reached  this  point,  the  relargage  is  commenced,  the  ob- 
ject of  which  is  to  make  the  soap  more  alkaline  and  separate  it 
from  the  lyes;  to  which  effect  a  workman  throws  in  gradually,  on 
the  surface  of  the  kettle,  a  salt  lye,  marking  from  20°  to  25°,  while 
another  stirs  the  whole  continually,  when  the  paste,  hitherto  homo- 
geneous and  viscid,  is  converted  into  clots,  which  separate  from  the 
aqueous  liquid.  It  is  allowed  to  rest  for  2  or  3  hours,  when  the 
lye  is  drawn  off.  After  this  operation,  which  is  called  epinage^  it 
is  again  treated  twice  with  fresh  salt-lye,  in  order  to  give  the  proper 
consistency  to  the  soap ;  and  then,  after  having  drawn  off  the  last 
water,  the  paste  is  worked  with  shovels  to  render  it  homogeneous, 
small  quantities  of  weak  lyes  or  fresh  water  being  frequently  added, 
according  to  the  njiture  of  the  soap  to  be  made ;  after  which  it  is 
run  into  moulds,  and  cut  into  small  pieces  after  cooling. 

§  1737.  Two  kinds  of  soap  are  found  in  commerce ;  the  white 
and  marbled  soap.  The  bluish  veins  observed  in  the  latter  are  pro- 
duced by  a  small  quantity  of  soap  having  a  base  of  alumina  and 
protoxide  of  iron,  and  by  sulphide  of  iron  yielded  by  a  small  quan- 
tity of  sulphide  of  sodium  which  always  exists  in  the  lye.  Of  them- 
selves, these  foreign  substances  are  of  no  use,  and  may  even  in  some 
cases  be  injurious  ;  but  as  their  presence  is  a  certain  index  that  the 
soap  does  not  contain  more  than  30  per  cent,  of  water,  marbled 
soap  is  highly  valued  on  that  account.  When  the  paste  contains 
more  water,  it  is  more  fluid  and  light,  and  metallic  compounds  are 
easily  deposited  in  it,  and  cannot  be  distributed  through  the  soap 
in  veins. 

White  soap  is  made  by  diluting  the  paste  at  a  moderate  temper- 
ature, in  weak  lyes,  and  allowing  it  to  rest  in  tight  kettles ;  when 
the  soaps  of  alumina  and  iron  falling  to  the  bottom,  the  supernatant 
white  soap  is  removed  and  carried  to  the  moulds.  In  order  to  pre- 
pare marbled  soap,  less  lye  is  added,  and  the  soaps  of  alumina  and 
iron  are  not  so  completely  deposited,  and  separate  in  veins  through- 
out the  mass.  Cakes  of  marbled  soap  generally  lose  their  colour 
in  the  air,  because  the  protoxide  and  sulphide  of  iron  are  converted 
into  sesquioxide ;  but  the  marbling  is  always  seen  in  freshly  cut 
soap.  Marbled  soaps  generally  contain  30  per  cent,  of  water,  and 
white  soaps  not  less  than  40  or  50. 

Resins  form,  with  the  alkalies,  salts  which  exhibit  characters  re- 
sembling those  of  the  soaps ;  and  yellow  soaps  are  now  made,  the 
fatty  acids  of  which  are  partly  replaced  by  colophony. 

§  1738.  Soft  soaps  are  made  with  hempseed,  linseed,  colza,  and 
other  oils,  the  base  being  potassa.  Their  natural  colour  is  of  a 
brownish-yellow,  while  a  greenish  tinge  is  generally  given  to  them 
by  the  addition  of  a  small  quantity  of  indigo.     The  process  is  nearly 


DYEING.  781 

tie  same  as  that  of  making  hard  soaps,  except  that  lyes  of  potassa 
are  substituted  for  those  of  soda;  and  when  saponification  is  com- 
pleted, and  the  soap  has  become  transparent,  it  is  evaporated  to 
the  proper  consistency,  and  run  into  hogsheads.  This  soap  is 
always  more  alkaline  than  soda-soap,  and  dissolves  more  easily  in 
water. 

Toilet-soaps  are  made  with  soda,  and  are  generally  highly  hy- 
drated,  being  prepared  either  from  olive-oil  or  tallow,  and  their 
agreeable  odour  is  owing  to  essential  oils  mixed  with  them  in  the 
moulds.  Colourless  or  coloured  transparent  s,oaps  are  made  by  dis- 
solving in  alcohol  well-dried  soap  made  of  beef-suet,  concentrating 
it  properly  by  distillation,  and  pouring  the  limpid  and  transparent 
fluid  into  moulds,  where  it  becomes  solid.  Yarious  organic  colouring 
matters  may  be  incorporated  with  it. 

CHEMICAL  PRINCIPLES  OF  THE  ART  OF  DYEINa. 

§  1739.  The  art  of  dyeing  has  been  of  late  so  scientifically  culti- 
vated, that  it  would  require  much  greater  space  than  the  limits  of 
an  elementary  course  can  afibrd,  to  give  a  complete  idea  of  it ;  and 
we  shall  therefore  be  obliged  to  confine  ourselves  to  the  explanation 
of  the  chemical  principles  on  which  is  based  the  preliminary  prepa- 
ration of  the  textile  fibres  to  render  them  fitted  for  the  manufacture 
of  tissues,  and  those  on  which  is  founded  the  art  of  fastening  colour- 
ing matters. 

Preliminary  Preparation  of  the  Textile  Fibres, 

§1740.  The  textile  fibres  used  in  manufactures  are  either  of 
vegetable  or  animal  origin ;  the  first  being  chiefly  hemp,  flax,  and 
cotton,  and  the  second  wool,  hair  of  animals,  and  silk  spun  by  the 
silkworm. 

Cotton  is  nearly  pure  lignin,  while  hemp  and  flax  are  composed 
of  lignin  in  long  filaments,  which,  when  dry,  adhere  to  each  other 
by  means  of  a  gelatinous  substance,  called  pectin^  although  it  differs 
probably  from  that  found  in  fruits,  and  which  must  be  removed  to 
render  them  fit  for  spinning  and  weaving.  For  this  purpose,  they 
are  rotted^  which  operation  consists  in  plunging  them,  tied  in  bun- 
dles, into  water,  where  they  are  left  until  fermentation  commences, 
which  is  manifested,  in  stagnant  waters,  by  a  very  disagreeable 
odour.  The  bundles  are  then  withdrawn  from  the  rotting-pond^ 
and,  after  having  been  dried  in  the  air,  are  subjected  to  mechanical 
operations,  of  which  the  object  is  to  detach  the  foreign  substances, 
which  have  become  friable  by  the  desiccation  ensuing  on  the  rotting, 
and  to  isolate  the  fibres.  Hemp  and  flax  thus  prepared  are  fit  to 
be  converted  by  spinning  into  unbleached  thready  which  may  be  im- 
mediately used  for  weaving.  Cotton  undergoes  no  preliminary  pre- 
paration, and  may  be  immediately  spun  and  woven. 

§  1741.  Wool,  as  it  is  found  on  the  living  animal,  is  impregnated 


782  TECHNICAL  ORGANIC   CHEMISTRY. 

with  a  considerable  quantity  of  foreign  substances,  commonly  called 
grease,"^  (suint,)  and  which  consist  essentially  of  substances  soluble 
in  water,  and  fatty  substances  insoluble  in  that  fluid.  Sheep  are 
usually  washed  before  being  shorn,  and  then  yield  what  is  called 
tvashed  wool,  which  has  thus  lost  a  large  portion  of  its  soluble  mat- 
ters, and  a  portion  of  the  fatty  matters,  which  separated  in  the  state 
of  an  emulsion.  Wool  which  has  not  undergone  this  operation  is 
called  unwashed  wool;  and  the  process  by  which  the  grease  is 
removed  from  wool  is  known  by  the  name  of  scouring. 

Unwashed  is  scoured  with  washed  wool,  in  a  bath  of  300  litres  of 
water  and  72  to  78  of  putrid  urine,  the  whole  being  heated  to  122° 
or  140°  for  soft  wool,  and  to  158°  or  167°  for  harsh  wool.  After 
dipping  3  or  4  kilog.  of  unwashed  wool  into  the  bath,  and  stirring 
it  with  a  stick  for  10  minutes,  they  are  removed,  and  allowed  to 
drain  over  the  kettle  ;  the  same  being  done  with  another  lot  of  3  or 
4  kilog.,  until  about  40  kilog.  in  all  have  been  thus  treated.  6  or 
7  kilog.  of  putrid  urine  are  then  added,  and  50  kilog.  of  washed 
wool  passed  through  it,  which  is  scoured,  both  by  the  carbonate  of 
ammonia  of  the  putrefied  urine  and  the  alkaline  substances  yielded 
by  the  unwashed  wool.  The  same  operation  is  repeated  on  a  new 
lot  of  40  kilog.  of  washed  wool ;  after  which  a  new  dose  of  6  or  7 
litres  of  putrid  urine  is  added,  and  20  kilog.  of  unwashed  wool 
washed  in  it.  This  alternate  scouring  of  washed  and  unwashed 
wool  is  continued  during  the  whole  day,  adding  urine  at  each  fresh 
quantity  of  unwashed  wool.  After  this  operation,  the  unwashed 
should  be  considered  as  washed  wool,  and  treated  accordingly. 

When  the  wool-scourer  has  no  unwashed  wool,  he  makes  his  bath 
of  650  litres  of  water  and  300  litres  of  urine,  heats  it  to  120°  or 
140°,  and  passes  through  it  30  kilog.  of  wool  in  5  lots,  each  of  which 
he  leaves  in  the  bath  for  12  or  15  minutes,  after  which  he  adds  1 
litre  of  water  and  2  of  urine,  and  then  scours  an  additional  portion 
of  30  kilog.,  and  so  on.  Some  scourers  add  marly  clay  to  their 
bath. 

Washed  wool  contains  less  than  15  per  cent,  of  grease,  while  un- 
washed contains  much  more;  and,  by  washing,  scouring,  and  drying, 
loses  as  much  as  60  or  70  per  cent,  of  its  weight.  When  the  washed 
wools  contain  less  than  5  per  cent,  of  grease,  they  are  scoured  with 
soap  or  carbonate  of  soda. 

The  nature  of  the  fatty  matters  of  the  grease  is  peculiar,  and  they 
have  been  called  stearerin  and  elaierin  ;  the  first  of  which  is  souble 
but  uncrystallizable,  while  the  second  is  oleaginous.  These  fats  are 
not  saponified  by  weak  alkaline  lyes,  but,  when  they  are  boiled  for 
a  long  time  with  a  solution  of  caustic  potassa,  the  liquid  is  found 
to  contain  two  salts  of  potassa,  formed  by  peculiar  fat  acids,  which 
have  been  called  stearefic  and  elaieric  acids;  while  nothing  analo- 


*  In  England  it  is  called  the  yolk. — Trans. 


DYEING.  783 

gous  to  glycerin  has  yet  been  found.  The  oxygen  of  the  air  may 
possibly  have  some  share  in  the  formation  of  these  fat  acids. 

After  scouring,  the  wool  is  washed  in  river-water  in  willow  baskets. 
When  it  is  intended  to  be  perfectly  white,  it  is  exposed  for  some 
time  in  a  moist  state  in  rooms  in  which  sulphur  is  burned,  when  the 
sulphurous  acid  finishes  the  bleaching,  (§  131,)  and  the  excess  of  it 
is  removed  by  fresh  washings.  It  is  important  not  to  prolong  too 
much  the  action  of  the  sulphurous  acid,  because  it  exerts  a  decom- 
posing agency  on  the  nitrogenous  substance  of  the  wool. 

Wool  contains,  in  addition,  a  proximate  sulphuretted  principle, 
which  may  be  separated  by  successive  immersions  in  limewater. 
Wool  which  has  been  heated  with  a  weak  alkaline  solution  disen- 
gages sulf  hydric  acid  when  it  is  again  heated  with  acidulated  water, 
and  is  blackened  when  boiled  with  a  solution  of  a  salt  of  lead  or 
protoxide  of  tin. 

§  1742.  Raw  silk,  as  it  is  obtained  from  the  cocoons,  is  impregnated 
with  a  gelatinous  substance,  which  makes  it  very  stiff,  and  generally 
gives  it  a  golden-yellow  tinge.  This  substance,  which  forms  about 
^  of  the  weight  of  raw  silk,  dissolves  readily  in  alkaline  liquids ;  but 
as  the  caustic  alkalies  attack  the  silk  itself,  soap  is  almost  always 
used,  and  sometimes,  though  rarely,  carbonate  of  soda. 

This  operation,  which  is  called  scouring  (ddcreusage)  the  silk,  is 
divided  into  three  stages :  the  ungumming,  (degommage,)  boiling,  and 
bleaching.  The  ungumming  is  done  in  a  tinned  boiler,  containing, 
for  every  100  parts  of  silk,  1800  or  2500  parts  of  water  and  30  of 
soap.  It  is  first  boiled  to  dissolve  the  soap,  and  then  cold  water  is 
added,  so  as  to  lower  the  temperature  to  about  200°,  when  the  silk 
is  dipped  into  it  in  skeins,  supported  by  sticks,  called  lisoirs,  being 
there  left  until  all  the  gelatinous  matter  is  dissolved,  and  afterward 
wound  on  a  bobbin.  This  operation  lasts  from  f  to  IJ  hour.  Seve- 
ral skeins  are  then  united,  forming  a  hank,  which  is  boiled  for  la- 
bours in  a  bath  containing  20  or  30  parts  of  soap  for  2000  of  water, 
which  constitutes  the  boiling,  (cuite.)  The  hanks  are  undone,  twisted 
into  skeins,  wound  on  a  bobbin,  and  then  washed  in  a  weak  solution 
of  carbonate  of  soda  and  in  river-water.  The  bleaching  consists  in 
dipping  the  silk  held  by  the  lisoirs  into  a  bath  heated  to  203°,  and 
composed  of  300  litres  of  water  and  from  500  to  750  grammes  of 
white  Marseilles  soap.  Silks  which  are  intended  to  be  brilliantly 
white  are  exposed,  in  addition,  to  sulphurous  acid. 

PRELIMINARY  PREPARATION  OF  STUFFS. 

§  1743.  Before  being  printed,  cotton  stuffs  are  singed  or  shorn, 
with  the  intention  of  removing  the  filaments  which  project  from  the 
tissue.  The  shearing  is  performed  by  machines,  called  shearing- 
machines,  composed  of  two  revolving  cylinders,  one  of  which,  fur- 
nished with  brushes,  raises  the  nap,  while  the  other,  provided  with 
knives  arranged  spirally,  shears  it.     In  singing,  the  stuff  is  passed 


784  TECHNICAL   ORGANIC   CHEMISTRY. 

rapidly  over  a  metallic  cylinder,  heated  to  nearly  a  white-heat,  which 
burns  off  the  down. 

§  1744.  Cotton  stuffs  which  are  intended  to  be  perfectly  white 
are  previously  bleached,  which  operation  is  also  more  or  less  com- 
pletely performed  on  goods  which  are  to  be  printed. 

Linen  and  cotton  goods  are  bleached  by  two  different  processes: 

1.  By  washing  them  in  alkaline  lyes,  and  exposing  them  on  the 
grass;  2.  By  chlorine  or  the  alkaline  hypochlorites. 

The  first  is  the  oldest,  and  was  used  particularly  for  bleaching 
flax  and  hempen  goods.  It  is  divided  into  the  following  opera- 
tions : — 1.  Scouring,  which  consists  in  dipping  the  stuffs  for  24  hours 
in  a  weak  solution  of  caustic  potassa,  heated  to  about  99°,  wash- 
ing, and  then  boiling  them  for  20  minutes  in  the  same  alkaline  lye. 

2.  The  boiling,  which  consists  in  boiling  (as  was  stated  §  1743)  the 
scoured  stuffs,  after  having  washed  them  in  water,  and  compressed 
them  between  cylinders,  3.  Bleaching,  which  consists  in  boiling 
them  for  6  hours  with  an  alkaline  lye,  containing  1  part  of  caustic 
potassa  for  16  parts  of  stuff,  washing  them,  and  exposing  them  for 
5  or  6  hours  on  the  grass ;  the  alkaline  washings  and  exposure  on 
the  grass  being  renewed  until  the  stuffs  are  perfectly  bleached. 
During  the  exposure  on  the  grass,  the  colouring  matters  are  bleached 
by  the  influence  of  the  solar  rays  and  moisture ;  the  absorption  of 
oxygen  converting  them  into  new  substances  more  readily  soluble 
in  the  alkaline  liquors.  Lastly,  the  stuffs  are  passed  through  water 
heated  to  105°  or  120°,  containing  about  -^^  of  sulphuric  acid,  which 
dissolves  the  metallic  oxides;  after  which  they  are  washed  and 
calendered. 

This  process  requires  a  great  length  of  time,  and  bleaching  by 
chlorine  or  the  hypochlorites  is  more  expeditious.  The  chlorine 
acting  on  the  colouring  matters,  in  the  presence  of  water,  decomposes 
the  water  into  hydrogen,  which  combines  with  the  chlorine  to  form 
chlorohydric  acid ;  while  the  oxygen  in  the  nascent  state  oxidizes 
the  resinous  and  colouring  matters,  and  renders  them  soluble  in 
alkaline  lixiviae.  The  hypochlorites  are  reduced  to  the  state  of  me- 
tallic chlorides,  and  act  at  the  same  time  by  means  of  the  nascent 
oxygen  given  off  by  the  hypochlorous  acid  and  the  base ;  while  the 
concurrence  of  an  acid  effecting  the  decomposition  of  the  hypochlo- 
rites hasten  the  bleaching.  Thus  in  both  processes  it  is  in  the  end 
always  an  oxidizing  action  which  effects  the  bleaching  and  destruc- 
tion of  the  foreign  substances. 

Hypochlorite  of  lime,  dissolved  in  water,  is  now  solely  used  in 
bleaching;  and  it  is  preferable  to  all  dilute  solutions,  because  it  is 
less  liable  to  injure  the  ligneous  fibre  of  the  tissue;  although  the 
bleaching  then  requires  more  time. 

The  stuffs,  after  being  passed  over  the  heated  cylinder  to  be 
singed,  are  immediately  dipped  into  a  vat  filled  with  water  to  cool 
them,  where  they  then  remain  for  24  hours,  and  lose  a  considerable 


DYEING.  V85 

portion  of  tlieir  soluble  principles.  They  are  then  to  be  perfectly 
dried,  either  by  being  beaten  or  compressed  between  cylinders, 
and  then  kept  for  12  hours  in  a  vat  filled  with  water  heated  by 
steam,  where  they  are  arranged  in  alternate  layers  with  slaked  Lime. 
After  being  again  beaten,  they  are  left  for  12  hours  in  a  lye  of 
caustic  soda,  consisting,  for  300  parts  of  stuffs,  of  10  parts  of  caus- 
tic soda  for  1500  of  water.  This  lye  is  replaced  by  another  con- 
taining only  7.5  of  soda,  which  is  also  allowed  to  act  for  12  hours; 
after  which  the  stuffs,  pressed  dry,  are  passed  through  the  hypochlo- 
rite of  lime,  and  then  through  sulphuric  acid.  The  bath  of  hypo- 
chlorite generally  contains  0.15  litre  of  chlorine  in  a  litre  of  water; 
and  the  stuffs,  after  being  immersed  in  it,  are  passed  between  two 
wooden  cylinders,  descending  thence  immediately  into  a  bath  acidu- 
lated with  sulphuric  or  chlorohydric  acid,  which  hastens  the  bleaching 
by  isolating  the  hypochlorous  acid.  After  being  washed  in  fresh 
water,  they  are  for  a  second  time  subjected  to  the  action  of  alkaline 
lyes,  hypochlorite  of  lime,  and  the  acid  bath;  and  lastly,  after  an- 
other washing  in  fresh  water,  they  are  dried  in  drying-machines, 
and  more  body  is  given  to  them  by  dressing  them  with  starch. 

Mordants. 

§  1745.  The  tissues  of  muslin  or  linen  stuffs  have,  for  a  great 
number  of  colouring  substances,  an  affinity  sufficiently  powerful  to 
fasten  them  on  their  surface,  and  to  acquire  a  deep  colour;  while 
the  combination  is  rarely  strong  enough  to  enable  them  to  resist 
washing,  particularly  with  alkaline  soaps.  They  are  made  fast,  and 
at  the  same  time  the  colour  is  heightened,  by  previously  depositing 
on  the  tissues  certain  substances  which  have  a  greater  affinity  for 
these  tissues  than  the  colouring  matters,  and  which  possess,  at  the 
same  time,  the  property  of  forming  with  the  colouring  matters  com- 
pounds sufficiently  fixed  to  resist  washing  in  fresh  water  and  in  soap- 
suds. These  substances,  which  thus  play  an  intermediate  part 
between  the  woven  fabric  and  the  colouring  matters,  are  called 
mordants.  The  affinities  by  virtue  of  which  they  are  fastened  on  the 
fabric  exhibit  this  essential  difference  from  those  observed  in  ordinary 
chemical  operations,  that,  in  the  latter,  combination  generally  ensues 
only  between  disaggregated  substances,  and  if  one  of  the  substances 
is  originally  aggregated,  it  becomes  disaggregated  by  the  simple 
fact  of  combination;  while,  in  dyeing,  the  woven  fabric  retains  its 
form  and  consistence  without  being  in  the  slightest  degree  disaggre- 
gated by  the  mordants  and  colouring  matters. 

Certain  mordants  do  not  change  the  shade  of  the  colouring 
matters,  such,  for  example,  as  the  salts  of  alumina  and  chlorides  of 
tin;  while  others,  on  the  contrary,  alter  the  colour,  as  the  salts  of 
iron,  manganese,  and  copper.  The  salts  of  alumina  used  as  mor- 
dants are  the  sulphate,  and  acetate  of  alumina,  and  alum ;  the  fast- 
ening of  colours  with  alum  being  also  called  aluming. 

Vol.  il.— jO 


786  TECHNICAL    ORGANIC    CHEMISTRY. 

In  order  to  alum  cotton,  flax,  or  hempen  stuffs,  they  are  left  for 
24  hours  in  a  tepid  bath  containing  1  part  of  alum  for  6  parts  of 
fabric,  when  a  portion  of  the  alum  adhering  to  the  stuff  renders  the 
latter  fit  for  dyeing.  For  dark  colours,  the  ordinary  alum  of  com- 
merce is  used ;  Roman,  or  purified  alum,  (§  600,)  being  preferred  for 
bright  colours,  because  common  alum  always  contains  a  small 
quantity  of  sulphate  of  iron,  which  would  modify  the  shade. 

Wool  is  alumed  by  being  first  boiled  in  bran-water  for  an  hour 
and  washed  in  fresh  water,,  and  then  kept  for  2  hours  in  a  boiling 
solution  which  contains  10  to  15  per  cent,  of  alum,  a  small  quantity 
of  cream  of  tartar  being  generally  added,  which  facilitates  the  de- 
posit of  the  alumina  on  the  tissue,  perhaps  by  converting  a  portion 
of  the  sulphate  of  alumina  into  a  tartrate  of  more  easy  decomposi- 
tion. When  the  wool  is  alumed,  it  is  left  to  rest  for  2  days,  before 
dyeing,  in  order  to  render  the  combination  of  the  mordant  with  the 
fibres  more  intimate. 

Silk  is  alumed  when  cold,  by  keeping  it  for  15  or  16  hours  in  a 
bath  containing  ^  of  alum ;  after  which  it  is  removed  and  washed. 

Acetate  of  alumina,  w^hich  is  often  used  as  a  mordant  for  ligneous 
stuffs,  and  for  certain  colours,  is  prepared  by  decomposing  alum  by 
acetate  of  lead ;  the  solution  of  acetate  of  alumina  thus  obtained 
being  generally  thickened  with  starch  or  gum. 

Stuffs  of  lignin  mordanted  with  alum,  are  again  subjected,  before 
being  dyed,  to  another  operation,  the  effect  of  which  is  not  well  un- 
derstood :  they  are  immersed,  for  some  time,  in  two  baths  of  water, 
containing  6  or  8  per  cent,  of  cow-dung.  To  the  first  of  these  baths  a 
certain  quantity  of  chalk  is  added,  the  intention  of  which  appears 
to  be  to  saturate  the  acid  partly  adhering  to  the  tissue  with  the 
mordant ;  while  the  second  contains  only  water  and  dung.  The 
temperature  of  these  two  baths  varies  according  to  the  nature  of 
the  stuffs  and  that  of  the  mordants.  The  cow-dung  appears  to  act 
by  means  of  the  phosphates  it  contains,  for  a  mixture  of  phosphate 
of  soda  and  lime  can  be  substituted  for  it. . 

Protochloride  of  tin  is  chiefly  used  for  obtaining  the  oxide  of  tin 
as  a  mordant,  which  adheres  very  firmly  to  the  tissues.  Bichloride 
of  tin  is  often  used  for  freshening  colours,  particularly  those  of 
cochineal  and  madder.  The  mordant  of  oxide  of  iron  is  furnished 
by  the  protacetate  of  iron,  prepared  by  the  reaction  of  pyroligneous 
acid  on  old  iron. 

Dyeing. 

§  1746.  After  the  stuffs  are  mordanted,  they  are  immersed,  in  order 
to  be  dyed,  in  solutions  of  colouring  matter,  of  various  temperatures, 
and  then  left  for  a  longer  or  shorter  time,  according  to  the  nature  of 
the  stuff  and  the  tint  of  colour  to  be  obtained.  It  is  essential  that 
all  parts  of  the  fabric  should  remain  the  same  length  of  time  in  the 
dye  ;  to  which  effect  it  is  rolled  around  a  wooden  roller  suspended 


CALICO    PRINTING,  ETC.  787 

over  the  dye-tub,  and  is  unrolled  through  the  tub ;  this  process  being 
continued  until  the  colour  has  obtained  the  shade  required.  In 
order  to  obtain  a  uniform  shade,  it  is  better  to  use  several  successive 
baths  of  different  strength,  commencing  with  the  weakest.  The 
baths  are  sometimes  composed  of  a  single  colouring  matter,  and 
sometimes  of  a  mixture  of  several,  while  at  other  times  the  stuff  is 
passed  successively  through  two  baths  containing  different  colours, 
and  thus  an  intermediate  shade  is  obtained.  The  colours  are  fast- 
ened by  washing  in  soapsuds  or  in  other  solutions. 

It  would  lead  us  too  far  to  give  a  description  of  the  methods  of 
preparing  the  different  solutions  for  dyeing,  and  the  manipulations 
of  the  process. 

Oalico  and  other  printing.  < 

§  1747.  Designs  of  various  colours  are  printed  on  smooth  goods ; 
the  impression  being  effected  either  by  an  actual  printing  off  of  the 
colouring  matter  by  means  of  wooden  blocks  carved  in  relief,  or 
engraved  rollers  of  copper  ;  or  by  the  sole  application  of  mordants 
followed  by  dyeing  in  the  tub.  In  the  latter  case,  the  colouring 
matter  adheres  only  to  the  mordanted  designs,  the  latter  retaining 
the  shade  desired,  and  the  ground  of  the  stuff  preserving  its  original 
colour  after  being  washed. 

Colouring  matters  printed  directly  on  stuffs  should  be  thickened, 
so  that  they  will  not  run,  and  that  the  designs  may  retain  their 
sharpness.  The  thickening  substances  used  are  starch,  gum-sene- 
gal,  and  gum-tragacanth,  to  which  a  certain  quantity  of  pipe-clay, 
and  sometimes  of  gelatin,  is  often  added.  The  stuffs  should  be  pre- 
viously mordanted,  or  the  mordant  incorporated  with  the  colour. 

§  1748.  In  order  to  explain  how  designs  are  produced  by  dyeing, 
we  shall  give  some  examples.  Let  us  suppose  that  a  red  design  is 
to  be  produced  on  a  white  ground:  the  design  is  then  printed  on 
the  stuff  with  a  thickened  mordant  of  alum,  and  the  stuff  passed 
through  the  madder-tub  ;  when  the  colouring  matter  adheres  firmly 
only  to  the  mordanted  design,  which  alone  will  remain  red  after 
washing.  If,  on  the  contrary,  a  white  picture  is  to  be  produced  on 
a  red  ground,  the  picture  is  first  printed  with  a  properly  thickened 
oleaginous  substance,  and  passed  through  the  mordant,  by  which 
means  the  picture  is  reserved,  and  when  the  stuff  is  passed  through 
the  madder-tub  the  ground  alone  will  be  dyed  red.  Another  method 
still  may  be  employed  by  dyeing  the  stuff  of  a  uniform  red  colour, 
and  printing  the  design  with  a  non-volatile  vegetable  acid,  such  as, 
for  example,  citric  or  tartaric,  sufficiently  thickened  ;  after  which  it 
is  passed  through  a  bath  of  hypochlorite  of  lime,  which  imme- 
diately destroys  the  picture,  without  attacking  the  ground.  This 
process  is  called  discharging  the  colour. 

In  order  to  obtain  a  violet  design  on  a  more  or  less  deep  red 
ground,  the  stuff  is  mordanted  with  alum,  and  the  design  printed 


Y88  TECHNICAL   ORGANIC    CHEMISTRY. 

with  a  thickened  mordant  of  iron,  and  then  passed  througlf  the 
inadder-tub ;  when  the  ground  will  become  red,  and  the  design 
violet.  If,  on  the  contrary,  a  red  design  on  a  violet  ground  is  de- 
sired,  the  stuiF  is  passed  through  a  mordant  of  alumina,  and  the 
design  printed  with  an  oily  substance ;  and  after  being  mordanted 
with  acetate  of  iron,  the  oily  reserve  is  removed  by  alkaline  lyes, 
and  the  stuiF  is  passed  through  the  madder-tub. 

Designs  of  more  than  two  colours  are  obtained  by  machines  com- 
posed of  several  cylinders,  each  of  which  prints  a  peculiar  mordant, 
or  reserve,  or  acid  on  the  stuff,  which  then  passes  into  the  dif- 
ferent dye-vats.  Although  the  processes  described  are  far  from 
being  the  only  ones  used  in  dyeing,  they  will  serve  to  give  a  general 
idea  of  the  art. 

Fixing  of  Colours  hy  Steam. 

§  1749.  Many  colours  are  more  firmly  fastened  and  afford  more 
beautiful  shades  when  the  dyestuffs  are  exposed  to  the  action  of 
steam.  Under  the  influence  of  heat,  the  woven  fabric  and  colouring 
matters  become  more  closely  combined,  and  the  shades  are  often 
modified  in  a  peculiar  manner. 

TANNING. 

§1750.  Skins  of  animals  soon  become  putrid  in  moist  air;  and 
although  they  will  preserve  for  a  long  time  in  dry  air,  they  become 
hard  and  brittle.  The  intention  of  tanning  is  to  combine  the  ani- 
mal substance  with  a  certain  quantity  of  tannin,  which  renders 
them  imputrescible,  and  gives  them  softness  and  impermeability; 
while  the  latter  properties  are  still  further  increased  by  the  process 
of  currying.  A  tanned  hide  is  called  leather.  Three  kinds  of 
skins  are  used  in  tanning :  green  hides,  or  the  fresh  skins  brought 
to  the  tanner  soon  after  the  death  of  the  animal ;  and  dry  and  salt 
hides,  which  come  from  foreign  countries,  chiefly  from  South  Ame- 
rica. Hides  are  divided  into  two  kinds :  soft  hides,  which  retain 
their  suppleness  after  tanning,  and  hard  hides,  which,  on  the  con- 
trary, are  to  be  very  hard,  and  as  impervious  as  possible.  Soft 
hides  are  made  from  the  skins  of  cows,  calves,  horses,  etc. ;  while 
those  of  the  ox  and  buffalo  are  reserved  for  hard  hides.  Yery  thin 
and  soft  hides  are  prepared  from  the  skins  of  sheep  and  goats, 
which  are  used  for  making  gloves  or  in  the  manufacture  of  mo- 
rocco. 

Skins  intended  for  soft  hides  are  subjected  to  a  previous  washing 
in  running  water,  in  order  to  soften  and  soak  them,  and  remove  all 
their  soluble  principles ;  which  operation  lasts  only  for  2  or  3  days 
for  green  skins,  but  for  a  much  longer  time  for  dry  or  salt  skins, 
because  the  latter  must  be  submitted  to  several  washings,  treadings, 
and  stretchings,  before  they  acquire  the  necessary  pliancy. 

After  being  soaked,  the  skins  are  carried  to  the  scalding-vats^ 


TANNING.  789 

consfsting  generally  of  five  vessels  filled  with  milk  of  lime,  of  greater 
or  less  strength.  The  skins  pass  successively  through  them,  com- 
mencing with  the  weakest.  Each  vat  contains  from  200  to  300 
jkins  ;  the  whole  operation  lasting  3  or  4  weeks. 

This  being  done,  the  hair  is  removed,  by  scraping  the  skins  from 
above  downward,  with  a  dull  knife:  after  which  they  are' washed 
and  worked  on  the  horse-beam :  1st.  In  order  to  remove  any  scraps 
of  flesh  which  might  adhere  to  them ;  2dly.  To  remove  the  useless 
portions,  and  the  edges,  which  are  always  thicker  than  the  other 
parts ;  3dly.  To  smooth  the  asperities  which  cover  the  skin  on  the 
hairy  side,  which  is  done  with  a  piece  of  well-cemented,  hard  sand- 
stone ;  4thly.  To  completely  cleanse  both  sides  of  the  skin,  which 
is  done  with  a  circular  knife,  wetting  the  skin  frequently.  After 
these  various  operations,  the  skins  are  raised;  that  is,  they  are  left 
for  several  days  in  weak  acids,  for  which  purpose  the  ooze,  (jusde,) 
or  infusion  of  tan,  is  generally  used,  consisting  of  the  tan  exhausted 
by  the  tanning  of  skins  in  the  vats,  and  which,  after  having  become 
acid  in  the  air,  contains  a  certain  quantity  of  lactic  acid.  During 
the  first  four  days,  the  skins  are  removed  every  day,  fresh  ooze 
being  added  each  time ;  after  which  they  are  allowed  to  remain  for 
3  or  4  days  in  the  ooze,  and  are  then  carried  to  a  weak  infusion  of 
new  tan,  where  they  remain  for  15  days,  increasing  the  strength  of 
the  liquid  from  time  to  time.  They  thus  undergo  a  kind  of  preli- 
minary tanning,  and  are  prepared  for  the  ultimate  tanning,  in  the 
vats.  The  latter,  which  are  of  mason-work,  are  first  charged  with 
a  layer  of  old  tan,  about  0.15  m.  in  thickness,  then  with  a  layer  of 
fresh  tan,  only  a  few  centifnetres  thick ;  after  which  the  skins  are 
laid  upon  each  other,  being  separated  by  layers  of  tan ;  and  lastly, 
above  the  last  coat  of  tan  a  layer  of  old  tan  is  placed,  0.3  m.  in 
thickness;  when  the  whole  is  covered  with  boards,  kept  down  by 
heavy  stones.  Enough  water  is  then  let  in  to  moisten  the  whole 
mass,  dissolve  the  tannin,  and  bring  it  successively  in  contact  with 
the  skins.  The  vats  thus  filled,  and  containing  600  or  700  skins, 
are  left  for  5  or  8  months,  during  which  time  the  skins  are  only 
once  taken  out,  in  order  to  renew  the  tan  between  them. 

§  1751.  In  making  coarse  leather,  the  scalding,  which  here  is  not 
suflficiently  efficient,  is  replaced  by  a  slight  putrid  fermentation  of 
the  skins,  in  rooms  warmed  by  steam.  The  hair  is  then  removed 
in  the  ordinary  way,  and  they  are  placed  in  the  ooze,  the  raising 
being  accelerated  by  the  addition  of  a  small  quantity  of  sulphuric 
acid  from  time  to  time ;  after  which  they  are  buried  with  the  tan 
in  the  vats,  where  they  are  left  for  18  months  or  two  years. 

Hides  may  be  tanned  much  more  rapidly,  by  keeping  the  swollen 
skins  for  2  or  3  weeks  in  infusions  of  tan,  which  are  frequently  re- 
placed by  stronger  ones.  The  leather  thus  made  is  not  so  strong, 
and  has  a  deep  colour,  which  keeps  down  its  price. 

§  1752.  After  being  tanned,  the  hides  are  cleaned  on  tables,  with 


790  TECHNICAL   ORGANIC   CHEMISTRY. 

brushes,  and  then  dried  in  the  air,  when  they  are  hammered  or 
rolled,  so  as  to  give  them  the  proper  consistence ;  after  which  they 
are  sold  to  the  currier,  when  they  undergo  various  mechanical  ope- 
rations, and  are  impregnated  with  fatty  substances,  according  to  the 
uses  to  which  they  are  destined.  Leather  is  generally  coloured 
black  with  acetate  of  iron,  made  by  dissolving  scraps  of  old  iron  in 
sour  beer ;  several  coats  of  this  salt  being  passed  over  the  surface 
of  the  leather ;  when  the  tannin  combines  with  the  protoxide  of 
iron,  which,  by  the  action  of  the  air,  passes  into  the  state  of  sesqui- 
oxide,  and  produces  a  very  intense  black. 

§  1753.  The  sheep  and  kid  skins  used  for  glove  making  are  cleaned 
by  smearing  the  fleshy  side  with  a  mixture  of  lime  and  orpiment, 
when  in  24  hours  the  hair  comes  off  with  the  greatest  ease.  The 
skins  are  then  worked  into  various  shapes  on  the  beam,  and  are 
then  immersed  for  3  weeks  in  winter,  and  only  2  or  3  days  in  sum- 
mer, in  a  bran-bath,  which,  by  fermentation,  produces  lactic  acid, 
and  effects  the  raising  of  the  skins.  The  latter  are  then  made  im- 
putrescible,  not  by  tannin,  but  by  chloride  of  aluminum,  for  wlijch 
purpose  they  are  dipped  into  a  hot  solution,  containing,  for  each 
skin,  600  to  900  gm.  of  alum,  and  150  to  200  gm.  of  sea-salt.  They 
are  then  bleached,  by  immersion  for  12  hours  in  a  bath  composed, 
for  each  skin,  of  600  or  700  gm.  of  flour,  and  the  half  of  the  yolk 
of  an  egg,  which  is  beaten  to  the  consistence  of  honey,  adding  the 
tepid  liquor  which  was  used  for  aluming.  The  skins  are  then  dried, 
and  subjected  to  various  mechanical  operations. 

§  1754.  Morocco  is  chiefly  made  from  goat-skins,  which,  after 
being  fleshed,  and  deprived  of  their  hair  by  lime,  are  washed  for  a 
long  time  with  the  greatest  care,  in  order  to  entirely  remove  the 
lime,  which  would  injure  their  quality ;  and  to  effect  this  more  per- 
fectly, they  are  left  for  24  hours  in  a  bath  of  sour  bran.  Skins 
intended  to  be  dyed  red  are  sewn  together  by  twos,  the  fleshy  side 
within,  so  as  to  form  a  bag  which  will  hold  air ;  after  which  they  are 
dipped  into  a  bath  of  chloride  of  tin,  which  acts  as  a  mordant,  and 
subsequently  into  one  of  cochineal,  to  dye  them.  After  being 
rinsed,  one  side  of  the  bag  is  ripped  open,  and  the  tanning  matter 
introduced,  the  latter  in  this  case  consisting  of  sumac,  which  is  much 
richer  in  tannin  than  tan  is ;  and  they  are  then  stirred  for  4  hours 
in  a  weak  solution  of  sumac,  where  they  are  left  for  two  days. 
Morocco  which  is  to  be  dyed  of  any  other  colour  than  red  is  tanned 
before  being  dyed ;  and  in  all  cases  the  skins  are  subjected  to  nu- 
merous mechanical  operations  before  being  fit  for  sale. 

CARBONIZATION  OF  WOOD  AND  BITUMINOUS  COAL. 

§  1755.  The  greater  portion  of  charcoal  used  is  made  in  the  woods, 
by  carbonizing  wood  inpits."^     On  a  very  hard  hearth,  three  or  four 

*The  American  technical  term  "pits,"  for  the  heaps  of  wood  to  be  carbonized, 


MANUFACTURE  OF  CHARCOAL,  ETC.  791 

large  sticks,  forming  a  chimney  of  from  0.25  m.  to  0.30  m.  in 
length,  are  arranged  vertically ;  and  around  this  chimney  the  wood 
is  set  upright,  in  three  diflferent  stories,  the  diameters  of  which 
diminish  successively,  so  as  to  form  the  trunk  of  a  cone  resting  on 
its  larger  base.  The  largest  sticks  are  placed  nearest  the  axis  of  the 
kiln,  and  the  smallest,  with  the  branches,  near  the  surface ;  after 
which  the  pit-kiln  is  covered  with  earth,  leaves,  and  coal-dust  aris- 
ing from  preceding  operations.  Holes  pierced  through  the  base  of 
the  pit  allow  of  the  introduction  of  the  air  necessary  to  combustion. 

When  the  pit  is  built,  a  fire  of  pine-wood  is  made  in  the  chim- 
ney, and  kept  up  for  2  or  3  hours,  at  the  end  of  which  time  it 
has  communicated  to  the  neighbouring  logs,  and  the  chimney  is 
almost  wholly  filled  with  small  charcoal :  it  is  then  covered,  and 
holes,  which  act  as  chimneys  and  draw  combustion  to  the  parts  they 
penetrate,  are  made  around  the  upper  part  of  the  pit.  Thick, 
white  smoke  at  first  escapes,  but  it  soon  becomes  transparent  and 
bluish,  which  is  a  sign  that  combustion  is  progressing  in  the  upper 
part  of  the  kiln.  The  upper  holes  are  then  closed,  and  others  made 
somewhat  lower  down,  which  are  again  closed  when  the  same  smoke 
again  appears,  others  being  made,  and  so  on,  until  the  bottom  of 
the  pit  is  reached.  Carbonization  thus  extends  from  above  down- 
ward ;  and  the  surface  of  separation  of  the  carbonized  wood  and 
that  yet  untouched  by  the  fire,  is  an  inverted  cone,  having  the  same 
axis  with  that  of  the  pit,  and  spreading  more  and  more  as  carboni- 
zation advances,  to  be  at  last  lost  in  the  base  of  the  pit.  The  wood 
diminishes  considerably  in  volume  by  carbonization,  and  the  pit  be- 
comes smaller.  When  carbonization  is  terminated,  the  openings 
are  closed,  and  the  fire  is  allowed  to  go  out,  after  which  the  heap  is 
overturned,  and  the  imperfectly  carbonized  pieces  are  picked  out, 
which  would  smoke  in  the  fire. 

The  gases  evolved  during  combustion  are  composed  of  nitrogen, 
which  proceeded  from  the  air  used  in  combustion ;  carbonic  acid 
and  oxide,  produced  partly  by  active  combustion  of  the  wood,  and 
partly  by  its  calcination  ;  hydrogen  ;  vapour  of  water ;  and  several 
organic  substances  furnished  by  the  distillation  of  the  wood,  among 
which  may  be  distinguished  acetic  acid,  wood-spirit,  and  tarry  sub- 
stances. The  relative  proportion  of  all  these  products  varies  at  the 
diiferent  stages  of  the  process. 

Wood  yields,  by  carbonization  in  pits,  about  15  per  cent,  of  char- 
coal, and  25  to  30  by  distillation  in  close  vessels;  but  the  latter 
process  is  one  adopted  with  advantage  only  in  the  making  of  pyro- 
ligneous  acid  and  tar,  the  charcoal  thus  obtained  being  not  much 
valued  on  account  of  its  lightnese. 

§  1756.  Bituminous  coal  is  often  carbonized  in  pits  in  the  vicinity 

must  not  be  confounded  with  the  usual  meaning  of  the  word.  The  German  name 
meiler  is  used  in  England. —  W.  L.  F. 


792  TECHNICAL   ORGANIC   CHEMISTRY. 

of  the  mines.  The  pits  generally  receive  an  elongated  prismatic 
shape,  and  contain  horizontal,  longitudinal,  and  transverse  canals, 
besides  vertical  chimneys,  for  the  circulation  of  air.  The  largest 
lumps  of  coal  are  placed  on  the  inside  and  the  smallest  on  the  out- 
side ;  while  the  covering  is  made  of  coal-dust  and  coke,  moistened 
to  give  it  more  consistence.  The  process  closely  resembles  that  of 
Qiaking  wood-charcoal. 

Coke  is  also  made  by  subjecting  the  bituminous  coal  to  imperfect 
combustion  in  furnaces,  where  the  ingress  of  air  is  so  regulated  as 
to  consume  the  least  possible  quantity  of  carbon. 

Lastly,  coke  is  obtained  by  the  distillation  of  bituminous  coal  in 
retorts,  the  principal  product  being  illuminating  gas,  while  the  coke  is 
only  an  accessory  product ;  and  as  it  is  very  light,  it  is  used  only  for 
domestic  purposes. 

ILLUMINATING  GAS. 

§  1757.  Illuminating  gas  is  generally  obtained  from  the  calcina- 
tion of  bituminous  coal ;  but  all  kinds  are  not  equally  adapted  to  the 
purpose,  the  best  being  those  designated  (§  1315)  under  the  name  of 
bituminous  coal  burning  with  a  long  flame.  The  coals  of  Mons  and 
Commentry,  which  are  generally  used  in  Paris,  yield  on  an  average 
23  cubic  metres  of  gas  for  100  kilog.  Distillation  is  effected  in  large 
cylindrical  cast-iron  retorts,  ranged  parallel  to  each  other,  to  the 
number  of  2,  3,  or  5,  over  the  same  furnace ;  each  retort  being  pro- 
vided with  a  vertical  tube,  through  which  the  coal  is  introduced,  and 
to  which  is  fastened  the  pipe  for  the  discharge  of  the  gas.  The 
temperature  of  the  furnace  should  be  kept  at  a  bright  cherry  red, 
because,  if  it  is  greater,  the  gas  does  not  give  much  light,  for  the 
bicarburetted  hydrogen  gas,  and  the  very  volatile  oils,  to  which  the 
brilliancy  of  the  flame  is  chiefly  owing,  deposit  carbon,  and  are  con- 
verted into  protocarburetted  hydrogen,  the  combustion  of  which 
gives  but  little  light;  and  if,  on  the  contrary,  the  temperature  is 
too  low,  a  large  quantity  of  essential  oil  is  formed,  which  cannot 
remain  in  suspension  in  the  gas,  but  is  deposited  in  the  refrigerators. 
The  duration  of  distillation  varies  according  to  the  quality  of  the 
coal,  its  hygrometric  state,  and  the  arrangment  of  the  apparatus ;  and 
the  residue  consists  of  a  light  coke,  much  used  for  domestic  purposes. 

The  gas  produced  by  the  distillation  of  bituminous  coal  is  com- 
posed chiefly  of  protocarburetted  hydrogen,  mixed  with  various 
quantities  of  bicarburetted  hydrogen,  hydrogen,  oxide  of  carbon, 
carbonic  acid,,  nitrogen,  oleaginous  matters  more  or  less  easily  con- 
densed, ammonjacal  and  sulphuretted  compounds,  and  tarry  sub- 
stances. As  in  this  state  it  exhales  a  very  fetid  smell,  and  the  pro- 
ducts of  its  combustion  are  themsplves  odoriferous,  it  is  necessary 
to  purify  it,  especially  for  domestic  use ;  to  which  effect  it  is  con- 
veyed from  the  retort  into  a  small  barrel,  partly  filled  with  water, 
through  a  pipe  entering  the  liquid  to  the  depth  of  2  or  3  centime- 
tres, so  as  to  intercept  the  communication  of  the  retort  with  the 


ILLUMINATING   GAS.  793 

apparatus  in  which  the  gas  is  collected.  The  greater  part  of  the 
water  and  tar  condenses  in  the  barrel,  which  is  furnished  with  a 
discharging-pipe  to  maintain  a  constant  level  in  the  barrel,  and  to 
allow  the  excess  of  the  condensed  products  to  escape.  The  gas  on 
leaving  the  barrel  traverses  a  series  of  pipes  more  or  less  cooled,  in 
which  the  condensation  of  the  water  and  tar  is  completed,  is  then 
conducted  through  boxes  containing  metallic  salts,  chiefly  chloride 
of  manganese  and  sulphate  of  iron,  which  decompose  the  ammoniacal 
salts,  and  isolate  the  sulf  hydric  acid ;  and  finally  passes  through  other 
boxes  containing  hydrated  lime,  which  absorbs  the  sulf  hydric  gas, 
the  carbon  acid,  and  the  other  acid  vapours.  But  these  purifications 
must  not  be  pushed  too  far,  because  the  gas  would  be  deprived  of 
too  much  of  its  oily  vapours,  and  its  illuminating  power  would  be 
sensibly  decreased. 

The  gas  is  collected  in  gasometers^  resembling  immense  bells,  made 
of  sheet-iron,  and  inverted  in  cisterns  of  corresponding  size,  built  of 
hydraulic  mason-work,  and  filled  with  water.  The  weight  of  the 
gasometer  is  partially  balanced  by  counterpoises,  which  should  leave  it 
only  the  weight  necessary  to  the  pressure  required  for  the  distribution 
of  the  gas  to  the  various  jets  it  is  to  feed.  The  pressure  is  composed 
of,  1st.  The  resistance  which  the  gas  meets  in  circulating  through 
pipes  ordinarily  of  great  extent;  2dly.  The  excess  of  elastic  force 
which  it  miist  retain  in  order  to  feed  the  jets ;  3dly.  The  pressure 
necessary  to  drive  it  to  the  highest  points,  the  level  of  wh^ch  is  often 
higher  than  that  of  the  gasometer.  The  last  pressure  may  be  easily 
calculated  after  ascertaining  the  difference  h  of  the  level  of  the 
gasometer  and  the  highest  jet,  and  the  density  d  of  the  gas  as  com- 
pared to  that  of  the  air,  when  it  is  equal  to  the  weight  of  a  column 
of  water,  the  height  of  which  is  represented  by  0.001293  hd."^ 

*  A  more  economical  process  of  manufacturing  gas  has  recently  been  put  in 
operation  in  Manchester,  England.  Three  or  five  retorts  are  used,  the  central  one 
of  which  is  charged  with  metallic  iron  and  coke,  or  with  coke  alone,  and  traversed 
by  a  current  of  steam,  which  thus  is  decomposed  into  hydrogen  and  oxygen.  These 
gases  are  led  through  the  other  retorts,  in  which  coal  is  being  distilled,  when  the 
free  hydrogen  combines  with  the  nascent  carbon  resulting  from  the  decomposition 
of  different  hydrocarbons,  and  forms  defiant  gas,  which  imparts  a  great  brilliancy 
to  the  flame.  The  gas  thus  manufactured  is  called  hydrocarbon  gas ;  and  I  had 
opportunity  to  assure  myself  that  its  illuminating  power  is  double  that  of  ordinary 
gas  under  the  same'  circumstances,  while  the  cost  of  producing  it  is  at  least  not 
higher.— IF.  L.  F. 


GENEEAL  INDEX 


Acetates,  ii.  546. 

Acetic  acid,  ii.  542. 

Acetone,  ii.  549. 

Acids,  vegetable,  ii.  594. 

Aconitic  acid,  ii.  597. 

Acumination  of  crystals,  1.  18. 

Adipic  acid,  ii,  697. 

Air,  analysis  of,  by  the  eudiometer,  i.  129. 

Air,  atmospheinc,  i.  119. 

Air,  only  a  mixture,  i.  131. 

Air-thermometer,  (note,)  ii.  414. 

Albumen,  ii.  453. 

Albuminous  vegetable  substanoes,  ii.451. 

Alcarsiu,  ii.  551. 

Alcohol,  ii.  511. 

Alcoholic  fermentation,  ii.  505. 

Alcoholometry,  ii,  513. 

Alcohol  and  ether,  oxidation  of,  ii.  541. 

Aldehyde,  ii,  541. 

Alkalimetry,  i.  448. 

Alkaline  earths,  their  separation    and 

determination,  i.  564. 
Alkaline  metals,  i.  434. 
Alkalino-earthy  metals,  i.  528. 
Alkaloids,  ii.  612. 
Alloys,  i.  377. 
Allyl,  ii.  675. 
Almaden,  extraction  of  mercury  at,  ii. 

291, 
Aluminum,  i.  567. 
Alumina,  salts  of,  570. 
Alumina,  characters  of  the  salts  of,  i. 

578. 
Alumina,  silicates  of,  i.  575. 

'*        sulphates  of,  i.  57a 
Alums,  manufacture  of,  i.  671. 
Amalgams,  ii.  289. 
Ammonia  and  alkalies,  determination  of, 

i.  572. 
Ammonia,  behaviour  of  potassium  and 

sodium  to,  i.  520. 
Ammonia,  carbonates  of,  i.  620. 


Ammonia,  chlorohydrate  of,  i.  616. 
"         compounds  of,  i.  514. 
"         phosphates  of,  i,  519. 
"   ^      sulf hydrate  of,  i,  518. 
Ammoniacal  salts,  distinctive  character 

of,  i.  521. 
Ammoniacal  solution,  action  of  the  bat- 
tery on  an,  i.  521. 
Amygdalin,  ii.  650. 
Amylaceous  substances,  ii.  461. 
Amylammonia,  ii.  624. 
Amylic  alcohol,  ii.  665. 
Amylic  ethers,  ii.  669. 
Analysis,  i.  138. 

*'       of  gases,  ii.  422. 
"      proximate,    of    organic    sub- 
stances, ii.  363. 
"      ultimate,    of     organic      sub- 
stances, ii.  366,  386. 
Anilin,  ii.  621. 
Animal  chemistry,  ii.  719. 

*'      heat,  ii,  734. 
Anisic  acid,  ii.  662. 
Antimony,  ii.  211. 

"  alloys  of,  ii.  221. 

Antimony,    analytic   determination   of, 

ii.  219. 
Antimony,  behaviour  of  salts  of,  ii.  213. 

"  chlorides  of,  ii.  217. 

Antimony,  detection  of  in  poisoning,  ii 

221, 
Antimony,  metallurgy  of,  ii.  222. 

"         oxides  and  acids  of,  ii.  212. 
**         salts  of,  ii.  214. 
"         sulphides  of,  ii.  215. 
Arabin,  ii.  468, 
Arseniates  and  arsenites,  determination 

of,  i.  429. 
Arsenic  acid,  i.  282. 

*'        *'    antidotes  to  poisoning  by,  L 

285. 
"        "    its  preparation,  i.  280. 
795 


796 


GENERAL   INDEX. 


Arsenic  acid,  its  properties,  i.  279. 
Arsenic  acid,  researches  in  poisoning  by, 

i.  285. 
Arsenious  acid,  analysis  of,  i.  281. 

"  *'      properties  of,  i.  281. 

Arsenious  acid,  detection  of,  in  animal 

matter,  i.  289. 
Asparagin,  ii.  627. 
Atmosphere,  action  of  plants  on  the,  ii. 

716. 
Atmospheric  air,  i.  119. 

B. 

Balsams,  ii.  660. 

Bar-iron,  composition  of,  ii.  116. 

"        from  cast-iron,  ii.  82. 
Bassorin,  ii.  468. 
Barium,  and  its  oxides,  i.  528. 
"       chloride  of,  i.  533. 
"       sulphide  of,  i.  533. 
Baryta,  salts  of,  i.  582. 
Baryta,  distinctive  character  of  the  salts 

of,  i.  584. 
Beet-sugar,  manufacture  of,  ii.  771. 
Belgium,  reduction  of  zinc  in,  ii.  147. 
Benzamide,  ii.  643. 
Benzil,  ii.  648. 
Benzin,  ii.  648. 
Benzoic  acid,  ii.  644. 

"      ethers,  ii.  645. 
Bezoaric  acid,  ii.  609. 
Bile,  ii.  746. 
Biliary  calculi,  ii.  747. 
Bismuth,  ii.  204. 

«'      alloys  of,  ii.  208. 
Bismuth,  analytic  determination  of,  ii. 

208. 
Bismuth,  metallurgy  of,  ii.  209. 
"       oxides  of,  ii.  205. 
**      salts  of,  ii.  206. 
Bitter  almonds,  oil  of,  ii.  642. 
Blast-furnace,  ii.  66. 
Bleaching  by  chlorine,  i.  218. 

"        by  sulphurous  acid,  i.  177. 
"        salt,  manufacture  of,  i.  551. 
Blistered  steel,  ii.  104. 
Blood,  analysis  of,  ii.  742. 
*'      coagulum,  ii.  740. 
"      circulation  of  the,  ii.  782. 
"      globules,  ii.  739. 
Blooming  iron,  ii.  92. 
Blowpipe,  hydroxygen,  i.  92. 

"        with  atmospheric  air,  i.  87. 
r.lue  vitriol,  ii.  240. 
Bodies,  simple  and  compound,  i.  10. 

•'       states  of,  i.  11. 
Bodies,  external  characters  used  to  dis- 
tinguish, i.  13. 
Bohemian  glass,  i.  627. 
Boiling  points  of  saline  solutions,  i.  41 0. 


Bone,  ii.  721. 

Bone-black,  decoloring  power  of,  i.^07. 

'*  manufacture  of,  ii.  777. 

Boracic  acid,  i.  292. 

*•         "      analysis  of,  i.  295. 
Boracic  ether,  ii.  532. 
Borates,  determination  of,  i.  430. 
Borax,  manufacture  of,  i.  491. 

"     test,  i.  493. 
Borneo  camphor,  ii.  640. 
Boron,  i.  292. 

•*      action  of  the  metals  on,  i.  377. 

"      equivalent  of,  i.  295. 

♦'      fluoride  of,  i.  296. 
Brake-table,  ii.  20. 
Brass,  ii.  264. 

"      analysis  of,  ii.  270. 
Brass  and  copper  turning,  ii.  269. 
Bread,  making,  ii.  764. 
Brewing,  ii.  766. 
British  gum,  ii.  486. 
Bromates,  determination  of,  i.  426. 
Bromic  acid,  i.  241. 
Bromides,  i.  423. 

**        properties  of  metallic,  i.  387. 
Bromine  in  organic  bodies  determined^ 

ii.  386.  "^ 

Bromine,  preparation  and  properties  of, 

i.  240. 
Bromohydric  acid,  i.  242. 
Brucin,  Ii.  617. 
Butter,  making,  ii.  752. 
Butyric  acid,  ii.  574. 

'*       fermentation,  ii.  669. 
Butyramide,  ii.  574. 

0. 

Cacodyl,  ii.  551. 

Cadmium  and  its  compounds,  ii.  153. 

Cafein,  ii.  618. 

Calcium,  determination  of  the  equiva- 
lent of,  i.  588. 

Calcium,  distinctive    character  of  the 
salts  of,  i.  557. 

Calcium,  oxides  of,  i.  637. 

Calcium,  sulphide,  chloride,  and  fluoride 
of,  i.  556. 

Calculi,  urinary,  ii.  762. 

Calico  printing,  ii.  787. 

Calomel,  ii.  282. 

Camphilen,  ii.  637. 

Camphor,  ii.  639. 

Candles,  stearic  acid,  ii.  690. 

Cane-sugar,  ii.  470. 

<*  manufacture  of,  ii.  773. 

Cannon  casting,  ii.  266. 

Cantharidin,  ii.  626. 

Caoutchouc,  ii.  671. 

Capric  acid,  ii.  699. 

Caproic  acid,  ii.  699. 

Caprylic  acid,  ii.  699. 


GENERAL  INDEX. 


797 


Caramel,  ii.  471. 

Carbolic  acid,  ii.  682. 

Carbonated  waters,  i.  311. 

Carbonates,  determination  of,  i.  430. 

Carbon,  action  of  on  metals,  i.  377. 

Carbon,  hydrogen,  and  oxygen,  analysis 
of  compounds  of,  i.  323. 

Carbon,  nitrogen,  compounds  of,  i.  337. 

'     "       oxygen,  compounds  of,  i.  309. 
"       sulphur,  compounds  of,  i.  333. 
"       different  forms  of,  i.  304. 
"       organic  determination  of,  ii.  367. 

Carbonic  acid,  analysis  of  gaseous,  i.  316. 
"  liquid  and  solid,  i.  313. 

Carbonic  acid,  preparation  and  proper- 
ties of,  i.  309. 

Carbonic  ethers,  ii.  533. 

Carbonic  oxide,  eudiometric  analysis  of, 
i.  321. 

Carbonic  oxide,  preparation  of,  i.  319. 

Carburet  of  iron,  ii.  53. 

Carotin,  ii.  709. 

Cartilage,  ii.  722 

Casein,  ii.  748. 

"        vegetable,  ii.  460. 

Cassius's  purple,  ii.  325. 

Cast-iron,  ii.  53. 

*<        analysis  of,  ii.  111. 
"        composition  of,  ii.  110. 
"        reduced  to  bar,  ii.  82. 

Castor-oil,  ii.  700. 

Cast-steel,  ii.  104. 

Catalonian  forge,  ii.  61. 

Caustic,  lunar,  ii.  297. 

Cedrin,  ii.  641. 

Cellulose,  ii.  446. 

Cementing  apparatus,  i.  622. 

Cement,  manufacture  of  hydraulic,  i.  616. 

Cerasin,  ii.  468. 

Cerebral  substance,  ii.  728. 

Cerin,  ii.  703. 

Cerium,  i.  583. 

Charcoal,  i.  592. 

Charcoal,  power  of  to  condense  gases,  i. 
307. 

Charring  wood,  ii.  790. 

Cheese,  ii.  753. 

Chemical  affinity,  i.  12. 

Chemical  and  physical  phenomena,  dif- 
ference between,  i.  9. 

Chemical  nomenclature,  i.  93. 

Chemical  notation  and  formulas,  i.  73. 

Chemistry,  definition  of,  i.  10. 

Chelidonic  acid,  ii.  611. 

Chloral,  ii.  561. 

Chlorates,  i.  425. 

Chloric  acid,  i.  219. 

Chlorides,  determination  of,  i.  423. 

Chlorides,  metallic,  preparation  and  pro- 
perties of.  i.  386. 

Chlorometry,  i.  552. 


Chlorine  and  hydrogen,  compounds  of,  i. 

230. 
Chlorine  and  nitrogen,  compounds  of,  i. 

227. 
Chlorine  and  oxygen,  compounds  of,  i.219 
Chlorine,  behaviour  of  to  metallic  oxides, 

i.  385. 
Chlorine,  bleaching  by,  i.  218. 
"       equivalent  of,  i.  228. 
"       preparation  of,  i.  215. 
"        organic  determination,  ii.  336. 
Chloroform,  ii.  586. 
Chlorohydric  acid  and  its  compound,  i. 

230. 
Chlorohydric  ether,  ii.  536. 
Chlorophyll,  ii.  709. 
Chlorous  acid,  i.  225. 
Chloroxycarbonic  gas,  i.  321. 
Cholesterin,  ii.  647. 
Cholic  acid,  ii.  746. 
Chromates,  ii.  125. 
Chronic  acid,  ii.  122. 
Chromium,  analytic  determination  of,  ii. 

128. 
Chromium,  oxides  of,  ii.  118. 

"  salts  of,  ii.  123. 

Chyle,  ii.  748. 
Cider,  ii.  768. 
Cinnabar,  ii.  281. 
Cinnamic  acid,  ii.  659. 
Cinnamon,  oil  of,  ii.  658. 
Cinchonin,  ii.  614. 
Citric  acid,  ii.  596. 
Circular  polarization,  (note,)  ii.  454. 
Clay,  i.  652. 

Cleavage  of  crystals,  i.  15. 
Cloves,  oil  of,  ii.  665. 
Coal,  table  of  composition  of,  ii.  500. 

"    varieties  of,  ii.  496. 
Cobalt,  analytic  determination  of,  ii.  133. 
"      oxides  of,  ii.  130. 
*'      salts  of,  ii.  131. 
Cochineal,  ii.  710. 
Codein,  ii.  617. 
Cohesion,  i.  12. 
Coin,  ii.  312. 
Coking  coal,  ii.  790. 
Collodion,  ii.  492. 
Colouring  matters,  organic,  ii.  704. 
Columbium,  ii.  174. 
Concrete,  manufacture  of,  i.  618. 
Conicin,  ii.  620. 
Coumarin,  ii.  661. 
Copper,  ii.  236. 

"      alloys  of,  and  zinc,  ii.  263. 
♦'  "  tin,  ii.  265. 

"      analytic  determination  of,  ii.  245. 
«*       and  brass,  tinning,  ii.  269. 
"       chlorides  of,  ii.  244. 
Copper,  English  process  of  smelting,  ii. 

256. 


798 


GENERAL   INDEX. 


Copper,  Mansfeld  process  of  smelting, 

ii.  249. 
Copper,  metallurgy  of,  ii.  247. 

«♦      oxides  of,  ii.  237. 

«       salts  of,  ii.  239. 

"      sulphides,  ii.  243. 
Creatin,  ii.  724. 
Creasote,  ii.  683. 
Crucibles,  i.  667. 
Crystalline  forms,  six  systems  of,  i.  20. 

1.  Regular  system,  i.  21. 

2.  Dimetric,  i.  25. 

3.  Hexagonal,  i.  30. 

4.  Trimetric,  i.  36. 
6.  Monoclinic,  i.  40. 
6.  Triclinic,  i.  42. 

Crystallization  of  the  metals,  i.  367. 

"  water  of,  i.  398. 

Crystallography,  i.  14. 
Crystals,  axes  of,  i.  19. 

**         cleavage  of,  i.  15. 

"         fundamental  forms  of,  i.  15. 

"         imperfections  of,  i.  55. 
Cumin,  cuminic  acid,  ii.  664. 
Cupellation,  ii.  198,  313. 
Cyanides,  i.  424. 

Cyanhydric  or  prussic  acid,  i.  342. 
Cyanhydric  or  prussic  acid,  analysis  of, 

i.  344. 
Cyanogen,  analysis  of,  i.  339. 
Cyanogen,  origin  and  preparation  of,  i. 

338. 
Cyanogen,  products  of,  ii.  630. 

D. 

Decoloring  power  of  bone  black,  i.  307. 
Deliquescence  and  efflorescence,  i.  98. 
Density  of  vapours,  ii.  406. 
Deposit-trough  for  ores,  ii.  18. 
Deutoxide  of  nitrogen,  i.  145. 
Dextrin,  ii.  485. 
Diastase,  ii.  487. 
Didymium,  i.  583. 
Digestion,  ii.  730. 

Dimorphism  and  polymorphism,  i.  60. 
Distillation  of  oil  of  vitriol,  i.  179. 
"  phosphorus,  i.  256. 

Dry  distillation   of  organic   bodies,  ii. 

678. 
Ductility  of  metals,  i.  368. 
Dutch  liquid,  ii.  523. 
Dyeing,  principles  of,  ii.  781. 

E. 

Earthenware,  various  kinds,  i.  664,  667. 

"  glaze  for,  i.  666. 

"  analysis  of,  i.  671. 

Earths,  analytic  determination  of,  i.  594. 
Earthy  metals,  i.  569. 
Ellagic  acid,  ii.  609. 


Elements,  classification  of,  i.  76. 
"        tabular  view  of,  i.  64. 
Emulsin,  ii,  651. 
Enanthic  acid,  ii.  670. 
Engraving  by  fluohydric  acid,  i.  251. 
Equisetic  acid,  ii.  596. 
Erbium,  i.  583. 
Essential  oils,  ii.  634. 
Ethal,  ii.  701. 
Ether,  ii.  516. 
Ethers,  compound,  ii.  529. 
Ethionic  acid,  ii.  522. 
Ethyl  theory,  (note,)  ii.  568. 
Ethylammonia,  ii.  622. 
Eudiometer,  i.  104. 
Eudiometer,  analysis  by  the,  i.  129, 145 

321. 
Eugenic  acid,  ii.  665. 
Euxanthic  acid,  ii.  708. 
Evaporation,  i.  100. 

"  of  salines,  i.  500. 

Excrements,  ii.  763. 
Excretions,  ii.  754. 

F. 

Fats,  ii.  684. 
Ferment,  ii.  507. 
Fermentation,  alcoholic,  ii.  505. 

' '  butyric  and  lactic,  ii.  569. 

Fibrin,  ii.  724. 

*«     vegetable,  ii.  460. 
Fire-brick,  i.  667. 
Flame,  the  nature  of,  487. 
Flameless  lamp,  ii.  341. 
Fluohydric  acid,  analysis  of,  i.  251. 

*'  "     engraving  by,  i.  251. 

**  "     preparation  of,  i.  250 

Fluorides,  analytic  determination  of,  i. 

424. 
Fluorine,  i.  424. 
Fluor-spar,  i.  556. 
Fluosilicic  acid,  i,  301. 
Forge-hearth,  ii.  83. 
Forge-steel,  ii.  103. 
Formic  acid,  ii.  583. 
Formula,  construction  of  organic,  ii.  387, 
Freiberg,  extraction  of  silver  at,  ii.  305. 
Frigorific  mixtures,  i.  412. 
Fruit-sugar,  ii.  474. 
Fuel,  mineral,  ii.  494. 
Fulminating  mercury,  ii.  279. 

«<         silver,  ii.  295. 
Fulminic  acid,  ii,  632. 
Fumaric  acid,  ii.  596. 
Fuming  sulphuric  acid,  i.  185. 
Fusible  metal,  ii.  208. 

a. 

Gallic  acid,  ii.  607. 

Galvanic  gilding  and  silvering,  ii.  883 


GENERAL  INDEX. 


799 


Galvanoplastics,  ii.  335. 
Garlic,  oil  of,  ii.  675. 
Gases,  analysis  of,  ii.  422. 

"     collection  of,  over  mercury,  i.  94. 
Gases,  condensation  of,  by  charcoal,  i. 

307. 
Gases,  solubility  of,  in  water,  i.  101. 
Gasometer,  i.  82. 
Gastric  juice,  ii.  744. 
Gelatin,  ii.  726. 

Gelatinous  principles  in  plants,  ii.  478. 
Geology,  i.  351. 
Geological  division  of  the  formations,  i. 

361. 
German  silver,  ii.  138. 
Gilding,  ii.  331. 

"■      galvanic,  ii.  333. 
Glass,  analysis  of,  i.  648. 

"      blowing  on  the  table,  i.  642. 

"      composition  of,  i.  623. 

"      kinds  of,  i.  626. 

«      manufacture  of,  i.  627-640. 

"      properties  of,  i.  641. 
Glaze,  i.  659. 
Glucic  acid,  ii.  476. 
Glucinum  and  its  compounds,  i.  579. 
Glucose,  manufacture  of,  ii.  487. 
Glue,  ii.  726. 
Gluten,  ii.  460. 
Glycerin,  ii.  689. 
Glycocoll,  ii.  727. 
Glycyrrhizin,  ii.  628. 
Gold  and  its  compounds,  ii.  322. 

"     analytic  determination  of,  ii.  326. 

«     alloys  of,  ii.  329. 

"     assay  of,  ii.  366. 

"    parting  by  acids,  ii.  331. 
Goniometer,  i.  51. 
Graduating  glasses,  i.  103. 
Grape-sugar,  ii.  475. 
Gums,  ii.  468. 
Gun-cotton,  ii.  491. 
Gunpowder,  analysis  of,  i.  608. 
"  composition  of,  589. 

"  manufacture  of,  i.  595. 

Gunpowder,  testing  the  strength  of,  i. 

606. 
Gunpowder,  theory  of  its  effects,  i.  587. 
Gutta-percha,  i.  673. 

H. 

Hair,  ii.  723. 

Haloid  salts,  i.  397. 

Hematosin,  ii.  740. 

Hemitrope  crystals,  i.  59. 

Hexagonal  system  of  crystals,  i.  30. 

Hippuric  acid,  ii.  760. 

Horn,  ii.  722. 

Hot-blast,  ii.  77. 

Humin,  ii.  489. 


Hydraulic  lime,  i.  614. 

Hydrogen,  behaviour  of  to  oxides,  i.  383, 

"         equivalent  of,  i.  11. 
Hydrogen,  organic  determination  of,  ii. 

367. 
Hydrogen,  preparation  of,  i.  89. 

"  and  arsenic,  i.  282. 

*«         and  chlorine,  i.  230. 

"         and  iodine,  i.  247. 

"  and  nitrogen,  i.  162. 

"  and  oxygen,  i.  96. 

"         and  phosphorus,  i.  270, 

"  and  sulphur,  i.  201. 

Hydroxygen  blowpipe,  i.  92. 
Hypochlorates,  analysis  of,  i.  425. 
Hypochloric  acid,  i.  227. 
Hypochlorites,  i.  467. 
Hypochlorite  of  lime,  i.  550. 
Hypochlorous  acid,  i.  223. 
Hyponitric  acid,  i.  155. 
Hypophosphites,  i.  428. 
Hypophosphorous  acid,  i.  266. 
Hyposulphates,  i.  427. 
Hyposulphite  of  soda,  i.  494. 
Hyposulphites,  i.  428. 
Hyposulphuric  acid,  i.  197. 

*'  "  sulphuretted,  i.  197. 

Hyposulphurous  acid,  i.  196. 


Ichthyocolla,  ii.  727. 
Idria,  extraction  of  mercury  in,  ii.  290. 
Illuminating  gas,  ii.  792. 
Ilmenium,  ii.  174. 
Indigo,  ii.  714. 
Inosic  acid,  ii.  725. 
Intestinal  gases,  ii.  763. 
"        juice,  ii.  747. 
Introduction  to  general  chemistry,  i.  9. 
Introduction  to  organic  chemistry,  ii. 

361-445. 
Inulin,  ii.  467. 
lodates,  i.  426. 
Iodides,  metallic,  i.  387. 
Iodides,  analytic    determination    of,  i. 

424. 
Iodine,  action  of  on  the  metals,  i.  377. 

"     organic  determination  of,  ii.  386. 
Iodine,  properties  and  preparation  of,  i. 

244. 
Iridium,  ii.  353. 
Iron,  analytic  determination  of,  ii.  54. 

*'   analysis  of  cast,  and  steel,  ii.  111. 

"   and  its  oxides,  ii.  36. 

**    cast,  converted  into  bar-iron,  ii.  82. 
Iron,  composition  of  bar,  cast,  and  steel, 

ii.  116. 
Iron,  dry  assay  of  ores  of,  ii.  108. 

"    making  steel,  ii.  102. 

"    ores  of,  ii.  59. 


800 


GENERAL  INDEX. 


Iron,  reduction  of  the  ores  of,  ii.  61. 

"     salts  of,  ii.  44. 

"     sheet,  and  tin-plate,  ii.  98. 

"     wire-drawing,  ii.  101. 
Isatin,  ii.  715. 
Isomorphism,  i.  61. 

J. 

Japan  camphor,  ii.  639. 
Jigging  machine,  ii.  16. 

K. 

Kermes  mineral,  ii.  218. 
Kyanole,  ii.  621. 


Lactic  acid,  ii.  573. 

*♦     fermentation,  ii.  669. 
Lactometry,  ii.  750. 
Lanthanum,  i.  588. 
Law  of  multiple  proportions,  i.  12. 
Laws  of  combination  of  gases,  i.  158. 

**         constitution  of  salts,  i.  391. 
Lead,  alloys  of,  ii.  189. 

**      analytic  determination  of,  ii.  188. 

"      and  its  oxides,  ii.  174. 

"      casting  shot,  ii.  203. 

"     cupellation  of,  ii.  198. 
Lead,  desilverized  by  crystallization,  ii. 

202. 
Lead,  metallurgy  of,  ii.  190. 

"     red,  or  minium,  ii.  178. 

«      salts  of,  ii.  179. 

"  "        acetates,  ii.  183. 

*'  "         carbonates,  ii.  184. 

"  "        behaviour  of,  ii.  186. 

"      sheet,  and  pipe,  ii.  202. 

•«     glass,  i.  673. 
Lemons,  oil  of,  ii.  638. 
Leucole,  ii.  620. 
Lichenin,  ii.  467. 
Lichens,  ii.  710. 
Lignin,  ii.  449. 
Lime,  i.  537. 

**     for  mortar,  i.  611. 

"     hydraulic,  i.  614. 

"     hypochlorite  of,  i.  550. 

"    kiln,  i.  539. 

*'     native  carbonates  of,  i.  547. 

"    phosphates  of,  i.  549. 

"     salts  of,  i.  542. 
Limestones,  composition  of,  i.  615. 

'*  analysis  of,  i.  618. 

Litharge,  ii.  175. 
Lixiviation  of  nitre-beds,  i.  456. 
Logwood,  ii.  706. 
Lunar  caustic,  ii.  297. 
Lustre,  metallic,  i.  366. 
Lymph,  ii.  743. 


M. 


Madder,  ii.  705. 
Magnesia,  i.  558. 

"        salts  of,  i.  559. 
**        phosphates  of,  i.  561. 
"        behaviour  of  salts  of,  i.  663. 
Magnesium,  i.  558. 
Malic  acid,  ii.  595. 
Manganese,  and  its  oxides,  ii.  23. 
Manganese,  analytic  determination  of, 

ii.  31. 
Manganese,  acids  of,  ii.  25. 

"  salts  of,  ii.  28. 

Mannite,  ii.  484. 

Mansfeld,  extraction  of  silver  in,  ii.  309. 
"  "  copper  in,  ii.  249. 

Margaric  acid,  ii.  692. 
Marsh  gas,  i.  330,  and  ii.  682. 
Marsh's  apparatus  for  arsenic,  1.286. 
Matches,  phosphoric,  i.  259. 
Meconic  acid,  ii.  609. 
Menthen,  ii.  641. 
Mercaptan,  ii.  589. 
Mercurial  cistern,  i.  94. 
Mercury,  ii.  271. 

♦*        amalgams,  ii.  289. 
Mercury,  analytic  determination  of,  ii. 

288. 
Mercury,  chlorides  of,  ii.  282. 

*'         metallurgy  of,  in  Idria,  ii.290. 
Mercury,  metallurgy  of,  at  Almaden,  ii. 

291. 
Mercury,  oxides  of,  ii,  273. 
"         salts  of,  ii.  275. 
"  sulphides  of,  ii.  281. 

Mesitylen,  ii.  550. 
Metallic  veins,  i.  363. 
Metals,  i.  349. 

'*        action  of  oxygen  on,  i.  374. 
Metals,  action  of  sulphur  and  chlorine 

on,  i.  376. 
Metals,  action  of  other  metalloids  on,  i. 

377. 
Metals,  alkaline,  i.  434. 

"        alkalino-earthy,  i.  528. 

"        chemical  properties  of,  i.  371. 

««        classification  of,  i.  372. 

"       crystallization  of,  i.  367. 
Metals,  malleability  and  ductility  of,  i. 

368. 
Metals,  opacity,  lustre,  and  colour  of,  i. 

368. 
Metals,  physical  properties  of,  i.  365. 

"       properties  of  oxides  of,  i.  380. 

"  "  chlorides  of,  i.  386i. 

"      relations  of,  to  heat,  i.  371. 
Metalloids,  i.  79. 

"  equivalents  of  the,  i.  346. 

Methylal,  ii.  585. 


GENERAL  INDEX. 


801 


Methylic  alcohol,  ii.  575. 

"       compounds,  table  of,  ii.  591. 
Methylic  ethers,  ii.  548. 
Methylammonia,  ii.  623. 
Milk,  ii.  748. 

"     sugar  of,  ii.  751. 
Minium,  ii.  178. 
Mineral  fuel,  ii.  494. 

"       green,  ii.  242. 
Mirrors,  ii.  289. 
Molecular  decrements,  i.  44. 
Molybdenum,  ii.  233. 
Monobasic  and  polybasic  salts,  i.  895. 
Monoclinic  system,  i.  40. 
Monometric       "      i.  21. 
Mordant,  ii.  785. 
Morphin,  ii.  615. 
Mortar,  i.  611. 
Mucic  acid,  ii.  493. 

*'      ether,  ii.  536. 
Multiple  proportions,  law  of,  i.  12. 
Muscular  tissue,  ii.  723. 
Mustard,  oil  of,  ii.  676. 
Myricin,  ii.  703. 
Myronic  acid,  ii.  677. 


N. 


Naphtha,  ii.  683. 

Naphthalin,  ii.  678. 

Narcotin,  ii.  616. 

Nickel,    analytic   determination    of,  ii. 

139. 
Nickel,  in  German  silver,  ii.  138. 
**      oxides  of,  ii.  136. 
"      salts  of,  ii.  137. 
Nicking-buddle,  ii.  19. 
Nicotin,  ii.  618. 
Niobium,  ii.  174. 
Nitrates  and  nitrites,  determination  of, 

i.  424. 
Nitre-beds,  i.  454. 
Nitric  acid,  i.  133. 

<'  analysis  of,  i.  138. 

Nitric  acid,  formation  and  preparation 

of,  i.  135. 
Nitric  acid,  manufacture  of,  i.  137. 

"      ether,  ii.  530. 

"      oxide,  analysis  of,  i.  150. 
Nitrils,  ii.  629. 
Nitrogen,  i.  117. 
Nitrogen  and  carbon,  compounds  of,  i. 

337. 
Nitrogen  and  chlorine,  compounds  of,  i. 

227. 
Nitrogen  and  hydrogen,  compounds  of, 

i.  162. 
Nitrogen  and  iodine,   compounds  of,  i. 

248. 
Nitrogen  and  oxvgen.  compounds  of,  i. 

1M2. 

Vol.  IL— 51 


Nitrogen  and  phosporus,  compounds  of, 
i.  275. 

Nitrogen,  chemical  and  physical  proper- 
ties of,  i.  119. 

Nitrogen,  deutoxide  of,  or  nitric  oxide, 
i.  145. 

Nitrogen,  equivalent  of,  i.  159. 

Nitrogen,  organic  determination    of,  i. 
P,80. 

Nitrogen,  preparation  of,  i.  119. 
"        protoxide  of,  i.  142. 

Nitrous  acid,  analysis  of,  i.  154. 

Nitrous  acid,  preparation  and  properties 
of,  i.  153. 

Nitrous  matters,  lixiviation  of,  i.  456. 

Nutrition,  ii.  729.      ' 


0. 


Oil  of  aniseed,  ii.  662. 

*«     bitter-almonds,  ii.  642. 

"      cinnamon,  ii.  658. 

"      garlic,  ii.  675. 

'*      mustard,  ii.  676. 

*'      spireea,  ii.  654. 

"      wine,  ii.  528. 
Oils,  essential,  ii.  634. 
Olefiant  gas,  ii.  520. 
Oleic  acid,  ii.  693. 
Opacity  of  the  metals,  i.  365. 
Optical  glass,  ii.  639. 
Ores,  crushing,  ii.  11. 

"     preparation  of,  ii.  9. 

"     stamping,  ii.  17. 

"     washing,  ii.  10. 
Ornaments  and  painting  of  earthenware, 

i.  667. 
Osmium,  ii.  350. 

'<         extraction  of,  ii.  352.  ^ 

Oxalates  of  potassa,  i.  467. 
Oxalic  acid,  i.  322,  ii.  594. 

*'     ethers,  ii.  534. 
Oxides,  preparation  of,  i.  381. 

**      determination  of,  i.  422. 
Oxygen  and  arsenic,   compounds  of,  i 

280. 
Oxygen  and  carbon,  compounds  of,  i 

309. 
Oxygen  and  chlorine,  compounds  of,  i 

219. 
Oxygen  and  hydrogen,  compounds  of,  i 

96. 
Oxygen  and  nitrogen,  compounds  of,  i 

132. 
Oxygen  and  phosphorus,  compounds  of, 

i.  266. 
Oxygen,  preparation  of,  i.  79. 

"        properties  of,  i.  85. 
Oxysaccharic  acid,  ii.  491. 


802 


GENERAL   INDEX. 


P. 


Palladium,  ii.  356. 
Palm-oil,  ii.  700. 
Pancreatic  juice,  ii.  747. 
Paraffin,  ii.  681. 

Parting  of  gold  and  silver,  ii.  329. 
Pearl-white,  ii.  206. 
Pectic  acids,  table  of,  ii.  483. 
Pectose,  ii.  478. 
Pelopium,  ii.  174. 
Perchloric  acid,  i.  222. 
Percussion-table,  ii.  20. 
Perry,  ii.  768. 
Peru,  balsam  of,  ii.  660. 
Phenic  acid,  ii.  682. 
Phloridzin,  ii.  628. 
Phosphates,  determination  of,  i.  428 
Phosphoric  acid,  preparation  of,  i.  260. 
"  *'     analysis  of,  i.  263. 

*'  matches,  i.  259. 

Phosphorous  acid,  i.  264. 
Phosphorus,  properties  of,  i.  254. 
*'  preparation  of,  i.  257. 

"  equivalent  of,  i.  268. 

**  and  hydrogen,  i.  270. 

"  and  oxygen,  i.  260. 

Phosphorus,  organic  determination  of, 

ii.  385. 
Phosphovinic  acid,  ii.  530. 
Phosphurets,  i.  389. 

"  determination  of,  i.  423. 

Physical  and  chemical  phenomena,  i.  9. 
Physical  properties  of  the  metals,  i.  365. 
Picrotoxin,  ii.  626. 
Pig-metal,  ii.  80. 
Pimaric  acid,  ii,  674. 
Piperin,  ii.  626. 
Plants,  proximate  principles  of,  ii.  446. 

*'        decomposition  of,  ii.  494. 
Plate,  silver,  ii.  312. 
Platinum,  ii.  339. 

"  ammonia-bases  of,  ii.  346. 

Platinum,  analytic  determination  of,  ii. 

348. 
Platinum  black,  ii.  340. 

<'         extraction  of,  ii.  349. 
"         oxides  and  salts  of,  ii.  342. 
Polarization,  circular,  (note,)  ii.  454. 
Porcelain,  materials  for,  i.  652. 
*'  ware,  making,  i.  655. 

"         glazing  and  burning,  i.  659. 
Potassa,  i.  441. 

salts  of,  i.  446,  471. 
Potassiam,  compounds  of,  i.  368. 
"  equivalent  of,  i.  445. 

Pottery,  i.  651. 

"        porous,  i.  664. 
Proximate  analysis  of  organic  bodies,  ii. 

362. 
Proximate  principles  of  plants,  ii.  446. 
Prussic  acid,  i,  342. 
Puddling-furnace,  ii.  87. 


Purple  of  Cassius,  ii.  825. 
Pyroligneous  acid,  ii.  545. 


Quartation,  assay  by,  ii.  336. 
Quercitron,  ii.  707. 
Quinic  acid,  ii.  611. 
Quinin,  ii.  613. 
Quinolein,  ii.  620. 

Racemic  acid,  ii,  603. 

Red-lead,  ii.  178. 

Resins,  ii.  673, 

Respiration,  ii.  734. 

Rhodium,  ii.  358. 

Rhombic  system,  i.  36. 

Rocks,  principal  kinds  of,  i.  358. 

Rocks,  stratified  and  non-stratified,  ii. 

352. 
Rocks,  metallic  veins  in,  ii.  303. 
Rupert's  drops,  ii.  641. 
Ruthenium,  ii.  360. 


Safety-tubes,  i.  148. 

Saffron,  ii.  707. 

Salicin,  ii.  652. 

Salicylic  acid,  ii,  656. 

Saliva,  ii,  652, 

Salines,  i,  500. 

Saline  solutions,  boiling  points  of,  i.  410. 

Salt,  determination  of  the  electronega- 
tive body  of  a,  i.  421. 

Salt,  extraction  of  rock,  i.  496. 

Saltpeter  and  sulphur,  pulverization  of, 
i.  691. 

Saltpeter,  refining,  i.  459. 
"        testing,  i.  461. 

Salts,  i.  389. 

Salts,  coloured  tests  of  the  neutrality  of, 
i.  390. 

Salts,  decomposition  of,  by  acids,  i.  413. 
"  "  by  bases,  i.  416. 

Salts,  determination  of  the  solubility  of, 
i.  404. 

"Salts,  determination  of  the  curves  of  so- 
lubility of,  i.  406. 

Salts,  haloid,  i.  397. 

"     law  of  the  constitution  of,  i.  291. 

Salts,  laws  of  the  decompositions  of,  i. 
414. 

Salts,  monobasic  and  polybasic,  i.  395. 

Salts,  mutual  action  of,  in  the  dry  way, 
i.  418. 

Salts,  mutual  action  of,  in  the  wet  way, 
i.  418. 

Salts,  neutral,  acid,  and  basic,  i.  389. 

Salts,  reciprocal  action  of,  on  salts,  i. 
417. 


GENERAL   INDEX. 


803 


Salts,  solubility  dT,  i.  402. 

Salt-works,  working  up  residues  of,  i. 

506. 
Scheele's  green,  ii.  242. 
Scotch  hearth,  ii.  198. 
Sea-salt,  extraction  of,  i.  503. 
Sebacic  acid,  ii.  698. 
Secretions,  ii.  738. 
Selenic  and  selenious  acids,  i.  209. 
Selenium,  i.  208. 
Sheet-iron,  ii.  98. 

"     lead,  ii.  202. 
Shot-casting,  ii.  203. 
Silica,  preparation  of,  1.  298. 
Silicic  ethers,  ii.  532. 
Silicium,  i.  298.  > 

*'       fluoride  of,  i.  301. 
Silicofluohydric  acid,  i.  802. 
Silesian  extraction  of  zinc,  ii.  150. 
Silver,  ii.  293. 

"     alloys  of,  ii.  311. 

"  "  assay  of,  ii.  313. 

"      analytic  determination  of,  ii.  303. 

"      assay  of  ores  of,  ii.  321. 

<•     chloride  of,  301. 

"     extraction  from  copper,  ii.  251. 

"  "  *'      lead,  ii.  198. 

"      fulminating,  ii.  295. 

"     metallurgy  of,  ii.  304. 

"     oxides  of,  ii.  294. 

"     parted  from  gold,  ii.  329. 

«*      salts  of,  ii.  296. 
Silvering,  ii.  331. 

"         galvanic,  ii.  334. 
Simple  and  compound  bodies,  i.  10. 

"  "  crystals,  i.  16. 

Sinaptas,  ii.  657. 
Skin,  ii.  723. 
Sleeping-table,  ii.  19. 
Smalt,  ii.  134. 

Soap,  manufacture  of,  ii.  778. 
Soda,  borates  of,  i.  486. 

"     carbonates  of,  477. 

"     caustic,  i.  474; 

"      hyposulphite  of,  i.  494. 

"     phosphates  of,  i.  480. 
Soda,  distinctive  character  of  the  salts 

of,  i.  610. 
Soda-ash,  manufacture  of,  i.  477. 
Sodas,  test  of  commercial,  i.  480. 
Sodium,  i.  473. 

**       chloride  of,  i.  495. 
Soft  solder,  ii.  189. 
Solubility  of  gases  in  water,  i.  101.  "^ 
Spermaceti,  i.  701. 
Stamping  ores,  i,  17. 
Steam-colours,  i.  788. 
Stearic  acid,  i.  690. 
Steel,  analysis  of,  ii.  111. 

**      composition  of,  ii.  116. 

"     manufacture  of,  ii.  102. 

"      tempering  of,  ii.  107. 
Stoneware,  i.  664. 


Strontia,  its  salts,  i.  535. 
Strontium,  i.  535. 
Strychnin,  ii.  617. 
Suberic  acid,  ii.  698. 
Succinic  acid,  ii.  697. 
Sugar,  ii.  469. 

"      extraction  of,  ii.  771. 
*'      refining  of,  ii.  785. 
"      of  milk,  ii.  751. 
"      of  lead,  ii.  183. 
Sulfhydric  ethers,  ii.  538. 
Sulphates,  analysis  of,  i.  426. 
Sulphides,  analysis  of,  i.  422. 

"  properties  of  metallic,  i.  387. 

Sulphocarbonic  acid,  i.  335. 
Sulphocyanides,  ii.  633. 
Sulphosalts,  analysis  of,  i.  431. 
Sulphovinic  acid,  ii.  515. 
Sulphur,  i.  169. 

"        action  of,  on  the  metals,  i.  376. 
"        and  chlorine,  i.  234. 
"        and  hydrogen,  i.  201. 
"        and  oxygen,  i.  173. 
"        equivalent  of,  i.  198. 
"        organic  determination  of,  ii.385. 
Sulphuretted  hydrogen,  i.  201. 
Sulphuric  acid,  i.  178. 

"  "     analysis  of,  i.  180. 

"  "    fuming,  i.  185. 

"         ether,  ii.  516. 
Sulphurous  acid,  preparation  and  pro- 
perties of,  i.  174. 
Sulphurous  acid,  bleaching  by,  1.  177. 
Sweat,  ii.  763. 
Swing-sieve  for  ores,  ii.  15. 
Synthetic  composition  of  water,  i.  103. 


T. 


Tannic  acid,  ii.  605. 

Tanning,  ii.  788. 

Tartaric  acid,  ii.  598. 

Tartar  emetic,  ii.  600. 

Teeth,  ii.  722. 

Tenacity  of  metals,  i.  370. 

Terbium,  i.  583. 

Terebilen,  ii.  637. 

Terpentine,  oil  of,  ii.  635. 

Textile  fabrics,  colouring,  ii.  781. 

Thein,  ii.  618. 

Thenard's  blue,  ii.  135. 

Thermometers,  temperatures  in  diflfer- 

ent,  ii.  413. 
Thermometers,  air,  (note,)  ii.  414. 
Thiosinnamin,  ii.  676. 
Thorinum,  i.  583. 
Tiles,  i.  666. 
Tin  and  its  oxides,  ii.  156. 

"    alloys  of  copper  and,  ii.  265. 

'*    behaviour  of  salts  of,  ii.  164. 

"    chlorides  of,  ii.  162. 

♦*    metallurgy  of,  ii.  166. 


804 


GENERAL   INDEX. 


Tin,  salts  of,  ii.  160. 

Tin-plate,  ii.  98. 

Tinning  copper  and  brass,  ii.  269. 

Titanium,  ii.  169. 

Toluidin,  ii.  663. 

Truncation  of  crystals,  i.  17. 

Tungsten,  ii.  230. 

Type-metal,  ii.  189. 

Tyrolese  bowls,  ii.  328. 

u. 

Uranium,  ii.  224. 

Urea,  ii.  754. 

Uric  acid  and  its  derivatives,  ii.  755. 

Urinary  calculi,  ii.  762. 

Urine,  analysis  of,  ii.  761. 

V. 

Valerianic  acid,  ii.  667. 
Vanadium,  ii.  235. 
Vapours,  density  of,  406. 
Verdigris,  ii.  243. 
Vitriol,  blue,  ii.  240. 

w. 

Washing  gelatinous  precipitates,  i.  584. 
Water,  i.  96. 

"  analysis  of,  by  galvanism,  i.  110. 
Water  and  carbonic  acid,  determination 

of,  i.  121. 


Water,  evaporation  ol^  i.  100. 

"      of  crystallization,  i.  398. 

"      solubility  of  gases  in,  i.  101. 

"      synthetic  composition  of,  i.  103. 
Watera,  carbonated,  i.  311.. 
Wax,  ii.  703. 

White  precipitate,  ii.  285. 
Wine-making,  ii.  796. 
Winter-green,  oil  of,  ii.  656. 
Wire-drawing,  ii.  101. 
Wood,  charring,  ii.  790. 

"       spirit,  ii.  575. 
Woolf 's  bottles,  theory  of,  i.  147. 

X. 

Xanthic  acid,  ii.  536. 


Yeast,  ii.  507. 
Yttrium,  i.  583. 


Y. 


Z. 


Zaffre,  ii.  134. 

Zinc  and  its  oxide,  ii.  141. 

"     salts  of,  ii.  143. 

"     analytic  determination  of,  ii  144. 

"     metallm'gy  of,  ii.  146. 
Zirconium,  ii.  582. 


THE  END. 


I 


4n»br) 


\ 


":.  \ 


